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; }