//-------------------------------------------------------------------
//	pipedemo.cpp
//
//	This program illustrates use of asynchronous notification to
//	signal a parent-process that some new data from its child is 
//	now ready to be read from one of its open input-pipes.   
//
//	programmer: ALLAN CRUSE
//	written on: 27 APR 2005
//-------------------------------------------------------------------

#include <stdio.h>	// for printf(), perror() 
#include <fcntl.h>	// for open() 
#include <stdlib.h>	// for exit() 
#include <unistd.h>	// for read(), write(), close() 
#include <signal.h>	// for sigaction()
#include <string.h>	// for strlen()
#include <sys/fcntl.h>	// for fcntl()

int done = 0;

void my_sigaction( int signo, siginfo_t *info, void *data )
{
	if ( signo == SIGCHLD ) done = 1; 
	else	if ( signo != SIGUSR1 ) return;

	char	inbuf[ 128 ] = {0};
	int	nbytes = read( info->si_fd, inbuf, sizeof( inbuf )-1 );
	if ( nbytes < 0 ) return; 
	if ( !done ) printf( "received from %d: %s \n", info->si_fd, inbuf );
}


int main( int argc, char **argv )
{
	// create the pair of pipes and the child-process
	int	fd1[2], fd2[2];
	pipe( fd1 ); pipe( fd2 );
	int	pid = fork();

	if ( pid == 0 ) 
		{
		// this is the child process
		close( fd1[0] ); close( fd2[0] ); sleep( 2 );

		char	msg1[] = " Hello ";
		write( fd1[1], msg1, strlen( msg1 ) ); sleep( 1 );
		write( fd2[1], msg1, strlen( msg1 ) ); sleep( 1 );
	
		char	msg2[] = " Goodbye ";
		write( fd1[1], msg2, strlen( msg2 ) ); sleep( 1 );
		write( fd2[1], msg2, strlen( msg2 ) ); sleep( 1 );

		exit( 0 );
		}

	// this is the parent-process	
	close( fd1[1] );
	close( fd2[1] );
	
	// install signal-handler for SIGUSR1
	struct sigaction	oa, sa = {0};
	sigemptyset( &sa.sa_mask );
	sa.sa_flags = SA_SIGINFO;
	sa.sa_sigaction = my_sigaction;
	sigaction( SIGUSR1, &sa, &oa );
	sigaction( SIGCHLD, &sa, &oa );

	// specify that parent-process receives the notifications
	fcntl( fd1[0], F_SETOWN, getpid() );
	fcntl( fd2[0], F_SETOWN, getpid() );
	
	// enable anynchronous notification for these input-pipes
	fcntl( fd1[0], F_SETFL, fcntl( fd1[0], F_GETFL )|FASYNC );
	fcntl( fd2[0], F_SETFL, fcntl( fd2[0], F_GETFL )|FASYNC );

	// specify the signal-number for the input-notifications	
	fcntl( fd1[0], F_SETSIG, SIGUSR1 );
	fcntl( fd2[0], F_SETSIG, SIGUSR1 );

	// main loop to wait for the SIGCHLD signal
	while ( !done ) pause();

	// restore the original signal-handler for SIGUSR1 and quit
	sigaction( SIGUSR1, &oa, NULL );	
	printf( "now parent is quitting\n" );
	exit( 0 );
}