pthread_mutex_lock function
C
Function
Reference manual
@see pthread_mutex_init function, pthread_mutex_destroy function, pthread_mutex_unlock function
The pthread_mutex_lock function is used to acquire a lock on a mutex object. If the mutex is already locked by another thread, the calling thread will block until the mutex becomes available.
Remember to destroy the mutex with the pthread_mutex_destroy function once you are done using it.
Syntax
#include <pthread.h>
int pthread_mutex_lock(pthread_mutex_t *mutex);
Parameters
- mutex: A pointer to a variable of type pthread_mutex_t representing the mutex to be locked.
Return value
-
If the mutex is successfully locked, the function returns 0.
-
If an error occurs, a non-zero error code is returned. Possible error codes include EINVAL (invalid mutex) and EDEADLK (deadlock detected).
Usage example
In the following example we initialize a global mutex variable mutex using pthread_mutex_init, then we create three threads, each executing the thread_function function. Each thread locks the mutex with pthread_mutex_lock, enters a critical section where it prints its ID, and then unlocks the mutex with pthread_mutex_unlock. After all threads have finished executing, we destroy the mutex using pthread_mutex_destroy. This example demonstrates how to use mutexes to protect critical sections of code from concurrent execution by multiple threads.
#include <stdlib.h>
#include <stdio.h>
#include <pthread.h>
pthread_mutex_t mutex;
void *thread_function(void *arg)
{
int *thread_id;
pthread_mutex_lock(&mutex); // Lock the mutex
*thread_id = arg;
printf("Thread %d is inside the critical section\n", *thread_id);
pthread_mutex_unlock(&mutex); // Unlock the mutex
return (NULL);
}
int main(void)
{
pthread_t threads[3];
int thread_args[3] = {1, 2, 3};
// Initialize the mutex
int init_result = pthread_mutex_init(&mutex, NULL);
if (init_result != 0) {
fprintf(stderr, "Error initializing mutex: %d\n", init_result);
return (EXIT_FAILURE);
}
// Create three threads
for (int i = 0; i < 3; i++) {
int create_result = pthread_create(&threads[i], NULL, thread_function, &thread_args[i]);
if (create_result != 0) {
fprintf(stderr, "Error creating thread %d: %d\n", i+1, create_result);
return (EXIT_FAILURE);
}
}
// Join all threads
for (int i = 0; i < 3; i++) {
int join_result = pthread_join(threads[i], NULL);
if (join_result != 0) {
fprintf(stderr, "Error joining thread %d: %d\n", i+1, join_result);
return (EXIT_FAILURE);
}
}
// Destroy the mutex
int destroy_result = pthread_mutex_destroy(&mutex);
if (destroy_result != 0) {
fprintf(stderr, "Error destroying mutex: %d\n", destroy_result);
return (EXIT_FAILURE);
}
printf("All threads have finished executing\n");
return (EXIT_SUCCESS);
}