/*
 * From at opengroup.org pthread_rwlock_unlock[1]:
 *
 * If an implementation detects that the value specified by the rwlock argument
 * to pthread_rwlock_unlock() refers to a read-write lock object for which the
 * current thread does not hold a lock, it is recommended that the function
 * should fail and report an [EPERM] error.
 *
 * EPERM used to be a specified return value prior to Issue 7:
 * The [EPERM] error for a read-write lock object for which the current thread
 * does not hold a lock is removed; this condition results in undefined
 * behavior.
 *
 * [1] http://pubs.opengroup.org/onlinepubs/9699919799/functions/pthread_rwlock_unlock.html
 * 
 * cc -pthread -o rwlock rwlock.c && ./rwlock
 */

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

pthread_rwlock_t rwlock = PTHREAD_RWLOCK_INITIALIZER;

#define CHECK(x) do {						\
	int e, r;						\
	char buf[256];						\
	printf("invoking %s\n", #x);				\
	r = x;							\
	e = errno;						\
	strerror_r(r, buf, sizeof(buf));			\
	printf("%s returned %d (%s)\n", #x, r, buf);		\
	if (r != 0) {						\
		strerror_r(e, buf, sizeof(buf));		\
		printf("errno %d (%s)\n", e, buf);		\
	}							\
} while(0)

void *
unlock(void *arg)
{
	CHECK(pthread_rwlock_unlock(&rwlock));
}

int main(int argc, char **argv)
{
	int rc=0;
	pthread_t td;

	printf("Enter Testcase - %s\n", argv[0]);
	CHECK(pthread_rwlock_wrlock(&rwlock));
	CHECK(pthread_create(&td, NULL, unlock, NULL));
	CHECK(pthread_join(td, NULL));
	return 0;
}