Listing 1. C Source Code for hello_world

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

#define THREAD_COUNT        32

/* String output data */
static const char   *string = "Hello World!\n";
static int          cursor = 0;
pthread_mutex_t     print_lock = PTHREAD_MUTEX_INITIALIZER;

/* Runtime statistics */
static int          chars_printed = 0;
pthread_mutex_t     statistics_lock = PTHREAD_MUTEX_INITIALIZER;

/* Print one character of the string "Hello World!" to stdout */
/* Returns a pointer to the character printed */
static char *say_hello(void)
{
    char *printed_letter = NULL;

    printf("%c", string[cursor]);
    if (++cursor > strlen(string)) {
        cursor = 0;
        fflush(stdout);
    }

    printed_letter = (char *) malloc(1);
    if (printed_letter) {
        *printed_letter = string[cursor];
    }

    return printed_letter;
}

/* A "bug-free" printer function */
static void *good_printer(void *data)
{
    char *c = NULL;

    while(1) {
        c = NULL;
        pthread_mutex_lock(&print_lock);
        pthread_mutex_lock(&statistics_lock);
        c = say_hello();
        if (c) free(c);
        chars_printed++;
        pthread_mutex_unlock(&statistics_lock);
        pthread_mutex_unlock(&print_lock);
    }
    return NULL;
}

/* A buggy printer function */
static void *bad_printer(void *data)
{
    while(1) {

ed_mutex_lock(&statistics_lock);
        pthread_mutex_lock(&print_lock);
        say_hello();
        chars_printed++;
        pthread_mutex_unlock(&print_lock);
        pthread_mutex_unlock(&statistics_lock);
    }
    return NULL;
}

int main (int argc, char **argv)
{
    pthread_t threads[THREAD_COUNT];
    int i;

    /* Spawn many good children threads */
    for (i = 1; i < THREAD_COUNT; i++) {
        if (0 != pthread_create(&threads[i], NULL, good_printer, NULL)) {
            perror("pthread_create");
            exit(EXIT_FAILURE);
        }
    }

    /* Spawn one bad child thread */
    if (0 != pthread_create(&threads[0], NULL, bad_printer, NULL)) {
        perror("pthread_create");
        exit(EXIT_FAILURE);
    }

    pthread_join(threads[0], NULL);

    return EXIT_SUCCESS;
}