The **[`SynchronizedCollection&lt;T&gt;`** class][1] was introduced first in .NET 2.0 to provide a thread-safe collection class. It does this via locking so that you essentially have a `List&lt;T&gt;` where every access is wrapped in a `lock` statement.

The **[`System.Collections.Concurrent`][2]** namespace is much newer. It wasn&#39;t introduced until .NET 4.0 and it includes a substantially improved and more diverse set of choices. These classes no longer use locks to provide thread safety, which means they should scale better in a situation where multiple threads are accessing their data simultaneously. However, a class implementing the `IList&lt;T&gt;` interface is notably absent among these options.

So, if you&#39;re targeting version 4.0 of the .NET Framework, you should use one of the collections provided by the `System.Collections.Concurrent` namespace whenever possible. Just as with choosing between the various types of collections provided in the [`System.Collections.Generic` namespace][3], you&#39;ll need to choose the one whose features and characteristics best fit your specific needs.

If you&#39;re targeting an older version of the .NET Framework or need a collection class that implements the `IList&lt;T&gt;` interface, you&#39;ll have to opt for the `SynchronizedCollection&lt;T&gt;` class.

This article on MSDN is also worth a read: [When to Use a Thread-Safe Collection][4]


  [1]: http://msdn.microsoft.com/en-us/library/ms668265.aspx
  [2]: http://msdn.microsoft.com/en-us/library/system.collections.concurrent.aspx
  [3]: http://msdn.microsoft.com/en-us/library/system.collections.generic.aspx
  [4]: http://msdn.microsoft.com/en-us/library/dd997373.aspx

For quite a while I&#39;d been looking into a way in my iPhone app to poll every X minutes to check the data counters. After much reading of the Background Execution documentation and a few trial apps I&#39;d dismissed this as impossible without abusing the background APIs.

Last week I found this application which does exactly that. http://itunes.apple.com/us/app/dataman-real-time-data-usage/id393282873?mt=8

It runs in the background and keeps track of the count of Cellular/WiFi data you&#39;ve used. I suspect that the developer is registering his app as tracking location changes but the location services icon isn&#39;t visible while the app is running, which I thought was a requirement.

Does anyone have any clues as to how this can be accomplished? 

iPhone - Backgrounding to poll for events

I have a python list with strings in this format:

    A1 = [&#39; &quot;29.0&quot; &#39;,&#39; &quot;65.2&quot; &#39;,&#39; &quot;75.2&quot; &#39;]

How do I convert those strings into decimal numbers to perform arithmetic operations on the list elements?

Python: Converting string into decimal number

How does `SynchronizedCollection&lt;T&gt;` and the concurrent collections in the `System.Collections.Concurrent` namespace differ from each other, apart from Concurrent Collections being a namespace and `SynchronizedCollection&lt;T&gt;` being a class?

`SynchronizedCollection&lt;T&gt;` and all of the classes in Concurrent Collections provide thread-safe collections. How do I decide when to use one over the other, and why?

What is the difference between SynchronizedCollection&lt;T&gt; and the other concurrent collections?

<p>How does <code>SynchronizedCollection&#x3C;T></code> and the concurrent collections in the <code>System.Collections.Concurrent</code> namespace differ from each other, apart from Concurrent Collections being a namespace and <code>SynchronizedCollection&#x3C;T></code> being a class?</p>
<p><code>SynchronizedCollection&#x3C;T></code> and all of the classes in Concurrent Collections provide thread-safe collections. How do I decide when to use one over the other, and why?</p>


Trying to get my project updated to MVC3, something I just can&#39;t find:

I have a simple datatype of ENUMS:

    public enum States()
    {
      AL,AK,AZ,...WY
    }

Which I want to use as a DropDown/SelectList in my view of a model that contains this datatype:

    public class FormModel()
    {
        public States State {get; set;}
    }

Pretty straight forward: when I go to use the auto-generate view for this partial class, it ignores this type.

I need a simple select list that sets the value of the enum as the selected item when I hit submit and process via my AJAX - JSON POST Method. 

And than the view (???!):

        &lt;div class=&quot;editor-field&quot;&gt;
            @Html.DropDownListFor(model =&gt; model.State, model =&gt; model.States)
        &lt;/div&gt;

thanks in advance for the advice!

MVC3 Razor DropDownListFor Enums

I have implemented an algorithm that will generate unique names for files that will save on hard drive. I&#39;m appending `DateTime`: **Hours,Minutes,Second and Milliseconds** but still it generates duplicate name of files because im uploading multiple files at a time. 

What is the best solution to generate unique names for files to be stored on hard drive so no 2 files are same?

How to Generate unique file names in C#

I have some code and when it executes, it throws a `NullReferenceException`, saying:

&gt;Object reference not set to an instance of an object.

What does this mean, and what can I do to fix this error?

