I recently upgraded to 2.6.22 to get the priority based futex wakeup
behavior. However, when I run a simple program (see below), based on
either a pthread_mutex_t or a sem_t, it seems that threads are woken up
in FIFO order. I am using glibc 2.3.6 with NPTL and TLS, based off
crossdev-0.43. Could someone help me get priority-based wakeup or point
me to a better place to get this question answered?
Thank you,
Michael
Code:
pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
void *important(void *ign)
{
sleep(1);
printf("important waiting for mutex\n");
if(pthread_mutex_lock(&mymutex)) {
perror("sem_wait");
exit(1);
} else {
printf("important got mutex!\n");
pthread_mutex_unlock(&mymutex);
}
return NULL;
}
void *unimportant(void *ign)
{
printf("unimportant waiting for mutex\n");
if(pthread_mutex_lock(&mymutex)) {
perror("sem_wait");
exit(1);
} else {
printf("unimportant got mutex!\n");
pthread_mutex_unlock(&mymutex);
}
return NULL;
}
int main()
{
struct sched_param p;
pthread_attr_t attr;
pthread_t i, u;
pthread_mutex_lock(&mymutex);
p.__sched_priority = sched_get_priority_min(SCHED_FIFO);
if(-1 == p.__sched_priority) {
perror("sched_get_priority_min");
return 1;
}
pthread_attr_init(&attr);
pthread_attr_setschedpolicy(&attr, SCHED_FIFO);
pthread_attr_setschedparam(&attr, &p);
pthread_create(&u, &attr, unimportant, NULL);
p.__sched_priority = sched_get_priority_max(SCHED_FIFO);
pthread_attr_setschedparam(&attr, &p);
pthread_create(&i, &attr, important, NULL);
sleep(5);
printf("main unlocking mutex\n");
pthread_mutex_unlock(&mymutex);
pthread_join(u, NULL);
pthread_join(i, NULL);
return 0;
}
Which produces:
unimportant waiting for mutex
important waiting for mutex
main unlocking mutex
unimportant got mutex!
important got mutex!
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