在Linux上执行pthread

Question

我开始在linux上进行pthread编程,在第一个程序中我完全搞糊涂了.以下是我正在运行的程序

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>

void *print_message_function( void *ptr );

int main(){
 pthread_t thread1, thread2;
 char *message1 = "Thread 1";
 char *message2 = "Thread 2";
 int  iret1, iret2;

/* Create independent threads each of which will execute function */

 iret1 = pthread_create( &thread1, NULL, print_message_function, (void*) message1);
 iret2 = pthread_create( &thread2, NULL, print_message_function, (void*) message2);

 /* Wait till threads are complete before main continues. Unless we  */
 /* wait we run the risk of executing an exit which will terminate   */
 /* the process and all threads before the threads have completed.   */

 pthread_join( thread1, NULL);
 printf("amit");
 pthread_join( thread2, NULL); 

 printf("Thread 1 returns: %d\n",iret1);
 printf("Thread 2 returns: %d\n",iret2);
 exit(0);
}

void *print_message_function( void *ptr ){
 char *message;
 message = (char *) ptr;
 printf("%s \n", message);
}

我想知道的第一件事是线程执行的顺序不是顺序的？

第二件事是我内心打印("amit"); 看看main在thread1被终止期间真的停止但在输出中我们可以看到printf语句首先被执行.整个过程的输出是

线程1

线程2

amitThread 1返回:0

线程2返回:0

Answer 1

你是对的,说线程执行的顺序不是顺序的.在某种程度上,这是使用线程的全部要点,即同时运行其他任务.

您看到的输出符合预期,可能会有所不同.

也许这会有所帮助:

   main            thread1     thread2
    |                
    |--create--------+-----------\
    |                |           |   
    |            "Thread 1"      |   "Thread 2" can
    |                |           |<- occur anywhere
    |               /            |   along this line
   join(1) ---------             |
    |                            |
    |                            |
  "amit"                         |
    |                            |
    |                            |
   join(2) ---------------------/
    |
    |
"Thread 1 returns"
"Thread 2 returns"
    |
  exit(0)

您唯一的保证是:

• " Thread 1"将始终在" amit" 之前打印(因为pthread_join()在主程序可以继续之前等待线程1结束)
• Thread X returns ...在两个线程终止后," "语句总是会结束.