互斥量（对数据结构保护）

#include<stdio.h>#include<stdlib.h>#include<pthread.h>/* * 当一个以上的线程需要访问动态分配的内存时，可以引入计数变量 */struct foo{    int f_count;    pthread_mutex_t f_lock;    int f_id;};struct foo* foo_alloc(int id)//allocate the object{    struct foo* fp;    if((fp = (struct foo*)malloc(sizeof(struct foo))) != NULL)    {        fp->f_id = id;        fp->f_count = 1;//引用计数加 1        if(pthread_mutex_init(&fp->f_lock, NULL) != 0)        {            free(fp);            return NULL;        }    }    return fp;}/* * 功能：增加一个引用 * 返回：无 */void foo_hold(struct foo *fp){    pthread_mutex_lock(&fp->f_lock);    fp->f_count++;    pthread_mutex_unlock(&fp->f_lock);}/* * 功能：销毁结构体 */void foo_rele(struct foo *fp){    //操作结构体之前锁住互斥量    pthread_mutex_lock(&fp->f_lock);    if(--fp->f_count == 0)//是最后的引用    {        pthread_mutex_unlock(&fp->f_lock);        pthread_mutex_destroy(&fp->f_lock);        free(fp);    }    else        pthread_mutex_unlock(&fp->f_lock);}void printfoo(char *str, struct foo *fp){    printf("%s", str);    printf("f_count = %d\n", fp->f_count);    printf("f_id = %d\n", fp->f_id);}/* * 功能：线程函数 */void* thread_func(void *arg){    struct foo *fp = (struct foo*)arg;    foo_hold(fp);    fp->f_id = 2;    foo_rele(fp);    pthread_exit(NULL);}int main(void){    int err;    struct foo *fp;    pthread_t thid;    if((fp = foo_alloc(1)) == NULL)    {        printf("foo_alloc failed\n");        exit(EXIT_FAILURE);    }    else        printf("foo_alloc success\n");    printfoo("main thread\n", fp);    err = pthread_create(&thid, NULL, thread_func, (void*)fp);    if(err != 0)    {        printf("thread_create failed\n");        exit(EXIT_FAILURE);    }    err = pthread_join(thid, NULL);    if(err != 0)    {        printf("pthread_join failed\n");        exit(EXIT_FAILURE);    }    printfoo("after thread:\n", fp);    foo_rele(fp);    return 0;}