4、Linux多线程，线程同步（2）

#include <stdio.h>
#include <pthread.h>
#include "stdlib.h"
#include "unistd.h"

pthread_mutex_t mutex;
pthread_cond_t cond;

void hander(void *arg)
{
    free(arg);
    (void)pthread_mutex_unlock(&mutex);
}

void *thread1(void *arg)
{
     pthread_cleanup_push(hander, &mutex);
while(1)
     {
         printf("thread1 is running\n");
         pthread_mutex_lock(&mutex);
         pthread_cond_wait(&cond,&mutex);
         printf("thread1 applied the condition\n");
         pthread_mutex_unlock(&mutex);
         sleep(4);
     }
     pthread_cleanup_pop(0);
 }

void *thread2(void *arg)
{
while(1)
     {
         printf("thread2 is running\n");
         pthread_mutex_lock(&mutex);
         pthread_cond_wait(&cond,&mutex);
         printf("thread2 applied the condition\n");
         pthread_mutex_unlock(&mutex);
         sleep(1);
     }
}
int main()
{
     pthread_t thid1,thid2;
     printf("condition variable study!\n");
     pthread_mutex_init(&mutex,NULL);
     pthread_cond_init(&cond,NULL);
     pthread_create(&thid1,NULL,thread1,NULL);
     pthread_create(&thid2,NULL,thread2,NULL);
     sleep(1);
do
     {
         pthread_cond_signal(&cond);
     }while(1);
     sleep(20);
     pthread_exit(0);
return 0;
}

#include <pthread.h> 
#include <unistd.h> 
#include "stdio.h"
#include "stdlib.h"


static pthread_mutex_t mtx = PTHREAD_MUTEX_INITIALIZER; 
static pthread_cond_t cond = PTHREAD_COND_INITIALIZER; 

struct node 
{ 
int n_number; 
struct node *n_next; 
} *head = NULL; 

/*[thread_func]*/ 
static void cleanup_handler(void *arg) 
{ 
    printf("Cleanup handler of second thread./n"); 
    free(arg); 
    (void)pthread_mutex_unlock(&mtx); 
} 

static void *thread_func(void *arg) 
{ 
struct node *p = NULL; 

    pthread_cleanup_push(cleanup_handler, p); 
while (1) 
    { 
//这个mutex主要是用来保证pthread_cond_wait的并发性
        pthread_mutex_lock(&mtx);          
while (head == NULL)   
        {               
//这个while要特别说明一下，单个pthread_cond_wait功能很完善，为何
//这里要有一个while (head == NULL)呢？因为pthread_cond_wait里的线
//程可能会被意外唤醒，如果这个时候head != NULL，则不是我们想要的情况。
//这个时候，应该让线程继续进入pthread_cond_wait

// pthread_cond_wait会先解除之前的pthread_mutex_lock锁定的mtx，
//然后阻塞在等待对列里休眠，直到再次被唤醒（大多数情况下是等待的条件成立
//而被唤醒，唤醒后，该进程会先锁定先pthread_mutex_lock(&mtx);，再读取资源
//用这个流程是比较清楚的/*block-->unlock-->wait() return-->lock*/
            pthread_cond_wait(&cond, &mtx);         
            p = head; 
            head = head->n_next; 
            printf("Got %d from front of queue/n", p->n_number); 
            free(p); 
        }
        pthread_mutex_unlock(&mtx);             //临界区数据操作完毕，释放互斥锁
    } 
    pthread_cleanup_pop(0); 
return 0; 
} 

int main(void) 
{ 
    pthread_t tid; 
int i; 
struct node *p; 
//子线程会一直等待资源，类似生产者和消费者，但是这里的消费者可以是多个消费者，而
//不仅仅支持普通的单个消费者，这个模型虽然简单，但是很强大
    pthread_create(&tid, NULL, thread_func, NULL);   
    sleep(1);
for (i = 0; i < 10; i++) 
    { 
        p = (struct node*)malloc(sizeof(struct node)); 
        p->n_number = i; 
        pthread_mutex_lock(&mtx);             //需要操作head这个临界资源，先加锁，
        p->n_next = head; 
        head = p; 
        pthread_cond_signal(&cond); 
        pthread_mutex_unlock(&mtx);           //解锁
        sleep(1); 
    } 
    printf("thread 1 wanna end the line.So cancel thread 2./n"); 

//关于pthread_cancel，有一点额外的说明，它是从外部终止子线程，子线程会在最近的取消点，退出
//线程，而在我们的代码里，最近的取消点肯定就是pthread_cond_wait()了。
    pthread_cancel(tid);            
    pthread_join(tid, NULL); 
    printf("All done -- exiting/n"); 
return 0; 
}