c - 不阻塞 main() 的 pthread_join() 版本 : POSIX

我正在尝试编写一个在调用 main() 时不会阻塞 pthread_join() 的代码:
即基本上试图实现我在下面提到的上一个问题:

https://stackoverflow.com/questions/24509500/pthread-join-and-main-blocking-multithreading

以及相应的解释:

pthreads - Join on group of threads, wait for one to exit

根据建议的答案:
You'd need to create your own version of it - e.g. an array of flags (one flag per thread) protected by a mutex and a condition variable; where just before "pthread_exit()" each thread acquires the mutex, sets its flag, then does "pthread_cond_signal()". The main thread waits for the signal, then checks the array of flags to determine which thread/s to join (there may be more than one thread to join by then).
我试过如下:

我的状态数组跟踪哪些线程已完成:

typedef struct {
    int Finish_Status[THREAD_NUM];
    int signalled;

    pthread_mutex_t mutex;
    pthread_cond_t FINISHED;
    }THREAD_FINISH_STATE;

线程例程，它在线程完成时设置相应的数组元素，并通知条件变量:

void* THREAD_ROUTINE(void* arg)
{
    THREAD_ARGUMENT* temp=(THREAD_ARGUMENT*) arg;
    printf("Thread created with id %d\n",temp->id);
    waitFor(5);
    pthread_mutex_lock(&(ThreadFinishStatus.mutex));
    ThreadFinishStatus.Finish_Status[temp->id]=TRUE;
    ThreadFinishStatus.signalled=TRUE;
    if(ThreadFinishStatus.signalled==TRUE)
    {
      pthread_cond_signal(&(ThreadFinishStatus.FINISHED));
      printf("Signal that thread %d finished\n",temp->id);
     }
    pthread_mutex_unlock(&(ThreadFinishStatus.mutex));

    pthread_exit((void*)(temp->id));
    }

我无法编写相应的部分 pthread_join() 和 pthread_cond_wait() 函数。有几件事我无法实现。

1) 如何在我的 pthread_cond_wait() 中写出相应的部分 main() ？

2)我想把它写成:

   pthread_mutex_lock(&(ThreadFinishStatus.mutex));
    while((ThreadFinishStatus.signalled != TRUE){
     pthread_cond_wait(&(ThreadFinishStatus.FINISHED), &(ThreadFinishStatus.mutex));
     printf("Main Thread signalled\n");
     ThreadFinishStatus.signalled==FALSE; //Reset signalled
     //check which thread to join
    }
    pthread_mutex_unlock(&(ThreadFinishStatus.mutex));

但是没有进入while循环。

3) 如何使用 pthread_join() 以便我可以获取存储在我的 arg[i].returnStatus 中的返回值
即在我的主要内容中放置以下语句的位置:

`pthread_join(T[i],&(arg[i].returnStatus));`

完整代码

#include <stdio.h>
#include <pthread.h>
#include <time.h>

#define THREAD_NUM 5
#define FALSE 0
#define TRUE 1


void waitFor (unsigned int secs) {
    time_t retTime;
    retTime = time(0) + secs;     // Get finishing time.
    while (time(0) < retTime);    // Loop until it arrives.
}

typedef struct {
    int Finish_Status[THREAD_NUM];
    int signalled;

    pthread_mutex_t mutex;
    pthread_cond_t FINISHED;
    }THREAD_FINISH_STATE;

typedef struct {
    int id;
    void* returnStatus;
    }THREAD_ARGUMENT;

THREAD_FINISH_STATE ThreadFinishStatus;

void initializeState(THREAD_FINISH_STATE* state)
{
 int i=0;
 state->signalled=FALSE;
 for(i=0;i<THREAD_NUM;i++)
 {
     state->Finish_Status[i]=FALSE;
     }
 pthread_mutex_init(&(state->mutex),NULL);
 pthread_cond_init(&(state->FINISHED),NULL);
    }

void destroyState(THREAD_FINISH_STATE* state)
{
 int i=0;
 for(i=0;i<THREAD_NUM;i++)
 {
     state->Finish_Status[i]=FALSE;
     }
 pthread_mutex_destroy(&(state->mutex));
 pthread_cond_destroy(&(state->FINISHED));
    }