What is a NullReferenceException, and how do I fix it?

Is it possible to create a generic object from a reflected type in C# (.Net 2.0)?


    void foobar(Type t){
        IList&lt;t&gt; newList = new List&lt;t&gt;(); //this doesn&#39;t work
        //...
    }

The Type, t, is not known until runtime.

C# instantiate generic List from reflected Type

How can I convert between these two color types?

How to convert from System.Drawing.Color to System.Windows.Media.Color?

Assume, I have a constant number of collections (e.g. 3 ArrayLists) as members of a class. Now, I want to expose all the elements to other classes so they can simply iterate over all elements (ideally, read only).
I&#39;m using guava collections and I wonder how I could use guava iterables/iterators to generate a logical view on the internal collections **without** making temporary copies.

Combine multiple Collections into a single logical Collection?

In Java you can build up an `ArrayList` with items and then call:

    Collections.sort(list, comparator);

Is there anyway to pass in the Comparator at the time of list, creation like you can do with `TreeMap`? 

The goal is to be able add an element to the list and instead of having it automatically appended to the end of the list, the list would keep itself sorted based on the `Comparator` and insert the new element at the index determined by the `Comparator`. So basically the list might have to re-sort upon every new element added.

Is there anyway to achieve this in this way with the `Comparator` or by some other similar means?



Java List Sorting: Is there a way to keep a list permantly sorted automatically like TreeMap?

I am familiar with Java Collection Framework which contains basic interfaces: `Collection` and `Map`. I am wondering why the Framework doesn&#39;t contain structures as Tree and Graph which are basic collections. Both can be regarded as sub types of `Collection`. 

By the way, I know `TreeSet` is implemented by Red-Black Tree underlying. However, the `TreeSet` is not a Tree but a `Set`, so there&#39;s no real Tree in the framework.

Why Java Collection Framework doesn&#39;t contain Tree and Graph

Is there a way to have a &lt;code&gt;defaultdict(defaultdict(int))&lt;/code&gt; in order to make the following code work?

    for x in stuff:
        d[x.a][x.b] += x.c_int

&lt;code&gt;d&lt;/code&gt; needs to be built ad-hoc, depending on &lt;code&gt;x.a&lt;/code&gt; and &lt;code&gt;x.b&lt;/code&gt; elements.

I could use:


    for x in stuff:
        d[x.a,x.b] += x.c_int

but then I wouldn&#39;t be able to use:

    d.keys()
    d[x.a].keys()


defaultdict of defaultdict?

I love `string.IsNullOrEmpty` method. I&#39;d love to have something that would allow the same functionality for IEnumerable. Is there such? Maybe some collection helper class? The reason I am asking is that in `if` statements the code looks cluttered if the patter is `(mylist != null &amp;&amp; mylist.Any())`. It would be much cleaner to have `Foo.IsAny(myList)`. 

This post doesn&#39;t give that answer: https://stackoverflow.com/questions/3779817/ienumerable-is-empty.



How to check if IEnumerable is null or empty?

I have a list of types (System.Type) which need te be queried on the database.

For each of this types, I need to call the following extensionmethod (which is part of LinqToNhibernate): 

    Session.Linq&lt;MyType&gt;()

However I do not have MyType, but I want to use a Type instead.

What I have is: 

    System.Type typeOne;

But I cannot perform the following: 

    Session.Linq&lt;typeOne&gt;()

How can I use a Type as a Generic parameter?

C# use System.Type as Generic parameter

How can I restart a WPF Application?
In windows Forms I used

`System.Windows.Forms.Application.Restart();`

How to do it in WPF?

How do I restart a WPF application?

I&#39;m new to .Net 4.0&#39;s Tasks and I wasn&#39;t able to find what I thought would be a Task based replacement or implementation of a Timer, e.g. a periodic Task. Is there such a thing?

***Update***
I came up with what I think is a solution to my needs which is to wrap the &quot;Timer&quot; functionality inside a Task with child Tasks all taking advantage of the CancellationToken and returns the Task to be able to participate in further Task steps.  

    public static Task StartPeriodicTask(Action action, int intervalInMilliseconds, int delayInMilliseconds, CancellationToken cancelToken)
    { 
        Action wrapperAction = () =&gt;
        {
            if (cancelToken.IsCancellationRequested) { return; }
    
            action();
        };
    
        Action mainAction = () =&gt;
        {
            TaskCreationOptions attachedToParent = TaskCreationOptions.AttachedToParent;
    
            if (cancelToken.IsCancellationRequested) { return; }
    
            if (delayInMilliseconds &gt; 0)
                Thread.Sleep(delayInMilliseconds);
    
            while (true)
            {
                if (cancelToken.IsCancellationRequested) { break; }
    
                Task.Factory.StartNew(wrapperAction, cancelToken, attachedToParent, TaskScheduler.Current);
    
                if (cancelToken.IsCancellationRequested || intervalInMilliseconds == Timeout.Infinite) { break; }
    
                Thread.Sleep(intervalInMilliseconds);
            }
        };
    
        return Task.Factory.StartNew(mainAction, cancelToken);
    }      



Is there a Task based replacement for System.Threading.Timer?

