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  • What's the differenct between passing a function and the function call itself in javascript?

    - by Mingus Rude
    In the application I'm building I'm polling for a status update and I have noticed that if the call is made as follows the timeout fires continuously: setTimeout($.get("http://localhost:8080/status", function(data) { UpdateStatus(data);}), 1000); While if use a function instead the timeout fires every 1000 ms: setTimeout(function() {$.get("http://localhost:8080/status", function(data) { UpdateStatus(data);})}, 1000); Why?

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  • Php, passing data between pages without using the url?

    - by terabytest
    I have a php page that has a form that asks for an e-mail. When you press the send button, it gets to another php page, which gets the form data and does its stuff. I need to then be able to go back to the old page (the one that contained the form) and give it some data so that it will be able to change itself and say "You've sent your e-mail successfully, and will not display the form. How do I do it?

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  • Prevent coersion to a single type in unlist() or c(); passing arguments to wrapper functions

    - by Leo Alekseyev
    Is there a simple way to flatten a list while retaining the original types of list constituents?.. Is there a way to programmatically construct a heterogeneous list?.. For instance, I want to create a simple wrapper for functions like png(filename,width,height) that would take device name, file name, and a list of options. The naive approach would be something like my.wrapper <- function(dev,name,opts) { do.call(dev,c(filename=name,opts)) } or similar code with unlist(list(...)). This doesn't work because opts gets coerced to character, and the resulting call is e.g. png(filename,width="500",height="500"). If there's no straightforward way to create heterogeneous lists like that, is there a standard idiomatic way to splice arguments into functions without naming them explicitly (e.g. do.call(dev,list(filename=name,width=opts["width"]))? -- Edit -- Gavin Simpson answered both questions below in his discussion about constructing wrapper functions. Let me give a summary of the answer to the title question: It is possible to construct a heterogeneous list with c() provided the arguments to c() are lists. To wit: > foo <- c("a","b"); bar <- 1:3 > c(foo,bar) [1] "a" "b" "1" "2" "3" > c(list(foo),list(bar)) [[1]] [1] "a" "b" [[2]] [1] 1 2 3 > c(as.list(foo),as.list(bar)) ## this creates a flattened heterogeneous list [[1]] [1] "a" [[2]] [1] "b" [[3]] [1] 1 [[4]] [1] 2 [[5]] [1] 3

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  • Is passing a struct value to a method by-reference in C# an acceptable optimization?

    - by Arc
    Say I have a struct: struct MyStruct { public int X public int Y } And a method in some class that is iterated over many times elsewhere: public bool MyMethod( MyStruct myStruct ) { return ... } Is changing the MyMethod signature to the following an acceptable optimization? public bool MyMethod( ref MyStruct myStruct ) If so, how much of an advantage would it really be? If not, about how many fields would a struct need for a big enough advantage using ref this way?

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  • Passing Func<T> to controller constructure when using Unity IoC with MVC, advantages?

    - by user1361315
    I was looking at a sample of how to setup Unity IoC with MVC, and noticed someone who recommended the approach of having the parameters of Func. I believe the advantage is this is kind of like lazy loading the service, if it never gets called it will never get executed and not consume any resources. private readonly Func<IUserService> _userService; public CourseController(Func<IUserService> userService) { this._userService = userService; } Versus a parameter without a Func: private readonly IUserService _userService; public CourseController(IUserService userService) { this._userService = userService; } Can someone explain to me the differences, is it really more effecient?

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  • Delphi : What is the best way for passing data between forms?

    - by Flom Enol
    It may seem a little newbie, but I really have got problem with it. I have a form (not the main one)for getting many different data form the user and I want to pass it to a manager class for creating an object with these. The problem is that I can't have this class to use the other unit (getting circle uses) and also it doesn't have access to the manager class instance (which is in main form). So, what shall I do? I've already considered using public variable but I have a bad feeling about it (regarding OOD patterns). Any ideas? thanks in advance.

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  • VB .NET Passing a Structure containing an array of String and an array of Integer into a C++ DLL

    - by DanJunior
    Hi everyone, I'm having problems with marshalling in VB .NET to C++, here's the code : In the C++ DLL : struct APP_PARAM { int numData; LPCSTR *text; int *values; }; int App::StartApp(APP_PARAM params) { for (int i = 0; i < numLines; i++) { OutputDebugString(params.text[i]); } } In VB .NET : <StructLayoutAttribute(LayoutKind.Sequential)> _ Public Structure APP_PARAM Public numData As Integer Public text As System.IntPtr Public values As System.IntPtr End Structure Declare Function StartApp Lib "AppSupport.dll" (ByVal params As APP_PARAM) As Integer Sub Main() Dim params As APP_PARAM params.numData = 3 Dim text As String() = {"A", "B", "C"} Dim textHandle As GCHandle = GCHandle.Alloc(text) params.text = GCHandle.ToIntPtr(textHandle) Dim values As Integer() = {10, 20, 30} Dim valuesHandle As GCHandle = GCHandle.Alloc(values) params.values = GCHandle.ToIntPtr(heightHandle) StartApp(params) textHandle.Free() valuesHandle.Free() End Sub I checked the C++ side, the output from the OutputDebugString is garbage, the text array contains random characters. What is the correct way to do this?? Thanks a lot...

