use peterson method to implement semaphore

gistfile1.cpp

/*
 * =====================================================================================
 *
 *       Filename:  mutex_semaphore.c
 *
 *    Description: use peterson method to implement semaphore 
 *
 *        Version:  1.0
 *        Created:  04/16/2013 03:27:04 PM
 *       Revision:  none
 *       Compiler:  gcc
 *
 *         Author:  Chaoyu Yang, 
 *   Organization:  
 *
 * =====================================================================================
 */
#include <stdlib.h>
#include <stdio.h>
#include <pthread.h>
#include <sched.h>
#include <unistd.h>
#define FALSE 0
#define TRUE  1
#define N 4 // number of processes, from 1 to 4
 
int account1 = 0, account2 = 0;
 
int turn[N];
int stage[N+1];
 
void enterRegion(int process) {
    int i, j;
 
    for (i = 1; i <= N - 1; i++) {
        stage[process] = i;
        turn[i] = process;
        for (j = 1; j <= N; j++) {
            if (j == process)
                continue;
            while (stage[j] >= i  && turn[i] == process)
                ;
        }
    }
}
 
void leaveRegion(int process) {
    stage[process] = FALSE;
}
 
typedef struct {
    int value;
}semaphore;
 
semaphore S;
 
void init(semaphore *s, int v) {
    s->value = v;
}
 
void wait(semaphore *s, int i) {
    enterRegion(i);
    while(s->value <= 0) {
        leaveRegion(i);
        /*sched_yield();*/
        sleep(0);
        enterRegion(i);
    }
    s->value--;
    leaveRegion(i);
}
 
void signal(semaphore *s, int i) {
    enterRegion(i);
    s->value ++;
    leaveRegion(i);
}
 
void * bankingTranscation(void *arg)
{
    int counter = 0;
    int i = (int)arg;
 
    do {
        int r = rand()%100;
        if(r % 2 == 1)
            r *= -1;
 
        wait(&S, i);
        //criticial region
        account1 -= r;
        account2 += r;
        //end of creticial region
        signal(&S, i);
 
        counter++;
    } while(counter < 1000000);
 
    if (account1 + account2 != 0)
        printf("Error\n");
 
    pthread_exit((void *)2);
}
 
int main ()
{
    clock_t begin, end;
    double time_spent;
    begin = clock();
 
    init(&S,1);
    pthread_t tid1, tid2, tid3, tid4;
 
    pthread_create(&tid1, NULL, bankingTranscation, (void *)1);
    pthread_create(&tid2, NULL, bankingTranscation, (void *)2);
    pthread_create(&tid3, NULL, bankingTranscation, (void *)3);
    pthread_create(&tid4, NULL, bankingTranscation, (void *)4);
 
    pthread_join(tid1, NULL);
    pthread_join(tid2, NULL);
    pthread_join(tid3, NULL);
    pthread_join(tid4, NULL);
 
    end = clock();
    time_spent = (double)(end - begin) / CLOCKS_PER_SEC;
    printf("Time consumed: %.6g \n", time_spent);
 
    pthread_exit(NULL);
}