互斥线程 - 代码似乎没有正确退出

Question

所以我这里有创建两种线程的代码。一种 "produces" 数据，另一种 "consumes" 数据。任何时候只能存在一定数量的数据，所以一旦创建了一定数量的数据（即sharedData = BUFFER时），生产者就会暂停生产，而当sharedData = 0时，消费者会暂停. 也只能制作这么多数据（dataleft中存储的数量），一旦制作和消费完所有数据，程序就应该结束了。

出于某种原因，我在代码末尾的 printf() 行似乎从未触发过。因此，我无法判断线程是否正确关闭。感觉自己做了一件很蠢的事，但是看不出问题所在

开头的几个定义：

#define                 NUMCONSUMERS    4
#define                 NUMPRODUCERS    4
#define                 PACKETS         10
#define                 tryMainlock     pthread_mutex_trylock(&dataMutex)
#define                 openMainlock    pthread_mutex_lock(&dataMutex)
#define                 closeMainlock   pthread_mutex_unlock(&dataMutex)
#define                 waitMainlock    pthread_cond_wait(&dataPresentCondition, &dataMutex);
#define                 signalMainlock  pthread_cond_signal(&dataPresentCondition);

#define                 trydatalock     pthread_mutex_trylock(&IsthereDataleft)
#define                 opendatalock    pthread_mutex_lock(&IsthereDataleft)
#define                 closedatalock   pthread_mutex_unlock(&IsthereDataleft)

pthread_mutex_t         dataMutex = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t          dataPresentCondition = PTHREAD_COND_INITIALIZER;

pthread_mutex_t         IsthereDataleft = PTHREAD_MUTEX_INITIALIZER;

int                     sharedData=0;   //amount of data present
int                     BUFFER = 5;
int                     dataleft=PACKETS;

主要功能：

int main(int argc, char **argv)
{
int rc;                                 
int i;
pthread_t  consumer[NUMCONSUMERS];
pthread_t  producer[NUMPRODUCERS];

rc = opendatalock;                      //lock to determine whether there's any point waiting for data

for (i=0; i <NUMPRODUCERS; i++) {       //Build up the producers
    rc = pthread_create(&producer[i], NULL, Producer, (void *)i);
    if (rc)
        printf("Error building Producer Thread: %x\n", i);
}

for (i=0; i <NUMCONSUMERS; i++) {       //Build up the consumers
    rc = pthread_create(&consumer[i], NULL, Consumer, (void *)i);
    if (rc)
        printf("Error building Consumer Thread: %x\n", i);
}

printf("All Producers and Consumers created\n");

for (i=0; i <NUMPRODUCERS; i++) {       //Join up the producers
    rc = pthread_join(producer[i], NULL);
    if (rc)
        printf("Error: Producer %x: Failed to join\n", i);
}

rc = closedatalock;                     //producers finished, no data left to make

printf("datalock closed, consumers finishing...\n");
for (i=0; i <NUMCONSUMERS; i++) {       //Join up the consumers
    rc = pthread_join(consumer[i], NULL);
    if (rc)
        printf("Error: Consumer %x: Failed to join\n", i);
}
rc = pthread_mutex_destroy(&dataMutex);
rc = pthread_cond_destroy(&dataPresentCondition);
rc = pthread_mutex_destroy(&IsthereDataleft);

printf("All Threads finished. Exiting....\n");
return 0;
}

消费者线程：

void *Consumer(void *threadid){
int rc;
printf("Consumer Thread %x: Created\n", (int)threadid);
while (1)
{
    printf("Consumer %x: Entering Loop\n", (int)threadid);
    rc = openMainlock;      //take hold of main lock
    if (rc)
    {
        printf("Consumer %x: Waiting...\n", (int)threadid);
        rc = waitMainlock;  //if main lock is taken, wait
        if (rc)             //if wait fails, exit the thread.
        {
            printf("Consumer Thread %x: wait for Main Lock failed\n", threadid);
            exit(0);
        }
    }

    while (sharedData == 0) //if the buffer is empty
    {
        rc = trydatalock;
        if (!rc)
        {
            printf("Consumer %x: Completed. Exiting...\n");
            exit(0);
        }
        rc = closeMainlock;
        if (rc)
        {
            printf("code.\n");
        }
        rc = waitMainlock;
        if (rc)
        {
            printf("code.\n");
        }
    }
    sharedData--;
    rc = closeMainlock;
    rc = signalMainlock;
    if (rc)
        {
            printf("code.\n");
        }
    printf("Consumer %x: Releasing Lock\n", (int)threadid);         
}
}