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  • Passing arguments to javascript file, how does it work?

    - by vietean
    From the tutorial ScriptJSONOptions of FirebugLite page, I found the below: Script JSON options It is possible to set options using a JSON object inside the linked script: <script type="text/javascript" src="https://getfirebug.com/firebug-lite.js"> { overrideConsole: false, startInNewWindow: true, startOpened: true, enableTrace: true } </script> It means that we can pass the arguments to javascript file. But I don't know how does it work? Update: My question is how to get the arguments inside the js file? P/S: I also looked into code, but I could not find the code is implemented this feature.

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  • Why does the compiler give an ambiguous invocation error when passing inherited types?

    - by Matt Mitchell
    What is happening in the C# compiler to cause the following ambiguous invocation compilation error? The same issue applies to extension methods, or when TestClass is generic and using instance rather than static methods. class Type1 { } class Type2 : Type1 {} class TestClass { public static void Do<T>(T something, object o) where T : Type1 {} public static void Do(Type1 something, string o) {} } void Main() { var firstInstance = new Type1(); TestClass.Do(firstInstance, new object()); // Calls Do(Type1, obj) TestClass.Do(firstInstance, "Test"); // Calls Do<T>(T, string) var secondInstance = new Type2(); TestClass.Do(secondInstance, new object()); // Calls Do(Type1, obj) TestClass.Do(secondInstance, "Test"); // "The call is ambiguous" compile error }

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  • How do I link to another action in Magento whilst passing a parameter to the controller?

    - by desbest
    I need to pass a parameter, because I would like to redirect back to the module and query string of the current page. So I can get from showdown/index?id=35 --click--- showdown/vote?id=1 showdown/vote?id=1 --redirect-- showdown/index?id=35 The vote action is not seen. (The redirect method doesn't work as it takes the index.php url only and no actions, and I cannot find a helper in Magento for creating hyperlinks.) Does Magneto have a link helper for this? Example of stuff I want: <a href="<?php echo Mage::Helper->Link->($url, $array); ?> then $array or whatever variables gets sent to the controller.

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  • Incorrect data when passing pointer a list of pointers to a function. (C++)

    - by Phil Elm
    I'm writing code for combining data received over multiple sources. When the objects received (I'll call them MyPacket for now), they are stored in a standard list. However, whenever I reference the payload size of a partial MyPacket, the value shows up as 1 instead of the intended size. Here's the function code: MyPacket* CombinePackets(std::list<MyPacket*>* packets, uint8* current_packet){ uint32 total_payload_size = 0; if(packets->size() <= 0) return NULL; //For now. std::list<MyPacket*>::iterator it = packets->begin(); //Some minor code here, not relevant to the problem. for(uint8 index = 0; index < packets->size(); index++){ //(*it)->GetPayloadSize() returns 1 when it should show 1024. I've tried directly accessing the variable and more, but I just can't get it to work. total_payload_size += (*it)->GetPayloadSize(); cout << "Adding to total payload size value: " << (*it)->GetPayloadSize() << endl; std::advance(it,1); } MyPacket* packet = new MyPacket(); //Byte is just a typedef'd unsigned char. packet->payload = (byte) calloc(total_payload_size, sizeof(byte)); packet->payload_size = total_payload_size; it = packets->begin(); //Go back to the beginning again. uint32 big_payload_index = 0; for(uint8 index = 0; index < packets->size(); index++){ if(current_packet != NULL) *current_packet = index; for(uint32 payload_index = 0; payload_index < (*it)->GetPayloadSize(); payload_index++){ packet->payload[big_payload_index] = (*it)->payload[payload_index]; big_payload_index++; } std::advance(it,1); } return packet; } //Calling code std::list<MyPacket*> received = std::list<MyPacket*>(); //The code that fills it is here. std::list<MyPacket*>::iterator it = received.begin(); cout << (*it)->GetPayloadSize() << endl; // Outputs 1024 correctly! MyPacket* final = CombinePackets(&received,NULL); cout << final->GetPayloadSize() << endl; //Outputs 181, which happens to be the number of elements in the received list. So, as you can see above, when I reference (*it)-GetPayloadSize(), it returns 1 instead of the intended 1024. Can anyone see the problem and if so, do you have an idea on how to fix this? I've spent 4 hours searching and trying new solutions, but they all keep returning 1... EDIT:

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  • Parallelism in .NET – Part 18, Task Continuations with Multiple Tasks

    - by Reed
    In my introduction to Task continuations I demonstrated how the Task class provides a more expressive alternative to traditional callbacks.  Task continuations provide a much cleaner syntax to traditional callbacks, but there are other reasons to switch to using continuations… Task continuations provide a clean syntax, and a very simple, elegant means of synchronizing asynchronous method results with the user interface.  In addition, continuations provide a very simple, elegant means of working with collections of tasks. Prior to .NET 4, working with multiple related asynchronous method calls was very tricky.  If, for example, we wanted to run two asynchronous operations, followed by a single method call which we wanted to run when the first two methods completed, we’d have to program all of the handling ourselves.  We would likely need to take some approach such as using a shared callback which synchronized against a common variable, or using a WaitHandle shared within the callbacks to allow one to wait for the second.  Although this could be accomplished easily enough, it requires manually placing this handling into every algorithm which requires this form of blocking.  This is error prone, difficult, and can easily lead to subtle bugs. Similar to how the Task class static methods providing a way to block until multiple tasks have completed, TaskFactory contains static methods which allow a continuation to be scheduled upon the completion of multiple tasks: TaskFactory.ContinueWhenAll. This allows you to easily specify a single delegate to run when a collection of tasks has completed.  For example, suppose we have a class which fetches data from the network.  This can be a long running operation, and potentially fail in certain situations, such as a server being down.  As a result, we have three separate servers which we will “query” for our information.  Now, suppose we want to grab data from all three servers, and verify that the results are the same from all three. With traditional asynchronous programming in .NET, this would require using three separate callbacks, and managing the synchronization between the various operations ourselves.  The Task and TaskFactory classes simplify this for us, allowing us to write: var server1 = Task.Factory.StartNew( () => networkClass.GetResults(firstServer) ); var server2 = Task.Factory.StartNew( () => networkClass.GetResults(secondServer) ); var server3 = Task.Factory.StartNew( () => networkClass.GetResults(thirdServer) ); var result = Task.Factory.ContinueWhenAll( new[] {server1, server2, server3 }, (tasks) => { // Propogate exceptions (see below) Task.WaitAll(tasks); return this.CompareTaskResults( tasks[0].Result, tasks[1].Result, tasks[2].Result); }); .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; } This is clean, simple, and elegant.  The one complication is the Task.WaitAll(tasks); statement. Although the continuation will not complete until all three tasks (server1, server2, and server3) have completed, there is a potential snag.  If the networkClass.GetResults method fails, and raises an exception, we want to make sure to handle it cleanly.  By using Task.WaitAll, any exceptions raised within any of our original tasks will get wrapped into a single AggregateException by the WaitAll method, providing us a simplified means of handling the exceptions.  If we wait on the continuation, we can trap this AggregateException, and handle it cleanly.  Without this line, it’s possible that an exception could remain uncaught and unhandled by a task, which later might trigger a nasty UnobservedTaskException.  This would happen any time two of our original tasks failed. Just as we can schedule a continuation to occur when an entire collection of tasks has completed, we can just as easily setup a continuation to run when any single task within a collection completes.  If, for example, we didn’t need to compare the results of all three network locations, but only use one, we could still schedule three tasks.  We could then have our completion logic work on the first task which completed, and ignore the others.  This is done via TaskFactory.ContinueWhenAny: var server1 = Task.Factory.StartNew( () => networkClass.GetResults(firstServer) ); var server2 = Task.Factory.StartNew( () => networkClass.GetResults(secondServer) ); var server3 = Task.Factory.StartNew( () => networkClass.GetResults(thirdServer) ); var result = Task.Factory.ContinueWhenAny( new[] {server1, server2, server3 }, (firstTask) => { return this.ProcessTaskResult(firstTask.Result); }); .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; } Here, instead of working with all three tasks, we’re just using the first task which finishes.  This is very useful, as it allows us to easily work with results of multiple operations, and “throw away” the others.  However, you must take care when using ContinueWhenAny to properly handle exceptions.  At some point, you should always wait on each task (or use the Task.Result property) in order to propogate any exceptions raised from within the task.  Failing to do so can lead to an UnobservedTaskException.

