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• CreateDelegate with unknown types

  - by Giorgi

  Hello, I am trying to create Delegate for reading/writing properties of unknown type of class at runtime. I have a generic class Main<T> and a method which looks like this: Delegate.CreateDelegate(typeof(Func<T, object>), get) where get is a MethodInfo of the property that should be read. The problem is that when the property returns int (I guess this happens for value types) the above code throws ArgumentException because the method cannot be bound. In case of string it works well. To solve the problem I changed the code so that corresponding Delegate type is generated by using MakeGenericType. So now the code is: Type func = typeof(Func<,>); Type generic = func.MakeGenericType(typeof(T), get.ReturnType); var result = Delegate.CreateDelegate(generic, get) The problem now is that the created delegate instance of generic so I have to use DynamicInvoke which would be as slow as using pure reflection to read the field. So my question is why is that the first snippet of code fails with value types. According to MSDN it should work as it says that The return type of a delegate is compatible with the return type of a method if the return type of the method is more restrictive than the return type of the delegate and how to execute the delegate in the second snippet so that it is faster than reflection. Thanks.

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• How to remove the error "Cant find PInvoke DLL SQLite.interop.dll"

  - by Shailesh Jaiswal

  I am developing windows mobile application. I am using the SQLlite database. I am using the following code to connect to this database as follows SQLiteConnection cn = new SQLiteConnection(); SQLiteDataReader SQLiteDR; cn.ConnectionString = @"Data Source=F:\CompNetDB.db3"; cn.Open(); SQLiteCommand cmd = new SQLiteCommand(); cmd.CommandText = "select * from CustomerInfo"; cmd.CommandType = CommandType.Text; cmd.Connection = cn; SQLiteDR = cmd.ExecuteReader(); In the above case I am getting the error "Cant find PInvike DLL SQLite.interop.dll". I have added the DLL System.Data.SQLLite from the \SQLite.NET\bin\compactframework this folder. This is the folder which is installed by default when I installed the SQLite. In the same folder there is one DLL file named SQLlite.Interop.66.DLL. When I try to add reference to this dll it is giving error that dll can not be added. Are the two dlls SQLlite.Interop.dll & System.Interop.066.dll same ? In the above code how to solve the error "Cant find PInvoke.SQLite.Interop.dll" Please can you tell whether there is mistake in my code or I am missing something in my application?

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• jQuery carousel in a div with display:none

  - by Fred Kafka

  I have to use on my site a jQuery responsive carousel with 4 displayed items that slide one at a time, etc etc. The point is: this carousel is placed in a div with display:none and it appears clicking on a button with a slideToggle script (jQuery). Well, when the div appears the carousel is not displayed. Nothing! Notice that if I remove the display:none the carousel shows perfectly. I've tried a bunch of carousel plugin (bxslider, caroufredsel, elastislide, flexslider) and this issue happens for all of them. And then... I'm going crazy!! Excuse meSorry friends, here is the code: HTML (here is the case of FlexSlider but the code is similar for the other plugins) <div id="hiddenDiv"> <div id="hiddenDivInner"> <div class="flexslider"> <ul class="slides"> <li>...</li> <li>...</li> <li>...</li> </ul> </div> </div> </div> CSS #hiddenDiv{ display:none; padding-bottom:10px; background: url("../img/xxx.gif") repeat left bottom #FFFFFF; } SCRIPT (copy-paste from the site. This script is between $(document).ready together with other scripts. Alredy tried to remove the load function) $(window).load(function() { $('.flexslider').flexslider({ animation: "slide", animationLoop: false, itemWidth: 300, itemMargin: 5, minItems: 1, maxItems: 4 }); }); $("#trigger").click(function () { $("#hiddenDiv").slideToggle(400, "easeInOutExpo"); }); I remind you that with this code and no display:none every carousels work, also if I slide up and then down the div using the slideToggle button (#trigger).

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• What's the Matlab equivalent of NULL, when it's calling COM/ActiveX methods?

  - by David M

  Hi, I maintain a program which can be automated via COM. Generally customers use VBS to do their scripting, but we have a couple of customers who use Matlab's ActiveX support and are having trouble calling COM object methods with a NULL parameter. They've asked how they do this in Matlab - and I've been scouring Mathworks' COM/ActiveX documentation for a day or so now and can't figure it out. Their example code might look something like this: function do_something() OurAppInstance = actxserver('Foo.Application'); OurAppInstance.Method('Hello', NULL) end where NULL is where in another language, we'd write NULL or nil or Nothing, or, of course, pass in an object. The problem is this is optional (and these are implemented as optional parameters in most, but not all, cases) - these methods expect to get NULL quite often. They tell me they've tried [] (which from my reading seemed the most likely) as well as '', Nothing, 'Nothing', None, Null, and 0. I have no idea how many of those are even valid Matlab keywords - certainly none work in this case. Can anyone help? What's Matlab's syntax for a null pointer / object for use as a COM method parameter? Update: Thanks for all the replies so far! Unfortunately, none of the answers seem to work, not even libpointer. The error is the same in all cases: Error: Type mismatch, argument 2 This parameter in the COM type library is described in RIDL as: HRESULT _stdcall OurMethod([in] BSTR strParamOne, [in, optional] OurCoClass* oParamTwo, [out, retval] VARIANT_BOOL* bResult); The coclass in question implements a single interface descending from IDispatch.

