Maximum number of threads in a process

  • Thread starter Thread starter Edward Diener
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Edward Diener

Is there an operating system limit to the number of threads in a process ? A
test program I was writing created approximately 105 threads for a process
( many unused because of some thread pool code ), and an out of memory error
occurred when an attempt was made to create more threads. Since I do not
believe that the application was using much memory compared to the nearly 1
GIG of total virtual memory, I assume that the out of memory exception had
to do with exceeding a thread creation limit for a single process.
 
Edward Diener said:
Is there an operating system limit to the number of threads in a process ?
Click to expand...

No. The limiting factor usually turns out to be memory. Every thread by
_default_ gets a 1MB stack. Sooner or later you run out of contiguous
virtual address space.

I am surprised though that you hit the wall at 105. I have seen native
programs can several hundred more threads before giving up the ghost. I
haven't seen any reports about likely limits under .Net

<aside>
That said, where high performance is required, it is rarely a good idea to
have so many threads if all of them can compete for the processor. On the
native side of things, a thread pool and an I/O completion port scale
better.
</aside>

Regards,
Will
 
You can set a smaller stack size for your threads maybe that helps.
But in general if you have lots of threads thread pooling is the best
solution.
 
William DePalo said:
No. The limiting factor usually turns out to be memory. Every thread by
_default_ gets a 1MB stack. Sooner or later you run out of contiguous
virtual address space.

I am surprised though that you hit the wall at 105. I have seen native
programs can several hundred more threads before giving up the ghost. I
haven't seen any reports about likely limits under .Net
Click to expand...

I realized that the number of threads created was closer to 300 rather than
100. Each thread pool was creating 25 threads. I have since corrected the
test program I am running to use a single thread pool rather than the dozen
or so I was previously using, and everything runs fine now. Thanks for your
explanation about each thread using a 1MB stack. That would explain why I
ran out of memory.
<aside>
That said, where high performance is required, it is rarely a good idea to
have so many threads if all of them can compete for the processor. On the
native side of things, a thread pool and an I/O completion port scale
better.
</aside>
Click to expand...

There was a thread pool but it was encapsulated in a class which I was
instantiating numerous times even though I really only needed one instance
of the class.
 
Edward,

Are you aware that .NET has a built-in thread pool available. You made
it sound as if you've created your own and that maybe fine if there are
special requirements. I just thought I'd give you a friendly heads-up
in case you were not aware of it.

Brian
 
Brian Gideon said:
Edward,

Are you aware that .NET has a built-in thread pool available. You made
it sound as if you've created your own and that maybe fine if there are
special requirements. I just thought I'd give you a friendly heads-up
in case you were not aware of it.
Click to expand...

Yes, I was aware of it and the decision to use another thread pool was not
mine. Thanks, nonetheless for the heads-up.
 
cody said:
You can set a smaller stack size for your threads maybe that helps.
But in general if you have lots of threads thread pooling is the best
solution.
Click to expand...

Thanks for the info about setting a smaller stack size. I will look into
this.
 
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