生产者线程：

void *Producer(void *threadid){
int rc;
printf("Producer Thread %x: Created\n", (int)threadid);
while (1)
{
    printf("Producer %x: Entering Loop\n", (int)threadid);
    rc = openMainlock;          //take hold of the lock
    if (rc)                     //if lock is currently being used by a consumer or a producer
    {   
        printf("Producer %x: Waiting...\n", (int)threadid);
        rc = waitMainlock;      //wait here until lock is released
        if (rc)
        {
            printf("Producer Thread %x: wait for Main Lock failed\n", threadid);
            exit(0);
        }
    }
    if (!dataleft)              //If there's no data left to add to the stream, close the thread
    {
        printf("Producer Thread %x: Completed, exiting...\n", (int)threadid);
        exit(0);
    }
    while (sharedData >=BUFFER)
    {
        rc = closeMainlock;
        if (rc)
        {
            printf("code.\n");
        }
        rc = waitMainlock;
        if (rc)
        {
            printf("code.\n");
        }
    }
    printf("Producer %x: Lock Acquired\n", (int)threadid);
    sharedData++;
    dataleft--;
    rc = closeMainlock;
    rc = signalMainlock;
    if (rc)
        {
            printf("code.\n");
        }
    printf("Producer %x: Releasing Lock\n", (int)threadid);
}
}

Answer 1

您对 openMainlock 的使用似乎有问题，它扩展为 pthread_mutex_lock 调用。

一方面，你不应该期望从 openMainlock 得到一个非零的 return 值：pthread_mutex_lock 应该 return 零（获得锁) 或块，除非互斥锁未初始化或者是错误检查互斥锁。

此外，一旦获得锁，如果生产者完成，即dataleft为零，线程调用exit(0)，这将终止整个进程而不是终止线程。 pthread_exit 应该改用，或者只是函数中的 return，但请注意，此时您仍然拥有主锁，它不会被释放。

Answer 2

查看这段代码：

    if (!rc)
    {
        printf("Consumer %x: Completed. Exiting...\n");
        exit(0);
    }

如果消费者已经完成，则进程（！）终止。您需要使用 pthread_exit() 代替，或者只是使用线程函数中的 return。

那么，还有

../nptl/pthread_mutex_lock.c:80:
    __pthread_mutex_lock: Assertion `mutex->__data.__owner == 0' failed.

其中我得到了几次运行的代码。这可能是由例如双重解锁或其他一些无效使用。我将从清理奇怪的宏开始，以便您可以自由查看程序本身的逻辑。

此外，关于互斥量的一个重要建议：始终准确记录哪些数据应受互斥量保护。关键是它并不总是很清楚，弄错意味着您不小心访问了没有同步的数据。为了使这一点非常清楚，请使用如下结构：

 struct {
     pthread_mutex_t mutex;
     pthread_cond_t cond;
     int data;
 } synced_data = {
     PTHREAD_MUTEX_INITIALIZER,
     PTHREAD_COND_INITIALIZER,
     0
 };

实际上，文档的重要性不仅仅在于共享数据。考虑例如 IsthereDataleft：这是一个互斥体，但它不保护任何东西，对吗？相反，它用于向启动的线程发出信号，表明没有什么可做的，对吧？记录下来不仅可以帮助其他人理解您的代码，而且可以确保您了解自己的意图。有时，在尝试解释它时，您会发现自己有些事情没有意义。

互斥线程 - 代码似乎没有正确退出

Mutex Threading - Code doesn't seem to Exit Properly

c

multithreading

mutex