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Re: 256 threads maximum?

Panagiotis Issaris wrote:

The following simple testprogram tries to create the number of threads given as argv[1].
When I'm using a 2.6.3 kernel with glibc 2.3.2/NPTL 0.60, the maximum number of threads this application can create is 255. With any number higher it complains about memory allocation failing.

I bet you're using a 32-bit machine with an 8 MiB stack. The top bit is reserved for kernel use, IIRC, so a program can only address 2 GiB of virtual memory. 2 GiB / 8 MiB = 256. One thread already exists. If you ran a

    $ ulimit -s 4096
    $ ./thr 511

It would succeed, I'd think. And 512 would fail.

I'm not sure why LinuxThreads was able to allocate more threads. Maybe it determines the stack size in a different way?

What am I doing wrong? I know that NPTL can do a lot better then this, since I have been reading reports on NPTL creating thousands of threads ( I think I recall someone stating creating 300000 threads from one process).

You can do a little better by decreasing the stack space per thread, as mentioned above. But I think they must have been doing this test on a 64-bit machine.


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