//////////////////////////////////////////////////////////////
// From 
// https://linuxprograms.wordpress.com/2007/12/29/threads-programming-in-linux-examples/
//
// Modified by bruce.land@cornell.edu
///////////////////////////////////////////////////////////////

// needed for CPU_SET, which is needed to
// force threads onto one processor
#define _GNU_SOURCE 
//
#include <stdio.h>
#include <pthread.h>
#include <semaphore.h>
#include <stdlib.h>

#define TRUE 1
#define FALSE 0

char input_buffer[64];


// access to text buffer
pthread_mutex_t buffer_lock= PTHREAD_MUTEX_INITIALIZER;
// counter protection
pthread_mutex_t count_lock= PTHREAD_MUTEX_INITIALIZER;

// the two semaphores  
sem_t enter_cond ; // tells read1 that print is done
sem_t print_cond ; // tells write1 that read is done

// globals for perfromance
int count1, count2;

///////////////////////////////////////////////////////////////
// read the keyboard
///////////////////////////////////////////////////////////////
void * read1() {
	while(1){
		//wait for print done
		sem_wait(&print_cond);
		
		pthread_mutex_lock(&buffer_lock);
		// the actual enter				
		printf("Enter a string: ");
		scanf("%s",input_buffer);
		// unlock the input_buffer
		pthread_mutex_unlock(&buffer_lock);
		
		// and tell write1 thread that enter is complete
		sem_post(&enter_cond);
	} // while(1)
}

///////////////////////////////////////////////////////////////
// write the input string
///////////////////////////////////////////////////////////////
void * write1() {	
	while(1){
		// wait for enter done
		sem_wait(&enter_cond);
		
		pthread_mutex_lock(&buffer_lock);
		// the protected print (with protected counter)
		pthread_mutex_lock(&count_lock);
		printf("The string entered is %s, %d\n",input_buffer, count1);
		count1 = 0;
		pthread_mutex_unlock(&count_lock);
		// unlock the input_buffer
		pthread_mutex_unlock(&buffer_lock);
		
		// and tell read1 thread that print is done
		sem_post(&print_cond);         
	} // while(1)
}

///////////////////////////////////////////////////////////////
// counter 1
///////////////////////////////////////////////////////////////
// with mutex, about 9 to 10 million/sec
// -- adding a second copy drops rate to about 4 million/sec
// -- adding a second copy pegs BOTH processors at 100%
// without mutex about 200 to 400 millon/sec
// 
void * counter1() {
	while(1){
		// count as fast as possible
		pthread_mutex_lock(&count_lock);
		count1++;    
		pthread_mutex_unlock(&count_lock);
					  
	} // while(1)
}

///////////////////////////////////////////////////////////////
int main()
{
	// from 
	// http://man7.org/linux/man-pages/man3/pthread_setaffinity_np.3.html
	// see also
	// http://man7.org/linux/man-pages/man3/CPU_SET.3.html
	// The cpu_set_t structure is opaque and must be manipulated with
	// the following macros
	cpu_set_t cpuset;
	CPU_ZERO(&cpuset);  
	// put just one processsor into the list
	CPU_SET(0, &cpuset);
	
	// the thread identifiers
	pthread_t thread_read, thread_write, thread_count1, thread_count2;
	
	// the semaphore inits
	// read is not ready becuase nothing has been input yet
	sem_init(&enter_cond, 0, 0);
	// print is ready at init time
	sem_init(&print_cond, 0, 1); 
	
	//For portability, explicitly create threads in a joinable state 
	// thread attribute used here to allow JOIN
	pthread_attr_t attr;
	pthread_attr_init(&attr);
	pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);
	
	// now the threads
	pthread_create(&thread_read,NULL,read1,NULL);
	pthread_create(&thread_write,NULL,write1,NULL);
	pthread_create(&thread_count1,NULL,counter1,NULL);
	// second copy of counter
	pthread_create(&thread_count2,NULL,counter1,NULL);
	
	// for efficiency, force counting threads onto processor ZERO
	// comment out to see effect of counting on two processors: 
	// which is a factor of 2 slowdown
	pthread_setaffinity_np(thread_count1, sizeof(cpu_set_t), &cpuset);
	pthread_setaffinity_np(thread_count2, sizeof(cpu_set_t), &cpuset);
	
	// In this case the thread never exit
	pthread_join(thread_read,NULL);
	pthread_join(thread_write,NULL);
	return 0;
}
///////////////////////////////////////////////////////////////