datetime operation - Page 86

Using CreateWindow() to make additional Window on a thread - C

- by Jamie Keeling

Hello, I have a windows form that has a simple menu and performs a simple operation, I want to be able to create another windows form with all the functionality of a menu bar, message pump etc.. as a separate thread so I can then share the results of the operation to the second window. I.E. 1) Form A opens Form B opens as a separate thread 2)Form A performs operation 3)Form A passes results via memory to Form B 4)Form B display results I'm confused as to how to go about it, the main app runs fine but i'm not sure how to add a second window if the first one already exists. I think that using CreateWindow will allow me to make another window but again i'm not sure how to access the message pump so I can respond to certain events like WM_CREATE on the second window. I hope it makes sense. Thanks!

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Does UIActivityIndicator require manual threading on iPhone

- by Akusete

I am running creating an iPhone application which performs a costly operation and I wanted to create an activityIndicator to let the user know the application has not frozen. The operation is performed entirely in one event call... so there is no chance for the UI framework to receive control to actually display and animate this indicator. The sample apps which use the UIActivityIndicator (or any other similar animation) start and stop the animation in different events, triggered separately at different stages of the program. Do I need to manually create a separate thread to run my operation in, or is there already default support for this kind of behavior?

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Servlets, long operations

- by asrijaal

Hi there, I'm refactoring a big piece of code atm where a long taking operation is executed in a servlet. Now sometimes I don't get a response after the operation has finished. (It has finished because it is printed into the logs) What I wish to achieve would some "fire and forget" behavior by the servlet. I would pass my params to the action and the servlet would immediately return a status (something like: the operation has started, check your logs for further info) Is this possible with servlet 2.5 spec? I think I could get such a behavior with JMS maybe any other solutions out there?

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Force redraw before long running operations

- by Joshua

When you have a button, and do something like: Private Function Button_OnClick Button.Enabled = False [LONG OPERATION] End Function Then the button will not be grayed, because the long operation prevents the UI thread from repainting the control. I know the right design is to start a background thread / dispatcher, but sometimes that's too much hassle for a simple operation. So how do I force the button to redraw in disabled state? I tried .UpdateLayout() on the Button, but it didn't have any effects. I also tried System.Windows.Forms.DoEvents() which normally works when using WinForms, but it also had no effect.

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Any array function or user defned function to pick up only first occurance of value from the array?

- by OM The Eternity

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Creating additional Window by a thread - C

- by Jamie Keeling

Hello, I have a windows form that has a simple menu and performs a simple operation, I want to be able to create another windows form with all the functionality of a menu bar, message pump etc.. as a separate thread so I can then share the results of the operation to the second window. I.E. 1) Form A opens Form B opens as a separate thread 2)Form A performs operation 3)Form A passes results via memory to Form B 4)Form B display results I'm confused as to how to go about it, the main app runs fine but i'm not sure how to add a second window if the first one already exists. I hope it makes sense. Thanks!

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How to select latest change done in the given Table structure?

- by OM The Eternity

I have a Table structure as id, trackid, table_name, operation, oldvalue, newvalue, field, changedonetime Now if I have 3 rows for the same "trackid" same "field", then how can i select the latest out of the three? i.e. for e.g.: id = 100 trackid = 152 table_name = jos_menu operation= UPDATE oldvalue = IPL newvalue = IPLcccc field = name live = 0 changedonetime = 2010-04-30 17:54:39 and id = 101 trackid = 152 table_name = jos_menu operation= UPDATE oldvalue = IPLcccc newvalue = IPL2222 field = name live = 0 changedonetime = 2010-04-30 18:54:39 As u can see above the secind entry is the latest change, Now what query I shoud use to get the only one and Latest row out of many such rows...

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Creating two Windows by running one as a process from another - C

- by Jamie Keeling

Hello, I have a windows form that has a simple menu and performs a simple operation, I want to be able to create another windows form with all the functionality of a menu bar, message pump etc.. as a seperate process so I can then share the results of the operation to the second window. I.E. 1) Form A opens Form B opens as a separate process 2)Form A performs operation 3)Form A passes results via memory to Form B 4)Form B display results I'm confused as to how to go about it, the main app runs fine but i'm not sure how to add a second window if the first one already exists. I hope it makes sense. Thanks!

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How to continue after exception occurred in C#

- by Manisha

static string SomeMethodThatMightThrow(string s) { if (s[4] == 'C') throw new InvalidOperationException(); return @"C:\newFolder\" + s; } static void Main(string[] args) { string[] files = { "fileA.txt", "B.txC", "fileC.txt","fileD.txt" }; var exceptionDemoQuery = from file in files let n = SomeMethodThatMightThrow(file) select n; try { foreach (var item in exceptionDemoQuery) { Console.WriteLine("Processing {0}", item); } } catch (InvalidOperationException e) { Console.WriteLine(e.Message); } Console.WriteLine("Press any key to exit"); Console.ReadKey(); } Output is Processing C:\newFolder\fileA.txt Operation is not valid due to the current state of the object. But i need the Output as: Processing C:\newFolder\fileA.txt Operation is not valid due to the current state of the object. Operation is not valid due to the current state of the object. Processing C:\newFolder\fileD.txt Please help in this.............

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How to skip interstitial in a django view if a user hits the back button?

- by Jose Boveda

I have an application with an interstitial page to hold the user while an intensive operation runs in the background (takes anywhere from 30 secs to 1 minute). Once the operation is done, the user is redirected to the results page. Once on the result page, typical user behavior is to hit the 'back' button to perform the operation on a different input set. However, the back button takes them to the interstitial, not the original form. The desired behavior is to go back to the original form, skipping the interstitial entirely. I'd like this to be default behavior if the user goes to the interstitial page from anywhere but the original form. I thought I could create this by using the @never_cache function decorator in my view for the interstitial, and logic based on request.META['HTTP_REFERER'], however the page doesn't respect these. The browser's back button still trumps this behavior. Any ideas on how to solve this issue?

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Ruby and Rails Async

- by Edijs Petersons

I need to perform long-running operation in ruby/rails asynchronously. Googling around one of the options I find is Sidekiq. class WeeklyReportWorker include Sidekiq::Worker def perform(user, product, year = Time.now.year, week = Date.today.cweek) report = WeeklyReport.build(user, product, year, week) report.save end end # call WeeklyReportWorker.perform_async('user', 'product') Everything works great! But there is a problem. If I keep calling this async method every few seconds, but the actual time heavy operation performs is one minute things won't work. Let me put it in example. 5.times { WeeklyReportWorker.perform_async('user', 'product') } Now my heavy operation will be performed 5 times. Optimally it should have performed only once or twice depending on whether execution of first operaton started before 5th async call was made. Do you have tips how to solve it?

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C++ Pointers to functions.

- by Andy Leman

using namespace std; int addition (int a, int b) { return (a+b); } int subtraction (int a, int b) { return (a-b); } int operation (int x, int y, int (*functocall)(int,int)) { int g; g = (*functocall)(x,y); return(g); } int main() { int m,n; int (*minus)(int,int) = subtraction; m = operation (7,5,addition); n = operation (20,m,minus); cout << n; return 0; } Can anybody explain this line for me int (*minus)(int,int) = subtraction; Thanks a lot!

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Textures loaded with NSOperation are blank

- by Omega

So I call this method: -(void)beginExecution { NSOperationQueue *queue = [NSOperationQueue new]; NSInvocationOperation *operation = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(execute) object:nil]; [queue addOperation:operation]; [operation release]; } Which triggers this: -(void)execute { [[CCSpriteFrameCache sharedSpriteFrameCache]addSpriteFramesWithFile:@"MyTexture.plist"]; loaded = YES; // This tells me whenever loading is done. } However, when I create a sprite and try to use the texture MyTexture.png, the sprite is a blank canvas. Why is that?

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question about missing element in array

- by davit-datuashvili

i have following problem from book introduction algorithm second edition by MIT university problem is following An array A[1 . . n] contains all the integers from 0 to n except one. It would be easy to determine the missing integer in O(n) time by using an auxiliary array B[0 . . n] to record which numbers appear in A. In this problem, however, we cannot access an entire integer in A with a single operation. The elements of A are represented in binary, and the only operation we can use to access them is “fetch the j th bit of A[i],” which takes constant time. Show that if we use only this operation, we can still determine the missing inte- ger in O(n) time please help

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Can a variable like 'int' be considered a primitive/fundamental data structure?

- by Ravi Gupta

A rough definition of a data structure is that it allows you to store data and apply a set of operations on that data while preserving consistency of data before and after the operation. However some people insist that a primitive variable like 'int' can also be considered as a data structure. I get that part where it allows you to store data but I guess the operation part is missing. Primitive variables don't have operations attached to them. So I feel that unless you have a set of operations defined and attached to it you cannot call it a data structure. 'int' doesn't have any operation attached to it, it can be operated upon with a set of generic operators. Please advise if I got something wrong here.

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Optimality of Binary Search

- by templatetypedef

Hello all- This may be a silly question, but does anyone know of a proof that binary search is asymptotically optimal? That is, if we are given a sorted list of elements where the only permitted operation on those objects is a comparison, how do you prove that the search can't be done in o(lg n)? (That's little-o of lg n, by the way.) Note that I'm restricting this to elements where the only operation permitted operation is a comparison, since there are well-known algorithms that can beat O(lg n) on expectation if you're allowed to do more complex operations on the data (see, for example, interpolation search). Thanks so much! This has really been bugging me since it seems like it should be simple but has managed to resist all my best efforts. :-)

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Want to avoid the particular rows from select join query... See description

- by OM The Eternity

I have a Select Left Join Query whis displays me the rows for the latest changedone(its a time) column name ("field" should not be equal) column name ("trackid" should not be equal), and column name "Operation should be "UPDATE" ", below is the query I am talking about... SELECT j1. * FROM jos_audittrail j1 LEFT OUTER JOIN jos_audittrail j2 ON ( j1.trackid != j2.trackid AND j1.field != j2.field AND j1.changedone < j2.changedone ) WHERE j1.operation = 'UPDATE' AND j2.id IS NULL Now here I don't want a row to be displayed with a two particular column's value i.e. "field's value" the value is "LastvisitDate" and "hits" Now if if append the condition in the above query that " AND j1.field != 'lastvistDate' AND j1.field != 'hits' " theni do not get any result... The table structure is jos_audittrail: id trackid operation oldvalue newvalue table_name live changedone(its a time) I hope i have given the details properly If u still find something missing I will try to provide it more better way... Pls help me to avoid those two rows with those to mentioned value of "field"

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Is the syntax written in descrition is correct for MySQL Triggers? will it work?

- by Parth

Is the syntax written in descrition is correct for MySQL Triggers? will it work? CREATE OR REPLACE TRIGGER myTableAuditTrigger 2 AFTER INSERT OR DELETE OR UPDATE ON myTable 3 FOR EACH ROW 4 BEGIN 5 IF INSERTING THEN 6 INSERT INTO myTableAudit (id, Operation, NewName, NewPhone) 7 VALUES (1, 'Insert ', :NEW.Name, :NEW.PhoneNo); 8 ELSIF DELETING THEN 9 INSERT INTO myTableAudit (id, Operation, OldName, OldPhone) 10 VALUES (1, 'Delete ', :OLD.Name, :OLD.PhoneNo); 11 ELSIF UPDATING THEN 12 INSERT INTO myTableAudit (id, Operation, 13 OldName, OldPhone, NewName, NewPhone) 14 VALUES (1, 'Update ', 15 :OLD.Name, :OLD.PhoneNo, :NEW.Name, :NEW.PhoneNo); 16 END IF; 17 END; 18 /

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Best neural network for certain type of pattern analysis?

