Critical Section Problem

README.md

Critical Section Problem

Use the following commands to compile and link the examples:

$ gcc -std=c17 -pedantic-errors -O0 -g -o problem problem.c -lpthread
$ gcc -std=c17 -pedantic-errors -O0 -g -o peterson0 peterson0.c -lpthread

peterson0.c

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

#define PING "ping"
#define PONG "pong"

void critical(const char * str) {
  size_t len = strlen(str);
  for (size_t i = 0; i < len; ++i) {
    printf("%c", str[i]);
  } // for
  printf("\n");
} // str

int getid(const char * msg) {
  if (strcmp(msg, PING) == 0) return 0;
  if (strcmp(msg, PONG) == 0) return 1;
} // getid

volatile bool flag [2] = { false, false };
volatile int turn;

void * pingpong(void * p) {
  char * msg = (char *) p;
  int id = getid(msg);
  for (;;) {
    flag[id] = true;
    turn = 1-id;
    while (flag[1-id] && turn == (1-id));
    critical(msg);
    flag[id] = false;
  } // for 
} // pingpong

int main() {
  setvbuf(stdout, NULL, _IONBF, 0);
  pthread_t ping;
  pthread_t pong;
  pthread_create(&ping, NULL, pingpong, PING);
  pthread_create(&pong, NULL, pingpong, PONG);
  for(;;);
  return 0;
} // main

problem.c

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

#define PING "ping"
#define PONG "pong"

void critical(const char * str) {
  size_t len = strlen(str);
  for (size_t i = 0; i < len; ++i) {
    printf("%c", str[i]);
  } // for
  printf("\n");
} // critical

void * pingpong(void * p) {
  char * msg = (char *) p;
  for (;;) {
    critical(msg);
  } // for 
} // pingpong

int main() {
  setvbuf(stdout, NULL, _IONBF, 0);
  pthread_t ping;
  pthread_t pong;
  pthread_create(&ping, NULL, pingpong, PING);
  pthread_create(&pong, NULL, pingpong, PONG);
  for(;;);
  return 0;
} // main