c,c++编程求助，急！！！感激不尽

gstatham 2017-09-04 06:55:13

A.h
struct ContextX
{
int running;
};

extern struct ContextX CX;

A.cpp

线程B:
事件A发生时，CX.running = 0;
事件B发生时，CX.running = 1;

==========================================
main.cpp

struct ContextX CX;

线程A：
void *threadA(void *param)
{
struct ContextX *CX = (struct ContextX *)param;
while(CX.running)
{
//do something
}
}
现在问题是，线程B中的事件A发生时，线程A不会进入while循环，事件B发生时，线程A无法进入循环，这是为什么？

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gstatham 2017-09-05

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#include <iostream>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>

using namespace std;

pthread_t IDA;
pthread_t IDB;

struct _status
{
    int running;
    int value;
};

_status status;

void *testA(void *param)
{
    while(1)
    {
        sleep(10);
        printf("shut down thread B..\n");
        status.running = 0;

        sleep(10);
        status.running = 1;
        printf("start thread B..\n");
    }
}

void *testB(void *param)
{
    while(status.running)
    {
        printf("thread B is running...\n");
        sleep(1);
    }
}

int main(int argc, char *argv[])
{
    status.running = 1;
    pthread_create(&IDA, NULL, testA, NULL);
    pthread_create(&IDB, NULL, testB, NULL);

    pthread_join(IDA, NULL);
    pthread_join(IDB, NULL);

    return 0;
}

程序运行结果如下， thread B is running... thread B is running... thread B is running... thread B is running... shut down thread B.. start thread B.. shut down thread B.. start thread B.. 这是上面问题的总结为什么线程B中的内容没有被再次运行呢？

gstatham 2017-09-05

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现在已经清楚的定位到，当事件B发生时，CX.running = 1; 线程A中的while内容无法执行，没有搞懂为什么会这样。。

821586284 2017-09-05

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http://blog.csdn.net/yeyuangen/article/details/37593533 参考这篇文章，建议用信号量的方法

gstatham 2017-09-05

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感谢各位的回答，自己给出一套解决方案

#include <iostream>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>

using namespace std;

pthread_t IDA;
pthread_t IDB;

pthread_mutex_t mut = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t cond = PTHREAD_COND_INITIALIZER;

#define RUN 1
#define STOP 0

int status = RUN;

void * thread_function(void *param)
{
    static int i = 0;
    while (1)
    {
        pthread_mutex_lock(&mut);
        while (!status)
        {
            pthread_cond_wait(&cond, &mut);
        }
        pthread_mutex_unlock(&mut);

        //do actual something
        printf("thread is running...\n");
        sleep(1);
    }
}

void thread_resume()
{
    if (status == STOP)
    {
        pthread_mutex_lock(&mut);
        status = RUN;
        pthread_cond_signal(&cond);
        printf("pthread run!\n");
        pthread_mutex_unlock(&mut);
    }
}

void thread_pause()
{
    if (status == RUN)
    {
        pthread_mutex_lock(&mut);
        status = STOP;
        printf("thread stop!\n");
        pthread_mutex_unlock(&mut);
    }
}

void *test(void *param)
{
    while(1)
    {
        sleep(5);
        thread_pause();
        sleep(10);
        thread_resume();
        sleep(5);
    }
}


int main(int argc, char *argv[])
{
    pthread_create(&IDA, NULL, test, NULL);
    pthread_create(&IDB, NULL, thread_function, NULL);

    pthread_join(IDA, NULL);
    pthread_join(IDB, NULL);

    return 0;
}