Subject: Re: PTHREAD_PROCESS_SHARED not implemented (was PTHREAD_MUTEX_SHARED on Cygwin)
From: Brian Inglis <[email-masked]>
To: [email-masked]
Date: Sat, 9 Jan 2021 15:16:04 -0700
List-Id: General Cygwin discussions and problem reports <cygwin.cygwin.com>

On 2021-01-09 12:58, Brian Inglis wrote:
> On 2021-01-09 11:23, Thomas Koenig via Cygwin wrote:
>> there is a branch of gfortran for implementing coarrays based on a
>> shared memory implementation instead of MPI, the devel_coarray/native
>> branch.
>>
>> I tried it out on Cygwin, but it doesn't work there (hangs on the
>> first sync).
>>
>> The branch uses pthread mutexes and condition variables
>> with PTHREAD_PROCESS_SHARED for synchronization between processes.
>>
>> I also ran the attached test program, which gave the output
>>
>> pthread_mutexattr_setpshared(&mattr, PTHREAD_PROCESS_SHARED)failed: No error
>>
>>
>> Is it correct that PTHREAD_PROCESS_SHARED is not supported on
>> Cygwin?  Is it supported for condition variables, or is the fact
>> that it is reported as working an oversight?
> 
> The function is supported but that parameter is not implemented or tested and 
> returns EINVAL:
> 
> https://sourceware.org/git?p=newlib-cygwin.git;a=blob;f=winsup/cygwin/thread.cc;hb=HEAD#l16 
> 
> 
> https://sourceware.org/git?p=newlib-cygwin.git;a=blob;f=winsup/cygwin/thread.cc;hb=HEAD#l1889 
> 
> 
>> If PTHREAD_PROCESS_SHARED does not work, are there known workarounds?
> 
> If you have the ability and time to work on this, one of the Cygwin 
> developers/maintainers may be able to assist.

It looks like there was nothing on this between implementation circa 2002 and:

https://sourceware.org/pipermail/cygwin/2019-February/240178.html

Presumably your goal is to support or disqualify gfortran coarrays:

https://gcc.gnu.org/pipermail/fortran/2021-January/055542.html

For more about Windows limitations and alternatives see:

https://www.boost.org/doc/libs/1_75_0/doc/html/interprocess/sharedmemorybetweenprocesses.html#interprocess.sharedmemorybetweenprocesses.sharedmemory.emulation

and the internal page link target:

https://www.boost.org/doc/libs/1_75_0/doc/html/interprocess/sharedmemorybetweenprocesses.html#interprocess.sharedmemorybetweenprocesses.sharedmemory.windows_shared_memory

-- 
Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada

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