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• How to solve timing problems in automated UI tests with C# and Visual Studio?

  - by Lernkurve

  Question What is the standard approach to solve timing problems in automated UI tests? Concrete example I am using Visual Studio 2010 and Team Foundation Server 2010 to create automated UI tests and want to check whether my application has really stopped running: [TestMethod] public void MyTestMethod() { Assert.IsTrue(!IsMyAppRunning(), "App shouldn't be running, but is."); StartMyApp(); Assert.IsTrue(IsMyAppRunning(), "App should have been started and should be running now."); StopMyApp(); //Pause(500); Assert.IsTrue(!IsMyAppRunning(), "App was stopped and shouldn't be running anymore."); } private bool IsMyAppRunning() { foreach (Process runningProcesse in Process.GetProcesses()) { if (runningProcesse.ProcessName.Equals("Myapp")) { return true; } } return false; } private void Pause(int pauseTimeInMilliseconds) { System.Threading.Thread.Sleep(pauseTimeInMilliseconds); } StartMyApp() and StopMyApp() have been recorded with MS Test Manager 2010 and reside in UIMap.uitest. The last assert fails because the assertion is executed while my application is still in the process of shutting down. If I put a delay after StopApp() the test case passes. The above is just an example to explain my problem. What is the standard approach to solve these kinds of timing issues? One idea would be to wait with the assertion until I get some event notification that my app has been stopped.

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• Is there the equivalent of cloud computing for modems?

  - by morpheous

  I asked this question on SF, and someone recommended that I ask it here - (I don't think I have enough points to move a question from SF to SO - and in any case, I don't know how to do it - so here is the question again): I am interested in the concept of PAAS (platform as a service). However, all talk about SAAS/PAAS seems to focus on only the computer itself - not its peripherals. Is it possible to 'outsource' modems as a resource - so that an app running remotely can pump data to a modem in the cloud? As a bit of background to the question, a group of us are thinking of starting a company that offers similar services to companies like twilio etc - but I want to 'outsource' both the computing hardware (thats PAAS - the easy bit) and the modems (thats what I cant seem to find any info on). Does anyone know if modems can be bundled as part of a PAAS service? - alternatively, is there a way that an application running on one computer can communicate (i.e. pump data) to a remote modem residing on another machine?. I assume I can come up with some protocol over UDP or TCP - but there is no point reinventing the wheel - if such a protocol like that already exists (or if it some open source software allows one to do this). Any suggestions on how to solve this problem?

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• Slow Databinding setup time in C# .NET 4.0

  - by Svisstack

  Hello, I have got a problem. I have windows forms application with dynamic generated layout, but i have a problem in performance. In this form i use DataBinding from .NET 4.0 and databinding after setup works fine, but he binding setup time for ONE control blocking my application on approx 0.7 second. I have some controls and time of binging setuping is around 2 minutes. I trying all possible solutions, I dont have any ideas without write self binding class. Why is wrong with my code? case "Boolean": { Binding b = new Binding("Checked", __bindingsource, __ep.Name); CheckBox cb = new CheckBox(); /* * HERE is the problem */ cb.DataBindings.Add(b); /* * HERE is the end of problem */ __flp.Controls.Add(cb); __bindingcontrol.AddBinding(b); break; } Without problem code lines all works fast and without binding ;-( but i want binding turn on in normal speed. PS1. I have suspended layout in generation time. PS2. I have same problem with binding TextBox'es, PictureBoxe's, CheckBox is only example. How to do that?

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• HttpURLConnection: What's the deal with having to read the whole response?

  - by stormin986

  My current problem is very similar to this one. I have a downloadFile(URL) function that creates a new HttpURLConnection, opens it, reads it, returns the results. When I call this function on the same URL multiple times, the second time around it almost always returns a response code of -1 (But throws no exception!!!). The top answer in that question is very helpful, but there are a few things I'm trying to understand. So, if setting http.keepAlive to false solves the problem, it indicates what exactly? That the server is responding in a way that violates the http protocol? Or more likely, my code is violating the protocol in some way? What will the trace tell me? What should I look for? And what's the deal with this: You need to read everything from error stream. Otherwise, it's going to confuse next connection and that's the cause of -1. Does this mean if the response is some type of error (which would be what response code(s)?), the stream HAS to be fully read? Also, every time I am attempting an http request I am basically creating a new connection, and then disconnect()ing it at the end. However, in my case I'm not getting a 401 or whatever. It's always a 200. But my second connection almost always fails. Does this mean there's some other data I should be reading that I'm not (in a similar manner that the error stream must be fully read)? Please help shed some light on this? I feel like there's some fundamental http protocol understanding I'm missing.

