pthread_equal() in C

The pthread_equal() function is used to check whether two threads are equal or not. This returns 0 or non-zero value. For equal threads, it will return non-zero, otherwise it returns 0. The syntax of this function is like below −

int pthread_equal (pthread_t th1, pthread_t th2);

Now let us see the pthread_equal() in action. In the first case, we will check the self-thread to check the result.

Example

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <pthread.h>
pthread_t sample_thread;
void* my_thread_function(void* p) {
   if (pthread_equal(sample_thread, pthread_self())) { //pthread_self will return current thread id
      printf("Threads are equal\n");
   } else {
      printf("Threads are not equal\n");
   }
}
main() {
   pthread_t th1;
   sample_thread = th1; //assign the thread th1 to another thread object
   pthread_create(&th1, NULL, my_thread_function, NULL); //create a thread using my thread function
   pthread_join(th1, NULL); //wait for joining the thread with the main thread
}

Output

Threads are equal

Now we will see the result, if we compare between two different threads.

Example

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <pthread.h>
pthread_t sample_thread;
void* my_thread_function1(void* ptr) {
   sample_thread = pthread_self(); //assign the id of the thread 1
}
void* my_thread_function2(void* p) {
   if (pthread_equal(sample_thread, pthread_self())) { //pthread_self will return current thread id
      printf("Threads are equal\n");
   } else {
      printf("Threads are not equal\n");
   }
}

main() {
   pthread_t th1, th2;
   pthread_create(&th1, NULL, my_thread_function1, NULL); //create a thread using my_thread_function1
   pthread_create(&th1, NULL, my_thread_function2, NULL); //create a thread using my_thread_function2
   pthread_join(th1, NULL); //wait for joining the thread with the main thread
   pthread_join(th2, NULL);
}

Output

Threads are not equal