回顾一下生产者消费者模型。
#include <stdio.h> #include <stdlib.h> #include <string.h> #include <semaphore.h> #include <unistd.h> #include <sys/types.h> #include <pthread.h> #define ERR_EXIT(m) do { perror(m); exit(EXIT_FAILURE); }while(0) #define CONSUMERS_COUNT 1 #define PRODUCERS_COUNT 2 #define BUFFSIZE 10 int g_buffer[BUFFSIZE]; unsigned short in = 0; unsigned short out = 0; unsigned short product_id = 0; unsigned short consume_id = 0; sem_t g_sen_full; sem_t g_sen_empty; pthread_mutex_t g_mutex; pthread_t g_thread[CONSUMERS_COUNT+PRODUCERS_COUNT]; void* consume(void* arg) { int i; while(1) { sem_wait(&g_sen_empty); pthread_mutex_lock(&g_mutex); for (i = 0; i < BUFFSIZE; ++i) { /* code */ printf("%02d\n", i); if(g_buffer[i] == -1) printf("%s", "null"); else printf("%d\n", g_buffer[i]); if(i == out) printf("\t<--consume\n"); printf("\n"); } consume_id = g_buffer[out]; printf("begin consume product %d\n", consume_id); g_buffer[out] = -1; out = (out + 1) % BUFFSIZE; pthread_mutex_unlock(&g_mutex); sem_post(&g_sen_full); sleep(1); } return NULL; } void* produce(void *arg) { int num = (int)arg; int i; while(1) { printf("%d waiting buffer_full\n", num); sem_wait(&g_sen_full); pthread_mutex_lock(&g_mutex); for (i = 0; i < BUFFSIZE; ++i) { /* code */ printf("%02d\n", i); if(g_buffer[i] == -1) printf("%s", "null"); else printf("%d\n", g_buffer[i]); if(i == in) printf("\t<--produce\n"); printf("\n"); } printf("begin produce product %d\n", product_id); g_buffer[in] = product_id; in = (in +1) % BUFFSIZE; printf("end produce product %d\n", product_id++); pthread_mutex_unlock(&g_mutex); sem_post(&g_sen_empty); } return NULL; } int main(int argc, const char *argv[]) { int i; for (i = 0; i < BUFFSIZE; ++i) { /* code */ g_buffer[i] = -1; } // 初始化信号量 sem_init(&g_sen_full, 0, BUFFSIZE); sem_init(&g_sen_empty, 0, 0); // 初始化锁 pthread_mutex_init(&g_mutex, NULL); for (i = 0; i < CONSUMERS_COUNT; ++i) { /* code */ pthread_create(&g_thread[i], NULL, consume, (void*)i); } for (i = 0; i < PRODUCERS_COUNT; ++i) { /* code */ pthread_create(&g_thread[CONSUMERS_COUNT+i], NULL, produce, (void*)i); } for (i = 0; i < CONSUMERS_COUNT+PRODUCERS_COUNT; ++i) { /* code */ pthread_join(g_thread[i], NULL); } sem_destroy(&g_sen_empty); sem_destroy(&g_sen_full); pthread_mutex_destroy(&g_mutex); return 0; }
东莞东方
再写一个 条件变量的版本。
#include <stdio.h> #include <stdlib.h> #include <string.h> #include <semaphore.h> #include <unistd.h> #include <sys/types.h> #include <pthread.h> #define ERR_EXIT(m) do { perror(m); exit(EXIT_FAILURE); }while(0) #define CONSUMERS_COUNT 2 #define PRODUCERS_COUNT 1 #define BUFFSIZE 10 unsigned short in = 0; unsigned short out = 0; unsigned short product_id = 0; unsigned short consume_id = 0; sem_t g_sen_full; sem_t g_sen_empty; pthread_mutex_t g_mutex; pthread_cond_t g_cond; pthread_t g_thread[CONSUMERS_COUNT+PRODUCERS_COUNT]; int nready = 0; void* consume(void* arg) { int num = (int)arg; while(1) { pthread_mutex_lock(&g_mutex); while(nready==0) { printf("begin wait a condtion\n"); pthread_cond_wait(&g_cond, &g_mutex); } printf("no.%dend of wait a condtion ....\n", num); --nready; printf("消费者%d消耗一个产品\n", num); pthread_mutex_unlock(&g_mutex); } return NULL; } void* produce(void *arg) { int num = (int)arg; while(1) { pthread_mutex_lock(&g_mutex); ++nready; printf("生产者%d生产了一个产品并发送signal..\n", num); pthread_cond_signal(&g_cond); pthread_mutex_unlock(&g_mutex); sleep(5); } return NULL; } int main(int argc, const char *argv[]) { int i; pthread_mutex_init(&g_mutex, NULL); pthread_cond_init(&g_cond, NULL); for (i = 0; i < CONSUMERS_COUNT; ++i) { /* code */ pthread_create(&g_thread[i], NULL, produce, (void*)i); } for (i = 0; i < PRODUCERS_COUNT; ++i) { /* code */ pthread_create(&g_thread[i+CONSUMERS_COUNT], NULL, consume, (void*)i); } for (i = 0; i < CONSUMERS_COUNT+PRODUCERS_COUNT; ++i) { /* code */ pthread_join(g_thread[i], NULL); } pthread_mutex_destroy(&g_mutex); pthread_cond_destroy(&g_cond); return 0; }
pthread_cond_wait这个函数的原语:
一。对g_mutex进行解锁,让其他线程可以进入临界区
二。等待条件,直到有线程可以唤醒它,然后让出CPU
三。当被唤醒时,它会重新对g_mutex进行加锁
对于生产者&消费者进行判断为啥使用while而不是if,我们已经之前讨论过了
if值判断一次,而重新上锁之后并不能保证它还满足情况。
时间: 2024-10-12 18:48:53