Linux多线程之同步

pthread_cond_init(&cond_pro, NULL);pthread_cond_init(&cond_con, NULL);pthread_cond_destroy(&cond_pro);pthread_cond_destroy(&cond_pro);

3. 等待和激发条件

#include <pthread.h>int pthread_cond_wait(pthread_cond_t *restrict cond,  pthread_mutex_t *restrict mutex);int pthread_cond_broadcast(pthread_cond_t *cond);int pthread_cond_signal(pthread_cond_t *cond);

    pthread_cond_wait(&cond_pro,&mutex); pthread_cond_broadcast(&cond_pro);pthread_cond_signal(&cond_pro);

#include <stdio.h>#include <stdlib.h>#include <string.h>#include <pthread.h>#include <unistd.h>#define CELL 10#define FLORE 0int i = 0; pthread_mutex_t mutex;              pthread_cond_t cond_pro, cond_con;  void* pro_handler(void *arg){    pthread_detach(pthread_self());           while(1)    {        pthread_mutex_lock(&mutex);        while(i >= CELL)        {            pthread_cond_wait(&cond_pro,&mutex);                                                         }        i++;        if(i == 1)        {                        pthread_cond_signal(&cond_con);            }        printf("add i: %d /n", i);        pthread_mutex_unlock(&mutex);        sleep(rand() % 5 + 1);    }}void* con_handler(void *arg){    pthread_detach(pthread_self());    while(1)    {        pthread_mutex_lock(&mutex);        while(i <= FLORE)        {            pthread_cond_wait(&cond_cno,&mutex);        }        i--;        if(i == 9)         {            pthread_cond_signal(&cond_pro);        }        printf("con i: %d /n", i);        pthread_mutex_unlock(&mutex);        sleep(rand() % 5 + 1);    }}int main(int argc, char *argv[]) // exe +num -num{    srand(getpid());    int con_cnt, pro_cnt;    pro_cnt = atoi(argv[1]);    con_cnt = atoi(argv[2]);    pthread_mutex_init(&mutex,NULL);    pthread_cond_init(&cond_pro,NULL);    pthread_cond_init(&cond_con,NULL);    pthread_t *arr = (pthread_t*)calloc(con_cnt + pro_cnt , sizeof(pthread_t));    int index = 0;    while(pro_cnt > 0)    {        pthread_create(arr + index, NULL, pro_handler, NULL);        index++;        pro_cnt--;    }    while(con_cnt > 0)    {        pthread_create(arr + index, NULL, con_handler, NULL);        index++;        con_cnt--;    }    while(1);    pthread_mutex_destroy(&mutex);    pthread_cond_destroy(&cond_pro);    pthread_cond_destroy(&cond_con);    return 0;}

无论是在生产者线程，还是在消费者线程中。标记黄色部分的判断条件必须用while。以生产者线程举例，当i>=CELL时，也就是i满时，此时执行pthread_cond_wait(&cond_cno,&mutex); 该生产者线程被挂起。必须等到消费者线程pthread_cond_signal(&cond_pro); 将其唤醒。但是消费者将其signal还不够，被挂其的生产者线程必须重新拿到锁，才可以被激活。但是，由于在消费者signal的同时，生产者并不能立即抢到锁，所以此时可能i值又改变变为大于等于10了。因此必须用while。不然可能导致i>10。