In the previous post, a simple example of using shared locks was given.This post introduces a slightly more complex example.

There is a global variable array out containing 100 elements, all initialized to zero.Then open two sub-threads to assign the array out at the same time.In this process, shared locks should be enabled to synchronize the assignment code.The code is as follows:

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

pthread_mutex_t number_mutex;

//Out array is a global variable, all 100 elements are initialized to zero, two threads together assign values to out array
int out[100];

//Thread 1
void thread1()
{
    int i;

    while(1){
        printf("Thread 1 operated.\n");
        pthread_mutex_lock(&number_mutex);
        for(i=0;i<100;i++){
            if(out[i]==0){				//Elements that have not been assigned are assigned
                out[i]=1111;
                break;
            }
        }
        
		//If the last element has been assigned, unlock and exit the thread
        if(out[99]!=0)
        {
            pthread_mutex_unlock(&number_mutex);
            return;
        }

        pthread_mutex_unlock(&number_mutex);
    }
}

//Thread 2
void thread2()
{
    int i;

    while(1){
        printf("Thread 2 operated.\n");
        pthread_mutex_lock(&number_mutex);
        for(i=0;i<100;i++){
            if(out[i]==0){
                out[i]=2222;
                break;
            }
        }
        
        if(out[99]!=0)
        {
            pthread_mutex_unlock(&number_mutex);
            return;
        }

        pthread_mutex_unlock(&number_mutex);
    }
}

main()
{
	//Initialize 100 elements of an out array
    int i;
    for(i=0;i<100;i++){
        out[i]=0;
    }

    pthread_t thid1,thid2;
    printf("This is Main Thread.\n");
    pthread_mutex_init(&number_mutex,NULL);

    pthread_create(&thid1,NULL,thread1,NULL);
    pthread_create(&thid2,NULL,thread2,NULL);

    int status1,status2;
    pthread_join(thid1,(void*)&status1);
    pthread_join(thid2,(void*)&status2);

    pthread_mutex_destroy(&number_mutex);

	//Output Array New Value for 100 Elements
    for(i=0;i<100;i++){
        printf("%d, ",out[i]);
    }
    printf("\nMain Thread exit\n");
}

2 threads run alternately, assigning all 100 array elements new values.