- by fred basset

Hi All, I'm working on a system that will send telemetry data on machine operation back to a central server for analysis. One of the machine parameters we're measuring is motor current drawn vs time. After an operation is finished we plan to send back an array of currents vs time to the server. A successful operation would have a pattern like a trapezoid, problematic operations would have a pattern completely different, more like a large spike in values. Can anyone recommend a type of neural network that would be good at classifying these 1D vectors of current values into a pass/fail type output? Thanks, Fred

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Stored Procedures with SSRS? Hmm… not so much

- by Rob Farley

Little Bobby Tables’ mother says you should always sanitise your data input. Except that I think she’s wrong. The SQL Injection aspect is for another post, where I’ll show you why I think SQL Injection is the same kind of attack as many other attacks, such as the old buffer overflow, but here I want to have a bit of a whinge about the way that some people sanitise data input, and even have a whinge about people who insist on using stored procedures for SSRS reports. Let me say that again, in case you missed it the first time: I want to have a whinge about people who insist on using stored procedures for SSRS reports. Let’s look at the data input sanitisation aspect – except that I’m going to call it ‘parameter validation’. I’m talking about code that looks like this: create procedure dbo.GetMonthSummaryPerSalesPerson(@eomdate datetime) as begin /* First check that @eomdate is a valid date */ if isdate(@eomdate) != 1 begin select 'Please enter a valid date' as ErrorMessage; return; end /* Then check that time has passed since @eomdate */ if datediff(day,@eomdate,sysdatetime()) < 5 begin select 'Sorry - EOM is not complete yet' as ErrorMessage; return; end /* If those checks have succeeded, return the data */ select SalesPersonID, count(*) as NumSales, sum(TotalDue) as TotalSales from Sales.SalesOrderHeader where OrderDate >= dateadd(month,-1,@eomdate) and OrderDate < @eomdate group by SalesPersonID order by SalesPersonID; end Notice that the code checks that a date has been entered. Seriously??!! This must only be to check for NULL values being passed in, because anything else would have to be a valid datetime to avoid an error. The other check is maybe fair enough, but I still don’t like it. The two problems I have with this stored procedure are the result sets and the small fact that the stored procedure even exists in the first place. But let’s consider the first one of these problems for starters. I’ll get to the second one in a moment. If you read Jes Borland (@grrl_geek)’s recent post about returning multiple result sets in Reporting Services, you’ll be aware that Reporting Services doesn’t support multiple results sets from a single query. And when it says ‘single query’, it includes ‘stored procedure call’. It’ll only handle the first result set that comes back. But that’s okay – we have RETURN statements, so our stored procedure will only ever return a single result set. Sometimes that result set might contain a single field called ErrorMessage, but it’s still only one result set. Except that it’s not okay, because Reporting Services needs to know what fields to expect. Your report needs to hook into your fields, so SSRS needs to have a way to get that information. For stored procs, it uses an option called FMTONLY. When Reporting Services tries to figure out what fields are going to be returned by a query (or stored procedure call), it doesn’t want to have to run the whole thing. That could take ages. (Maybe it’s seen some of the stored procedures I’ve had to deal with over the years!) So it turns on FMTONLY before it makes the call (and turns it off again afterwards). FMTONLY is designed to be able to figure out the shape of the output, without actually running the contents. It’s very useful, you might think. set fmtonly on exec dbo.GetMonthSummaryPerSalesPerson '20030401'; set fmtonly off Without the FMTONLY lines, this stored procedure returns a result set that has three columns and fourteen rows. But with FMTONLY turned on, those rows don’t come back. But what I do get back hurts Reporting Services. It doesn’t run the stored procedure at all. It just looks for anything that could be returned and pushes out a result set in that shape. Despite the fact that I’ve made sure that the logic will only ever return a single result set, the FMTONLY option kills me by returning three of them. It would have been much better to push these checks down into the query itself. alter procedure dbo.GetMonthSummaryPerSalesPerson(@eomdate datetime) as begin select SalesPersonID, count(*) as NumSales, sum(TotalDue) as TotalSales from Sales.SalesOrderHeader where /* Make sure that @eomdate is valid */ isdate(@eomdate) = 1 /* And that it's sufficiently past */ and datediff(day,@eomdate,sysdatetime()) >= 5 /* And now use it in the filter as appropriate */ and OrderDate >= dateadd(month,-1,@eomdate) and OrderDate < @eomdate group by SalesPersonID order by SalesPersonID; end Now if we run it with FMTONLY turned on, we get the single result set back. But let’s consider the execution plan when we pass in an invalid date. First let’s look at one that returns data. I’ve got a semi-useful index in place on OrderDate, which includes the SalesPersonID and TotalDue fields. It does the job, despite a hefty Sort operation. …compared to one that uses a future date: You might notice that the estimated costs are similar – the Index Seek is still 28%, the Sort is still 71%. But the size of that arrow coming out of the Index Seek is a whole bunch smaller. The coolest thing here is what’s going on with that Index Seek. Let’s look at some of the properties of it. Glance down it with me… Estimated CPU cost of 0.0005728, 387 estimated rows, estimated subtree cost of 0.0044385, ForceSeek false, Number of Executions 0. That’s right – it doesn’t run. So much for reading plans right-to-left... The key is the Filter on the left of it. It has a Startup Expression Predicate in it, which means that it doesn’t call anything further down the plan (to the right) if the predicate evaluates to false. Using this method, we can make sure that our stored procedure contains a single query, and therefore avoid any problems with multiple result sets. If we wanted, we could always use UNION ALL to make sure that we can return an appropriate error message. alter procedure dbo.GetMonthSummaryPerSalesPerson(@eomdate datetime) as begin select SalesPersonID, count(*) as NumSales, sum(TotalDue) as TotalSales, /*Placeholder: */ '' as ErrorMessage from Sales.SalesOrderHeader where /* Make sure that @eomdate is valid */ isdate(@eomdate) = 1 /* And that it's sufficiently past */ and datediff(day,@eomdate,sysdatetime()) >= 5 /* And now use it in the filter as appropriate */ and OrderDate >= dateadd(month,-1,@eomdate) and OrderDate < @eomdate group by SalesPersonID /* Now include the error messages */ union all select 0, 0, 0, 'Please enter a valid date' as ErrorMessage where isdate(@eomdate) != 1 union all select 0, 0, 0, 'Sorry - EOM is not complete yet' as ErrorMessage where datediff(day,@eomdate,sysdatetime()) < 5 order by SalesPersonID; end But still I don’t like it, because it’s now a stored procedure with a single query. And I don’t like stored procedures that should be functions. That’s right – I think this should be a function, and SSRS should call the function. And I apologise to those of you who are now planning a bonfire for me. Guy Fawkes’ night has already passed this year, so I think you miss out. (And I’m not going to remind you about when the PASS Summit is in 2012.) create function dbo.GetMonthSummaryPerSalesPerson(@eomdate datetime) returns table as return ( select SalesPersonID, count(*) as NumSales, sum(TotalDue) as TotalSales, '' as ErrorMessage from Sales.SalesOrderHeader where /* Make sure that @eomdate is valid */ isdate(@eomdate) = 1 /* And that it's sufficiently past */ and datediff(day,@eomdate,sysdatetime()) >= 5 /* And now use it in the filter as appropriate */ and OrderDate >= dateadd(month,-1,@eomdate) and OrderDate < @eomdate group by SalesPersonID union all select 0, 0, 0, 'Please enter a valid date' as ErrorMessage where isdate(@eomdate) != 1 union all select 0, 0, 0, 'Sorry - EOM is not complete yet' as ErrorMessage where datediff(day,@eomdate,sysdatetime()) < 5 ); We’ve had to lose the ORDER BY – but that’s fine, as that’s a client thing anyway. We can have our reports leverage this stored query still, but we’re recognising that it’s a query, not a procedure. A procedure is designed to DO stuff, not just return data. We even get entries in sys.columns that confirm what the shape of the result set actually is, which makes sense, because a table-valued function is the right mechanism to return data. And we get so much more flexibility with this. If you haven’t seen the simplification stuff that I’ve preached on before, jump over to http://bit.ly/SimpleRob and watch the video of when I broke a microphone and nearly fell off the stage in Wales. You’ll see the impact of being able to have a simplifiable query. You can also read the procedural functions post I wrote recently, if you didn’t follow the link from a few paragraphs ago. So if we want the list of SalesPeople that made any kind of sales in a given month, we can do something like: select SalesPersonID from dbo.GetMonthSummaryPerSalesPerson(@eomonth) order by SalesPersonID; This doesn’t need to look up the TotalDue field, which makes a simpler plan. select * from dbo.GetMonthSummaryPerSalesPerson(@eomonth) where SalesPersonID is not null order by SalesPersonID; This one can avoid having to do the work on the rows that don’t have a SalesPersonID value, pushing the predicate into the Index Seek rather than filtering the results that come back to the report. If we had joins involved, we might see some of those being simplified out. We also get the ability to include query hints in individual reports. We shift from having a single-use stored procedure to having a reusable stored query – and isn’t that one of the main points of modularisation? Stored procedures in Reporting Services are just a bit limited for my liking. They’re useful in plenty of ways, but if you insist on using stored procedures all the time rather that queries that use functions – that’s rubbish. @rob_farley

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Loosely coupled .NET Cache Provider using Dependency Injection

