Threads and mutex with broadcast signal [closed] - c

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In scenario 2 why all threads are not getting triggered?
What is the problem with different mutex variable?
Scenario 1 :
I am creating four threads.Each threads were assigned to different cores all four threads are waiting for signal with same conditional and mutex variable.While passing broadcast signal with same conditional variable all threads were getting triggered.
#define _GNU_SOURCE
#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<pthread.h>
#include<sched.h>
pthread_cond_t condVar=PTHREAD_COND_INITIALIZER;
pthread_mutex_t mutexVar=PTHREAD_MUTEX_INITIALIZER;
void *thread1(void *ptr)
{
int iVar=1;
printf("Thread %d\n",iVar);
pthread_mutex_lock(&mutexVar);
pthread_cond_wait(&condVar,&mutexVar);
pthread_mutex_unlock(&mutexVar);
printf("Thread %d is unblocked...\n",iVar);
}
void *thread2(void *ptr)
{
int iVar=2;
printf("Thread %d\n",iVar);
pthread_mutex_lock(&mutexVar);
pthread_cond_wait(&condVar,&mutexVar);
pthread_mutex_unlock(&mutexVar);
printf("Thread %d is unblocked...\n",iVar);
}
void *thread3(void *ptr)
{
int iVar=3;
printf("Thread %d\n",iVar);
pthread_mutex_lock(&mutexVar);
pthread_cond_wait(&condVar,&mutexVar);
pthread_mutex_unlock(&mutexVar);
printf("Thread %d is unblocked...\n",iVar);
}
void *thread4(void *ptr)
{
int iVar=4;
printf("Thread %d\n",iVar);
pthread_mutex_lock(&mutexVar);
pthread_cond_wait(&condVar,&mutexVar);
pthread_mutex_unlock(&mutexVar);
printf("Thread %d is unblocked...\n",iVar);
}
int main()
{
int i,j=2;
pthread_t t[4];
cpu_set_t cpuset;
pthread_create(&t[0],0,thread1,0);
pthread_create(&t[1],0,thread2,0);
pthread_create(&t[2],0,thread3,0);
pthread_create(&t[3],0,thread4,0);
for(i=0;i<4;i++) //Assign dedicated core for each thread
{
CPU_ZERO(&cpuset);
CPU_SET(j,&cpuset);
if((pthread_setaffinity_np(t[i],sizeof(cpu_set_t),&cpuset))!=0)
perror("Set_affinity");
j+=2;
}
sleep(5);
pthread_cond_broadcast(&condVar);
while(1);
}
Output:
Thread 1
Thread 4
Thread 2
Thread 3
Thread 1 is unblocked...
Thread 4 is unblocked...
Thread 2 is unblocked...
Thread 3 is unblocked...
Scenario 2:
Instead of same mutex variable I have created different mutex to each thread.While passing broadcast signal among the four,only one thread is getting triggered remaining threads were waiting for signal.
Output for scenario 2 :
Thread 1
Thread 2
Thread 4
Thread 3
Thread 1 is unblocked...

Answer 1

Instead of same mutex variable I have created different mutex to each thread.While passing broadcast signal among the four,only one thread is getting triggered remaining threads were waiting for signal.
That's a misuse of condition variables and undefined behavior. Per the POSIX pthread_cond_wait() documentation:
When a thread waits on a condition variable, having specified a particular mutex to either the pthread_cond_timedwait() or the pthread_cond_wait() operation, a dynamic binding is formed between that mutex and condition variable that remains in effect as long as at least one thread is blocked on the condition variable. During this time, the effect of an attempt by any thread to wait on that condition variable using a different mutex is undefined.