#include<stdio.h>//for printf
#include<string.h>//for strerror
#include<stdlib.h>//for srandom and random
#include<pthread.h>//for threads
#define MAX_SLEEP 10//maximum sleeping time in seconds
#define perror2(s,e) fprintf(stderr,"%s: %s\n",s,strerror(e))

void *sleeping(void *);

main(int argc,char *argv[])
{
	int n,i,s1,err;
	pthread_t *tids;
	if(argc>1) n=atoi(argv[1]);
	else exit(0);
	if(n>50){
		printf("Number of threads should be up to 50\n");
		exit(0);
	}
	if((tids=(pthread_t*)malloc(n*sizeof(pthread_t)))==NULL){
		perror("malloc");
		exit(1);
	}
	srandom((unsigned int)time(NULL));
	for(i=0;i<n;i++)
	{
		s1=random()%MAX_SLEEP+1;
		if(err=pthread_create(tids+i,NULL,sleeping,(void*)s1)){
			perror2("pthread_create",err);
			exit(1);
		}
	}
	
	for(i=0;i<n;i++)
	{
	  if(err=pthread_join(*(tids+i),NULL)){
	  	perror2("pthread_join",err);
	  	exit(1);
	  }	
	}	
	printf("all %d threads have terminated\n",n);	
}

void *sleeping(void *arg)
{
	int s1=(int)arg;
	printf("thread %d sleeping %d seconds ...\n",pthread_self(),s1);
	sleep(s1);
	printf("thread %d awakening\n",pthread_self());
	pthread_exit(NULL);
}