- by Rhames

I have recently been reading the excellent book “Dependency Injection in .NET”, written by Mark Seemann. I do not generally buy software development related books, as I never seem to have the time to read them, but I have found the time to read Mark’s book, and it was time well spent I think. Reading the ideas around Dependency Injection made me realise that the Cache Provider code I wrote about earlier (see http://geekswithblogs.net/Rhames/archive/2011/01/10/using-the-asp.net-cache-to-cache-data-in-a-model.aspx) could be refactored to use Dependency Injection, which should produce cleaner code. The goals are to: Separate the cache provider implementation (using the ASP.NET data cache) from the consumers (loose coupling). This will also mean that the dependency on System.Web for the cache provider does not ripple down into the layers where it is being consumed (such as the domain layer). Provide a decorator pattern to allow a consumer of the cache provider to be implemented separately from the base consumer (i.e. if we have a base repository, we can decorate this with a caching version). Although I used the term repository, in reality the cache consumer could be just about anything. Use constructor injection to provide the Dependency Injection, with a suitable DI container (I use Castle Windsor). The sample code for this post is available on github, https://github.com/RobinHames/CacheProvider.git ICacheProvider In the sample code, the key interface is ICacheProvider, which is in the domain layer. 1: using System; 2: using System.Collections.Generic; 3: 4: namespace CacheDiSample.Domain 5: { 6: public interface ICacheProvider<T> 7: { 8: T Fetch(string key, Func<T> retrieveData, DateTime? absoluteExpiry, TimeSpan? relativeExpiry); 9: IEnumerable<T> Fetch(string key, Func<IEnumerable<T>> retrieveData, DateTime? absoluteExpiry, TimeSpan? relativeExpiry); 10: } 11: } This interface contains two methods to retrieve data from the cache, either as a single instance or as an IEnumerable. the second paramerter is of type Func<T>. This is the method used to retrieve data if nothing is found in the cache. The ASP.NET implementation of the ICacheProvider interface needs to live in a project that has a reference to system.web, typically this will be the root UI project, or it could be a separate project. The key thing is that the domain or data access layers do not need system.web references adding to them. In my sample MVC application, the CacheProvider is implemented in the UI project, in a folder called “CacheProviders”: 1: using System; 2: using System.Collections.Generic; 3: using System.Linq; 4: using System.Web; 5: using System.Web.Caching; 6: using CacheDiSample.Domain; 7: 8: namespace CacheDiSample.CacheProvider 9: { 10: public class CacheProvider<T> : ICacheProvider<T> 11: { 12: public T Fetch(string key, Func<T> retrieveData, DateTime? absoluteExpiry, TimeSpan? relativeExpiry) 13: { 14: return FetchAndCache<T>(key, retrieveData, absoluteExpiry, relativeExpiry); 15: } 16: 17: public IEnumerable<T> Fetch(string key, Func<IEnumerable<T>> retrieveData, DateTime? absoluteExpiry, TimeSpan? relativeExpiry) 18: { 19: return FetchAndCache<IEnumerable<T>>(key, retrieveData, absoluteExpiry, relativeExpiry); 20: } 21: 22: #region Helper Methods 23: 24: private U FetchAndCache(string key, Func retrieveData, DateTime? absoluteExpiry, TimeSpan? relativeExpiry) 25: { 26: U value; 27: if (!TryGetValue(key, out value)) 28: { 29: value = retrieveData(); 30: if (!absoluteExpiry.HasValue) 31: absoluteExpiry = Cache.NoAbsoluteExpiration; 32: 33: if (!relativeExpiry.HasValue) 34: relativeExpiry = Cache.NoSlidingExpiration; 35: 36: HttpContext.Current.Cache.Insert(key, value, null, absoluteExpiry.Value, relativeExpiry.Value); 37: } 38: return value; 39: } 40: 41: private bool TryGetValue(string key, out U value) 42: { 43: object cachedValue = HttpContext.Current.Cache.Get(key); 44: if (cachedValue == null) 45: { 46: value = default(U); 47: return false; 48: } 49: else 50: { 51: try 52: { 53: value = (U)cachedValue; 54: return true; 55: } 56: catch 57: { 58: value = default(U); 59: return false; 60: } 61: } 62: } 63: 64: #endregion 65: 66: } 67: } The FetchAndCache helper method checks if the specified cache key exists, if it does not, the Func retrieveData method is called, and the results are added to the cache. Using Castle Windsor to register the cache provider In the MVC UI project (my application root), Castle Windsor is used to register the CacheProvider implementation, using a Windsor Installer: 1: using Castle.MicroKernel.Registration; 2: using Castle.MicroKernel.SubSystems.Configuration; 3: using Castle.Windsor; 4: 5: using CacheDiSample.Domain; 6: using CacheDiSample.CacheProvider; 7: 8: namespace CacheDiSample.WindsorInstallers 9: { 10: public class CacheInstaller : IWindsorInstaller 11: { 12: public void Install(IWindsorContainer container, IConfigurationStore store) 13: { 14: container.Register( 15: Component.For(typeof(ICacheProvider<>)) 16: .ImplementedBy(typeof(CacheProvider<>)) 17: .LifestyleTransient()); 18: } 19: } 20: } Note that the cache provider is registered as a open generic type. Consuming a Repository I have an existing couple of repository interfaces defined in my domain layer: IRepository.cs 1: using System; 2: using System.Collections.Generic; 3: 4: using CacheDiSample.Domain.Model; 5: 6: namespace CacheDiSample.Domain.Repositories 7: { 8: public interface IRepository<T> 9: where T : EntityBase 10: { 11: T GetById(int id); 12: IList<T> GetAll(); 13: } 14: } IBlogRepository.cs 1: using System; 2: using CacheDiSample.Domain.Model; 3: 4: namespace CacheDiSample.Domain.Repositories 5: { 6: public interface IBlogRepository : IRepository<Blog> 7: { 8: Blog GetByName(string name); 9: } 10: } These two repositories are implemented in the DataAccess layer, using Entity Framework to retrieve data (this is not important though). One important point is that in the BaseRepository implementation of IRepository, the methods are virtual. This will allow the decorator to override them. The BlogRepository is registered in a RepositoriesInstaller, again in the MVC UI project. 1: using Castle.MicroKernel.Registration; 2: using Castle.MicroKernel.SubSystems.Configuration; 3: using Castle.Windsor; 4: 5: using CacheDiSample.Domain.CacheDecorators; 6: using CacheDiSample.Domain.Repositories; 7: using CacheDiSample.DataAccess; 8: 9: namespace CacheDiSample.WindsorInstallers 10: { 11: public class RepositoriesInstaller : IWindsorInstaller 12: { 13: public void Install(IWindsorContainer container, IConfigurationStore store) 14: { 15: container.Register(Component.For<IBlogRepository>() 16: .ImplementedBy<BlogRepository>() 17: .LifestyleTransient() 18: .DependsOn(new 19: { 20: nameOrConnectionString = "BloggingContext" 21: })); 22: } 23: } 24: } Now I can inject a dependency on the IBlogRepository into a consumer, such as a controller in my sample code: 1: using System; 2: using System.Collections.Generic; 3: using System.Linq; 4: using System.Web; 5: using System.Web.Mvc; 6: 7: using CacheDiSample.Domain.Repositories; 8: using CacheDiSample.Domain.Model; 9: 10: namespace CacheDiSample.Controllers 11: { 12: public class HomeController : Controller 13: { 14: private readonly IBlogRepository blogRepository; 15: 16: public HomeController(IBlogRepository blogRepository) 17: { 18: if (blogRepository == null) 19: throw new ArgumentNullException("blogRepository"); 20: 21: this.blogRepository = blogRepository; 22: } 23: 24: public ActionResult Index() 25: { 26: ViewBag.Message = "Welcome to ASP.NET MVC!"; 27: 28: var blogs = blogRepository.GetAll(); 29: 30: return View(new Models.HomeModel { Blogs = blogs }); 31: } 32: 33: public ActionResult About() 34: { 35: return View(); 36: } 37: } 38: } Consuming the Cache Provider via a Decorator I used a Decorator pattern to consume the cache provider, this means my repositories follow the open/closed principle, as they do not require any modifications to implement the caching. It also means that my controllers do not have any knowledge of the caching taking place, as the DI container will simply inject the decorator instead of the root implementation of the repository. The first step is to implement a BlogRepository decorator, with the caching logic in it. Note that this can reside in the domain layer, as it does not require any knowledge of the data access methods. BlogRepositoryWithCaching.cs 1: using System; 2: using System.Collections.Generic; 3: using System.Linq; 4: using System.Text; 5: 6: using CacheDiSample.Domain.Model; 7: using CacheDiSample.Domain; 8: using CacheDiSample.Domain.Repositories; 9: 10: namespace CacheDiSample.Domain.CacheDecorators 11: { 12: public class BlogRepositoryWithCaching : IBlogRepository 13: { 14: // The generic cache provider, injected by DI 15: private ICacheProvider<Blog> cacheProvider; 16: // The decorated blog repository, injected by DI 17: private IBlogRepository parentBlogRepository; 18: 19: public BlogRepositoryWithCaching(IBlogRepository parentBlogRepository, ICacheProvider<Blog> cacheProvider) 20: { 21: if (parentBlogRepository == null) 22: throw new ArgumentNullException("parentBlogRepository"); 23: 24: this.parentBlogRepository = parentBlogRepository; 25: 26: if (cacheProvider == null) 27: throw new ArgumentNullException("cacheProvider"); 28: 29: this.cacheProvider = cacheProvider; 30: } 31: 32: public Blog GetByName(string name) 33: { 34: string key = string.Format("CacheDiSample.DataAccess.GetByName.{0}", name); 35: // hard code 5 minute expiry! 36: TimeSpan relativeCacheExpiry = new TimeSpan(0, 5, 0); 37: return cacheProvider.Fetch(key, () => 38: { 39: return parentBlogRepository.GetByName(name); 40: }, 41: null, relativeCacheExpiry); 42: } 43: 44: public Blog GetById(int id) 45: { 46: string key = string.Format("CacheDiSample.DataAccess.GetById.{0}", id); 47: 48: // hard code 5 minute expiry! 49: TimeSpan relativeCacheExpiry = new TimeSpan(0, 5, 0); 50: return cacheProvider.Fetch(key, () => 51: { 52: return parentBlogRepository.GetById(id); 53: }, 54: null, relativeCacheExpiry); 55: } 56: 57: public IList<Blog> GetAll() 58: { 59: string key = string.Format("CacheDiSample.DataAccess.GetAll"); 60: 61: // hard code 5 minute expiry! 62: TimeSpan relativeCacheExpiry = new TimeSpan(0, 5, 0); 63: return cacheProvider.Fetch(key, () => 64: { 65: return parentBlogRepository.GetAll(); 66: }, 67: null, relativeCacheExpiry) 68: .ToList(); 69: } 70: } 71: } The key things in this caching repository are: I inject into the repository the ICacheProvider<Blog> implementation, via the constructor. This will make the cache provider functionality available to the repository. I inject the parent IBlogRepository implementation (which has the actual data access code), via the constructor. This will allow the methods implemented in the parent to be called if nothing is found in the cache. I override each of the methods implemented in the repository, including those implemented in the generic BaseRepository. Each override of these methods follows the same pattern. It makes a call to the CacheProvider.Fetch method, and passes in the parentBlogRepository implementation of the method as the retrieval method, to be used if nothing is present in the cache. Configuring the Caching Repository in the DI Container The final piece of the jigsaw is to tell Castle Windsor to use the BlogRepositoryWithCaching implementation of IBlogRepository, but to inject the actual Data Access implementation into this decorator. This is easily achieved by modifying the RepositoriesInstaller to use Windsor’s implicit decorator wiring: 1: using Castle.MicroKernel.Registration; 2: using Castle.MicroKernel.SubSystems.Configuration; 3: using Castle.Windsor; 4: 5: using CacheDiSample.Domain.CacheDecorators; 6: using CacheDiSample.Domain.Repositories; 7: using CacheDiSample.DataAccess; 8: 9: namespace CacheDiSample.WindsorInstallers 10: { 11: public class RepositoriesInstaller : IWindsorInstaller 12: { 13: public void Install(IWindsorContainer container, IConfigurationStore store) 14: { 15: 16: // Use Castle Windsor implicit wiring for the block repository decorator 17: // Register the outermost decorator first 18: container.Register(Component.For<IBlogRepository>() 19: .ImplementedBy<BlogRepositoryWithCaching>() 20: .LifestyleTransient()); 21: // Next register the IBlogRepository inmplementation to inject into the outer decorator 22: container.Register(Component.For<IBlogRepository>() 23: .ImplementedBy<BlogRepository>() 24: .LifestyleTransient() 25: .DependsOn(new 26: { 27: nameOrConnectionString = "BloggingContext" 28: })); 29: } 30: } 31: } This is all that is needed. Now if the consumer of the repository makes a call to the repositories method, it will be routed via the caching mechanism. You can test this by stepping through the code, and seeing that the DataAccess.BlogRepository code is only called if there is no data in the cache, or this has expired. The next step is to add the SQL Cache Dependency support into this pattern, this will be a future post.

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Is it possible to run dhcpd3 as non-root user in a chroot jail?

- by Lenain

Hi everyone. I would like to run dhcpd3 from a chroot jail on Debian Lenny. At the moment, I can run it as root from my jail. Now I want to do this as non-root user (as "-u blah -t /path/to/jail" Bind option). If I start my process like this : start-stop-daemon --chroot /home/jails/dhcp --chuid dhcp \ --start --pidfile /home/jails/dhcp/var/run/dhcp.pid --exec /usr/sbin/dhcpd3 I get stuck with these errors : Internet Systems Consortium DHCP Server V3.1.1 Copyright 2004-2008 Internet Systems Consortium. All rights reserved. For info, please visit http://www.isc.org/sw/dhcp/ unable to create icmp socket: Operation not permitted Wrote 0 deleted host decls to leases file. Wrote 0 new dynamic host decls to leases file. Wrote 0 leases to leases file. Open a socket for LPF: Operation not permitted strace : brk(0) = 0x911b000 fcntl64(0, F_GETFD) = 0 fcntl64(1, F_GETFD) = 0 fcntl64(2, F_GETFD) = 0 access("/etc/suid-debug", F_OK) = -1 ENOENT (No such file or directory) access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory) mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb775d000 access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory) open("/etc/ld.so.cache", O_RDONLY) = -1 ENOENT (No such file or directory) open("/lib/tls/i686/cmov/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/lib/tls/i686/cmov", 0xbfc2ac84) = -1 ENOENT (No such file or directory) open("/lib/tls/i686/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/lib/tls/i686", 0xbfc2ac84) = -1 ENOENT (No such file or directory) open("/lib/tls/cmov/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/lib/tls/cmov", 0xbfc2ac84) = -1 ENOENT (No such file or directory) open("/lib/tls/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/lib/tls", 0xbfc2ac84) = -1 ENOENT (No such file or directory) open("/lib/i686/cmov/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/lib/i686/cmov", 0xbfc2ac84) = -1 ENOENT (No such file or directory) open("/lib/i686/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/lib/i686", 0xbfc2ac84) = -1 ENOENT (No such file or directory) open("/lib/cmov/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/lib/cmov", 0xbfc2ac84) = -1 ENOENT (No such file or directory) open("/lib/libc.so.6", O_RDONLY) = 3 read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\260e\1\0004\0\0\0t"..., 512) = 512 fstat64(3, {st_mode=S_IFREG|0755, st_size=1294572, ...}) = 0 mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb775c000 mmap2(NULL, 1300080, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb761e000 mmap2(0xb7756000, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x138) = 0xb7756000 mmap2(0xb7759000, 9840, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xb7759000 close(3) = 0 mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb761d000 set_thread_area({entry_number:-1 - 6, base_addr:0xb761d6b0, limit:1048575, seg_32bit:1, contents:0, read_exec_only:0, limit_in_pages:1, seg_not_present:0, useable:1}) = 0 mprotect(0xb7756000, 4096, PROT_READ) = 0 open("/dev/null", O_RDWR) = 3 close(3) = 0 brk(0) = 0x911b000 brk(0x913c000) = 0x913c000 socket(PF_FILE, SOCK_DGRAM, 0) = 3 fcntl64(3, F_SETFD, FD_CLOEXEC) = 0 connect(3, {sa_family=AF_FILE, path="/dev/log"...}, 110) = 0 time(NULL) = 1284760816 open("/etc/localtime", O_RDONLY) = 4 fstat64(4, {st_mode=S_IFREG|0644, st_size=2945, ...}) = 0 fstat64(4, {st_mode=S_IFREG|0644, st_size=2945, ...}) = 0 mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb761c000 read(4, "TZif2\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\f\0\0\0\f\0\0\0\0\0"..., 4096) = 2945 _llseek(4, -28, [2917], SEEK_CUR) = 0 read(4, "\nCET-1CEST,M3.5.0,M10.5.0/3\n"..., 4096) = 28 close(4) = 0 munmap(0xb761c000, 4096) = 0 stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2945, ...}) = 0 send(3, "Sep 18 00:00:16 dhcpd: Intern"..., 73, MSG_NOSIGNAL) = 73 write(2, "Internet Systems Consortium DHCP "..., 46Internet Systems Consortium DHCP Server V3.1.1) = 46 write(2, "\n"..., 1 ) = 1 time(NULL) = 1284760816 stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2945, ...}) = 0 send(3, "Sep 18 00:00:16 dhcpd: Copyri"..., 75, MSG_NOSIGNAL) = 75 write(2, "Copyright 2004-2008 Internet Syst"..., 48Copyright 2004-2008 Internet Systems Consortium.) = 48 write(2, "\n"..., 1 ) = 1 time(NULL) = 1284760816 stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2945, ...}) = 0 send(3, "Sep 18 00:00:16 dhcpd: All ri"..., 47, MSG_NOSIGNAL) = 47 write(2, "All rights reserved."..., 20All rights reserved.) = 20 write(2, "\n"..., 1 ) = 1 time(NULL) = 1284760816 stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2945, ...}) = 0 send(3, "Sep 18 00:00:16 dhcpd: For in"..., 77, MSG_NOSIGNAL) = 77 write(2, "For info, please visit http://www"..., 50For info, please visit http://www.isc.org/sw/dhcp/) = 50 write(2, "\n"..., 1 ) = 1 socket(PF_FILE, SOCK_STREAM, 0) = 4 fcntl64(4, F_SETFL, O_RDWR|O_NONBLOCK) = 0 connect(4, {sa_family=AF_FILE, path="/var/run/nscd/socket"...}, 110) = -1 ENOENT (No such file or directory) close(4) = 0 socket(PF_FILE, SOCK_STREAM, 0) = 4 fcntl64(4, F_SETFL, O_RDWR|O_NONBLOCK) = 0 connect(4, {sa_family=AF_FILE, path="/var/run/nscd/socket"...}, 110) = -1 ENOENT (No such file or directory) close(4) = 0 open("/etc/nsswitch.conf", O_RDONLY) = 4 fstat64(4, {st_mode=S_IFREG|0644, st_size=475, ...}) = 0 mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb761c000 read(4, "# /etc/nsswitch.conf\n#\n# Example "..., 4096) = 475 read(4, ""..., 4096) = 0 close(4) = 0 munmap(0xb761c000, 4096) = 0 open("/lib/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) open("/usr/lib/tls/i686/cmov/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib/tls/i686/cmov", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/usr/lib/tls/i686/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib/tls/i686", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/usr/lib/tls/cmov/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib/tls/cmov", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/usr/lib/tls/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib/tls", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/usr/lib/i686/cmov/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib/i686/cmov", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/usr/lib/i686/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib/i686", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/usr/lib/cmov/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib/cmov", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/usr/lib/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/lib/i486-linux-gnu/tls/i686/cmov/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/lib/i486-linux-gnu/tls/i686/cmov", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/lib/i486-linux-gnu/tls/i686/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/lib/i486-linux-gnu/tls/i686", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/lib/i486-linux-gnu/tls/cmov/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/lib/i486-linux-gnu/tls/cmov", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/lib/i486-linux-gnu/tls/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/lib/i486-linux-gnu/tls", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/lib/i486-linux-gnu/i686/cmov/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/lib/i486-linux-gnu/i686/cmov", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/lib/i486-linux-gnu/i686/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/lib/i486-linux-gnu/i686", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/lib/i486-linux-gnu/cmov/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/lib/i486-linux-gnu/cmov", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/lib/i486-linux-gnu/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/lib/i486-linux-gnu", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/usr/lib/i486-linux-gnu/tls/i686/cmov/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib/i486-linux-gnu/tls/i686/cmov", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/usr/lib/i486-linux-gnu/tls/i686/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib/i486-linux-gnu/tls/i686", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/usr/lib/i486-linux-gnu/tls/cmov/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib/i486-linux-gnu/tls/cmov", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/usr/lib/i486-linux-gnu/tls/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib/i486-linux-gnu/tls", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/usr/lib/i486-linux-gnu/i686/cmov/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib/i486-linux-gnu/i686/cmov", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/usr/lib/i486-linux-gnu/i686/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib/i486-linux-gnu/i686", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/usr/lib/i486-linux-gnu/cmov/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib/i486-linux-gnu/cmov", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/usr/lib/i486-linux-gnu/libnss_db.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) stat64("/usr/lib/i486-linux-gnu", 0xbfc2ad5c) = -1 ENOENT (No such file or directory) open("/lib/libnss_files.so.2", O_RDONLY) = 4 read(4, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\320\30\0\0004\0\0\0\250"..., 512) = 512 fstat64(4, {st_mode=S_IFREG|0644, st_size=38408, ...}) = 0 mmap2(NULL, 41624, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 4, 0) = 0xb7612000 mmap2(0xb761b000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 4, 0x8) = 0xb761b000 close(4) = 0 open("/etc/services", O_RDONLY|O_CLOEXEC) = 4 fcntl64(4, F_GETFD) = 0x1 (flags FD_CLOEXEC) fstat64(4, {st_mode=S_IFREG|0644, st_size=18480, ...}) = 0 mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7611000 read(4, "# Network services, Internet styl"..., 4096) = 4096 read(4, "9/tcp\t\t\t\t# Quick Mail Transfer Pr"..., 4096) = 4096 read(4, "note\t1352/tcp\tlotusnotes\t# Lotus "..., 4096) = 4096 read(4, "tion\nafs3-kaserver\t7004/udp\nafs3-"..., 4096) = 4096 read(4, "backup\t2989/tcp\t\t\t# Afmbackup sys"..., 4096) = 2096 read(4, ""..., 4096) = 0 close(4) = 0 munmap(0xb7611000, 4096) = 0 time(NULL) = 1284760816 open("/etc/protocols", O_RDONLY|O_CLOEXEC) = 4 fstat64(4, {st_mode=S_IFREG|0644, st_size=2626, ...}) = 0 mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7611000 read(4, "# Internet (IP) protocols\n#\n# Upd"..., 4096) = 2626 close(4) = 0 munmap(0xb7611000, 4096) = 0 socket(PF_INET, SOCK_RAW, IPPROTO_ICMP) = -1 EPERM (Operation not permitted) time(NULL) = 1284760816 stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2945, ...}) = 0 send(3, "Sep 18 00:00:16 dhcpd: unable"..., 80, MSG_NOSIGNAL) = 80 write(2, "unable to create icmp socket: Ope"..., 53unable to create icmp socket: Operation not permitted) = 53 write(2, "\n"..., 1 ) = 1 open("/etc/dhcp3/dhcpd.conf", O_RDONLY) = 4 lseek(4, 0, SEEK_END) = 1426 lseek(4, 0, SEEK_SET) = 0 read(4, "#----------------------------\n# G"..., 1426) = 1426 close(4) = 0 mmap2(NULL, 401408, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb75b0000 mmap2(NULL, 401408, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb754e000 mmap2(NULL, 401408, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb74ec000 brk(0x916f000) = 0x916f000 close(3) = 0 socket(PF_FILE, SOCK_DGRAM, 0) = 3 fcntl64(3, F_SETFD, FD_CLOEXEC) = 0 connect(3, {sa_family=AF_FILE, path="/dev/log"...}, 110) = 0 time(NULL) = 1284760816 stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2945, ...}) = 0 send(3, "Sep 18 00:00:16 dhcpd: Inter"..., 74, MSG_NOSIGNAL) = 74 time(NULL) = 1284760816 stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2945, ...}) = 0 send(3, "Sep 18 00:00:16 dhcpd: Copyr"..., 76, MSG_NOSIGNAL) = 76 time(NULL) = 1284760816 stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2945, ...}) = 0 send(3, "Sep 18 00:00:16 dhcpd: All r"..., 48, MSG_NOSIGNAL) = 48 time(NULL) = 1284760816 stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2945, ...}) = 0 send(3, "Sep 18 00:00:16 dhcpd: For i"..., 78, MSG_NOSIGNAL) = 78 open("/var/lib/dhcp3/dhcpd.leases", O_RDONLY) = 4 lseek(4, 0, SEEK_END) = 126 lseek(4, 0, SEEK_SET) = 0 read(4, "# The format of this file is docu"..., 126) = 126 close(4) = 0 open("/var/lib/dhcp3/dhcpd.leases", O_WRONLY|O_CREAT|O_APPEND, 0666) = 4 fstat64(4, {st_mode=S_IFREG|0644, st_size=126, ...}) = 0 mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb74eb000 fstat64(4, {st_mode=S_IFREG|0644, st_size=126, ...}) = 0 _llseek(4, 126, [126], SEEK_SET) = 0 time(NULL) = 1284760816 time(NULL) = 1284760816 open("/var/lib/dhcp3/dhcpd.leases.1284760816", O_WRONLY|O_CREAT|O_TRUNC, 0664) = 5 fcntl64(5, F_GETFL) = 0x1 (flags O_WRONLY) fstat64(5, {st_mode=S_IFREG|0644, st_size=0, ...}) = 0 mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb74ea000 _llseek(5, 0, [0], SEEK_CUR) = 0 close(4) = 0 munmap(0xb74eb000, 4096) = 0 time(NULL) = 1284760816 stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2945, ...}) = 0 send(3, "Sep 18 00:00:16 dhcpd: Wrote"..., 70, MSG_NOSIGNAL) = 70 write(2, "Wrote 0 deleted host decls to lea"..., 42Wrote 0 deleted host decls to leases file.) = 42 write(2, "\n"..., 1 ) = 1 time(NULL) = 1284760816 stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2945, ...}) = 0 send(3, "Sep 18 00:00:16 dhcpd: Wrote"..., 74, MSG_NOSIGNAL) = 74 write(2, "Wrote 0 new dynamic host decls to"..., 46Wrote 0 new dynamic host decls to leases file.) = 46 write(2, "\n"..., 1 ) = 1 time(NULL) = 1284760816 stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2945, ...}) = 0 send(3, "Sep 18 00:00:16 dhcpd: Wrote"..., 58, MSG_NOSIGNAL) = 58 write(2, "Wrote 0 leases to leases file."..., 30Wrote 0 leases to leases file.) = 30 write(2, "\n"..., 1 ) = 1 write(5, "# The format of this file is docu"..., 126) = 126 fsync(5) = 0 unlink("/var/lib/dhcp3/dhcpd.leases~") = 0 link("/var/lib/dhcp3/dhcpd.leases", "/var/lib/dhcp3/dhcpd.leases~") = 0 rename("/var/lib/dhcp3/dhcpd.leases.1284760816", "/var/lib/dhcp3/dhcpd.leases") = 0 socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP) = 4 ioctl(4, SIOCGIFCONF, {0 - 64, NULL}) = 0 ioctl(4, SIOCGIFCONF, {64, {{"lo", {AF_INET, inet_addr("127.0.0.1")}}, {"eth0", {AF_INET, inet_addr("192.168.0.10")}}}}) = 0 ioctl(4, SIOCGIFFLAGS, {ifr_name="lo", ifr_flags=IFF_UP|IFF_LOOPBACK|IFF_RUNNING}) = 0 ioctl(4, SIOCGIFFLAGS, {ifr_name="eth0", ifr_flags=IFF_UP|IFF_BROADCAST|IFF_RUNNING|IFF_MULTICAST}) = 0 ioctl(4, SIOCGIFHWADDR, {ifr_name="eth0", ifr_hwaddr=00:c0:26:87:55:c0}) = 0 socket(PF_PACKET, SOCK_PACKET, 768) = -1 EPERM (Operation not permitted) time(NULL) = 1284760816 stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2945, ...}) = 0 send(3, "Sep 18 00:00:16 dhcpd: Open "..., 74, MSG_NOSIGNAL) = 74 write(2, "Open a socket for LPF: Operation "..., 46Open a socket for LPF: Operation not permitted) = 46 write(2, "\n"..., 1 ) = 1 exit_group(1) = ? I understand that dhcpd wants to create sockets on port 67... but I don't know how to authorize that through the chroot. Any idea?

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An Introduction to ASP.NET Web API

- by Rick Strahl

Microsoft recently released ASP.NET MVC 4.0 and .NET 4.5 and along with it, the brand spanking new ASP.NET Web API. Web API is an exciting new addition to the ASP.NET stack that provides a new, well-designed HTTP framework for creating REST and AJAX APIs (API is Microsoft’s new jargon for a service, in case you’re wondering). Although Web API ships and installs with ASP.NET MVC 4, you can use Web API functionality in any ASP.NET project, including WebForms, WebPages and MVC or just a Web API by itself. And you can also self-host Web API in your own applications from Console, Desktop or Service applications. If you're interested in a high level overview on what ASP.NET Web API is and how it fits into the ASP.NET stack you can check out my previous post: Where does ASP.NET Web API fit? In the following article, I'll focus on a practical, by example introduction to ASP.NET Web API. All the code discussed in this article is available in GitHub: https://github.com/RickStrahl/AspNetWebApiArticle [republished from my Code Magazine Article and updated for RTM release of ASP.NET Web API] Getting Started To start I’ll create a new empty ASP.NET application to demonstrate that Web API can work with any kind of ASP.NET project. Although you can create a new project based on the ASP.NET MVC/Web API template to quickly get up and running, I’ll take you through the manual setup process, because one common use case is to add Web API functionality to an existing ASP.NET application. This process describes the steps needed to hook up Web API to any ASP.NET 4.0 application. Start by creating an ASP.NET Empty Project. Then create a new folder in the project called Controllers. Add a Web API Controller Class Once you have any kind of ASP.NET project open, you can add a Web API Controller class to it. Web API Controllers are very similar to MVC Controller classes, but they work in any kind of project. Add a new item to this folder by using the Add New Item option in Visual Studio and choose Web API Controller Class, as shown in Figure 1. Figure 1: This is how you create a new Controller Class in Visual Studio Make sure that the name of the controller class includes Controller at the end of it, which is required in order for Web API routing to find it. Here, the name for the class is AlbumApiController. For this example, I’ll use a Music Album model to demonstrate basic behavior of Web API. The model consists of albums and related songs where an album has properties like Name, Artist and YearReleased and a list of songs with a SongName and SongLength as well as an AlbumId that links it to the album. You can find the code for the model (and the rest of these samples) on Github. To add the file manually, create a new folder called Model, and add a new class Album.cs and copy the code into it. There’s a static AlbumData class with a static CreateSampleAlbumData() method that creates a short list of albums on a static .Current that I’ll use for the examples. Before we look at what goes into the controller class though, let’s hook up routing so we can access this new controller. Hooking up Routing in Global.asax To start, I need to perform the one required configuration task in order for Web API to work: I need to configure routing to the controller. Like MVC, Web API uses routing to provide clean, extension-less URLs to controller methods. Using an extension method to ASP.NET’s static RouteTable class, you can use the MapHttpRoute() (in the System.Web.Http namespace) method to hook-up the routing during Application_Start in global.asax.cs shown in Listing 1.using System; using System.Web.Routing; using System.Web.Http; namespace AspNetWebApi { public class Global : System.Web.HttpApplication { protected void Application_Start(object sender, EventArgs e) { RouteTable.Routes.MapHttpRoute( name: "AlbumVerbs", routeTemplate: "albums/{title}", defaults: new { symbol = RouteParameter.Optional, controller="AlbumApi" } ); } } } This route configures Web API to direct URLs that start with an albums folder to the AlbumApiController class. Routing in ASP.NET is used to create extensionless URLs and allows you to map segments of the URL to specific Route Value parameters. A route parameter, with a name inside curly brackets like {name}, is mapped to parameters on the controller methods. Route parameters can be optional, and there are two special route parameters – controller and action – that determine the controller to call and the method to activate respectively. HTTP Verb Routing Routing in Web API can route requests by HTTP Verb in addition to standard {controller},{action} routing. For the first examples, I use HTTP Verb routing, as shown Listing 1. Notice that the route I’ve defined does not include an {action} route value or action value in the defaults. Rather, Web API can use the HTTP Verb in this route to determine the method to call the controller, and a GET request maps to any method that starts with Get. So methods called Get() or GetAlbums() are matched by a GET request and a POST request maps to a Post() or PostAlbum(). Web API matches a method by name and parameter signature to match a route, query string or POST values. In lieu of the method name, the [HttpGet,HttpPost,HttpPut,HttpDelete, etc] attributes can also be used to designate the accepted verbs explicitly if you don’t want to follow the verb naming conventions. Although HTTP Verb routing is a good practice for REST style resource APIs, it’s not required and you can still use more traditional routes with an explicit {action} route parameter. When {action} is supplied, the HTTP verb routing is ignored. I’ll talk more about alternate routes later. When you’re finished with initial creation of files, your project should look like Figure 2. Figure 2: The initial project has the new API Controller Album model Creating a small Album Model Now it’s time to create some controller methods to serve data. For these examples, I’ll use a very simple Album and Songs model to play with, as shown in Listing 2. public class Song { public string AlbumId { get; set; } [Required, StringLength(80)] public string SongName { get; set; } [StringLength(5)] public string SongLength { get; set; } } public class Album { public string Id { get; set; } [Required, StringLength(80)] public string AlbumName { get; set; } [StringLength(80)] public string Artist { get; set; } public int YearReleased { get; set; } public DateTime Entered { get; set; } [StringLength(150)] public string AlbumImageUrl { get; set; } [StringLength(200)] public string AmazonUrl { get; set; } public virtual List<Song> Songs { get; set; } public Album() { Songs = new List<Song>(); Entered = DateTime.Now; // Poor man's unique Id off GUID hash Id = Guid.NewGuid().GetHashCode().ToString("x"); } public void AddSong(string songName, string songLength = null) { this.Songs.Add(new Song() { AlbumId = this.Id, SongName = songName, SongLength = songLength }); } } Once the model has been created, I also added an AlbumData class that generates some static data in memory that is loaded onto a static .Current member. The signature of this class looks like this and that's what I'll access to retrieve the base data:public static class AlbumData { // sample data - static list public static List<Album> Current = CreateSampleAlbumData(); /// <summary> /// Create some sample data /// </summary> /// <returns></returns> public static List<Album> CreateSampleAlbumData() { … }} You can check out the full code for the data generation online. Creating an AlbumApiController Web API shares many concepts of ASP.NET MVC, and the implementation of your API logic is done by implementing a subclass of the System.Web.Http.ApiController class. Each public method in the implemented controller is a potential endpoint for the HTTP API, as long as a matching route can be found to invoke it. The class name you create should end in Controller, which is how Web API matches the controller route value to figure out which class to invoke. Inside the controller you can implement methods that take standard .NET input parameters and return .NET values as results. Web API’s binding tries to match POST data, route values, form values or query string values to your parameters. Because the controller is configured for HTTP Verb based routing (no {action} parameter in the route), any methods that start with Getxxxx() are called by an HTTP GET operation. You can have multiple methods that match each HTTP Verb as long as the parameter signatures are different and can be matched by Web API. In Listing 3, I create an AlbumApiController with two methods to retrieve a list of albums and a single album by its title .public class AlbumApiController : ApiController { public IEnumerable<Album> GetAlbums() { var albums = AlbumData.Current.OrderBy(alb => alb.Artist); return albums; } public Album GetAlbum(string title) { var album = AlbumData.Current .SingleOrDefault(alb => alb.AlbumName.Contains(title)); return album; }} To access the first two requests, you can use the following URLs in your browser: http://localhost/aspnetWebApi/albumshttp://localhost/aspnetWebApi/albums/Dirty%20Deeds Note that you’re not specifying the actions of GetAlbum or GetAlbums in these URLs. Instead Web API’s routing uses HTTP GET verb to route to these methods that start with Getxxx() with the first mapping to the parameterless GetAlbums() method and the latter to the GetAlbum(title) method that receives the title parameter mapped as optional in the route. Content Negotiation When you access any of the URLs above from a browser, you get either an XML or JSON result returned back. The album list result for Chrome 17 and Internet Explorer 9 is shown Figure 3. Figure 3: Web API responses can vary depending on the browser used, demonstrating Content Negotiation in action as these two browsers send different HTTP Accept headers. Notice that the results are not the same: Chrome returns an XML response and IE9 returns a JSON response. Whoa, what’s going on here? Shouldn’t we see the same result in both browsers? Actually, no. Web API determines what type of content to return based on Accept headers. HTTP clients, like browsers, use Accept headers to specify what kind of content they’d like to see returned. Browsers generally ask for HTML first, followed by a few additional content types. Chrome (and most other major browsers) ask for: Accept: text/html, application/xhtml+xml,application/xml; q=0.9,*/*;q=0.8 IE9 asks for: Accept: text/html, application/xhtml+xml, */* Note that Chrome’s Accept header includes application/xml, which Web API finds in its list of supported media types and returns an XML response. IE9 does not include an Accept header type that works on Web API by default, and so it returns the default format, which is JSON. This is an important and very useful feature that was missing from any previous Microsoft REST tools: Web API automatically switches output formats based on HTTP Accept headers. Nowhere in the server code above do you have to explicitly specify the output format. Rather, Web API determines what format the client is requesting based on the Accept headers and automatically returns the result based on the available formatters. This means that a single method can handle both XML and JSON results.. Using this simple approach makes it very easy to create a single controller method that can return JSON, XML, ATOM or even OData feeds by providing the appropriate Accept header from the client. By default you don’t have to worry about the output format in your code. Note that you can still specify an explicit output format if you choose, either globally by overriding the installed formatters, or individually by returning a lower level HttpResponseMessage instance and setting the formatter explicitly. More on that in a minute. Along the same lines, any content sent to the server via POST/PUT is parsed by Web API based on the HTTP Content-type of the data sent. The same formats allowed for output are also allowed on input. Again, you don’t have to do anything in your code – Web API automatically performs the deserialization from the content. Accessing Web API JSON Data with jQuery A very common scenario for Web API endpoints is to retrieve data for AJAX calls from the Web browser. Because JSON is the default format for Web API, it’s easy to access data from the server using jQuery and its getJSON() method. This example receives the albums array from GetAlbums() and databinds it into the page using knockout.js.$.getJSON("albums/", function (albums) { // make knockout template visible $(".album").show(); // create view object and attach array var view = { albums: albums }; ko.applyBindings(view); }); Figure 4 shows this and the next example’s HTML output. You can check out the complete HTML and script code at http://goo.gl/Ix33C (.html) and http://goo.gl/tETlg (.js). Figu Figure 4: The Album Display sample uses JSON data loaded from Web API. The result from the getJSON() call is a JavaScript object of the server result, which comes back as a JavaScript array. In the code, I use knockout.js to bind this array into the UI, which as you can see, requires very little code, instead using knockout’s data-bind attributes to bind server data to the UI. Of course, this is just one way to use the data – it’s entirely up to you to decide what to do with the data in your client code. Along the same lines, I can retrieve a single album to display when the user clicks on an album. The response returns the album information and a child array with all the songs. The code to do this is very similar to the last example where we pulled the albums array:$(".albumlink").live("click", function () { var id = $(this).data("id"); // title $.getJSON("albums/" + id, function (album) { ko.applyBindings(album, $("#divAlbumDialog")[0]); $("#divAlbumDialog").show(); }); }); Here the URL looks like this: /albums/Dirty%20Deeds, where the title is the ID captured from the clicked element’s data ID attribute. Explicitly Overriding Output Format When Web API automatically converts output using content negotiation, it does so by matching Accept header media types to the GlobalConfiguration.Configuration.Formatters and the SupportedMediaTypes of each individual formatter. You can add and remove formatters to globally affect what formats are available and it’s easy to create and plug in custom formatters.The example project includes a JSONP formatter that can be plugged in to provide JSONP support for requests that have a callback= querystring parameter. Adding, removing or replacing formatters is a global option you can use to manipulate content. It’s beyond the scope of this introduction to show how it works, but you can review the sample code or check out my blog entry on the subject (http://goo.gl/UAzaR). If automatic processing is not desirable in a particular Controller method, you can override the response output explicitly by returning an HttpResponseMessage instance. HttpResponseMessage is similar to ActionResult in ASP.NET MVC in that it’s a common way to return an abstract result message that contains content. HttpResponseMessage s parsed by the Web API framework using standard interfaces to retrieve the response data, status code, headers and so on[MS2] . Web API turns every response – including those Controller methods that return static results – into HttpResponseMessage instances. Explicitly returning an HttpResponseMessage instance gives you full control over the output and lets you mostly bypass WebAPI’s post-processing of the HTTP response on your behalf. HttpResponseMessage allows you to customize the response in great detail. Web API’s attention to detail in the HTTP spec really shows; many HTTP options are exposed as properties and enumerations with detailed IntelliSense comments. Even if you’re new to building REST-based interfaces, the API guides you in the right direction for returning valid responses and response codes. For example, assume that I always want to return JSON from the GetAlbums() controller method and ignore the default media type content negotiation. To do this, I can adjust the output format and headers as shown in Listing 4.public HttpResponseMessage GetAlbums() { var albums = AlbumData.Current.OrderBy(alb => alb.Artist); // Create a new HttpResponse with Json Formatter explicitly var resp = new HttpResponseMessage(HttpStatusCode.OK); resp.Content = new ObjectContent<IEnumerable<Album>>( albums, new JsonMediaTypeFormatter()); // Get Default Formatter based on Content Negotiation //var resp = Request.CreateResponse<IEnumerable<Album>>(HttpStatusCode.OK, albums); resp.Headers.ConnectionClose = true; resp.Headers.CacheControl = new CacheControlHeaderValue(); resp.Headers.CacheControl.Public = true; return resp; } This example returns the same IEnumerable<Album> value, but it wraps the response into an HttpResponseMessage so you can control the entire HTTP message result including the headers, formatter and status code. In Listing 4, I explicitly specify the formatter using the JsonMediaTypeFormatter to always force the content to JSON. If you prefer to use the default content negotiation with HttpResponseMessage results, you can create the Response instance using the Request.CreateResponse method:var resp = Request.CreateResponse<IEnumerable<Album>>(HttpStatusCode.OK, albums); This provides you an HttpResponse object that's pre-configured with the default formatter based on Content Negotiation. Once you have an HttpResponse object you can easily control most HTTP aspects on this object. What's sweet here is that there are many more detailed properties on HttpResponse than the core ASP.NET Response object, with most options being explicitly configurable with enumerations that make it easy to pick the right headers and response codes from a list of valid codes. It makes HTTP features available much more discoverable even for non-hardcore REST/HTTP geeks. Non-Serialized Results The output returned doesn’t have to be a serialized value but can also be raw data, like strings, binary data or streams. You can use the HttpResponseMessage.Content object to set a number of common Content classes. Listing 5 shows how to return a binary image using the ByteArrayContent class from a Controller method. [HttpGet] public HttpResponseMessage AlbumArt(string title) { var album = AlbumData.Current.FirstOrDefault(abl => abl.AlbumName.StartsWith(title)); if (album == null) { var resp = Request.CreateResponse<ApiMessageError>( HttpStatusCode.NotFound, new ApiMessageError("Album not found")); return resp; } // kinda silly - we would normally serve this directly // but hey - it's a demo. var http = new WebClient(); var imageData = http.DownloadData(album.AlbumImageUrl); // create response and return var result = new HttpResponseMessage(HttpStatusCode.OK); result.Content = new ByteArrayContent(imageData); result.Content.Headers.ContentType = new MediaTypeHeaderValue("image/jpeg"); return result; } The image retrieval from Amazon is contrived, but it shows how to return binary data using ByteArrayContent. It also demonstrates that you can easily return multiple types of content from a single controller method, which is actually quite common. If an error occurs - such as a resource can’t be found or a validation error – you can return an error response to the client that’s very specific to the error. In GetAlbumArt(), if the album can’t be found, we want to return a 404 Not Found status (and realistically no error, as it’s an image). Note that if you are not using HTTP Verb-based routing or not accessing a method that starts with Get/Post etc., you have to specify one or more HTTP Verb attributes on the method explicitly. Here, I used the [HttpGet] attribute to serve the image. Another option to handle the error could be to return a fixed placeholder image if no album could be matched or the album doesn’t have an image. When returning an error code, you can also return a strongly typed response to the client. For example, you can set the 404 status code and also return a custom error object (ApiMessageError is a class I defined) like this:return Request.CreateResponse<ApiMessageError>( HttpStatusCode.NotFound, new ApiMessageError("Album not found") ); If the album can be found, the image will be returned. The image is downloaded into a byte[] array, and then assigned to the result’s Content property. I created a new ByteArrayContent instance and assigned the image’s bytes and the content type so that it displays properly in the browser. There are other content classes available: StringContent, StreamContent, ByteArrayContent, MultipartContent, and ObjectContent are at your disposal to return just about any kind of content. You can create your own Content classes if you frequently return custom types and handle the default formatter assignments that should be used to send the data out . Although HttpResponseMessage results require more code than returning a plain .NET value from a method, it allows much more control over the actual HTTP processing than automatic processing. It also makes it much easier to test your controller methods as you get a response object that you can check for specific status codes and output messages rather than just a result value. Routing Again Ok, let’s get back to the image example. Using the original routing we have setup using HTTP Verb routing there's no good way to serve the image. In order to return my album art image I’d like to use a URL like this: http://localhost/aspnetWebApi/albums/Dirty%20Deeds/image In order to create a URL like this, I have to create a new Controller because my earlier routes pointed to the AlbumApiController using HTTP Verb routing. HTTP Verb based routing is great for representing a single set of resources such as albums. You can map operations like add, delete, update and read easily using HTTP Verbs. But you cannot mix action based routing into a an HTTP Verb routing controller - you can only map HTTP Verbs and each method has to be unique based on parameter signature. You can't have multiple GET operations to methods with the same signature. So GetImage(string id) and GetAlbum(string title) are in conflict in an HTTP GET routing scenario. In fact, I was unable to make the above Image URL work with any combination of HTTP Verb plus Custom routing using the single Albums controller. There are number of ways around this, but all involve additional controllers. Personally, I think it’s easier to use explicit Action routing and then add custom routes if you need to simplify your URLs further. So in order to accommodate some of the other examples, I created another controller – AlbumRpcApiController – to handle all requests that are explicitly routed via actions (/albums/rpc/AlbumArt) or are custom routed with explicit routes defined in the HttpConfiguration. I added the AlbumArt() method to this new AlbumRpcApiController class. For the image URL to work with the new AlbumRpcApiController, you need a custom route placed before the default route from Listing 1.RouteTable.Routes.MapHttpRoute( name: "AlbumRpcApiAction", routeTemplate: "albums/rpc/{action}/{title}", defaults: new { title = RouteParameter.Optional, controller = "AlbumRpcApi", action = "GetAblums" } ); Now I can use either of the following URLs to access the image: Custom route: (/albums/rpc/{title}/image)http://localhost/aspnetWebApi/albums/PowerAge/image Action route: (/albums/rpc/action/{title})http://localhost/aspnetWebAPI/albums/rpc/albumart/PowerAge Sending Data to the Server To send data to the server and add a new album, you can use an HTTP POST operation. Since I’m using HTTP Verb-based routing in the original AlbumApiController, I can implement a method called PostAlbum()to accept a new album from the client. Listing 6 shows the Web API code to add a new album.public HttpResponseMessage PostAlbum(Album album) { if (!this.ModelState.IsValid) { // my custom error class var error = new ApiMessageError() { message = "Model is invalid" }; // add errors into our client error model for client foreach (var prop in ModelState.Values) { var modelError = prop.Errors.FirstOrDefault(); if (!string.IsNullOrEmpty(modelError.ErrorMessage)) error.errors.Add(modelError.ErrorMessage); else error.errors.Add(modelError.Exception.Message); } return Request.CreateResponse<ApiMessageError>(HttpStatusCode.Conflict, error); } // update song id which isn't provided foreach (var song in album.Songs) song.AlbumId = album.Id; // see if album exists already var matchedAlbum = AlbumData.Current .SingleOrDefault(alb => alb.Id == album.Id || alb.AlbumName == album.AlbumName); if (matchedAlbum == null) AlbumData.Current.Add(album); else matchedAlbum = album; // return a string to show that the value got here var resp = Request.CreateResponse(HttpStatusCode.OK, string.Empty); resp.Content = new StringContent(album.AlbumName + " " + album.Entered.ToString(), Encoding.UTF8, "text/plain"); return resp; } The PostAlbum() method receives an album parameter, which is automatically deserialized from the POST buffer the client sent. The data passed from the client can be either XML or JSON. Web API automatically figures out what format it needs to deserialize based on the content type and binds the content to the album object. Web API uses model binding to bind the request content to the parameter(s) of controller methods. Like MVC you can check the model by looking at ModelState.IsValid. If it’s not valid, you can run through the ModelState.Values collection and check each binding for errors. Here I collect the error messages into a string array that gets passed back to the client via the result ApiErrorMessage object. When a binding error occurs, you’ll want to return an HTTP error response and it’s best to do that with an HttpResponseMessage result. In Listing 6, I used a custom error class that holds a message and an array of detailed error messages for each binding error. I used this object as the content to return to the client along with my Conflict HTTP Status Code response. If binding succeeds, the example returns a string with the name and date entered to demonstrate that you captured the data. Normally, a method like this should return a Boolean or no response at all (HttpStatusCode.NoConent). The sample uses a simple static list to hold albums, so once you’ve added the album using the Post operation, you can hit the /albums/ URL to see that the new album was added. The client jQuery code to call the POST operation from the client with jQuery is shown in Listing 7. var id = new Date().getTime().toString(); var album = { "Id": id, "AlbumName": "Power Age", "Artist": "AC/DC", "YearReleased": 1977, "Entered": "2002-03-11T18:24:43.5580794-10:00", "AlbumImageUrl": http://ecx.images-amazon.com/images/…, "AmazonUrl": http://www.amazon.com/…, "Songs": [ { "SongName": "Rock 'n Roll Damnation", "SongLength": 3.12}, { "SongName": "Downpayment Blues", "SongLength": 4.22 }, { "SongName": "Riff Raff", "SongLength": 2.42 } ] } $.ajax( { url: "albums/", type: "POST", contentType: "application/json", data: JSON.stringify(album), processData: false, beforeSend: function (xhr) { // not required since JSON is default output xhr.setRequestHeader("Accept", "application/json"); }, success: function (result) { // reload list of albums page.loadAlbums(); }, error: function (xhr, status, p3, p4) { var err = "Error"; if (xhr.responseText && xhr.responseText[0] == "{") err = JSON.parse(xhr.responseText).message; alert(err); } }); The code in Listing 7 creates an album object in JavaScript to match the structure of the .NET Album class. This object is passed to the $.ajax() function to send to the server as POST. The data is turned into JSON and the content type set to application/json so that the server knows what to convert when deserializing in the Album instance. The jQuery code hooks up success and failure events. Success returns the result data, which is a string that’s echoed back with an alert box. If an error occurs, jQuery returns the XHR instance and status code. You can check the XHR to see if a JSON object is embedded and if it is, you can extract it by de-serializing it and accessing the .message property. REST standards suggest that updates