CODEWITHSUNDEEP
c++multithreadingtermination
M.K.
M.K.

Reputation: 650

c++ waiting for thread exit

I wrote a program in C++ under Linux. For thread I am using pthread. In the program I start the thread and this thread is running until I call the function, that should stop it. Here you can see my code.

bool isRunning = false;
pthread_t thread;

void startThread() {
    isRunning = true;
    int thread_return = pthread_create(&thread, NULL, runThread, NULL);
}

bool stopThread() {
    isRunning = false;
    // wait until the thread will be finished
    return true;
}

void* runThread(void* ptr) {
    while(isRunning) {
        // do smth.
    }
    pthread_exit(NULL);
}

When the thread was started, it will do smth. until the value of isRunning will be false and the main program itself will do other stuff. The problem is, when I call the function stopThread, this function just sets isRunning to false and not waiting until the thread will finish its task inside the while-loop. My question is, how I can say to function stopThread, that it should wait for thread exit.

I tried to put pthread_join in stopThread function after I set isRunning to false. But sometimes it causes the problem, that the program waits infinitly. Because the thread was finished faster, than the program comes to wait for thread. Because the thread can be on different parts inside the while-loop. So I never know how much the thread need to exit.

Thank you

Upvotes: 1

Views: 8330

Answers (3)

shelleybutterfly
shelleybutterfly

Reputation: 3247

in this case you should be able to do a pthread_join() on it, but if for some reason that doesn't work you could try adding a hasFinished variable (and then waiting on hasFinished == true wherever you are closing the thread...)

bool isRunning = false;
pthread_t thread;

// TODO FIX: this is a workaround due to pthread_join() not working properly
bool hasFinished = false

void startThread() {
    isRunning = true;
    int thread_return = pthread_create(&thread, NULL, runThread, NULL);
}

bool stopThread() {
    isRunning = false;
    // wait until the thread will be finished
    return true;
}

void* runThread(void* ptr) {
    while(isRunning) {
        // do smth.
    }

    // TODO FIX: this is a workaround because pthread_join() is not working properly
    hasFinished = true;
    pthread_exit(NULL);

}

[edit for clarification:]

and wherever you stop thread

/**/
// TODO FIX: this following is a workaround due to pthread_join() not working
isRunning = false;

int TimeoutSleep_ms = 100;
// TimeoutSleep_ms * TimeoutCounter is the timeout time, 10 sec for this case
int TimeoutCounter = 100; 

while (!hasFinished && (--TimeoutCounter > 0))
    sleep(100);
// END TODO FIX
/**/

Upvotes: 1

Marc Butler
Marc Butler

Reputation: 1376

Look at the function pthread_join. Single UNIX specification documentation for pthread_join.

You will need to keep track of the thread id, to make use of this function. A common paradigm seems to be to have a Thread class, that encapsulated that information.

Upvotes: 1

user195488
user195488

Reputation:

From what I understand in your question, you should be using the concept of thread joining.

Like so,

bool stopThread() {
    int returnCode;
    isRunning = false;
    void *status;
    rc = pthread_join(your_thread, &status);

    // wait until the thread will be finished

    if (rc) {
        printf("ERROR; return code from pthread_join() 
                is %d\n", rc);
        exit(-1);
    }
    printf("Main: completed join with thread %ld having a status   
            of %ld\n",t,(long)status);

    return true;
}

Upvotes: 2

Related Questions