pthread example

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

volatile int beers = 2000000;
pthread_mutex_t p_thread_lock = PTHREAD_MUTEX_INITIALIZER;

struct {
    char a;
    char b;
    char c;
    char d;
    char e;
}data;
void* drink(void*a){
    int i;
    pthread_mutex_lock(&p_thread_lock);
    for(i=0; i<100000; i++){
        beers--;
    }
    pthread_mutex_unlock(&p_thread_lock);

    long thread_no = (long)a;
    return (void*)(thread_no +1);
}

int main(){
    pthread_t threads[20];
    int t = 0;
    for(t=0; t<20; t++){
        pthread_create(&threads[t],NULL,drink,(void*)t);
    }

    void* result;
    for(t=0; t<20; t++){
        pthread_join(threads[t], &result);
        printf("Thread %ld returned %ld\n",t,(long)result);
    }

    printf("There are now %i bottles of beer on the wall\n", beers);

}