thread同步

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

#define NUM 5
int queue[NUM];
sem_t blank_number, product_number;

void *producer ( void * arg )
{
    static int p = 0;

    for ( ;; ) {
        sem_wait( &blank_number );
        queue[p] = rand() % 1000;
        printf("Product %d \n", queue[p]);
        p = (p+1) % NUM;
        sleep ( rand() % 5);
        sem_post( &product_number );
    }
}
void *consumer ( void * arg )
{

    static int c = 0;
    for( ;; ) {
        sem_wait( &product_number );
        printf("Consume %d\n", queue[c]);
        c = (c+1) % NUM;
        sleep( rand() % 5 );
        sem_post( &blank_number );
    }
}

int main(int argc, char *argv[] )
{
    pthread_t pid, cid;
    sem_init( &blank_number, 0, NUM );
    sem_init( &product_number, 0, 0);
    pthread_create( &pid, NULL, producer, NULL);
    pthread_create( &cid, NULL, consumer, NULL);
    pthread_join( pid, NULL );
    pthread_join( cid, NULL );
    sem_destroy( &blank_number );
    sem_destroy( &product_number );
    return 0;
}

运行上述代码

截图：

 

  一个消费者线程，一个生产者线程。最大的空间为5（即空格+产品=5）

 

20191224%3 +4 =4（个）

改进后

代码：

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

#define NUM 3
int queue[NUM];
sem_t blank_number, product_number;

void *producer ( void * arg )
{
        static int p = 0;

        for ( ;; ) {
                sem_wait( &blank_number );
                queue[p] = rand() % 1000;
                printf("Product %d \n", queue[p]);
                p = (p+1) % NUM;
                sleep ( rand() % 4);
                sem_post( &product_number );
        }
}
void *consumer ( void * arg )
{

        static int c = 0;
        for( ;; ) {
                sem_wait( &product_number );
                printf("Consume %d\n", queue[c]);
                c = (c+1) % NUM;
                sleep( rand() % 5 );
                sem_post( &blank_number );
        }
}

int main(int argc, char *argv[] )
{
        pthread_t pid, cid;

        sem_init( &blank_number, 0, NUM );
        sem_init( &product_number, 0, 0);
        pthread_create( &pid, NULL, producer, NULL);
        pthread_create( &cid, NULL, consumer, NULL);
        pthread_create( &cid, NULL, consumer, NULL);
        pthread_create( &cid, NULL, consumer, NULL);
        pthread_create( &cid ,NULL, consumer, NULL);
        pthread_join( pid, NULL );
        pthread_join( cid, NULL );
        pthread_join( cid, NULL );
        pthread_join( cid, NULL );
        pthread_join( cid, NULL );
        sem_destroy( &blank_number );
        sem_destroy( &product_number );
        return 0;