linux – 为什么sleep()获取pthread_mutex_lock后会阻塞整个程序

1) pthread_mutex_lock()
    2) sleep(1)
    3) pthread_mutex_unlock()

但是,我发现经过一段时间后,两个线程中的一个将永远阻塞pthread_mutex_lock(),而另一个线程正常工作.这是一种非常奇怪的行为,我认为这可能是一个潜在的严重问题.通过Linux手册,获取pthread_mutex_t时不禁止sleep().所以我的问题是：这是一个真正的问题还是我的代码中有任何错误？

以下是测试程序.在代码中,第一个线程的输出定向到stdout,而第二个线程定向到stderr.所以我们可以检查这两个不同的输出,看看线程是否被阻塞.

我在linux内核(2.6.31)和(2.6.9)上测试过它.两个结果都是一样的.

//=======================  Test Program  ===========================
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <pthread.h>

#define THREAD_NUM 2
static int data[THREAD_NUM];
static int sleepFlag = 1;

static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
static void * threadFunc(void *arg)
{
        int* idx = (int*) arg;
        FILE* fd = NULL;
        if (*idx == 0)  
                fd = stdout;
  else
          fd = stderr;

        while(1) {
                fprintf(fd,"n[%d]Before pthread_mutex_lock is calledn",*idx);
    if (pthread_mutex_lock(&mutex) != 0) {
                exit(1);            
    }
          fprintf(fd,"[%d]pthread_mutex_lock is finisheded. Sleep some timen",*idx);
          if (sleepFlag == 1)
             sleep(1);
          fprintf(fd,"[%d]sleep donenn",*idx);


          fprintf(fd,"[%d]Before pthread_mutex_unlock is calledn",*idx);    
    if (pthread_mutex_unlock(&mutex) != 0) {
                exit(1);
    }
    fprintf(fd,"[%d]pthread_mutex_unlock is finisheded.n",*idx);    
        }
}

// 1. compile
//    gcc -o pthread pthread.c -lpthread
// 2. run
//    1) ./pthread sleep 2> /tmp/error.log     # Each thread will sleep 1 second after it acquires pthread_mutex_lock
//       ==> We can find that /tmp/error.log will not increase.
//    or
//    2) ./pthread nosleep 2> /tmp/error.log   # No sleep is done when each thread acquires pthread_mutex_lock
//       ==> We can find that both stdout and /tmp/error.log increase.

int main(int argc,char *argv[]) {
          if ((argc == 2) && (strcmp(argv[1],"nosleep") == 0))
                  {
                          sleepFlag = 0;
                  }
    pthread_t t[THREAD_NUM];

    int i;
    for (i = 0; i < THREAD_NUM; i++) {
      data[i] = i;
      int ret = pthread_create(&t[i],NULL,threadFunc,&data[i]);
      if (ret != 0) {
        perror("pthread_create errorn");
        exit(-1);
      }
    }   

    for (i = 0; i < THREAD_NUM; i++) {
      int ret = pthread_join(t[i],(void*)0);
      if (ret != 0) {
        perror("pthread_join errorn");
        exit(-1);
      }
    }

    exit(0);
}

这是输出：

在程序启动的终端上：

root@skyscribe:~# ./pthread sleep 2> /tmp/error.log

    [0]Before pthread_mutex_lock is called
    [0]pthread_mutex_lock is finisheded. Sleep some time
    [0]sleep done

    [0]Before pthread_mutex_unlock is called
    [0]pthread_mutex_unlock is finisheded.
    ...

在另一个终端上看到文件/tmp/error.log

root@skyscribe:~# tail -f /tmp/error.log 

    [1]Before pthread_mutex_lock is called

并且没有新的行从/tmp/error.log中输出