[1.7] pthread_mutex_lock/pthread_mutex_unlock strange blocking problem

[Thomas Stalder]

Hello,

Sometimes pthread_mutex_lock ou pthread_mutex_unlock block.

In order to reproduce the problem, I have made a test application
(test.c) who always block

$ gcc test.c -o test
$ ./test
thread id=1
after pthread_create 1
after pthread_create 2
thread id=2
thread id=3
after pthread_create 3
after pthread_create 4
thread id=4
thread id=5
after pthread_create 5
thread id=6
after pthread_create 6
after pthread_create 7

The application can create 1,2,3 threads or many more before blocking.

--
Thomas

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


static pthread_mutex_t my_mutex = PTHREAD_MUTEX_INITIALIZER;
static pthread_mutex_t my_mutex2 = PTHREAD_MUTEX_INITIALIZER;
int nb_thread=0;

void *thread_func(void *parm)
{
        int id;
        pthread_mutex_lock(&my_mutex);
        nb_thread++;
        id = nb_thread;
        pthread_mutex_unlock(&my_mutex);
        
        pthread_mutex_lock(&my_mutex2);
        printf("thread id=%d\n", id);
        pthread_mutex_unlock(&my_mutex2);

        pthread_exit(0);
        return NULL;
}

int main(void)
{
        int tmp_nb=0;
        while(1)
        {
                int err = 0;
                pthread_attr_t  attr;
                pthread_t thread_id;

                /*  Initialize the attribute */
                err = pthread_attr_init(&attr);
                if (err)
                {
                        printf("pthread_attr_init err=%d\n", err);
                }
                err = pthread_attr_setinheritsched(&attr, 
PTHREAD_INHERIT_SCHED);
                if (err)
                {
                        printf("pthread_attr_setinheritsched error\n");
                }

                err = 
pthread_attr_setdetachstate(&attr,PTHREAD_CREATE_DETACHED);
                if (err)
                {
                        printf("pthread_attr_setdetachstate error\n");
                }

                /*  Create the thread with our attribute */
                
                err = pthread_create(&thread_id, &attr, thread_func, NULL);
                if (err)
                {
                        printf("pthread_create error\n");
                }       
                pthread_mutex_lock(&my_mutex2);
                printf("after pthread_create %d\n", ++tmp_nb);
                pthread_mutex_unlock(&my_mutex2);
                pthread_attr_destroy(&attr);
        }
}

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