/////////////////////////////////////////////////////////////
//
// threads.cpp
//
// Jeff Ondich, 4/12/04
// Updated 11/14/05
//
// A simple demonstration of the use of pthreads.
// This demo uses two binary semaphores to force strict
// alternation between a pair of threads.
//
// Note that the two thread procedures include delay
// loops.  The point of this is to illustrate the passing
// of parameters to the thread procedures via the fourth
// pthread_create parameter.
//
// To compile:
//
//   g++ -Wall -o threads threads.cpp -lpthread
//
/////////////////////////////////////////////////////////////

#include <iostream>
#include <pthread.h>
using namespace std;


int gSharedCounter = 0;
pthread_mutex_t mutexA = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t mutexB = PTHREAD_MUTEX_INITIALIZER;

void *threadMainA( void *arg );
void *threadMainB( void *arg );
void delay( int limit );

int main()
{
    pthread_mutex_lock( &mutexB );

    pthread_t threadA, threadB;
    if( pthread_create( &threadA, NULL, threadMainA, (void *)20000 ) != 0 )
    {
        perror( "Can't create thread A" );
        exit( 1 );
    }

    if( pthread_create( &threadB, NULL, threadMainB, (void *)10000 ) != 0 )
    {
        perror( "Can't create thread B" );
        exit( 1 );
    }

    // Wait for children to return.  If you don't wait for them, the
    // process will return from main(), and thus shut down the whole
    // process, including the threads.

    pthread_join( threadA, NULL );
    pthread_join( threadB, NULL );

    return 0;
}


void *threadMainA( void *arg )
{
    while( 1 )
    {
        pthread_mutex_lock( &mutexA );
        gSharedCounter++;
        cerr << "Thread A: " << gSharedCounter << endl;
        delay( int(arg) );
        pthread_mutex_unlock( &mutexB );
    }

    return NULL;
}


void *threadMainB( void *arg )
{
    while( 1 )
    {
        pthread_mutex_lock( &mutexB );
        gSharedCounter--;
        cerr << "Thread B: " << gSharedCounter << endl;
        delay( int(arg) );
        pthread_mutex_unlock( &mutexA );
    }

    return NULL;
}


void delay( int limit )
{
    for( int j=0; j < limit; j++ )
    {
        for( int k=0; k < limit; k++ )
        {
        }
    }
}