Maximum number of threads in a NET app

Question

What is the maximum number of threads you can create in a C  application   And what happens when you reach this limit   Is an exception of some kind thrown

User · Accepted Answer

There is no inherent limit  The maximum number of threads is determined by the amount of physical resources available  See this article by Raymond Chen for specifics   If you need to ask what the maximum number of threads is  you are probably doing something wrong     Update  Just out of interest   NET Thread Pool default numbers of threads    1023 in Framework 4 0  32-bit environment  32767 in Framework 4 0  64-bit environment  250 per core in Framework 3 5 25 per core in Framework 2 0    These numbers may vary depending upon the hardware and OS

User · Answer

i did a test on a 64bit system with c  console  the exception is type of out of memory  using 2949 threads   I realize we should be using threading pool  which I do  but this answer is in response to the main question

User · Answer

You can test it by using this snipped code   private static void Main string   args       int threadCount   0     try            for  int i   0  i  lt  int MaxValue  i                      new Thread      gt  Thread Sleep Timeout Infinite   Start             threadCount                     catch            Console WriteLine threadCount         Console ReadKey true            Beware of 32-bit and 64-bit mode of application

User · Answer

Mitch is right  It depends on resources  memory    Although Raymond s article is dedicated to Windows threads  not to C  threads  the logic applies the same  C  threads are mapped to Windows threads    However  as we are in C   if we want to be completely precise  we need to distinguish between  started  and  non started  threads  Only started threads actually reserve stack space  as we could expect   Non started threads only allocate the information required by a thread object  you can use reflector if interested in the actual members    You can actually test it for yourself  compare       static void DummyCall                 Thread Sleep 1000000000              static void Main string   args                int count   0          var threadList   new List lt Thread gt             try                       while  true                                Thread newThread   new Thread new ThreadStart DummyCall   1024                   newThread Start                    threadList Add newThread                   count                                    catch  Exception ex                              with      static void DummyCall                 Thread Sleep 1000000000              static void Main string   args                int count   0          var threadList   new List lt Thread gt             try                       while  true                                Thread newThread   new Thread new ThreadStart DummyCall   1024                   threadList Add newThread                   count                                    catch  Exception ex                              Put a breakpoint in the exception  out of memory  of course  in VS to see the value of counter  There is a very significant difference  of course

User · Answer

Jeff Richter in CLR via C     With version 2 0 of the CLR  the maximum number of worker threads default to 25 per CPU in the machine  and the maximum number of I O threads defaults to 1000  A limit of 1000 is effectively no  limit at all    Note this is based on  NET 2 0   This may have changed in  NET 3 5    Edit  As  Mitch pointed out  this is specific to the CLR ThreadPool   If you re creating threads directly see the  Mitch and others comments

User · Answer

I would recommend running ThreadPool GetMaxThreads method in debug  ThreadPool GetMaxThreads out int workerThreadsCount  out int ioThreadsCount     Docs and examples  https   docs microsoft com en-us dotnet api system threading threadpool getmaxthreads view netframework-4 8

User · Answer

You should be using the thread pool  or async delgates  which in turn use the thread pool  so that the system can decide how many threads should run

[c#] Maximum number of threads in a .NET app?

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