posix threads (pthread_create and pthread_join)

Question

I am trying to learn Unix C and doing some exercises for practice. The current problem I am working on involves POSIX threads (mainly pthread_create() and pthread_join())

The problem asks to repeatedly print "Hello World" using two threads. One thread is to print "Hello" 1000 times, while the second thread prints "World" 1000 times. The main program/thread is to wait for the two threads to finish before proceeding.

Here is what I have right now.

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

void *print_hello(void *arg)
{
  int iCount;
  for(iCount = 0; iCount < 1000; iCount++)
  {
     printf("Hello\n");
  }
}

void *print_world(void *arg)
{
   int iCount;
   for(iCount = 0; iCount < 1000; iCount++)
   {
      printf("World\n");
   }
}

int main(void)
{
  /* int status; */
  pthread_t thread1;
  pthread_t thread2;

  pthread_create(&thread1, NULL, print_hello, (void*)0);
  pthread_create(&thread2, NULL, print_world, (void*)0);

  pthread_join(thread1, NULL);
  pthread_join(thread2, NULL);

  return 0;
}

This does not seem to work fully. It prints "Hello" as expected. But "World" is not printed at all. Seems like the second thread is not running at all. Not sure I am using pthread_join correctly. My intention is for the main thread to "wait" for these two threads as the exercise asks.

Any help would be appreciated.

Seems OK to me, and works as expected. You might want to add return NULL at the end of your thread functions though. — Chris White
– Chris White, Commented Jun 24, 2011 at 19:07
To comment on your code, NULL is usually defined as "(void*)0", so its a bit silly to use both. I'd suggest NULL - there is no guarantee that a null pointer is represented as 0 on all systems, while NULL will be defined to the appropriate value. — Aaron Dufour
– Aaron Dufour, Commented Jun 25, 2011 at 2:19

mah · Accepted Answer · 2011-06-24 19:05:46Z

7

What makes you think it isn't running both threads? I think the output is just screaming past you too quickly to notice -- you're going to get a large number of each thread's output in a single block.

Try redirecting the output to a file and reviewing what actually got printed.

answered Jun 24, 2011 at 19:05

mah

40.1k9 gold badges79 silver badges94 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

acm · Accepted Answer · 2011-06-24 19:05:14Z

2

I just ran your code.

$ gcc ./foo.c -pthread
$ ./a.out | grep World | wc -l
1000
$ ./a.out | grep Hello | wc -l
1000

Works for me on Ubuntu 10.10 with gcc-4.5.2. Double check your compilation and your output.

answered Jun 24, 2011 at 19:05

acm

12.8k5 gold badges43 silver badges75 bronze badges

Collectives™ on Stack Overflow

posix threads (pthread_create and pthread_join)

2 Answers 2

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related