thread_23

//多线程链表添加删除例子（使用条件变量实现互斥）：
 #include <stdlib.h>
#include <pthread.h>
#include <stdio.h>
#include <sched.h>
#include <string.h>
typedef struct _list_head list_head;
struct _list_head{
       list_head *next;
        list_head *prev;
        int used;
        int data;
 };

list_head _head = {&_head, &_head, 0, 0};
list_head *head = &_head;

void list_add(list_head *entry, list_head *head)
{
        head->next->prev = entry;
        entry->next = head->next;
        entry->prev = head;
        head->next = entry;
 }
 
 list_head *list_del(list_head *entry)
 {
        entry->next->prev = entry->prev;
        entry->prev->next = entry->next;
        return entry;
 }

pthread_cond_t cond;
pthread_mutex_t lock;
 
void *producer(void *arg)
 {
         do{
                list_head *node;
                if(node = malloc(sizeof(list_head)) )
                {
                        memset((void *)node, ‘\0‘, sizeof(list_head));
                         node->data = rand();
                }
                else
                        return NULL;

               pthread_mutex_lock(&lock);
                while(head->used != 0)
                {
                        pthread_cond_wait(&cond, &lock);
                }
                head->used = 1;
                pthread_mutex_unlock(&lock);

                list_add(node, head);
                printf("product %d\n", node->data);
 
                 head->used = 0;
                 pthread_cond_signal(&cond);
        }while(1);

 }
 
void *consumer(void *arg)
 {
         do{
                 list_head *node;

                pthread_mutex_lock(&lock);
               while(head->used != 0 || head->next == head->prev)
                {
                         pthread_cond_wait(&cond, &lock);
                 }
                head->used = 1;
                pthread_mutex_unlock(&lock);//这句代码一定要有，不然会发生死锁

                 node = head->next;
                 list_del(node);
                  printf("consumer %d\n", node->data);
                 free(node);
 
                head->used = 0;
               pthread_cond_signal(&cond);
         }while(1);
}

 int main(int argc, char *argv[])
 {
        pthread_t  t1, t2;
         int ret;
        pthread_cond_init(&cond, NULL);
        pthread_mutex_init(&lock, NULL);

        pthread_create(&t1, NULL, producer, NULL);
         pthread_create(&t2, NULL, consumer, NULL);
 
         pthread_join(t1, NULL);
        pthread_join(t2, NULL);
 
         return 1;
 }
//注意：最后两个join是必须的，否则主线程将提早结束，不会一直执行循环。
/*
***********pthread_cond_wait()的使用方法*********
    pthread_mutex_lock(&qlock);    
    pthread_cond_wait(&qready, &qlock);
    pthread_mutex_unlock(&qlock);
*****************************************************/