to existing resources should use PUT operations. REST standards aside, I’m not a big fan of separating out inserts and updates so I tend to have a single method that handles both. But if you want to follow REST suggestions, you can create a PUT method that handles updates by forwarding the PUT operation to the POST method:public HttpResponseMessage PutAlbum(Album album) { return PostAlbum(album); } To make the corresponding $.ajax() call, all you have to change from Listing 7 is the type: from POST to PUT. Model Binding with UrlEncoded POST Variables In the example in Listing 7 I used JSON objects to post a serialized object to a server method that accepted an strongly typed object with the same structure, which is a common way to send data to the server. However, Web API supports a number of different ways that data can be received by server methods. For example, another common way is to use plain UrlEncoded POST values to send to the server. Web API supports Model Binding that works similar (but not the same) as MVC's model binding where POST variables are mapped to properties of object parameters of the target method. This is actually quite common for AJAX calls that want to avoid serialization and the potential requirement of a JSON parser on older browsers. For example, using jQUery you might use the $.post() method to send a new album to the server (albeit one without songs) using code like the following:$.post("albums/",{AlbumName: "Dirty Deeds", YearReleased: 1976 … },albumPostCallback); Although the code looks very similar to the client code we used before passing JSON, here the data passed is URL encoded values (AlbumName=Dirty+Deeds&YearReleased=1976 etc.). Web API then takes this POST data and maps each of the POST values to the properties of the Album object in the method's parameter. Although the client code is different the server can both handle the JSON object, or the UrlEncoded POST values. Dynamic Access to POST Data There are also a few options available to dynamically access POST data, if you know what type of data you're dealing with. If you have POST UrlEncoded values, you can dynamically using a FormsDataCollection:[HttpPost] public string PostAlbum(FormDataCollection form) { return string.Format("{0} - released {1}", form.Get("AlbumName"),form.Get("RearReleased")); } The FormDataCollection is a very simple object, that essentially provides the same functionality as Request.Form[] in ASP.NET. Request.Form[] still works if you're running hosted in an ASP.NET application. However as a general rule, while ASP.NET's functionality is always available when running Web API hosted inside of an ASP.NET application, using the built in classes specific to Web API makes it possible to run Web API applications in a self hosted environment outside of ASP.NET. If your client is sending JSON to your server, and you don't want to map the JSON to a strongly typed object because you only want to retrieve a few simple values, you can also accept a JObject parameter in your API methods:[HttpPost] public string PostAlbum(JObject jsonData) { dynamic json = jsonData; JObject jalbum = json.Album; JObject juser = json.User; string token = json.UserToken; var album = jalbum.ToObject<Album>(); var user = juser.ToObject<User>(); return String.Format("{0} {1} {2}", album.AlbumName, user.Name, token); } There quite a few options available to you to receive data with Web API, which gives you more choices for the right tool for the job. Unfortunately one shortcoming of Web API is that POST data is always mapped to a single parameter. This means you can't pass multiple POST parameters to methods that receive POST data. It's possible to accept multiple parameters, but only one can map to the POST content - the others have to come from the query string or route values. I have a couple of Blog POSTs that explain what works and what doesn't here: Passing multiple POST parameters to Web API Controller Methods Mapping UrlEncoded POST Values in ASP.NET Web API Handling Delete Operations Finally, to round out the server API code of the album example we've been discussin, here’s the DELETE verb controller method that allows removal of an album by its title:public HttpResponseMessage DeleteAlbum(string title) { var matchedAlbum = AlbumData.Current.Where(alb => alb.AlbumName == title) .SingleOrDefault(); if (matchedAlbum == null) return new HttpResponseMessage(HttpStatusCode.NotFound); AlbumData.Current.Remove(matchedAlbum); return new HttpResponseMessage(HttpStatusCode.NoContent); } To call this action method using jQuery, you can use:$(".removeimage").live("click", function () { var $el = $(this).parent(".album"); var txt = $el.find("a").text(); $.ajax({ url: "albums/" + encodeURIComponent(txt), type: "Delete", success: function (result) { $el.fadeOut().remove(); }, error: jqError }); } Note the use of the DELETE verb in the $.ajax() call, which routes to DeleteAlbum on the server. DELETE is a non-content operation, so you supply a resource ID (the title) via route value or the querystring. Routing Conflicts In all requests with the exception of the AlbumArt image example shown so far, I used HTTP Verb routing that I set up in Listing 1. HTTP Verb Routing is a recommendation that is in line with typical REST access to HTTP resources. However, it takes quite a bit of effort to create REST-compliant API implementations based only on HTTP Verb routing only. You saw one example that didn’t really fit – the return of an image where I created a custom route albums/{title}/image that required creation of a second controller and a custom route to work. HTTP Verb routing to a controller does not mix with custom or action routing to the same controller because of the limited mapping of HTTP verbs imposed by HTTP Verb routing. To understand some of the problems with verb routing, let’s look at another example. Let’s say you create a GetSortableAlbums() method like this and add it to the original AlbumApiController accessed via HTTP Verb routing:[HttpGet] public IQueryable<Album> SortableAlbums() { var albums = AlbumData.Current; // generally should be done only on actual queryable results (EF etc.) // Done here because we're running with a static list but otherwise might be slow return albums.AsQueryable(); } If you compile this code and try to now access the /albums/ link, you get an error: Multiple Actions were found that match the request. HTTP Verb routing only allows access to one GET operation per parameter/route value match. If more than one method exists with the same parameter signature, it doesn’t work. As I mentioned earlier for the image display, the only solution to get this method to work is to throw it into another controller. Because I already set up the AlbumRpcApiController I can add the method there. First, I should rename the method to SortableAlbums() so I’m not using a Get prefix for the method. This also makes the action parameter look cleaner in the URL - it looks less like a method and more like a noun. I can then create a new route that handles direct-action mapping:RouteTable.Routes.MapHttpRoute( name: "AlbumRpcApiAction", routeTemplate: "albums/rpc/{action}/{title}", defaults: new { title = RouteParameter.Optional, controller = "AlbumRpcApi", action = "GetAblums" } ); As I am explicitly adding a route segment – rpc – into the route template, I can now reference explicit methods in the Web API controller using URLs like this: http://localhost/AspNetWebApi/rpc/SortableAlbums Error Handling I’ve already done some minimal error handling in the examples. For example in Listing 6, I detected some known-error scenarios like model validation failing or a resource not being found and returning an appropriate HttpResponseMessage result. But what happens if your code just blows up or causes an exception? If you have a controller method, like this:[HttpGet] public void ThrowException() { throw new UnauthorizedAccessException("Unauthorized Access Sucka"); } You can call it with this: http://localhost/AspNetWebApi/albums/rpc/ThrowException The default exception handling displays a 500-status response with the serialized exception on the local computer only. When you connect from a remote computer, Web API throws back a 500 HTTP Error with no data returned (IIS then adds its HTML error page). The behavior is configurable in the GlobalConfiguration:GlobalConfiguration .Configuration .IncludeErrorDetailPolicy = IncludeErrorDetailPolicy.Never; If you want more control over your error responses sent from code, you can throw explicit error responses yourself using HttpResponseException. When you throw an HttpResponseException the response parameter is used to generate the output for the Controller action. [HttpGet] public void ThrowError() { var resp = Request.CreateResponse<ApiMessageError>( HttpStatusCode.BadRequest, new ApiMessageError("Your code stinks!")); throw new HttpResponseException(resp); } Throwing an HttpResponseException stops the processing of the controller method and immediately returns the response you passed to the exception. Unlike other Exceptions fired inside of WebAPI, HttpResponseException bypasses the Exception Filters installed and instead just outputs the response you provide. In this case, the serialized ApiMessageError result string is returned in the default serialization format – XML or JSON. You can pass any content to HttpResponseMessage, which includes creating your own exception objects and consistently returning error messages to the client. Here’s a small helper method on the controller that you might use to send exception info back to the client consistently:private void ThrowSafeException(string message, HttpStatusCode statusCode = HttpStatusCode.BadRequest) { var errResponse = Request.CreateResponse<ApiMessageError>(statusCode, new ApiMessageError() { message = message }); throw new HttpResponseException(errResponse); } You can then use it to output any captured errors from code:[HttpGet] public void ThrowErrorSafe() { try { List<string> list = null; list.Add("Rick"); } catch (Exception ex) { ThrowSafeException(ex.Message); } } Exception Filters Another more global solution is to create an Exception Filter. Filters in Web API provide the ability to pre- and post-process controller method operations. An exception filter looks at all exceptions fired and then optionally creates an HttpResponseMessage result. Listing 8 shows an example of a basic Exception filter implementation.public class UnhandledExceptionFilter : ExceptionFilterAttribute { public override void OnException(HttpActionExecutedContext context) { HttpStatusCode status = HttpStatusCode.InternalServerError; var exType = context.Exception.GetType(); if (exType == typeof(UnauthorizedAccessException)) status = HttpStatusCode.Unauthorized; else if (exType == typeof(ArgumentException)) status = HttpStatusCode.NotFound; var apiError = new ApiMessageError() { message = context.Exception.Message }; // create a new response and attach our ApiError object // which now gets returned on ANY exception result var errorResponse = context.Request.CreateResponse<ApiMessageError>(status, apiError); context.Response = errorResponse; base.OnException(context); } } Exception Filter Attributes can be assigned to an ApiController class like this:[UnhandledExceptionFilter] public class AlbumRpcApiController : ApiController or you can globally assign it to all controllers by adding it to the HTTP Configuration's Filters collection:GlobalConfiguration.Configuration.Filters.Add(new UnhandledExceptionFilter()); The latter is a great way to get global error trapping so that all errors (short of hard IIS errors and explicit HttpResponseException errors) return a valid error response that includes error information in the form of a known-error object. Using a filter like this allows you to throw an exception as you normally would and have your filter create a response in the appropriate output format that the client expects. For example, an AJAX application can on failure expect to see a JSON error result that corresponds to the real error that occurred rather than a 500 error along with HTML error page that IIS throws up. You can even create some custom exceptions so you can differentiate your own exceptions from unhandled system exceptions - you often don't want to display error information from 'unknown' exceptions as they may contain sensitive system information or info that's not generally useful to users of your application/site. This is just one example of how ASP.NET Web API is configurable and extensible. Exception filters are just one example of how you can plug-in into the Web API request flow to modify output. Many more hooks exist and I’ll take a closer look at extensibility in Part 2 of this article in the future. Summary Web API is a big improvement over previous Microsoft REST and AJAX toolkits. The key features to its usefulness are its ease of use with simple controller based logic, familiar MVC-style routing, low configuration impact, extensibility at all levels and tight attention to exposing and making HTTP semantics easily discoverable and easy to use. Although none of the concepts used in Web API are new or radical, Web API combines the best of previous platforms into a single framework that’s highly functional, easy to work with, and extensible to boot. I think that Microsoft has hit a home run with Web API. Related Resources Where does ASP.NET Web API fit? Sample Source Code on GitHub Passing multiple POST parameters to Web API Controller Methods Mapping UrlEncoded POST Values in ASP.NET Web API Creating a JSONP Formatter for ASP.NET Web API Removing the XML Formatter from ASP.NET Web API Applications© Rick Strahl, West Wind Technologies, 2005-2012Posted in Web Api Tweet !function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0];if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src="//platform.twitter.com/widgets.js";fjs.parentNode.insertBefore(js,fjs);}}(document,"script","twitter-wjs"); (function() { var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true; po.src = 'https://apis.google.com/js/plusone.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s); })();

