test_mutext.c

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

pthread_mutex_t mutex;

void error(const char* str) {
  printf("str");
  exit(2);
}

void readFromFile(FILE* fp, char* buffer) {
  char ch = '\0';
  int i = 0;
  while ((ch = fgetc(fp)) != EOF) {
    buffer[i] = ch;
    i += 1;
  }
  buffer[i] = '\0';
}

void writeFile(FILE* fp, char* buffer) {
  rewind(fp);
  fwrite("Output", sizeof(char), strlen("Output"), fp);
}

void *printHello(void *threadId) {
  long tid;
  tid = (long)threadId;

  while (1) {
    /*int result = pthread_mutex_trylock(&mutex);*/
    int result = pthread_mutex_lock(&mutex);
    if (result != 0) {
      printf("%ld: Try Lock Failed\n", tid);
    } else {
      break;
    }
  }
  printf("%ld: Acquire lock!\n", tid);
  printf("Hello World! %ld!\n", tid);
  pthread_mutex_unlock(&mutex);
  pthread_exit(0);
}

void createThread(long tid) {
  pthread_t thread;
  int rc = pthread_create(&thread, NULL, printHello, (void*)tid);
  if (rc) {
    printf("ERROR %d", rc);
    exit(1);
  }
}


int main(int c, char* argv[]) {
  FILE* fp = fopen("data", "r+");
  if (fp == 0) {
    error("file open Error");
  }

  char buffer[256];
  readFromFile(fp, buffer);
  printf("%s", buffer);

  writeFile(fp, buffer);


  pthread_mutex_init(&mutex, NULL);
  pthread_mutex_lock(&mutex);

  createThread(1);
  createThread(2);

  sleep(3);
  pthread_mutex_unlock(&mutex);


  sleep(1);
  return 0;
}