Re: Win32 error in C program using openmp and fork()

[Corinna Vinschen <corinna-cygwin@cygwin.com>]

On Jul 23 13:28, Daniel Brown wrote:
> I've wiped my old version of Cygwin and installed it fresh on my computer
> and 1.7.21 doesn't work for me, either 32 or 64 bit. I have tried a
> Win 7 x86
> virtual machine and it worked, on a Win 8 x86 virtual machine though I see
> the same error. Therefore I guess it is a Windows 8 issue unless you are
> running it?

Yes, Windows 8/64 is my major test machine.
> 
> I tried replacing the cygwin1.dll with the latest snapshots 1.7.22s x86
> and that still had the fork error. I have also tried running in safe
> mode and
> stopping all my anti-virus software just incase that was interfering
> somehow.
> So I get as an output now...
> 
> Daniel@XPS15z ~
> $ uname -r
> 1.7.22s(0.268/5/3)
> 
> Daniel@XPS15z ~
> $ ./a.exe
> I'm an openmp thread...
> I'm an openmp thread...
> I'm an openmp thread...
> I'm an openmp thread...
> Parent fork 1 [main] a 5832 C:\cygwin\home\Daniel\a.exe: *** fatal
> error in forked process - failed
> to create new win32 semaphore, currentvalue -2, Win32 error 87
> 
> However if I reduce the number of threads from 4 to 2 with:
> 
> #pragma omp parallel num_threads(2)
> {
> printf("I'm an openmp thread...\n");
> }

Ah, now there's something different.  If I set the number of threads to
4, I can reproduce this problem almost every try with currentvalue -2,
occassionally with currentvalue -1.

> Looking at the source in thread.cc _fixup_after_fork() the win32
> error 87 is ERROR_INVALID_PARAMETER
> which is due to currentvalue < 0.
> 
> My only guess is that there is a race condition on the
> currentvalue-- operations perhaps?

Apparently.  I investigate...


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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