Question

我从每个帖子中得到了错误的ID，我怎样才能获得正确的ID？而且我必须创建一个像marshal那样允许副saing的线程，我怎么能解决这个问题呢？我使用主席台作为监视器来锁定或解锁互斥锁，这允许只能访问一个线程。

我有这段代码：

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <linux/sched.h>

typedef enum
{ false = 0, true } t_bool;

pthread_mutex_t mutex;
int rostrum;
rostrum = 0;

void *
deputy (void *arg)
{
  int tid = (int *) arg;
  printf ("Deputy no: %d in f() \n", tid);  // ??? no.1

  int SAID;
  SAID = 0;

  while (SAID == 0)
    {
      pthread_mutex_trylock (&rostrum);
      if (rostrum == 0)
      {
          rostrum = 1;
          printf ("\t Deputy no: %d is saing\n", tid);
          SAID = 1;
      }
      pthread_mutex_unlock (&rostrum);
    }
}

int
main ()
{
  pthread_t tid;
  int i = 0;
  for (i; i < 20; i++)
    {
        /* spurious characters deleted here */
        printf ("Deputy no: %d before f().\n", i);  // ??? no.2
        pthread_create (&tid, NULL, deputy, &tid);
    }
}

结果：

    Deputy no: 0 before f()
    Deputy no: 1 before f()
    Deputy no: 2 before f()
    Deputy no: -863940960 inf f() 
    Deputy no: -863940960 inf f() 
 Deputy no: -863940960 is saing
 Deputy no: -863940960 is saing
    Deputy no: 3 before f()
    Deputy no: -863940960 inf f() 
    Deputy no: 4 before f()
    Deputy no: -863940960 inf f() 
 Deputy no: -863940960 is saing
    Deputy no: 5 before f()
    Deputy no: -863940960 inf f() 
 Deputy no: -863940960 is saing
    Deputy no: 6 before f()
    Deputy no: 7 before f()
    Deputy no: -863940960 inf f() 
    Deputy no: 8 before f()
    Deputy no: -863940960 inf f() 
 Deputy no: -863940960 is saing
    Deputy no: 9 before f()
    Deputy no: 10 before f()
    Deputy no: 11 before f()
    Deputy no: -863940960 inf f() 
 Deputy no: -863940960 is saing
 Deputy no: -863940960 is saing
 Deputy no: -863940960 is saing
    Deputy no: 12 before f()
    Deputy no: -863940960 inf f() 
    Deputy no: -863940960 inf f() 
 Deputy no: -863940960 is saing
    Deputy no: -863940960 inf f() 
    Deputy no: -863940960 inf f() 
 Deputy no: -863940960 is saing
    Deputy no: 13 before f()
 Deputy no: -863940960 is saing
 Deputy no: -863940960 is saing
    Deputy no: 14 before f()
    Deputy no: -863940960 inf f() 
    Deputy no: -863940960 inf f() 
 Deputy no: -863940960 is saing
 Deputy no: -863940960 is saing
    Deputy no: 15 before f()
    Deputy no: -863940960 inf f() 
    Deputy no: 16 before f()
    Deputy no: -863940960 inf f() 
 Deputy no: -863940960 is saing
 Deputy no: -863940960 is saing
    Deputy no: -863940960 inf f() 
    Deputy no: 17 before f()
    Deputy no: 18 before f()
    Deputy no: -863940960 inf f() 
    Deputy no: -863940960 inf f() 
 Deputy no: -863940960 is saing
    Deputy no: 19 before f()
 Deputy no: -863940960 is saing
 Deputy no: -863940960 is saing

Answer 1

在你的main()中

pthread_t tid;

你没有初始化，所以它的内容是未定义的。

你在pthread_create这里传递一个指针作为你的参数：

pthread_create (&tid, NULL, deputy, &tid);

我认为您希望将&tid指定为pthread_create的第一个参数将覆盖tid中的值。但是，这有两个问题。首先，您无法保证何时会发生 - printf已经在新线程中运行了。第二个是，对pthread_create的后续调用可能会覆盖此值，即您可以在执行第一个pthread_create之前运行两个printf次调用。

然后使用它作为你的主题'id'。

int tid = (int *) arg;
printf ("Deputy no: %d in f() \n", tid);  // ??? no.1

这实际上会在每个线程中打印相同的未定义值。

如果要获取唯一的线程ID，请使用pthread_self，而不是查看传递的参数，并尝试将pthread_create调用的结果作为参数传递。

Answer 2

要从线程内部获取线程的PThread-id，请使用pthread_self()。

为此，请修改threas函数，如下所示：

void *
deputy (void * arg)
{
  pthread_t ptid = pthread_self();
  ...

如果你真的想存储在主线程中创建的每个线程的PThread-id 和传递它的引用，你需要为每个线程提供变量，如下所示：

int
main (void)
{
  pthread_t ptid[20];

  {
    size_t i = 0;
    for (; i < 20; ++i)
    {
      printf ("Deputy no: %zu before f().\n", i); 
      pthread_create (&ptid[i], NULL, deputy, &ptid[i]);
    }
  }

  /* Make sure main does not end before all threads ended, 
     as they make use of ptid[] which lives on main's stack. */
  {
    size_t i = 0;
    for (; i < 20; ++i)
    {
      pthread_join(ptid[i]);
    }
  }
}

另请注意，当传递pthread_t类型变量的地址时，线程函数也应该使用它，如下所示：

void *
deputy (void *arg)
{
  pthread_t ptid = *((pthread_t *) arg);
  ...

^ 2 pthread_t也是不透明的。所以它的表示是实现定义的。如果可以是整数或指针或... - 那么如果依赖于所使用的PThread库的特定实现，如何打印。

多线程，id不起作用，如何添加其他功能

2 个答案: