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From: Daniel Brown <DDB707 AT bham DOT ac DOT uk>
To: "cygwin AT cygwin DOT com" <cygwin AT cygwin DOT com>
Subject: Re: Win32 error in C program using openmp and fork()
Date: Tue, 23 Jul 2013 09:03:58 +0000
Message-ID: <57302C57257EF2428CCAAF9BA83EC0448222E6A7@mbx08.adf.bham.ac.uk>
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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?

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 AT XPS15z ~
$ uname -r
1.7.22s(0.268/5/3)

Daniel AT 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");
}

it works fine, if I use 3 threads then the error comes back. Interestingly the the value of currentvalue changes each time I run the program if I use 4 or more threads, if I use 3 then it is always -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?

Thanks,
Daniel

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