Question

创建一个脱离的线程时遇到问题。这是我写的代码：

void* testFunction() {

    pthread_attr_t attr;
    int chk,rc;

pthread_attr_init(&attr);
printf("thread_attr_init: %d\n",rc);

pthread_attr_getdetachstate(&attr, &chk);
printf("thread_attr_getdetachedstate: %d\n",rc);

if(chk == PTHREAD_CREATE_DETACHED ) 
    printf("Detached\n");
else if (chk == PTHREAD_CREATE_JOINABLE) 
    printf("Joinable\n");

return NULL;
}


int main (int argc, const char * argv[]) {

pthread_t thread1;
pthread_attr_t attr;

int rc;

rc = pthread_attr_init(&attr);

printf("attr_init: %d\n",rc);
rc = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
printf("attr_setdetachedstate: %d\n",rc);

rc = pthread_create(&thread1, &attr, testFunction, NULL);
printf("attr_create: %d\n",rc);

sleep(4);
pthread_cancel(thread1);

return 0;
}

问题是testFunction()始终打印“可加入”。谁能告诉我哪里出错了？

Answer 1

你的testFunction没有检查当前线程的任何内容，而只是刚刚创建的全新属性对象的初始分离标志。而且，在POSIX线程API中，完全不可能恢复创建线程的属性或确定线程是否已分离。您只需要相信实现的行为符合要求，就像您必须相信，如果malloc(100)返回非空指针，它指向一个可以存储至少100个字节的位置。这是C的本质。

Answer 2

尝试运行以下代码。这应该清除混乱。

/*------------------------------- join_01.c --------------------------------*
On Linux, compile with: 
cc -std=c99 -pthread join_01.c -o join_01  
    gcc join_01.c -o join_01 -std=c99 -lpthread (Ubuntu)

Check your system documentation how to enable C99 and POSIX threads on 
other Un*x systems.

Copyright Loic Domaigne. 
Licensed under the Apache License, Version 2.0.
*--------------------------------------------------------------------------*/

#include <unistd.h>  // sleep()
#include <pthread.h> 
#include <stdio.h>   
#include <stdlib.h>  // EXIT_SUCCESS
#include <string.h>  // strerror() 
#include <errno.h>

/***************************************************************************/
/* our macro for errors checking                                           */
/***************************************************************************/
#define COND_CHECK(func, cond, retv, errv) \
if ( (cond) ) \
{ \
   fprintf(stderr, "\n[CHECK FAILED at %s:%d]\n| %s(...)=%d (%s)\n\n",\
              __FILE__,__LINE__,func,retv,strerror(errv)); \
   exit(EXIT_FAILURE); \
}

#define ErrnoCheck(func,cond,retv)  COND_CHECK(func, cond, retv, errno)
#define PthreadCheck(func,rc) COND_CHECK(func,(rc!=0), rc, rc)

/*****************************************************************************/
/* thread- dummy thread                                                      */
/*****************************************************************************/
void*
thread(void* ignore)
{
   sleep(1);
   return NULL;
}

/*****************************************************************************/
/* detach_state. Print detachstate of a thread.                              */
/*****************************************************************************/
/* 
 * We find out indirectly if a thread is detached using pthread_join().  
 * If a thread is detached, then pthread_join() fails with EINVAL. 
 * Otherwise the thread is joined, and hence was joinable. 
 *
 */
void
detach_state(
   pthread_t   tid,  // thread to check detach status
   const char *tname // thread name
   )
{
   int rc; // return code

   rc = pthread_join(tid, NULL);
   if ( rc==EINVAL ) 
   {
      printf("%s is detached\n", tname);
   }
   else if ( rc==0 )  
   {  
      printf("%s was joinable\n", tname);
   }
   else 
   {
      printf("%s: pthread_join() = %d (%s)\n", 
             tname, rc, strerror(rc)
            );
   }
}

/*****************************************************************************/
/* main- main thread                                                         */
/*****************************************************************************/
int
main()
{
   pthread_t tid1, tid2, tid3; // thread 1,2 and 3.
   pthread_attr_t attr;        // thread's attribute
   int rc;  // return code

   /*--------------------------------------------------------*/
   /* 1st test: normal thread creation                       */
   /*--------------------------------------------------------*/
   rc = pthread_create(&tid1, NULL, thread, NULL);
   PthreadCheck("pthread_create", rc);
   detach_state(tid1, "thread1"); // expect: joinable 

   /*--------------------------------------------------------*/
   /* 2nd test: detach thread from main thread               */
   /*--------------------------------------------------------*/
   rc = pthread_create(&tid2, NULL, thread, NULL);
   PthreadCheck("pthread_create", rc);
   rc = pthread_detach(tid2);
   PthreadCheck("pthread_detach", rc);
   detach_state(tid2, "thread2"); // expect: detached

   /*--------------------------------------------------------*/
   /* 3rd test: create detached thread                       */
   /*--------------------------------------------------------*/

   // set detachstate attribute to DETACHED
   //
   rc=pthread_attr_init(&attr);
   PthreadCheck("pthread_attr_init", rc);
   rc=pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
   PthreadCheck("pthread_attr_setdetachstate", rc);

   // create thread now 
   //
   rc = pthread_create(&tid3, &attr, thread, NULL);
   PthreadCheck("pthread_create", rc);
   detach_state(tid3, "thread3");

   /*--------------------------------------------------------*/
   /* that's all folks!                                      */
   /*--------------------------------------------------------*/
   return EXIT_SUCCESS;
}

输出应为

$ ./join_01 
thread1 was joinable
thread2 is detached
thread3 is detached

Answer 3

您的testFunction没有读取当前线程的属性。如果pthread_attr_init()存在于您的系统中，pthread_getattr_np()可能会帮助您，但您需要将相关主题的pthread_t传递到查询的任何位置，而不是调用{{1}}。

Pthread创建为独立

3 个答案: