How to use mutithread in C ?

naihe2010 · 11-29-2005, 05:21 PM

I am studing mutithread programing in C, and meet a difficuty.
The source code is:

Code:

#include <string.h>
#include <pthread.h>

#define N 26

void disp(void *str);

int main(void)
{
  int i;
 
  char *chp;
  chp = (char*)malloc(sizeof(char) * N);
  for(i=0; i<N; *(chp+i)='a'+i++);

  pthread_t *thread;
  thread = (pthread_t*)malloc(sizeof(pthread_t) * N);

  for(i=0; i<N; ++i)pthread_create(thread+i, 0, (void*)&disp, (void*)(chp+i));
  sleep(1);
  
  putchar('\n');
  
  return 0;
}

void disp(void *str)
{
  char *strtemp;
  strtemp = (char*)str;
  putchar(*strtemp);
}

As you see, I use a word "sleep(1);" in the 20th line.
If I didn't use this, it can't work well.
What's the problem with my code, and why I must use the "sleep(1)" ?

Please help me.

BrianK · 11-29-2005, 06:43 PM

threads are not attached to the current process and the current process knows nothing about the thread execution. Because of this, without the sleep, the program continues to run & exits before all the threads complete. The sleep allows all threads to complete.

As a test, but the sleep after the putchar('\n'); you'll see the remainder of your output will show up as soon as the sleep stops blocking output from the main process

To fix, you'll need to include semaphors so that your process knows to wait for all threads to finsih before continuing.