void* THREAD_ROUTINE(void* arg)
{
    THREAD_ARGUMENT* temp=(THREAD_ARGUMENT*) arg;
    printf("Thread created with id %d\n",temp->id);
    waitFor(5);
    pthread_mutex_lock(&(ThreadFinishStatus.mutex));
    ThreadFinishStatus.Finish_Status[temp->id]=TRUE;
    ThreadFinishStatus.signalled=TRUE;
    if(ThreadFinishStatus.signalled==TRUE)
    {
      pthread_cond_signal(&(ThreadFinishStatus.FINISHED));
      printf("Signal that thread %d finished\n",temp->id);
     }
    pthread_mutex_unlock(&(ThreadFinishStatus.mutex));

    pthread_exit((void*)(temp->id));
    }

int main()
{
    THREAD_ARGUMENT arg[THREAD_NUM];
    pthread_t T[THREAD_NUM];
    int i=0;
    initializeState(&ThreadFinishStatus);

    for(i=0;i<THREAD_NUM;i++)
    {
        arg[i].id=i;
        }

    for(i=0;i<THREAD_NUM;i++)
        {
            pthread_create(&T[i],NULL,THREAD_ROUTINE,(void*)&arg[i]);
        }

    /*
     Join only if signal received
    */

    pthread_mutex_lock(&(ThreadFinishStatus.mutex));
    //Wait
    while((ThreadFinishStatus.signalled != TRUE){
     pthread_cond_wait(&(ThreadFinishStatus.FINISHED), &(ThreadFinishStatus.mutex));
     printf("Main Thread signalled\n");
     ThreadFinishStatus.signalled==FALSE; //Reset signalled
     //check which thread to join
    }
    pthread_mutex_unlock(&(ThreadFinishStatus.mutex));

    destroyState(&ThreadFinishStatus);
    return 0;
    }

最佳答案

下面是一个程序示例，它使用计数信号量来观察线程的完成情况，找出它是哪个线程，并查看来自该线程的一些结果数据。这个程序使用锁是有效的 - 服务员不会被虚假唤醒(注意线程是如何在释放互斥保护共享状态后才发布到信号量的)。

这种设计允许主程序在线程完成后立即处理某个线程的计算结果，而不需要主程序等待所有线程完成。如果每个线程的运行时间变化很大，这将特别有用。

最重要的是，这个程序不会死锁也不会竞争。

#include <pthread.h>
#include <semaphore.h>
#include <stdlib.h>
#include <stdio.h>
#include <queue>

void* ThreadEntry(void* args );

typedef struct {
    int threadId;
    pthread_t thread;
    int threadResult;
} ThreadState;

sem_t           completionSema;

pthread_mutex_t resultMutex;

std::queue<int> threadCompletions;

ThreadState* threadInfos;

int main() {

    int numThreads = 10;
    int* threadResults;
    void* threadResult;
    int doneThreadId;


    sem_init( &completionSema, 0, 0 );

    pthread_mutex_init( &resultMutex, 0 );

    threadInfos = new ThreadState[numThreads];

    for ( int i = 0; i < numThreads; i++ ) {

        threadInfos[i].threadId = i;
        pthread_create( &threadInfos[i].thread, NULL, &ThreadEntry, &threadInfos[i].threadId  );
    }

    for ( int i = 0; i < numThreads; i++ ) {
        // Wait for any one thread to complete; ie, wait for someone
        // to queue to the threadCompletions queue.
        sem_wait( &completionSema );


        // Find out what was queued; queue is accessed from multiple threads,
        // so protect with a vanilla mutex.
        pthread_mutex_lock(&resultMutex);
        doneThreadId = threadCompletions.front();
        threadCompletions.pop();
        pthread_mutex_unlock(&resultMutex);

        // Announce which thread ID we saw finish
        printf(
            "Main saw TID %d finish\n\tThe thread's result was %d\n",
            doneThreadId,
            threadInfos[doneThreadId].threadResult
        );

        // pthread_join to clean up the thread.
        pthread_join( threadInfos[doneThreadId].thread, &threadResult );
    }

    delete threadInfos;

    pthread_mutex_destroy( &resultMutex );
    sem_destroy( &completionSema );

}

void* ThreadEntry(void* args ) {
    int threadId = *((int*)args);

    printf("hello from thread %d\n", threadId );

    // This can safely be accessed since each thread has its own space
    // and array derefs are thread safe.
    threadInfos[threadId].threadResult = rand() % 1000;


    pthread_mutex_lock( &resultMutex );
    threadCompletions.push( threadId );
    pthread_mutex_unlock( &resultMutex );

    sem_post( &completionSema );

    return 0;
}

关于c - 不阻塞 main() 的 pthread_join() 版本 : POSIX，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/24517504/