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To: "cygwin AT cygwin DOT com" <cygwin AT cygwin DOT com>
Subject: PTHREAD_MUTEX_SHARED on Cygwin
Message-ID: <657c8576-2715-8c80-a59a-23453306230f@netcologne.de>
Date: Sat, 9 Jan 2021 19:23:39 +0100
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From: Thomas Koenig via Cygwin <cygwin AT cygwin DOT com>
Reply-To: Thomas Koenig <tkoenig AT netcologne DOT de>
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Hi,

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?

If PTHREAD_PROCESS_SHARED does not work, are there known workarounds?

Best regards

	Thomas

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#include <errno.h>
#include <fcntl.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <unistd.h>

#define ERR_CHK(x) \
  do { \
	if (x) { \
	  perror(#x "failed"); \
	  exit(1); \
	} \
  } while (0)

int
main(int argc, char **argv) {
  pthread_condattr_t cattr;
  pthread_mutexattr_t mattr;
  pthread_mutex_t *m;
  pthread_cond_t *c;
  void *mem;

  ERR_CHK((mem = mmap(0, 0x1000, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANON, -1, 0)) == MAP_FAILED);

  m = mem;
  c = mem + 0x800;

  ERR_CHK(pthread_mutexattr_init(&mattr));
  ERR_CHK(pthread_mutexattr_setpshared(&mattr, PTHREAD_PROCESS_SHARED));
  ERR_CHK(pthread_mutex_init(m, &mattr));
  ERR_CHK(pthread_mutexattr_destroy(&mattr));

  ERR_CHK(pthread_condattr_init(&cattr));
  ERR_CHK(pthread_condattr_setpshared(&cattr, PTHREAD_PROCESS_SHARED));
  ERR_CHK(pthread_cond_init(c, &cattr));
  ERR_CHK(pthread_condattr_destroy(&cattr));

  printf("Success\n");

  return 0;
}

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