how to get context switching between threads

[v3dant]

/* Includes */
#include <unistd.h>     /* Symbolic Constants */
#include <sys/types.h>  /* Primitive System Data Types */ 
#include <errno.h>      /* Errors */
#include <stdio.h>      /* Input/Output */
#include <stdlib.h>     /* General Utilities */
#include <pthread.h>    /* POSIX Threads */
#include <string.h>     /* String handling */
#include <semaphore.h>  /* Semaphore */
#include <time.h>

/* prototype for thread routine */
void handler ( void *ptr );
void producer ( void *ptr );

/* global vars */
/* semaphores are declared global so they can be accessed 
   in main() and in thread routine,
   here, the semaphore is used as a mutex */

sem_t mutex;
int counter=0; /* shared variable */



int main()
{
    int i;
    pthread_t prod[1000];  
    sem_init(&mutex, 0, 1);      /* initialize mutex to 1 - binary semaphore */
                                 /* second param = 0 - semaphore is local */
    srand((unsigned)time(NULL));                           
    for(i=0; i<1000; i++)
    {                                 
    	pthread_create (&prod[i], NULL, producer, (void *) &i);
	pthread_join (prod[i], NULL);
    }
    sem_destroy(&mutex); /* destroy semaphore */ 
    return(0);
}

void producer ( void *ptr )
{
	int x; int c;
	int z;
	int b;
	b = (rand() & 255);
	z = *((int *) ptr);
	for(x=0; x<b; x++)
	{
		if( (rand() & 1) == 0)
		{
			handler(&z);
		//	for(c=0; c<1000000; c++)
		//	{
		//	}
		
		}
	}	
}

void handler ( void *ptr )
{
    int x; 
    x = *((int *) ptr);
//  printf("Thread %d: Waiting to enter critical region...\n", x);
    sem_wait(&mutex);       /* down semaphore */
    /* START CRITICAL REGION */
//  printf("Thread %d: Now in critical region...\n", x);
//  printf("Thread %d: Counter Value: %d\n", x, counter);
//  printf("Thread %d: Incrementing Counter...\n", x);
    counter++;
    printf("Thread %d: New Counter Value: %d\n", x, counter);
//  printf("Thread %d: Exiting critical region...\n", x);
    /* END CRITICAL REGION */    
    sem_post(&mutex);       /* up semaphore */
    
   // pthread_exit(0); /* exit thread */
}

I want the threads to access the critical section randomaly, currently they just access it one by one, first thread 0 then thread 1 then thread 2...., how can i get some context switching going on in here using semaphores.

[v3dant]

sorry i accidentally posted in the C++ section should have been in the C