Question

pthread_join()函数在执行后终止线程，或者我们需要调用pthread_cancel() / pthread_exit()？

我正在调用pthread_cancel() / pthread_kill()，它返回3，即没有附加thread_id的线程。

#include <stdio.h>
#include <pthread.h>
#include <unistd.h>
#include <signal.h>

void * run (void *);

int main() {
pthread_t p1, p2;
int a = 9;
printf("%d\n", pthread_create(&p1, NULL, &run, (void*)&p1));
printf("%d\n", pthread_create(&p2, NULL, &run, (void*)&p2));

printf("%d\n", pthread_join(p1, NULL));
//usleep(1000);
printf("%d\n", pthread_join(p2, NULL));

printf("before exit\n");
printf("%d\n", pthread_cancel(p1));
printf("after exit\n");
printf("%d\n", pthread_cancel(p2));
printf("both thread exited\n");

printf("%d\n", pthread_join(p1, NULL));
printf("%d\n", pthread_join(p2, NULL));
printf("terminated\n");

printf("%d\n", pthread_kill(p1, 0));
printf("%d\n", pthread_kill(p2, 0));
printf("ext\n");

printf("%d\n", pthread_join(p1, NULL));
printf("%d\n", pthread_join(p2, NULL));
printf("jion\n");

return 0;
}

void *run (void *p) {

int *i = (int*)p;
printf("created i = %d\n", *i);
}

这是我正在使用的代码。在这个pthread_cancel上，所有函数返回3，这意味着线程已被杀死。

Answer 1

pthread_join不会杀死该线程，它等待线程完成。如果要杀死线程，请使用pthread_kill。但是必须在 pthread_join之前完成，否则线程已经退出。

pthread_cancel请求该帖子在下一个取消点终止，并且可能比使用pthread_kill更安全。

pthread_exit退出当前主题。

Answer 2

pthread_join()添加

之后

/* Last thing that main() should do */
   pthread_exit(NULL);

有关详细信息，请参阅here。

pthread_join（）用于使main（）线程等待，直到所有线程完成它的执行。当特定线程完成它的执行时，控制到达pthread_join（）。因此，如果您尝试取消/终止该特定线程，将返回错误。

示例代码

    #include <pthread.h>
    #include <stdio.h>
    #include <stdlib.h>
    #define NUM_THREADS 4

    void *BusyWork(void *t)
    {
       int i;
       long tid;
       tid = (long)t;
       printf("Thread %ld starting...\n",tid);
       pthread_exit((void*) t);                 //Exits that current thread.
    }

    int main (int argc, char *argv[])
    {
       pthread_t thread[NUM_THREADS];
       int rc;
       long t;
       void *status;

       for(t=0; t<NUM_THREADS; t++) {
          printf("Main: creating thread %ld\n", t);
          rc = pthread_create(&thread[t], NULL, BusyWork, (void *)t); 
          if (rc) {
             printf("ERROR; return code from pthread_create() is %d\n", rc);
             exit(-1);
             }
          }

      /* Wait for completion */
       for(t=0; t<NUM_THREADS; t++) {
          rc = pthread_join(thread[t], &status);
          if (rc) {
             printf("ERROR; return code from pthread_join() is %d\n", rc);
             exit(-1);
             }
printf("Main: completed join with thread %ld having a status of %ld\n",t,(long)status);
          }

    printf("Main: program completed. Exiting.\n");
    pthread_exit(NULL); // Exits main thread.
    }

@Joachim Pileborg

#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#define NUM_THREADS 4

void *BusyWork(void *t)
{
   int i;
   long tid;
   tid = (long)t;

   printf("Thread %ld starting...\n",tid);

   for(i = 0; i <10000000; i++)
        printf("\n Thread: %ld,  %d", tid, i);

   pthread_exit((void*) t);                 //Exits that current thread.
}

int main (int argc, char *argv[])
{
   pthread_t thread[NUM_THREADS];
   int rc;
   long t;
   void *status;

   for(t=0; t<NUM_THREADS; t++) {
      printf("Main: creating thread %ld\n", t);
      rc = pthread_create(&thread[t], NULL, BusyWork, (void *)t);
      if (rc) {
         printf("ERROR; return code from pthread_create() is %d\n", rc);
         exit(-1);
         }
      }

//printf("Main: program completed. Exiting.\n");
pthread_exit(NULL); // Exits main thread(work will be done).
//return 0;//( Threads will exit once main exits.)
}

Answer 3

某些上下文会很好......但是如果你只是等待一个线程（可能只有你关心的一个）来终止/返回，那么pthread_join就足够了。

pthread_join（）函数等待thread指定的线程终止。如果该线程已经终止，则pthread_join（）返回立即

http://www.kernel.org/doc/man-pages/online/pages/man3/pthread_join.3.html

检查手册页以了解使用/警告。

pthread_join函数在执行后杀死线程还是需要调用pthread_cancel / pthread_exit？

3 个答案: