hello_i_of_w_pri.c

/*
 * Copyright 2021 Jeisson Hidalgo-Cespedes - Universidad de Costa Rica
 * Creates a secondary thread that greets in the standard output
 */

#include <inttypes.h>
#include <pthread.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>

typedef struct private_thread_data {
  size_t thread_number;  // rank
  size_t thread_count;
} private_thread_data_t;

void* run(void* data);
int create_threads(size_t thread_count);

// TODO(you): do not use global variables
pthread_mutex_t stdout_mutex;

int main(int argc, char* argv[]) {
  int error = pthread_mutex_init(&stdout_mutex, /*attr*/ NULL);

  if (error == 0) {
    size_t thread_count = 1;
    if (argc >= 2) {
      thread_count = strtoull(argv[1], NULL, 10);
    }

    error = create_threads(thread_count);

    pthread_mutex_destroy(&stdout_mutex);
  } else {
    fprintf(stderr, "error: could not init mutex\n");
    error = 11;
  }

  return error;
}

int create_threads(size_t thread_count) {
  pthread_t* threads = (pthread_t*) malloc(thread_count * sizeof(pthread_t));
  int error = 0;

  private_thread_data_t* private_thread_data = (private_thread_data_t*)
    calloc(thread_count, sizeof(private_thread_data_t));

  if (threads && private_thread_data) {
    for (size_t index = 0; index < thread_count; ++index) {
      private_thread_data[index].thread_number = index;
      private_thread_data[index].thread_count = thread_count;

      error = pthread_create(&threads[index], NULL, run
        , &private_thread_data[index]);

      if (error) {
        fprintf(stderr, "error: could not create thread %zu\n", index);
        error = 21;
      }
    }

    pthread_mutex_lock(&stdout_mutex);
    printf("Hello from main thread\n");
    pthread_mutex_unlock(&stdout_mutex);

    for (size_t index = 0; index < thread_count; ++index) {
      pthread_join(threads[index], NULL);
    }

    free(private_thread_data);
    free(threads);
  } else {
    fprintf(stderr, "error: could not allocate memory for %zu threads\n"
      , thread_count);
    error = 22;
  }

  return error;
}

void* run(void* data) {
  private_thread_data_t* private_data = (private_thread_data_t*)data;
  // pthread_mutex_t* stdout_mutex = (pthread_mutex_t*)data;
  pthread_mutex_lock(&stdout_mutex);
  printf("Hello from secondary thread %zu of %zu\n"
    , (*private_data).thread_number, private_data->thread_count);
  pthread_mutex_unlock(&stdout_mutex);

  return NULL;
}