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[Shawn128]

I need a bit of help with a programming assignment and I was hoping someone here could point out what I'm doing wrong. Essentially, I'm trying to create a pthread inside my program. I've looked up literature in my books and also through google, yet I still return an error when I try to use pthread_create(). Here's basically what my code looks like (Oh this is in C btw if I haven't mentioned so already):

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

void *runner (void *param)
{
    printf("Inside pthread\n");
}

int main(int argc, char * argv[])
{
  int rc;
  pthread_t tid;
  pthread_attr_t attr;
  
  pthread_attr_init(&attr);
  printf("before\n");
  rc = pthread_create(&tid,NULL,runner,(void *)5);
  printf("after\n");
  
  if (rc){
    printf("ERROR; return code from pthread_create() is %d\n", rc);
    exit(-1);
  }

  pthread_join(tid,NULL); 
}

 

[BobJustBob]

You're casting a literal (the numeral 5) to a void pointer? I'm not sure you can do that.

Try storing the 5 in a variable and casting that instead.

 

[Shawn128]

Its not really the fact that I'm casting a numeral. The problem is getting into the pthread period. Even if I can't do that, I should be able to at least get the printf() in the runner function to print onscreen

 

[Shawn128]

This is what I get for my output:

>>a.out

before
after
ERROR; return code from pthread_create() is -1

>>

 

[Steve Youngblood]

It's been a while since I had to do Unix programming, but it seems like you had to pass a reference to a variable as your last parameter to p_thread_creat, just like you passed the reference to tid.

 

[Shawn128]

i think i just figured it out.

apparently you can't just compile it as gcc simple.c

you have to do it as: gcc simple.c -lpthread

Thanks for the help guys, but I'd like to keep the thread going. Anyone have any advice on pthreads in general?

 

[Steve Youngblood]

Yeah, just for consistency to what you had, if you declare an integer equal to 5, and pass a reference to it, it will compile. Also, unless you want inconsistent results where you might get the output:
before
after
inside pthread

or:
before
inside pthread
after

you might want to call the p_threadjoin immediately after creating the thread. That function is what tells main to wait for the thread to complete.