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• Query on object id in VQL

  - by Banang

  I'm currently working with the versant object database (using jvi), and have a case where I need to query the database based on an object id. What I'm trying to achieve is something along the lines of Employee employee = new Employee("Mr. Pickles"); session.commit(); FundVQLQuery q = new FundVQLQuery(session, "select * from Employee employee where employee = $1"); q.bind(employee); q.execute(); However, I'm finding out the hard way (I get an EVJ_NOT_A_VALID_KEY_TYPE error thrown at me) that this is infact not the way to do it. Anyone got any experience in working with VQL? Your help is much apreciated! A small clarification: The problem is I'm running some performance tests on the database using the pole position framework, and one of the tests in that framework requires me to fetch an object from the database using either an object reference or a low level object id. Thus, I'm not allowed to reference specific fields in the employee object, but must perform the query on the object in its entirety. So, it's not allowed for me to go "select * from Employee e where e.id = 4", I need it to use the entire object. Accepted answer: Since there is some sort of lunacy magic built into SO that prevents me to mark an accepted answer after a bounty has run out, readers should know that the answer posted by Chris Holmes solves this issue. Readers are encouraged to up-vote his post to further signalize the correctness of his answer to any future readers of this thread.

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• .NET: Allow NULLS in DB fields?

  - by mark smith

  Hi there, I have the task of re-factoring an SQLServer DB.... A lot of the tables and columns "ALLOW NULLS", Is this good practice... I seem to remember the authour of CSLA.NET saying it was really bad practice to allow nulls in a DB... If this is the case, what are my alternatives? Remove all "ALLOW NULLS" from all columns.... and in numeric columns use a value of -1 for example?? I would really appreciate any input anyone has. I am currently using a Model (from entity framework) from my DB and the db columns that "ALLOW NULLS" are null ... and some of the stored procedures require that i have a default value... i.e. BOOLEAN require FALSE as default ... but it is null.. Well i don't want to stray from my original question, ALLOW NULLS are a bad thing from what i can gather .... so how do i fix this ? Any help really appreciated

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• Convert a Relative URL to an Absolute URL in Actionscript / Flex

  - by Bear

  I am working with Flex, and I need to take a relative URL source property and convert it to an absolute URL before loading it. The specific case I am working with involves tweaking SoundEffect's load method. I need to determine if a file will be loaded from the local file system or over the network from looking at the source property, and the easiest way I've found to do this is to generate the absolute URL. I'm having trouble generating the absolute URL for sound effect in particular. Here were my initial thoughts, which haven't worked. Look for the DisplayObject that the Sound Effect targets, and use its loaderInfo property. The target is null when the SoundEffect loads, so this doesn't work. Look at FlexGlobals.topLevelApplication, at the url or loaderInfo properties. Neither of these are set, however. Look at the FlexGlobals.topLevelApplication.systemManager.loaderInfo. This was also not set. The SoundEffect.as code basically boils down to var url:String = "mySound.mp3"; /*>> I'd like to convert the URL to absolute form here and tweak it as necessary <<*/ var req:URLRequest = new URLRequest(url); var loader:Loader = new Loader(); loader.load(req); Does anyone know how to do this? Any help clarifying the rules of how relative urls are resolved for URLRequests in ActionScript would also be much appreciated. edit I would also be perfectly satisfied with some way to tell whether the url will be loaded from the local file system or over the network. Looking at an absolute URL it would just be easy to look at the prefix, like file:// or http://.

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• .NET RegEx - First N chars of First M lines

  - by George

  Hello! I want 4 general RegEx expressions for the following 4 basic cases: Up to A chars starting after B chars from start of line on up to C lines starting after D lines from start of file Up to A chars starting after B chars from start of line on up to C lines occurring before D lines from end of file Up to A chars starting before B chars from end of line on up to C lines starting after D lines from start of file Up to A chars starting before B chars from end of line on up to C lines starting before D lines from end of file These would allow to select arbitrary text blocks anywhere in the file. So far I have managed to come up with cases that only work for lines and chars separately: (?<=(?m:^[^\r]{N}))[^\r]{1,M} = UP TO M chars OF EVERY LINE, AFTER FIRST N chars [^\r]{1,M}(?=(?m:.{N}\r$)) = UP TO M chars OF EVERY LINE, BEFORE LAST N chars The above 2 expressions are for chars, and they return MANY matches (one for each line). (?<=(\A([^\r]*\r\n){N}))(?m:\n*[^\r]*\r$){1,M} = UP TO M lines AFTER FIRST N lines (((?=\r?)\n[^\r]*\r)|((?=\r?)\n[^\r]+\r?)){1,M}(?=((\n[^\r]*\r)|(\n[^\r]+\r?)){N}\Z) = UP TO M lines BEFORE LAST N lines from end These 2 expressions are equivalents for the lines, but they always return just ONE match. The task is to combine these expressions to allow for scenarios 1-4. Anyone can help? Note that the case in the title of the question, is just a subclass of scenario #1, where both B = 0 and D = 0. EXAMPLE: SOURCE: line1 blah 1 line2 blah 2 line3 blah 3 line4 blah 4 line5 blah 5 line6 blah 6 DESIRED RESULT: Characters 3-6 of lines 3-5: A total of 3 matches: <match>ne3 </match> <match>ne4 </match> <match>ne5 </match>

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• Best way for launching html/jsp to communicate with GWT module

  - by h2g2java

  I asked this at the GWT forum but I'm impatient for the answer and I seem to get rather good responses here. A html or jsp file is used to launch the xxx.nocache.js, which then decides which browser "permutation" to use. <head> <meta http-equiv="content-type" content="text/html;charset=UTF-8"> <title>xxx</title> <script type="text/javascript" language="javascript" src="xxx.nocache.js"></script> </head> In my case, I am using a jsp. When the JSP is executed, it discovers some conditions. I wish to pass these conditions as values to the GWT module being launched. The "elegant" GWT way to pass these values would be to persist them as request/memcache attributes and then have the GWT module perform RPC to retrieve those values. For example, the JSP discovers that the current user is Whoopy. Shouldn't I simply have the JSP generate javascript to store user = "Whoopy" as a top or namedframe level javascript variable and use JSNI within the module to retrieve the value for user? I have not tried it yet, but I would like to know how anyone might have done it without having to use RPC.

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• Are there scenarios where the ViewModel needs to invoke methods on the View w.r.t. MVVM in WPF?

  - by Gishu

  As per the pattern, the ViewModel exposes Properties(with change notification) and Commands (to notify the VM of user actions) that the View binds to. The only communication that flows from the VM to the View is the property change notifications (so that the View can refresh itself with updated data). In MVP or PresentationModel form of the pattern (if I'm not mistaken), the View implements a plain vanilla interface (consisting of methods, properties and/or events). With MVVM, it feels methods on the IView have been outlawed (along with IView itself). One scenario I could think of was to set the focus to a certain control in the View. (When the user does ActionX, the focus should immediately be set to FieldY). In MVP, I'd write this as IView.ActivateField(NameConstant), which the presenter or PM would invoke. In MVVM, this seems to be a fringe case that needs a workaround / little bit of code-behind. The VM implements an ActiveField Property, which it sets to NameConstant. The view picks up the change notification event and in a code-behind event handler, activates the Name control. Is the above just an exception to the norm? Or are there other such scenarios, where the VM needs to invoke a method on the View ?

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• Controlling the order of PicoContainer startup

  - by Trejkaz

  I have been tasked with doing some refactoring work on how we start up applications. Basically we have a bunch of console apps which were depending on the GUI application startup code, causing bogus dependencies which have kick-on effects for which libraries we need to ship, and which dependencies other modules need to declare. So I have written a simple startup framework where I basically just throw a bunch of Runnable objects into a list and then run them in order - and it works. But I was thinking - we already have PicoContainer in our project, so all these things that need to be run on startup could potentially be thrown into a PicoContainer, and if they implement Startable they will start... But in some cases we want to specify the ordering between them. For example, I don't want any other component writing to the log before we write a header into the log indicating that the application is starting up. I know I can introduce ordering by introducing injection dependencies, but this feels like a hack in this case - I would need to add the log header writer as a dependency for every other component which might write to the log, which isn't great at all. Nonetheless it seems like it would be nice to control the order of PicoContainer startup, so is there perhaps some other way? Alternatively I could just keep it simple and stick to my list of Runnable. It does, after all, work.

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• How to make a mapped field inherited from a superclass transient in JPA?

  - by Russ Hayward

  I have a legacy schema that cannot be changed. I am using a base class for the common features and it contains an embedded object. There is a field that is normally mapped in the embedded object that needs to be in the persistence id for only one (of many) subclasses. I have made a new id class that includes it but then I get the error that the field is mapped twice. Here is some example code that is much simplified to maintain the sanity of the reader: @MappedSuperclass class BaseClass { @Embedded private Data data; } @Entity class SubClass extends BaseClass { @EmbeddedId private SubClassId id; } @Embeddable class Data { private int location; private String name; } @Embeddable class SubClassId { private int thingy; private int location; } I have tried @AttributeOverride but I can only get it to rename the field. I have tried to set it to updatable = false, insertable = false but this did not seem to work when used in the @AttributeOverride annotation. See answer below for the solution to this issue. I realise I could change the base class but I really do not want to split up the embedded object to separate the shared field as it would make the surrounding code more complex and require some ugly wrapping code. I could also redesign the whole system for this corner case but I would really rather not. I am using Hibernate as my JPA provider.

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• Custom basic authentication fails in IIS7

  - by manu08

  I have an ASP.NET MVC application, with some RESTful services that I'm trying to secure using custom basic authentication (they are authenticated against my own database). I have implemented this by writing an HTTPModule. I have one method attached to the HttpApplication.AuthenticateRequest event, which calls this method in the case of authentication failure: private static void RejectWith401(HttpApplication app) { app.Response.StatusCode = 401; app.Response.StatusDescription = "Access Denied"; app.CompleteRequest(); } This method is attached to the HttpApplication.EndRequest event: public void OnEndRequest(object source, EventArgs eventArgs) { var app = (HttpApplication) source; if (app.Response.StatusCode == 401) { string val = String.Format("Basic Realm=\"{0}\"", "MyCustomBasicAuthentication"); app.Response.AppendHeader("WWW-Authenticate", val); } } This code adds the "WWW-Authenticate" header which tells the browser to throw up the login dialog. This works perfectly when I debug locally using Visual Studio's web server. But it fails when I run it in IIS7. For IIS7 I have the built-in authentication modules all turned off, except anonymous. It still returns an HTTP 401 response, but it appears to be removing the WWW-Authenticate header. Any ideas?

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• HTTP crawler in Erlang

  - by ctp

  I'm coding on a simple HTTP crawler but I have an issue running the code at the bottom. I'm requesting 50 URLs and get the content of 20+ back. I've generated few files with 150kB size each to test the crawler. So I think the 20+ responses are limited by the bandwidth? BUT: how to tell the Erlang snippet not to quit until the last file is not fetched? The test data server is online, so plz try the code out and any hints are welcome :) -module(crawler). -define(BASE_URL, "http://46.4.117.69/"). -export([start/0, send_reqs/0, do_send_req/1]). start() -> ibrowse:start(), proc_lib:spawn(?MODULE, send_reqs, []). to_url(Id) -> ?BASE_URL ++ integer_to_list(Id). fetch_ids() -> lists:seq(1, 50). send_reqs() -> spawn_workers(fetch_ids()). spawn_workers(Ids) -> lists:foreach(fun do_spawn/1, Ids). do_spawn(Id) -> proc_lib:spawn_link(?MODULE, do_send_req, [Id]). do_send_req(Id) -> io:format("Requesting ID ~p ... ~n", [Id]), Result = (catch ibrowse:send_req(to_url(Id), [], get, [], [], 10000)), case Result of {ok, Status, _H, B} -> io:format("OK -- ID: ~2..0w -- Status: ~p -- Content length: ~p~n", [Id, Status, length(B)]); Err -> io:format("ERROR -- ID: ~p -- Error: ~p~n", [Id, Err]) end. That's the output: Requesting ID 1 ... Requesting ID 2 ... Requesting ID 3 ... Requesting ID 4 ... Requesting ID 5 ... Requesting ID 6 ... Requesting ID 7 ... Requesting ID 8 ... Requesting ID 9 ... Requesting ID 10 ... Requesting ID 11 ... Requesting ID 12 ... Requesting ID 13 ... Requesting ID 14 ... Requesting ID 15 ... Requesting ID 16 ... Requesting ID 17 ... Requesting ID 18 ... Requesting ID 19 ... Requesting ID 20 ... Requesting ID 21 ... Requesting ID 22 ... Requesting ID 23 ... Requesting ID 24 ... Requesting ID 25 ... Requesting ID 26 ... Requesting ID 27 ... Requesting ID 28 ... Requesting ID 29 ... Requesting ID 30 ... Requesting ID 31 ... Requesting ID 32 ... Requesting ID 33 ... Requesting ID 34 ... Requesting ID 35 ... Requesting ID 36 ... Requesting ID 37 ... Requesting ID 38 ... Requesting ID 39 ... Requesting ID 40 ... Requesting ID 41 ... Requesting ID 42 ... Requesting ID 43 ... Requesting ID 44 ... Requesting ID 45 ... Requesting ID 46 ... Requesting ID 47 ... Requesting ID 48 ... Requesting ID 49 ... Requesting ID 50 ... OK -- ID: 49 -- Status: "200" -- Content length: 150000 OK -- ID: 47 -- Status: "200" -- Content length: 150000 OK -- ID: 50 -- Status: "200" -- Content length: 150000 OK -- ID: 17 -- Status: "200" -- Content length: 150000 OK -- ID: 48 -- Status: "200" -- Content length: 150000 OK -- ID: 45 -- Status: "200" -- Content length: 150000 OK -- ID: 46 -- Status: "200" -- Content length: 150000 OK -- ID: 10 -- Status: "200" -- Content length: 150000 OK -- ID: 09 -- Status: "200" -- Content length: 150000 OK -- ID: 19 -- Status: "200" -- Content length: 150000 OK -- ID: 13 -- Status: "200" -- Content length: 150000 OK -- ID: 21 -- Status: "200" -- Content length: 150000 OK -- ID: 16 -- Status: "200" -- Content length: 150000 OK -- ID: 27 -- Status: "200" -- Content length: 150000 OK -- ID: 03 -- Status: "200" -- Content length: 150000 OK -- ID: 23 -- Status: "200" -- Content length: 150000 OK -- ID: 29 -- Status: "200" -- Content length: 150000 OK -- ID: 14 -- Status: "200" -- Content length: 150000 OK -- ID: 18 -- Status: "200" -- Content length: 150000 OK -- ID: 01 -- Status: "200" -- Content length: 150000 OK -- ID: 30 -- Status: "200" -- Content length: 150000 OK -- ID: 40 -- Status: "200" -- Content length: 150000 OK -- ID: 05 -- Status: "200" -- Content length: 150000 Update: thanks stemm for the hint with the wait_workers. I've combined your and mine code but same behaviour :( -module(crawler). -define(BASE_URL, "http://46.4.117.69/"). -export([start/0, send_reqs/0, do_send_req/2]). start() -> ibrowse:start(), proc_lib:spawn(?MODULE, send_reqs, []). to_url(Id) -> ?BASE_URL ++ integer_to_list(Id). fetch_ids() -> lists:seq(1, 50). send_reqs() -> spawn_workers(fetch_ids()). spawn_workers(Ids) -> %% collect reference to each worker Refs = [ do_spawn(Id) || Id <- Ids ], %% wait for response from each worker wait_workers(Refs). wait_workers(Refs) -> lists:foreach(fun receive_by_ref/1, Refs). receive_by_ref(Ref) -> %% receive message only from worker with specific reference receive {Ref, done} -> done end. do_spawn(Id) -> Ref = make_ref(), proc_lib:spawn_link(?MODULE, do_send_req, [Id, {self(), Ref}]), Ref. do_send_req(Id, {Pid, Ref}) -> io:format("Requesting ID ~p ... ~n", [Id]), Result = (catch ibrowse:send_req(to_url(Id), [], get, [], [], 10000)), case Result of {ok, Status, _H, B} -> io:format("OK -- ID: ~2..0w -- Status: ~p -- Content length: ~p~n", [Id, Status, length(B)]), %% send message that work is done Pid ! {Ref, done}; Err -> io:format("ERROR -- ID: ~p -- Error: ~p~n", [Id, Err]), %% repeat request if there was error while fetching a page, do_send_req(Id, {Pid, Ref}) %% or - if you don't want to repeat request, put there: %% Pid ! {Ref, done} end. Running the crawler forks fine for a handful of files, but then the code even doesnt fetch the entire files (file size each 150000 bytes) - he crawler fetches some files partially, see the following web server log :( 82.114.62.14 - - [13/Sep/2012:15:17:00 +0200] "GET /10 HTTP/1.1" 200 150000 "-" "-" 82.114.62.14 - - [13/Sep/2012:15:17:00 +0200] "GET /1 HTTP/1.1" 200 150000 "-" "-" 82.114.62.14 - - [13/Sep/2012:15:17:00 +0200] "GET /3 HTTP/1.1" 200 150000 "-" "-" 82.114.62.14 - - [13/Sep/2012:15:17:00 +0200] "GET /8 HTTP/1.1" 200 150000 "-" "-" 82.114.62.14 - - [13/Sep/2012:15:17:00 +0200] "GET /39 HTTP/1.1" 200 150000 "-" "-" 82.114.62.14 - - [13/Sep/2012:15:17:00 +0200] "GET /7 HTTP/1.1" 200 150000 "-" "-" 82.114.62.14 - - [13/Sep/2012:15:17:00 +0200] "GET /6 HTTP/1.1" 200 150000 "-" "-" 82.114.62.14 - - [13/Sep/2012:15:17:00 +0200] "GET /2 HTTP/1.1" 200 150000 "-" "-" 82.114.62.14 - - [13/Sep/2012:15:17:00 +0200] "GET /5 HTTP/1.1" 200 150000 "-" "-" 82.114.62.14 - - [13/Sep/2012:15:17:00 +0200] "GET /50 HTTP/1.1" 200 150000 "-" "-" 82.114.62.14 - - [13/Sep/2012:15:17:00 +0200] "GET /9 HTTP/1.1" 200 150000 "-" "-" 82.114.62.14 - - [13/Sep/2012:15:17:00 +0200] "GET /44 HTTP/1.1" 200 150000 "-" "-" 82.114.62.14 - - [13/Sep/2012:15:17:00 +0200] "GET /38 HTTP/1.1" 200 150000 "-" "-" 82.114.62.14 - - [13/Sep/2012:15:17:00 +0200] "GET /47 HTTP/1.1" 200 150000 "-" "-" 82.114.62.14 - - [13/Sep/2012:15:17:00 +0200] "GET /49 HTTP/1.1" 200 150000 "-" "-" 82.114.62.14 - - [13/Sep/2012:15:17:00 +0200] "GET /43 HTTP/1.1" 200 150000 "-" "-" 82.114.62.14 - - [13/Sep/2012:15:17:00 +0200] "GET /37 HTTP/1.1" 200 150000 "-" "-" 82.114.62.14 - - [13/Sep/2012:15:17:00 +0200] "GET /46 HTTP/1.1" 200 150000 "-" "-" 82.114.62.14 - - [13/Sep/2012:15:17:00 +0200] "GET /48 HTTP/1.1" 200 150000 "-" "-" 82.114.62.14 - - [13/Sep/2012:15:17:00 +0200] "GET /36 HTTP/1.1" 200 150000 "-" "-" 82.114.62.14 - - [13/Sep/2012:15:17:01 +0200] "GET /42 HTTP/1.1" 200 150000 "-" "-" 82.114.62.14 - - [13/Sep/2012:15:17:01 +0200] "GET /41 HTTP/1.1" 200 150000 "-" "-" 82.114.62.14 - - [13/Sep/2012:15:17:01 +0200] "GET /45 HTTP/1.1" 200 150000 "-" "-" 82.114.62.14 - - [13/Sep/2012:15:17:01 +0200] "GET /17 HTTP/1.1" 200 150000 "-" "-" 82.114.62.14 - - [13/Sep/2012:15:17:01 +0200] "GET /35 HTTP/1.1" 200 150000 "-" "-" 82.114.62.14 - - [13/Sep/2012:15:17:01 +0200] "GET /16 HTTP/1.1" 200 150000 "-" "-" 82.114.62.14 - - [13/Sep/2012:15:17:01 +0200] "GET /15 HTTP/1.1" 200 17020 "-" "-" 82.114.62.14 - - [13/Sep/2012:15:17:01 +0200] "GET /21 HTTP/1.1" 200 120360 "-" "-" 82.114.62.14 - - [13/Sep/2012:15:17:01 +0200] "GET /40 HTTP/1.1" 200 117600 "-" "-" 82.114.62.14 - - [13/Sep/2012:15:17:01 +0200] "GET /34 HTTP/1.1" 200 60660 "-" "-" Any hints are welcome. I have no clue what's going wrong there :(

