thread scheduling at mutex unlock

Andriy Gapon avg at
Wed May 14 20:14:26 UTC 2008

on 14/05/2008 18:17 Andriy Gapon said the following:
> I am trying the small attached program on FreeBSD 6.3 (amd64,
> SCHED_4BSD) and 7-STABLE (i386, SCHED_ULE), both with libthr as threads
> library and on both it produces "BROKEN" message.
> I compile this program as follows:
> cc sched_test.c -o sched_test -pthread
> I believe that the behavior I observe is broken because: if thread #1
> releases a mutex and then tries to re-acquire it while thread #2 was
> already blocked waiting on that mutex, then thread #1 should be "queued"
> after thread #2 in mutex waiter's list.
> Is there any option (thread scheduler, etc) that I could try to achieve
> "good" behavior?
> P.S. I understand that all this is subject to (thread) scheduler policy,
> but I think that what I expect is more reasonable, at least it is more
> reasonable for my application.

Daniel Eischen has just kindly notified me that the code (as an 
attachment) didn't make it to the list, so here it is inline.

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <pthread.h>

pthread_mutex_t mutex;
int count = 0;

static void * thrfunc(void * arg)
     while (1) {

         if (count > 10) {
             fprintf(stderr, "you have a BROKEN thread scheduler!!!\n");



int main(void)
     pthread_t thr;

#if 0
     pthread_mutexattr_t attr;
     pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE_NP);
     pthread_mutex_init(&mutex, &attr);
     pthread_mutex_init(&mutex, NULL);

     pthread_create(&thr, NULL, thrfunc, NULL);


     count = 0;
     printf("you have good thread scheduler\n");

     return 0;

Andriy Gapon

More information about the freebsd-threads mailing list