互斥量实现线程同步有关问题

互斥量实现线程同步问题

C/C++ code

/*********************************************************************************//*    互斥量实现线程同步*//********************************************************************************/#include <stdio.h>#include <stdlib.h>#include <unistd.h>#include <pthread.h>struct foo{    int f_count;    pthread_mutex_t f_lock;    int data;};struct foo *foo_alloc(struct foo **fp)    //分配信号空间{    //struct foo *fp;    if ((*fp = (struct foo *)malloc(sizeof (struct foo))) != NULL)    {        (*fp)->f_count = 1;                //计数初始化为1        (*fp)->data = 1;                    //数据为1                                      if (pthread_mutex_init(&(*fp)->f_lock, NULL) != 0)         {             free(*fp);             return NULL;         }    }        return *fp;}void foo_hold(struct foo *fp)            //获取互斥量{    pthread_mutex_lock(&fp->f_lock);    fp->f_count ++;    pthread_mutex_unlock(&fp->f_lock);}void foo_rele(struct foo *fp)            //释放互斥量{    pthread_mutex_lock(&fp->f_lock);        if (-- fp->f_count == 0)    {        pthread_mutex_unlock(&fp->f_lock);        pthread_mutex_destroy(&fp->f_lock);        free(fp);    }    else    {        pthread_mutex_unlock(&fp->f_lock);    }}void * fun(void * arg){    struct foo *p = (struct foo *)arg;    foo_hold(p);    printf("in pthread1: %d\n", p->data);    p->data++;    printf("in pthread1: %d\n", p->data);    /************************************************问题？？***********************************************************/    //foo_rele(p);                                    //这里没有释放下一个进程怎么还怎么用啊？    pthread_exit((void *)1 );}void * fun1(void * arg){    struct foo *p = (struct foo *)arg;        foo_hold(p);    printf("in pthread2: %d\n", p->data);    p->data ++;    printf("in pthread2: %d\n", p->data);    foo_rele(p);            pthread_exit((void *)1 );}int main(){    pthread_t tid1;    pthread_t tid2;    int err;    struct foo *fp;        foo_alloc(&fp);    if ((err = pthread_create(&tid1, NULL, fun, (void *)fp)) != 0)    {        printf("pthread1 error!\n");    }            if ((err = pthread_create(&tid2, NULL, fun1, (void *)fp)) != 0)    {        printf("pthread1 error!\n");    }            //pthread_join(tid1, &p);     //获取传递的参数并等待该子线程结束。    sleep(2);    printf("in main pthread:\n");        return 0;}运行结果：[root@localhost work]# gcc 1.c -o 1 -lpthread[root@localhost work]# ./1in pthread1: 1in pthread1: 2in pthread2: 2in pthread2: 3in main pthread:[root@localhost work]# 

为什么没有释放互斥量下一个进程还能拥有数据啊？


[解决办法]
void foo_hold(struct foo *fp) //获取互斥量
{
pthread_mutex_lock(&fp->f_lock);
fp->f_count ++;
pthread_mutex_unlock(&fp->f_lock);
}

void foo_rele(struct foo *fp) //释放互斥量
{
pthread_mutex_lock(&fp->f_lock);

if (-- fp->f_count == 0)
{
pthread_mutex_unlock(&fp->f_lock);
pthread_mutex_destroy(&fp->f_lock);
free(fp);
}
else
{
pthread_mutex_unlock(&fp->f_lock);
}
}

这叫Hold么，加完就放掉了，很独立的函数，rele函数同理。


void * fun(void * arg)
{
struct foo *p = (struct foo *)arg;
foo_hold(p);
printf("in pthread1: %d\n", p->data);
p->data++;
printf("in pthread1: %d\n", p->data);

/************************************************问题？？***********************************************************/

//foo_rele(p); //这里没有释放下一个进程怎么还怎么用啊？
pthread_exit((void *)1 );
}


调用几次，它也不可能死锁，所以注释掉很随意。
[解决办法]
foo_hold里面不是lock又unlock里吗？
pthread_mutex_lock(&fp->f_lock);
fp->f_count ++;
pthread_mutex_unlock(&fp->f_lock);
已经解锁了啊。
foo_rele(p)只是释放资源啊

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