问题描述
全局变量初始化为0, 两个线程, 一个线程对它每次增１, 当大于等于100时， 给另一个线程发送条件. 重置为0
#include <stdio.h>#include <stdlib.h>#include <pthread.h>struct foo{ int f_count; pthread_mutex_t f_lock; pthread_cond_t f_cond;};/* 初始化互斥量与条件变量 */struct foo * foo_alloc(){ struct foo *fp; if((fp = malloc(sizeof(struct foo))) != NULL){fp->f_count = 0;pthread_mutex_init(&fp->f_lock, NULL);pthread_cond_init(&fp->f_cond, NULL); } return fp;}/* 加法 */void *foo_increase(void *arg){struct foo *fp; fp = (struct foo*)arg; while(1){pthread_mutex_lock(&fp->f_lock); fp->f_count++;/* 大于等于100时发送条件 */if(fp->f_count >= 100){ pthread_cond_signal(&fp->f_cond);}pthread_mutex_unlock(&fp->f_lock); }}/* 重新置０ */void *foo_print(void *arg){ struct foo *fp; fp = (struct foo*)arg; while(1){pthread_mutex_lock(&fp->f_lock);while(fp->f_count < 100){ //释放掉锁, 等待条件为真返回, 再次锁住. pthread_cond_wait(&fp->f_cond, &fp->f_lock);}printf('重置 : %dn', fp->f_count); /* 重新置0 */ fp->f_count = 0;pthread_mutex_unlock(&fp->f_lock); }}int main(void){ struct foo *fp; pthread_t tid_increase1, tid_print; //初始化 fp = foo_alloc(); //加法线程 pthread_create(&tid_increase1, NULL, foo_increase, fp);//重置线程 pthread_create(&tid_print, NULL, foo_print, fp); //防止主线程提前退出 sleep(20); exit(0);}
可是我在重置线程下打印出来为什么是下面这个结果, 不应该是100吗 ?重置线程已经把互斥量给锁住了, 但好像另一个线程仍然在不断累加.
置０前 : 54置０前 : 92置０前 : 47置０前 : 85置０前 : 51．．．
问题解答
回答1：#include <stdio.h>#include <stdlib.h>#include <pthread.h>#include <unistd.h>struct foo{ int f_count; pthread_mutex_t f_lock; pthread_cond_t f_cond;};/* 初始化互斥量与条件变量 */struct foo * foo_alloc(){ struct foo *fp; if((fp = (struct foo *)malloc(sizeof(struct foo))) != NULL){fp->f_count = 0;pthread_mutex_init(&fp->f_lock, NULL);pthread_cond_init(&fp->f_cond, NULL); } return fp;}/* 加法 */void *foo_increase(void *arg){struct foo *fp; fp = (struct foo*)arg; while(1){pthread_mutex_lock(&fp->f_lock);fp->f_count++;if(fp->f_count >= 100){ pthread_cond_signal(&fp->f_cond);//-------------------这里要等待，不然会再次循环+1 pthread_cond_wait(&fp->f_cond, &fp->f_lock);}pthread_mutex_unlock(&fp->f_lock); /* 大于等于100时发送条件 */ }}/* 重新置０ */void *foo_print(void *arg){ struct foo *fp; fp = (struct foo*)arg; while(1){pthread_mutex_lock(&fp->f_lock);while(fp->f_count < 100){//释放掉锁, 等待条件为真返回, 再次锁住. pthread_cond_wait(&fp->f_cond, &fp->f_lock);}printf('重置 : %dn', fp->f_count); /* 重新置0 */ fp->f_count = 0;//-------------------加这条就不会阻塞了foo_increase里的waitpthread_cond_signal(&fp->f_cond);pthread_mutex_unlock(&fp->f_lock); }}int main(void){ struct foo *fp; pthread_t tid_increase1, tid_print; //初始化 fp = foo_alloc(); //加法线程 pthread_create(&tid_increase1, NULL, foo_increase, fp);//重置线程 pthread_create(&tid_print, NULL, foo_print, fp); //防止主线程提前退出 sleep(2);这里这时要 free(fp);//DO NOT FORGET exit(0);
