Hello misc@,
doing some C programming with threads (yeah *ugh*), I discovered a
strange issue.
There seems to be some problem using "static mutexes" (a mutex not
created by pthread_mutex_init()).
Here is some test code which works very well on linux, but gives:
------> (ID:2238337024)
First
mutex_prob: thread1: pthread_mutex_unlock() (0): Undefined error: 0
on OpenBSD.
The output should look like:
------> (ID:<somenumber>)
First
Second
Thread <somenumber2> done
Thread <somenumber3> done
<------ (ID:<somenumber>)
the mutex is looked by the main-thread and only thread1 may print
without locking the mutex first, thus "First" will always be printed
first.
If this is not a bug, perhaps somebody can point out the API difference
between OpenBSD and Linux I missed.
Regards
ahb
Test code:
#include <err.h>
#include <errno.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
/* static mutex var */
static pthread_mutex_t fz_mutex = PTHREAD_MUTEX_INITIALIZER;
static void
thread1(void *name)
{
printf("First\n");
/* free Mutex */
if (pthread_mutex_unlock(&fz_mutex) != 0)
err(1, "thread1: pthread_mutex_unlock() (%d)", errno);
/* thread end */
pthread_exit((void *)pthread_self());
}
static void
thread2(void *name)
{
/* lock Mutex */
pthread_mutex_lock(&fz_mutex);
printf("Second\n");
/* free Mutex again */
if (pthread_mutex_unlock(&fz_mutex) != 0)
err(1, "thread2: pthread_mutex_unlock() (%d)", errno);
/* thread end */
pthread_exit((void *)pthread_self());
}
int
main(void)
{
static pthread_t th1, th2;
static int ret1, ret2;
/* main thread */
printf("\n------> (ID:%lu)\n", pthread_self());
/* lock mutex */
pthread_mutex_lock(&fz_mutex);
/* Threads erzeugen */
if (pthread_create(&th1, NULL, (void *)&thread1,NULL)
!= 0)
err(1, "pthread_create(th1)");
if (pthread_create(&th2, NULL, (void *)&thread2,NULL)
!= 0)
err(1, "pthread_create(th2)");
/* Wait for both threads to finish */
pthread_join(th1, (void *)&ret1);
pthread_join(th2, (void *)&ret2);
printf("Thread %lu done\n", th1);
printf("Thread %lu done\n", th2);
printf("<----- (ID: %lu)\n", pthread_self());
return EXIT_SUCCESS;
}
Compile:
gcc -o foo foo.c -lpthread