Simple enough question: I&#39;ve created a small app that is basically just a favourites that sits in my system tray so that I can open often-used sites/folders/files from the same place. Getting the default icons from my system for known file types isn&#39;t terribly complicated, but I don&#39;t know how to get the favicon from a website. (SO has the grey-&gt;orange stack icon in the address bar for instance)

Does anyone know how I might go about that?

How can I get a web site&#39;s favicon?

I&#39;m trying to compile my excel addin using C# 4.0, and started to get this problem when building my project in Visual Studio. It&#39;s important to tell you that I haven&#39;t had this problem before. What could cause this to happen?

Why am I getting &#39;Assembly &#39;*.dll&#39; must be strong signed in order to be marked as a prerequisite.&#39;?

Looking at the [SharedPreferences docs][1] it says: 

&gt; &quot;Note: currently this class does not
&gt; support use across multiple processes.
&gt; This will be added later.&quot;

So in and of itself it doesn&#39;t appear to be Thread Safe. However, what kind of guarantees are made in regards to commit() and apply()?

For example:

    synchronized(uniqueIdLock){
       uniqueId = sharedPreferences.getInt(&quot;UNIQUE_INCREMENTING_ID&quot;, 0);
       uniqueId++;
       sharedPreferences.edit().putInt(&quot;UNIQUE_INCREMENTING_ID&quot;, uniqueId).commit();
    }

Would it be guaranteed that the uniqueId was always unique in this case?

If not, is there a better way to keep track of a unique id for an application that persists?


  [1]: http://developer.android.com/reference/android/content/SharedPreferences.html

SharedPreferences and Thread Safety

I thought thread safe, in particular, means it must satisfy the need for multiple threads to access the same shared data. But, it seems this definition is not enough.

Can anyone please **list out the things to be done or taken care of to make an application thread safe**. If possible, give an answer with respect to C/C++ language.



how to make an application thread safe?

I was wondering if you have a static method that is **not** synchronised, but does **not** modify any static variables is it thread-safe? What about if the method creates local variables inside it? For example, is the following code thread-safe?

    public static String[] makeStringArray( String a, String b ){
        return new String[]{ a, b };
    }

So if I have two threads calling ths method continously and concurrently, one with dogs (say &quot;great dane&quot; and &quot;bull dog&quot;) and the other with cats (say &quot;persian&quot; and &quot;siamese&quot;) will I ever get cats and dogs in the same array? Or will the cats and dogs never be inside the same invocation of the method at the same time?

Are non-synchronised static methods thread safe if they don&#39;t modify static class variables?

If a synchronized method calls another synchronized method, is it thread safe?

    void synchronized method1() {
         method2()
    }
    
    void synchronized method2() {
    }

Is it safe to call a synchronized method from another synchronized method?

How do I find out whether the installed version of PHP is threadsafe or not thread safe?

Please note that I&#39;m not asking the difference between a threadsafe/non thread safe installation. I would like to find out what is installed currently.


Find if the installed PHP is threadsafe or nonthreadsafe?

I am trying to re-write some code using Dictionary to use ConcurrentDictionary. I have reviewed some examples but I am still having trouble implementing the AddOrUpdate function. This is the original code:

        dynamic a = HttpContext;
        Dictionary&lt;int, string&gt; userDic = this.HttpContext.Application[&quot;UserSessionList&quot;] as Dictionary&lt;int, String&gt;;
                                
       if (userDic != null)
       {
          if (useDic.ContainsKey(authUser.UserId))
          {
            userDic.Remove(authUser.UserId);
          }
       }
      else
      {
         userDic = new Dictionary&lt;int,string&gt;();
      }
      userDic.Add(authUser.UserId, a.Session.SessionID.ToString());
      this.HttpContext.Application[&quot;UserDic&quot;] = userDic;


I don&#39;t know what to add for the update portion:

    userDic.AddOrUpdate(authUser.UserId,
                        a.Session.SessionID.ToString(),
                        /*** what to add here? ***/);

Any pointers would be appreciated.

Content Type	Original Author	Original Content on Stackoverflow
Question	Batrickparry	View Question on Stackoverflow
Solution 1 - C#	Cody Gray	View Answer on Stackoverflow

What is the difference between SynchronizedCollection<T> and the other concurrent collections?

C# Problem Overview

C# Solutions

Solution 1 - C#

Python: Converting string into decimal number

iPhone - Backgrounding to poll for events

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