Create multiple threads and wait all of them to complete

Question

How can I create multiple threads and wait for all of them to complete

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Most proposed answers don t take into account a time-out interval  which is very important to prevent a possible deadlock  Next is my sample code   Note that I m primarily a Win32 developer  and that s how I d do it there       arrRunningThreads    List lt Thread gt     Wait for all threads const int knmsMaxWait   3   1000              3 sec timeout int nmsBeginTicks   Environment TickCount  foreach Thread thrd in arrRunningThreads          See time left     int nmsElapsed   Environment TickCount - nmsBeginTicks      int nmsRemain   knmsMaxWait - nmsElapsed      if nmsRemain  lt  0          nmsRemain   0         Then wait for thread to exit     if  thrd Join nmsRemain                   It didn t exit in time  terminate it         thrd Abort               Issue a debugger warning         Debug Assert false   Terminated thread

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I think you need WaitHandler WaitAll  Here is an example  public static void Main string   args        int numOfThreads   10      WaitHandle   waitHandles   new WaitHandle numOfThreads        for  int i   0  i  lt  numOfThreads  i                  var j   i             Or you can use AutoResetEvent ManualResetEvent         var handle   new EventWaitHandle false  EventResetMode ManualReset           var thread   new Thread      gt                                                                        Thread Sleep j   1000                                       Console WriteLine  quot Thread 0  exits quot   j                                       handle Set                                                waitHandles j    handle          thread Start              WaitHandle WaitAll waitHandles       Console WriteLine  quot Main thread exits quot        Console Read       FCL has a few more convenient functions   1  Task WaitAll  as well as its overloads  when you want to do some tasks in parallel  and with no return values   var tasks   new         Task Factory StartNew      gt  DoSomething1         Task Factory StartNew      gt  DoSomething2         Task Factory StartNew      gt  DoSomething3       Task WaitAll tasks     2  Task WhenAll when you want to do some tasks with return values  It performs the operations and puts the results in an array  It s thread-safe  and you don t need to using a thread-safe container and implement the add operation yourself  var tasks   new         Task Factory StartNew      gt  GetSomething1         Task Factory StartNew      gt  GetSomething2         Task Factory StartNew      gt  GetSomething3       var things   Task WhenAll tasks

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If you don t want to use the Task class  for instance  in  NET 3 5  you can just start all your threads  and then add them to the list and join them in a foreach loop  Example  List lt Thread gt  threads   new List lt Thread gt          Start threads for int i   0  i lt 10  i          int tmp   i     Copy value for closure     Thread t   new Thread      gt  Console WriteLine tmp        t Start      threads Add t         Await threads foreach Thread thread in threads        thread Join

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I don t know if there is a better way  but the following describes how I did it with a counter and background worker thread  private object  lock   new object    private int  runningThreads   0   private int Counter      get          lock  lock              return  runningThreads            set          lock  lock               runningThreads   value           Now whenever you create a worker thread  increment the counter  var t   new BackgroundWorker       Add RunWorkerCompleted handler     Start thread Counter     In work completed  decrement the counter  private void RunWorkerCompleted object sender  RunWorkerCompletedEventArgs e        Counter--     Now you can check for the counter anytime to see if any thread is running  if Couonter gt 0          Some thread is yet to finish

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It depends which version of the  NET Framework you are using   NET 4 0 made thread management a whole lot easier using Tasks   class Program       static void Main string   args                Task task1   Task Factory StartNew      gt  doStuff             Task task2   Task Factory StartNew      gt  doStuff             Task task3   Task Factory StartNew      gt  doStuff              Task WaitAll task1  task2  task3                   Console WriteLine  All threads complete               static void doStuff                   do stuff here           In previous versions of  NET you could use the BackgroundWorker object  use ThreadPool QueueUserWorkItem    or create your threads manually and use Thread Join   to wait for them to complete   static void Main string   args        Thread t1   new Thread doStuff       t1 Start         Thread t2   new Thread doStuff       t2 Start         Thread t3   new Thread doStuff       t3 Start         t1 Join        t2 Join        t3 Join         Console WriteLine  All threads complete

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In  NET 4 0  you can use the Task Parallel Library  In earlier versions  you can create a list of Thread objects in a loop  calling Start on each one  and then make another loop and call Join on each one

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In my case  I could not instantiate my objects on the the thread pool with Task Run   or Task Factory StartNew    They would not synchronize my long running delegates correctly  I needed the delegates to run asynchronously  pausing my main thread for their collective completion  The Thread Join   would not work since I wanted to wait for collective completion in the middle of the parent thread  not at the end  With the Task Run   or Task Factory StartNew    either all the child threads blocked each other or the parent thread would not be blocked      I couldn t figure out how to go with async delegates because of the re-serialization of the await syntax  Here is my solution using Threads instead of Tasks  using  EventWaitHandle wh   new EventWaitHandle false  EventResetMode ManualReset       int outdex   mediaServerMinConnections - 1    for  int i   0  i  lt  mediaServerMinConnections  i            new Thread      gt              sshPool Enqueue new SshHandler           if  Interlocked Decrement ref outdex   lt  1          wh Set           Start          wh WaitOne

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I ve made a very simple extension method to wait for all threads of a collection  using System Collections Generic  using System Threading   namespace Extensions       public static class ThreadExtension               public static void WaitAll this IEnumerable lt Thread gt  threads                        if threads  null                                foreach Thread thread in threads                    thread Join                                       Then you simply call  List lt Thread gt  threads new List lt Thread gt        Add your threads to this collection threads WaitAll

[c#] Create multiple threads and wait all of them to complete

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