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• Why is curl in Ruby slower than command-line curl?

  - by Stiivi

  I am trying to download more than 1m pages (URLs ending by a sequence ID). I have implemented kind of multi-purpose download manager with configurable number of download threads and one processing thread. The downloader downloads files in batches: curl = Curl::Easy.new batch_urls.each { |url_info| curl.url = url_info[:url] curl.perform file = File.new(url_info[:file], "wb") file << curl.body_str file.close # ... some other stuff } I have tried to download 8000 pages sample. When using the code above, I get 1000 in 2 minutes. When I write all URLs into a file and do in shell: cat list | xargs curl I gen all 8000 pages in two minutes. Thing is, I need it to have it in ruby code, because there is other monitoring and processing code. I have tried: Curl::Multi - it is somehow faster, but misses 50-90% of files (does not download them and gives no reason/code) multiple threads with Curl::Easy - around the same speed as single threaded Why is reused Curl::Easy slower than subsequent command line curl calls and how can I make it faster? Or what I am doing wrong? I would prefer to fix my download manager code than to make downloading for this case in a different way. Before this, I was calling command-line wget which I provided with a file with list of URLs. Howerver, not all errors were handled, also it was not possible to specify output file for each URL separately when using URL list. Now it seems to me that the best way would be to use multiple threads with system call to 'curl' command. But why when I can use directly Curl in Ruby? Code for the download manager is here, if it might help: Download Manager (I have played with timeouts, from not-setting it to various values, it did not seem help) Any hints appreciated.

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• EAGLContext, EAGLSharegroups, RenderBuffers, FrameBuffers, oh my!

  - by quixoto

  Hi all, I'm trying to wrap my head around the OpenGL object model on iPhone OS. I'm currently rendering into a few different UIViews (build on CAEAGLayers) on the screen. I currently have each of these as using separate EAGLContext, each of which has a color renderbuffer and a framebuffer. I'm rendering similar things in them, and I'd like to share textures between these instances to save memory overhead. My current understanding is that I could use the same setup (some number of contexts, each with a FBO/RBO) but if I spawn the later ones using the EAGLShareGroup of the first one, then I can simply use the texture names (GLuints) from the first one in the later ones. Is this accurate? If this is the case, I guess the followup question is: what's the benefit to having it be a "sharegroup"? Could I just reuse the same context, and attach multiple FBOs/RBOs to that context? I think I'm struggling with the abstraction layer of a sharegroup, which seems to share "objects" (textures and other named things) but not "state" (matrices, enabled/disabled states) which are owned by the context. What's the best way to think of this? Thanks for any enlightenment!

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• Simulating O_NOFOLLOW (2): Is this other approach safe?

  - by Daniel Trebbien

  As a follow-up question to this one, I thought of another approach which builds off of @caf's answer for the case where I want to append to file name and create it if it does not exist. Here is what I came up with: Create a temporary directory with mode 0700 in a system temporary directory on the same filesystem as file name. Create an empty, temporary, regular file (temp_name) in the temporary directory (only serves as placeholder). Open file name for reading only, just to create it if it does not exist. The OS may follow name if it is a symbolic link; I don't care at this point. Make a hard link to name at temp_name (overwriting the placeholder file). If the link call fails, then exit. (Maybe someone has come along and removed the file at name, who knows?) Use lstat on temp_name (now a hard link). If S_ISLNK(lst.st_mode), then exit. open temp_name for writing, append (O_WRONLY | O_APPEND). Write everything out. Close the file descriptor. unlink the hard link. Remove the temporary directory. (All of this, by the way, is for an open source project that I am working on. You can view the source of my implementation of this approach here.) Is this procedure safe against symbolic link attacks? For example, is it possible for a malicious process to ensure that the inode for name represents a regular file for the duration of the lstat check, then make the inode a symbolic link with the temp_name hard link now pointing to the new, symbolic link? I am assuming that a malicious process cannot affect temp_name.

