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From: Nicholas Sherlock <n DOT sherlock AT gmail DOT com>
Subject:  Cygwin PThreads bug?
Date:  Wed, 04 Mar 2009 14:29:54 +1300
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Hey everyone,

I'm writing a very thread-intensive application using Cygwin and 
Cygwin's PThreads implementation, and I'm running into a few problems. 
As far as I can tell from the spec:

http://www.opengroup.org/onlinepubs/000095399/functions/pthread_rwlock_rdlock.html

This C program:

#include <stdio.h>
#include <pthread.h>
#include <assert.h>
#include <errno.h>

int main() {
	pthread_rwlock_t rw_lock;

	pthread_rwlock_init(&rw_lock,NULL);

	//Lock it once for read...
	assert(pthread_rwlock_rdlock(&rw_lock)==0);
	
	//Lock it again for read...
	int err=pthread_rwlock_rdlock(&rw_lock);

	printf("Err %d\n", err);

	assert (err==EAGAIN || err==0);

	if (err!=EAGAIN)
	  pthread_rwlock_unlock(&rw_lock);

	pthread_rwlock_unlock(&rw_lock);

	pthread_rwlock_destroy(&rw_lock);
	
	return 0;
}

Should run correctly. That is, the second call to pthread_rwlock_rdlock 
should either succeed (returning zero), having acquired the read lock a 
second time, or it should fail and return EAGAIN, if the number of 
simultaneous allowed read locks has been exceeded. It should not fail 
and return EDEADLK (45), which it is currently doing. Am I reading the 
spec wrong or is Cygwin non-conforming?

Cheers,
Nicholas Sherlock


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