Simple use of the of example for the mutex mutex

A few important functions:

#include < pthread.h >

int pthread_mutex_init(pthread_mutex_t *restrict mutex, const pthread_mutex_t *restrict attr); // Initialize mutex

int pthread_mutex_destroy (pthread_mutex_t * mutex); // If mutex is dynamically allocated, this function is called before freeing memory.

int pthread_mutex_lock (pthread_mutex_t * mutex); / / lock

int pthread_mutex_trylock (pthread_mutex_t * mutex); // Return EBUSY if the lock is already held by another thread, otherwise return 0, no blocking.

int pthread_mutex_unlock (pthread_mutex_t * mutex); / / unlock

Routine:

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <pthread.h>
#include <errno.h>
int a = 100;
int b = 200;
pthread_mutex_t lock;
void * threadA()
{
    pthread_mutex_lock(&lock);
    printf("thread A got lock!\n");
    a -= 50;
    sleep(3);        // If you leave it unlocked, threadB The output will be 50 and 200
    b += 50;        // After locking sleep 3 After seconds, and is b add 50 threadB To print 
    pthread_mutex_unlock(&lock);
    printf("thread A released the lock!\n");
    a -= 50;
}
void * threadC()
{    
    sleep(1);
    while(pthread_mutex_trylock(&lock) == EBUSY) // Poll until you get the lock 
    {
        printf("thread C is trying to get lock!\n");
        usleep(100000);
    }
    printf("thread C got the lock!\n");
    a = 1000;
    b = 2000;
    pthread_mutex_unlock(&lock);
    printf("thread C released the lock!\n");

}
void * threadB()
{
    sleep(2);                // let threadA Can you perform 
    pthread_mutex_lock(&lock);
    printf("thread B got the lock! a=%d b=%d\n", a, b);
    pthread_mutex_unlock(&lock);
    printf("thread B released the lock!\n", a, b);
}
int main()
{
    pthread_t tida, tidb, tidc;
    pthread_mutex_init(&lock, NULL);
    pthread_create(&tida, NULL, threadA, NULL);
    pthread_create(&tidb, NULL, threadB, NULL);
    pthread_create(&tidc, NULL, threadC, NULL);
    pthread_join(tida, NULL);
    pthread_join(tidb, NULL);
    pthread_join(tidc, NULL);
    return 0;
}