/**
* compile with: $] gcc thread_example.c -lpthread -o thread_example
* run with: $] ./thread_example
*
*/

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <string.h>

// the function which a thread is supposed to run
// has the following prototype
void *thread1_function( void *ptr );
void *thread2_function( void *ptr );

int length = -1;
pthread_t thread1, thread2;

main()
{
	char *message1 = "Thread 1";
	int  iret1, iret2;

	/* Create independent threads each of which will execute function */
	
	iret1 = pthread_create( &thread1, NULL, thread1_function, (void*) message1);
	iret2 = pthread_create( &thread2, NULL, thread2_function, NULL);

	/* Wait till threads are complete before main continues. Unless we  */
	/* wait we run the risk of executing an exit which will terminate   */
	/* the process and all threads before the threads have completed.   */

	pthread_join( thread2, NULL); 

	// return value of 0 signifies success
	// typically the return value should be checked for error conditions
	printf("Thread 1 returns: %d\n",iret1);
	printf("Thread 2 returns: %d\n",iret2);
	exit(0);
}

/* The function executed by thread 1.
* For example, this thread could continuously listen on a socket for 
* incoming data, and update a (global) data structure.
*/
void *thread1_function( void *ptr )
{
	// this thread prints a message (passed as argument) and assigns
	// the length to a global variable
	char *message;
	message = (char *) ptr;
	printf("Thread 1 message:%s \n", message);
	length = strlen(message);
}

/* The function executed by thread 2.
* For example, this thread could listen for user input
* and then read from the data structure.
*/
void *thread2_function( void *ptr )
{
	// note that the argument is not used
	
	// we wait till thread1 has completed
	pthread_join( thread1, NULL);

	printf("Thread 2: length = %d\n", length);
}