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• Why should the "prime-based" hashcode implmentation be used instead of the "naive" one?

  - by Wilhelm

  I have seen that a prime number implmentation of the GetHashCode function is being recommend, for example here. However using the following code (in VB, sorry), it seems as if that implementation gives the same hash density as a "naive" xor implementation. If the density is the same, I would suppose there is the same probability of cllision in both implementations. Am I missing anything on why is the prime approach preferred? I am supossing that if the hash code is a byte I do not lose generality for the integer case. Sub Main() Dim XorHashes(255) As Integer Dim PrimeHashes(255) As Integer For i = 0 To 255 For j = 0 To 255 For k = 0 To 255 XorHashes(GetXorHash(i, j, k)) += 1 PrimeHashes(GetPrimeHash(i, j, k)) += 1 Next Next Next For i = 0 To 255 Console.WriteLine("{0}: {1}, {2}", i, XorHashes(i), PrimeHashes(i)) Next Console.ReadKey() End Sub Public Function GetXorHash(ByVal valueOne As Integer, ByVal valueTwo As Integer, ByVal valueThree As Integer) As Byte Return CByte((valueOne Xor valueTwo Xor valueThree) Mod 256) End Function Public Function GetPrimeHash(ByVal valueOne As Integer, ByVal valueTwo As Integer, ByVal valueThree As Integer) As Byte Dim TempHash = 17 TempHash = 31 * TempHash + valueOne TempHash = 31 * TempHash + valueTwo TempHash = 31 * TempHash + valueThree Return CByte(TempHash Mod 256) End Function

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• Yaml::load_file acting different between development and production (Rails)

  - by James

  Hi, I am completely stumped at the nature of this problem. We export data from our application into a 'cleaned' YAML file (stripping out IDs, created_at etc). Then we (will) allow users to import these files back into the application - it is the import that is completely bugging me out. In development, YAML::load_file(params[:uploaded_data].local_path) returns an array of YAML::Objects's (and it doesn't matter which of the number of different ways the file could be loaded): [#{"exception_count"="0", "title"="Start", "amount"="70.00", "colour"=nil, "repeat_type_id"="0", "repeat_interval"="1"}}, etc etc] Which is very nice, as the attributes also include the (associated model) exceptions that you see an exception_count for. However on production (rails 2.3.2, running REE 1.8.7 and 1.8.6 for testing, tested on two different production env's, and running production locally) it returns an array of the Objects within the YAML - in this case, Event: [#, repeat_type_id: 0, colour: nil, repeat_interval: 1, exception_count: 0, etc etc] Now this would be just perplexing if it also included the associated model Exception with it - however it doesn't. Can anyone at all shed some light on why the Yaml parser would behave so differently between production and development? I'm on rails 2.3.2, running REE 1.8.7; however I've also tested running Ruby 1.8.6 with exactly the same results. Thanks for any help!

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• System.Design cannot be referenced in Class Library?

  - by Alex Yeung

  Hi all, I have a very strange problem that I cannot fix and don't know what's going on... I am using VS 2010 Premium and .NET 4.0. Here are my steps to simulate the problem. Step 1. Create a new VB class library project named "MyClassLib" Step 2. Create a new class named "MyTestingClass". Public Class MyTestingClass Inherits System.ComponentModel.Design.CollectionEditor Public Sub New() MyBase.New(GetType(List(Of String))) End Sub End Class Step 3. Add two .net reference. "System.Design" and "System.Drawing". Step 4. Create a new VB console application named "MyClassExe" Step 5. Add "MyClassLib" reference to "MyClassExe". Step 6. Open Module1.vb in "MyClassExe" project Step 7. In the Main method, type Dim a = New MyClassLib.MyTestingClass() Step 8. Try to compile "MyClassLib". It doesn't have problem. Step 9. Try to compile "MyClassExe". It cannot compile because the WHOLE MyClassLib cannot be found!!! I have no idea what's going on? Moreover, the same case happens in C#. Does anyone know what's the problem with "System.Design"? Thank!!!

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• How do I locate a particular word in a text file using .NET

  - by cmrhema

  I am sending mails (in asp.net ,c#), having a template in text file (.txt) like below User Name :<User Name> Address : <Address>. I used to replace the words within the angle brackets in the text file using the below code StreamReader sr; sr = File.OpenText(HttpContext.Current.Server.MapPath(txt)); copy = sr.ReadToEnd(); sr.Close(); //close the reader copy = copy.Replace(word.ToUpper(),"#" + word.ToUpper()); //remove the word specified UC //save new copy into existing text file FileInfo newText = new FileInfo(HttpContext.Current.Server.MapPath(txt)); StreamWriter newCopy = newText.CreateText(); newCopy.WriteLine(copy); newCopy.Write(newCopy.NewLine); newCopy.Close(); Now I have a new problem, the user will be adding new words within an angle, say for eg, they will be adding <Salary>. In that case i have to read out and find the word <Salary>. In other words, I have to find all the words, that are located with the angle brackets (<). How do I do that?

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