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  • MySQL: how to enable Slow Query Log?

    - by Continuation
    Can you give me an example on how to enable MySQL's slow query log? According to the doc: As of MySQL 5.1.29, use --slow_query_log[={0|1}] to enable or disable the slow query log, and optionally --slow_query_log_file=file_name to specify a log file name. The --log-slow-queries option is deprecated. So how do I use that option? Can I put it in my.cnf? An example would be greatly appreciated. Thank you very much

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  • How do you cache web pages with a personalized header using caching reverse proxy such as Squid, Var

    - by Continuation
    Pretty much every page of my website is dynamically generated. However they don't change that frequently (kinda similar to a forum page). So I'd like to cache them using a caching reverse proxy such as Squid, varnish or Nginx. The problem is that for my logged-in users, each of them will see a personalized header saying "Welcome John Doe. Logout" on the upper right corner of the page (just like serverfault). While users who aren't logged in will see a header that says "Login" instead. So basically even though every user will see the same page in general, they all slightly different version due to that personalized header. Is there any way so that I can cache the "main" part of the page and serve it from cache while generate the personalized header dynamically for each individual user? This must be a very common problem. How is it solved in general?

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  • What is the best Linux filesystem for MySQL (InnoDB)?

    - by Continuation
    I tried to look for benchmark on the performances of various filesystems with MySQL InnoDB but couldn't find any. My database workload is the typical web-based OLTP, about 90% read, 10% write. Random IO. Among popular filesystems such as ext3, ext4, xfs, jfs, Reiserfs, Reiser4, etc. which one do you think is the best for MySQL?

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  • How to scale out image hosting/serving?

    - by Continuation
    I asked this question on stackoverflow and it was suggested that I try it here: I'm building a website where users can upload photos and I'd also convert uploaded photos into thumbnails. Planning ahead, if the website gets popular, how do I scale it out so that the images (both original and thumbnails) will be stored in and served from multiple servers? Maybe a cluster? Is there any open source software that would help me in this? Thanks.

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  • Linux: How to rename old mysqld when upgrading MySQL?

    - by Continuation
    I'm upgrading MySQL from MySQL 5.0 to Percona Server 5.1. I'm planning to just use yum remove and yum install to do the upgrade. However, I read in the documentation that it's a good idea to rename the old mysqld to mysqld-5.0. And if the upgrade doesn't work, I could just revert back to the old version. How exactly does this work? If I use yum remove, doesn't that mean the old mysqld is removed? So how do I rename it? Where is mysqld located? How do I find it? Thanks.

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  • How does virtualization improve server utilization?

    - by Continuation
    The biggest benefit of virtualization is usually said to be improved server utilization. But why do I need virtualization for that? Say I got N physical servers that are lightly used. Why don't I just combine all the apps on those N servers into 1 physical server? This way I don't incur the performance penalty of virtualization. What does virtualization buy me in this case?

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  • Does Tomcat or Jetty cache dynamic content?

    - by Continuation
    I'm working on a Servlet app with contents that are updated periodically. Hence, between updates any dynamic pages generated by the Servlet can be cached. Does Tomcat or Jetty (or any Servlet container) offer a way to cache dynamically generated pages? Or would I need to use a caching reverse proxy like Squid to accomplish that?

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  • How do you handle the task of changing the schema of a production MySQL database?

    - by Continuation
    One of the biggest complaints I have heard about MySQL is that it locks up a table if you try to change its schema like adding a column or adding an index. By "locking up the table" does it mean I can neither read nor write to the table? Sometimes for hours? That seems a pretty severe limitations. I was going to use MySQL for my new project but this gives me pause. Is there a workaround for this? How do you handle the task of changing the schema of your production MySQL database? By the way someone told me Postgresql doesn't have this problem. Is that true - I can both read and write to a Postgresql table while changing its schema? Is there any performance penalty incurred? Would love to hear your experiences.

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  • How to tell if any MySQL connections has been dropped or timed out?

    - by Continuation
    A client is using PHP to connect to MySQL. The PHP scripts and the MySQL database are located on 2 different Linux servers. He complained that database connections were being dropped or timed out and asked me to take a look. Is there any place in MySQL that can show me what and how many connections have been dropped or timed out? I looked into slow query log and didn't see anything. Any suggestions on how to diagnose this dropped/timed out database connection problem? Thanks EDIT: Slow query log is enabled in my.cnf: log-slow-queries=/var/log/mysql-slow-queries.log And when I do a mysql> show global status; I got: | Slow_queries | 11402347 | So there are a lot of slow queries. But the file /var/log/mysql-slow-queries.log doesn't exist. Why is that?

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