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Parallelism in .NET – Part 7, Some Differences between PLINQ and LINQ to Objects

- by Reed

In my previous post on Declarative Data Parallelism, I mentioned that PLINQ extends LINQ to Objects to support parallel operations. Although nearly all of the same operations are supported, there are some differences between PLINQ and LINQ to Objects. By introducing Parallelism to our declarative model, we add some extra complexity. This, in turn, adds some extra requirements that must be addressed. In order to illustrate the main differences, and why they exist, let’s begin by discussing some differences in how the two technologies operate, and look at the underlying types involved in LINQ to Objects and PLINQ . LINQ to Objects is mainly built upon a single class: Enumerable. The Enumerable class is a static class that defines a large set of extension methods, nearly all of which work upon an IEnumerable<T>. Many of these methods return a new IEnumerable<T>, allowing the methods to be chained together into a fluent style interface. This is what allows us to write statements that chain together, and lead to the nice declarative programming model of LINQ: double min = collection .Where(item => item.SomeProperty > 6 && item.SomeProperty < 24) .Min(item => item.PerformComputation()); .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Other LINQ variants work in a similar fashion. For example, most data-oriented LINQ providers are built upon an implementation of IQueryable<T>, which allows the database provider to turn a LINQ statement into an underlying SQL query, to be performed directly on the remote database. PLINQ is similar, but instead of being built upon the Enumerable class, most of PLINQ is built upon a new static class: ParallelEnumerable. When using PLINQ, you typically begin with any collection which implements IEnumerable<T>, and convert it to a new type using an extension method defined on ParallelEnumerable: AsParallel(). This method takes any IEnumerable<T>, and converts it into a ParallelQuery<T>, the core class for PLINQ. There is a similar ParallelQuery class for working with non-generic IEnumerable implementations. This brings us to our first subtle, but important difference between PLINQ and LINQ – PLINQ always works upon specific types, which must be explicitly created. Typically, the type you’ll use with PLINQ is ParallelQuery<T>, but it can sometimes be a ParallelQuery or an OrderedParallelQuery<T>. Instead of dealing with an interface, implemented by an unknown class, we’re dealing with a specific class type. This works seamlessly from a usage standpoint – ParallelQuery<T> implements IEnumerable<T>, so you can always “switch back” to an IEnumerable<T>. The difference only arises at the beginning of our parallelization. When we’re using LINQ, and we want to process a normal collection via PLINQ, we need to explicitly convert the collection into a ParallelQuery<T> by calling AsParallel(). There is an important consideration here – AsParallel() does not need to be called on your specific collection, but rather any IEnumerable<T>. This allows you to place it anywhere in the chain of methods involved in a LINQ statement, not just at the beginning. This can be useful if you have an operation which will not parallelize well or is not thread safe. For example, the following is perfectly valid, and similar to our previous examples: double min = collection .AsParallel() .Select(item => item.SomeOperation()) .Where(item => item.SomeProperty > 6 && item.SomeProperty < 24) .Min(item => item.PerformComputation()); However, if SomeOperation() is not thread safe, we could just as easily do: double min = collection .Select(item => item.SomeOperation()) .AsParallel() .Where(item => item.SomeProperty > 6 && item.SomeProperty < 24) .Min(item => item.PerformComputation()); In this case, we’re using standard LINQ to Objects for the Select(…) method, then converting the results of that map routine to a ParallelQuery<T>, and processing our filter (the Where method) and our aggregation (the Min method) in parallel. PLINQ also provides us with a way to convert a ParallelQuery<T> back into a standard IEnumerable<T>, forcing sequential processing via standard LINQ to Objects. If SomeOperation() was thread-safe, but PerformComputation() was not thread-safe, we would need to handle this by using the AsEnumerable() method: double min = collection .AsParallel() .Select(item => item.SomeOperation()) .Where(item => item.SomeProperty > 6 && item.SomeProperty < 24) .AsEnumerable() .Min(item => item.PerformComputation()); Here, we’re converting our collection into a ParallelQuery<T>, doing our map operation (the Select(…) method) and our filtering in parallel, then converting the collection back into a standard IEnumerable<T>, which causes our aggregation via Min() to be performed sequentially. This could also be written as two statements, as well, which would allow us to use the language integrated syntax for the first portion: var tempCollection = from item in collection.AsParallel() let e = item.SomeOperation() where (e.SomeProperty > 6 && e.SomeProperty < 24) select e; double min = tempCollection.AsEnumerable().Min(item => item.PerformComputation()); This allows us to use the standard LINQ style language integrated query syntax, but control whether it’s performed in parallel or serial by adding AsParallel() and AsEnumerable() appropriately. The second important difference between PLINQ and LINQ deals with order preservation. PLINQ, by default, does not preserve the order of of source collection. This is by design. In order to process a collection in parallel, the system needs to naturally deal with multiple elements at the same time. Maintaining the original ordering of the sequence adds overhead, which is, in many cases, unnecessary. Therefore, by default, the system is allowed to completely change the order of your sequence during processing. If you are doing a standard query operation, this is usually not an issue. However, there are times when keeping a specific ordering in place is important. If this is required, you can explicitly request the ordering be preserved throughout all operations done on a ParallelQuery<T> by using the AsOrdered() extension method. This will cause our sequence ordering to be preserved. For example, suppose we wanted to take a collection, perform an expensive operation which converts it to a new type, and display the first 100 elements. In LINQ to Objects, our code might look something like: // Using IEnumerable<SourceClass> collection IEnumerable<ResultClass> results = collection .Select(e => e.CreateResult()) .Take(100); If we just converted this to a parallel query naively, like so: IEnumerable<ResultClass> results = collection .AsParallel() .Select(e => e.CreateResult()) .Take(100); We could very easily get a very different, and non-reproducable, set of results, since the ordering of elements in the input collection is not preserved. To get the same results as our original query, we need to use: IEnumerable<ResultClass> results = collection .AsParallel() .AsOrdered() .Select(e => e.CreateResult()) .Take(100); This requests that PLINQ process our sequence in a way that verifies that our resulting collection is ordered as if it were processed serially. This will cause our query to run slower, since there is overhead involved in maintaining the ordering. However, in this case, it is required, since the ordering is required for correctness. PLINQ is incredibly useful. It allows us to easily take nearly any LINQ to Objects query and run it in parallel, using the same methods and syntax we’ve used previously. There are some important differences in operation that must be considered, however – it is not a free pass to parallelize everything. When using PLINQ in order to parallelize your routines declaratively, the same guideline I mentioned before still applies: Parallelization is something that should be handled with care and forethought, added by design, and not just introduced casually.

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December release of Microsoft All-In-One Code Framework is available now.

- by Jialiang

The code samples in Microsoft All-In-One Code Framework are updated on 2010-12-13. Download address: http://1code.codeplex.com/releases/view/57459#DownloadId=185534 Updated code sample index categorized by technologies: http://1code.codeplex.com/wikipage?title=All-In-One%20Code%20Framework%20Sample%20Catalog (it also allows you to download individual code samples instead of the entire All-In-One Code Framework sample package.) If it’s the first time that you hear about Microsoft All-In-One Code Framework, please watch the introduction video on YouTube http://www.youtube.com/watch?v=cO5Li3APU58, or read the introduction on our homepage http://1code.codeplex.com/, and this Port25 article http://port25.technet.com/archive/2010/01/18/the-all-in-one-code-framework.aspx. -------------- New ASP.NET Code Samples VBASPNETAJAXWebChat and CSASPNETAJAXWebChat Most of you have some experience in chatting with friends on the web. So you may want to know how to make a web chat application, it seems to be quite complicated. But ASP.NET gives you the power to buiild a chat room easily. In this code sample, we will construct our own web chat room with the amazing AJAX feature. The principle is simple relatively. As we all know, a base chat application need 4 base controls: one List control to show the chat room members, one List control to show the message list, one TextBox control to input messages and one button to send message. User inputs his message in the textbox first and then presses Send button, it will send the message to the server. The message list will update every 2 seconds to get the newest message list in the chat room from the server. We need to know, it is hard for us to make an AJAX web chat application like a windows form application because we cannot keep the connection after one web request ended. So a lot of events which communicates between client side and server side cannot be realized. The common workaround is to make web requests in every some seconds to check whether the server side has been updated. But another technique called COMET makes it possible. But it is different with AJAX and will not be talked in details in this KB. For more details about COMET, we can get some clues from the Reference. CSASPNETCurrentOnlineUserList and VBASPNETCurrentOnlineUserList This sample demos a system that needs to display a list of current online users' information. As a matter of fact, Membership.GetNumberOfUsersOnline Method can get the number of online users and there is a convenient approach to check whether the user is online by using Membership.GetUser(string userName).IsOnline property,however many asp.net projects are not using membership.So in this case,the sample shows how to display a list of current online users' information without using membership provider. It is not difficult to check whether the user is online by using session.Many projects tend to be used “Session_End” event to mark a user as “Offline”,however ,it may not be a good idea,because it can’t detect the user status accurately. In addition, "Session_End" event is only available in the "InProc" session mode. If you are storing session states in the State Server or SQL Server, "Session_End" event will never fire. To handle this issue, we need to save the user online status to a global DataTable or DataBase. In the sample application, define a global DataTable to store the information of online users.Use XmlHttpRequest in the pages to update and check user's last active time at intervals and also retrieve information on how many users are still online. The sample project can auto delete offline users' information from a global DataTable by checking users’ last active time. A step-by-step guide illustrating how to display a list of current online users' information without using membership provider: 1. Login page. Let user sign in and add current user’s information to a global datatable while Initialize the global datatable which used to store information of current online users. 2. Current online user list page. Use XmlHttpRequest in this page to update and check user's last active time at intervals and also retrieve information on how many users are still online. 3. If user closes the page without clicking the sign out link button ,the sample project can auto mark the user as offline and delete offline users' information from a global DataTable which used to store information of current online users by checking users’ last active time. Then the current online user list will be like this: CSASPNETIPtoLocation This sample demonstrates how to find the geographical location from an IP address. As we know, it is not hard for us to get the IP address of visitors via Request.ServerVariable property, but it is really difficult for us to know where they come from. To achieve this feature, the sample uses a free third party web service from http://freegeoip.appspot.com/, which returns the information about an IP address we send to the server in the format of XML, JSON or CSV. It makes all things easier. CSASPNETBackgroundWorker Sometimes we do an operation which needs long time to complete. It will stop the response and the page is blank until the operation finished. In this case, we want the operation to run in the background, and in the page, we want to display the progress of the running operation. Therefore, the user can know the operation is running and can know the progress. CSASPNETInheritingFromTreeNode In windows forms TreeView, each tree node has a property called "Tag" which can be used to store a custom object. Many customers want to implement the same tag feature in ASP.NET TreeView. This project creates a custom TreeView control named "CustomTreeView" to achieve this goal. CSASPNETRemoteUploadAndDownload and VBASPNETRemoteUploadAndDownload This code sample was created in response to a code sample request in our new code sample request frunction for customers. The code samples demonstrate uploading files to and downloading files from a remote HTTP or FTP server. In .NET Framework 2.0 and higher versions, there are some lightweight class libraries which support HTTP and FTP protocol transmission. By using these classes, we can achieve this programming requirement. CSASPNETImageEditUpload and VBASPNETImageEditUpload This demo will shows how to insert, edit and update a common image with the type of "jpg", "png", "gif" or "bmp" . We mainly use two different SqlDataSources with the same database to bind to GridView and FormView in order to establish the “cascading” effort. Besides we apply our self-made ImageHanlder to encoding or decoding images of different types, and use context to output the stream of images. We will explicitly assign the binary streams of images through the event of “FormView_ItemInserting” or “Form_ItemUpdating” to synchronize the stream both in what we can see on an aspx page as well as in what’s really stored in the database. WebBrowser Control, Network and other Windows General New Code Samples CSWebBrowserSuppressError and VBWebBrowserSuppressError The sample demonstrates how to make WebBrowser suppress errors, such as script error, navigation error and so on. CSWebBrowserWithProxy and VBWebBrowserWithProxy The sample demonstrates how to make WebBrowser use a proxy server. CSWebDownloadProgress and VBWebDownloadProgress The sample demonstrates how to show progress during the download. It also supplies the features to Start, Pause, Resume and Cancel a download. CppSetDesktopWallpaper, CSSetDesktopWallpaper and VBSetDesktopWallpaper This code sample application allows you select an image, view a preview (resized smaller to fit if necessary), select a display style among Tile, Center, Stretch, Fit (Windows 7 and later) and Fill (Windows 7 and later), and set the image as the Desktop wallpaper. CSWindowsServiceRecoveryProperty and VBWindowsServiceRecoveryProperty CSWindowsServiceRecoveryProperty example demonstrates how to use ChangeServiceConfig2 to configure the service "Recovery" properties in C#. This example operates all the options you can see on the service "Recovery" tab, including setting the "Enable actions for stops with errors" option in Windows Vista and later operating systems. This example also include how to grant the shut down privilege to the process, so that we can configure a special option in the "Recovery" tab - "Restart Computer Options...". New Office Development Code Samples CSOneNoteRibbonAddIn and VBOneNoteRibbonAddIn The code sample demonstrates a OneNote 2010 COM add-in that implements IDTExtensibility2. The add-in also supports customizing the Ribbon by implementing the IRibbonExtensibility interface. It is a skeleton OneNote add-in that developers can extend it to implement more functions. The code sample was requested by a customer in our code sample request service. We expect that this could help developers in the community. New Windows Shell Code Samples CppShellExtPreviewHandler, CSShellExtPreviewHandler and VBShellExtPreviewHandler In the past two months, we released the code samples of Windows Context Menu Handler, Infotip Handler, and Thumbnail Handler. This is the fourth part of the shell extension series: Preview Handler. The code samples demo the C++, C# and VB.NET implementation of a preview handler for a new file type registered with the .recipe extension. Preview handlers are called when an item is selected to show a lightweight, rich, read-only preview of the file's contents in the view's reading pane. This is done without launching the file's associated application. Windows Vista and later operating systems support preview handlers. To be a valid preview handler, several interfaces must be implemented. This includes IPreviewHandler (shobjidl.h); IInitializeWithFile, IInitializeWithStream, or IInitializeWithItem (propsys.h); IObjectWithSite (ocidl.h); and IOleWindow (oleidl.h). There are also optional interfaces, such as IPreviewHandlerVisuals (shobjidl.h), that a preview handler can implement to provide extended support. Windows API Code Pack for Microsoft .NET Framework makes the implementation of these interfaces very easy in .NET. The example preview handler provides previews for .recipe files. The .recipe file type is simply an XML file registered as a unique file name extension. It includes the title of the recipe, its author, difficulty, preparation time, cook time, nutrition information, comments, an embedded preview image, and so on. The preview handler extracts the title, comments, and the embedded image, and display them in a preview window. In response to many customers' request, we added setup projects in every shell extension samples in this release. Those setup projects allow you to deploy the shell extensions to your end users' machines. ---------- Download address: http://1code.codeplex.com/releases/view/57459#DownloadId=185534 Updated code sample index categorized by technologies: http://1code.codeplex.com/wikipage?title=All-In-One%20Code%20Framework%20Sample%20Catalog (it also allows you to download individual code samples instead of the entire All-In-One Code Framework sample package.) If you have any feedback for us, please email: [email protected]. We look forward to your comments.

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