Editing Pthreads (section)

==Example==
An example illustrating the use of pthreads in C:

<syntaxhighlight lang="c">
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <pthread.h>
#include <unistd.h>

#define NUM_THREADS 5

void *perform_work(void *arguments){
  int index = *((int *)arguments);
  int sleep_time = 1 + rand() % NUM_THREADS;
  printf("Thread %d: Started.\n", index);
  printf("Thread %d: Will be sleeping for %d seconds.\n", index, sleep_time);
  sleep(sleep_time);
  printf("Thread %d: Ended.\n", index);
  return NULL;
}

int main(void) {
  pthread_t threads[NUM_THREADS];
  int thread_args[NUM_THREADS];
  int i;
  int result_code;
  
  //create all threads one by one
  for (i = 0; i < NUM_THREADS; i++) {
    printf("In main: Creating thread %d.\n", i);
    thread_args[i] = i;
    result_code = pthread_create(&threads[i], NULL, perform_work, &thread_args[i]);
    assert(!result_code);
  }

  printf("In main: All threads are created.\n");

  //wait for each thread to complete
  for (i = 0; i < NUM_THREADS; i++) {
    result_code = pthread_join(threads[i], NULL);
    assert(!result_code);
    printf("In main: Thread %d has ended.\n", i);
  }

  printf("Main program has ended.\n");
  return 0;
}

</syntaxhighlight>

This program creates five threads, each executing the function ''perform_work'' that prints the unique number of this thread to standard output.  If a programmer wanted the threads to communicate with each other, this would require defining a variable outside of the scope of any of the functions, making it a [[global variable]]. This program can be compiled using the [[GNU Compiler Collection|gcc]] compiler with the following command:
 gcc pthreads_demo.c -pthread -o pthreads_demo
Here is one of the many possible outputs from running this program.
<syntaxhighlight lang="output">
In main: Creating thread 0.
In main: Creating thread 1.
In main: Creating thread 2.
In main: Creating thread 3.
Thread 0: Started.
In main: Creating thread 4.
Thread 3: Started.
Thread 2: Started.
Thread 0: Will be sleeping for 3 seconds.
Thread 1: Started.
Thread 1: Will be sleeping for 5 seconds.
Thread 2: Will be sleeping for 4 seconds.
Thread 4: Started.
Thread 4: Will be sleeping for 1 seconds.
In main: All threads are created.
Thread 3: Will be sleeping for 4 seconds.
Thread 4: Ended.
Thread 0: Ended.
In main: Thread 0 has ended.
Thread 2: Ended.
Thread 3: Ended.
Thread 1: Ended.
In main: Thread 1 has ended.
In main: Thread 2 has ended.
In main: Thread 3 has ended.
In main: Thread 4 has ended.
Main program has ended.
</syntaxhighlight>