[Wlug] C gurus

11 Aug 2004

      For all you C gurus out there.  I'm working on a little program that
when an event occurs, it dials out a Verizon Wireless AirCard, does
it's thing and then when all events are done, the last event close the
card.  To close the ppp connection you send it a Ctrl-C, which I'm
doing, however it is never working.  The code I'm using is as follows:

void *sound_alarm ( void * rd_struct )
{
	RADSPY_STRUCT *ptr_rd_struct;
	ptr_rd_struct = ( RADSPY_STRUCT * ) rd_struct;
	/* lock the modem_in_use variable to check to dial modem */
	pthread_mutex_lock ( &modem_mutex );
	if ( modem_in_use++ == 0 )
	{
		/* we need to dial out the modem */
		printf ( "Dialing the modem: %d\n", modem_in_use );
		modem_pid = fork();
		if ( 0 == modem_pid )
		{
			int ret;
			/* we are the child so dial out the modem */
			ret = execl ( "/usr/sbin/pppd", "pppd", "call", "ac555qnc", NULL );
			if ( -1 == ret )
				printf ( "Problem dialing modem: %s\n", strerror ( errno ) );
			printf ( "Got here.\n" );
			exit ( 0 );
		}
		/* hack to wait enough time to let the modem dial */
		sleep ( 10 );
	}
	pthread_mutex_unlock ( &modem_mutex );
	/* perform the sending of the data */
	printf ( "Sounding the alarm: %d.\n", modem_in_use );
	sleep ( 1 );           /* code to send away alarms will go here,
sleep for now */
	/* release the modem in use */
	pthread_mutex_lock ( &modem_mutex );
	if ( --modem_in_use == 0 )
	{
		/* we need to hangup the modem */
		printf ("Hanging up the modem: %d\n", modem_in_use );
		kill ( SIGINT, modem_pid );
	}
	pthread_mutex_unlock ( &modem_mutex );

	pthread_exit ( (void *) 0 );
}

This function is a thread that is spawned by the main loop when an
event occurs.  This event can occur multiple times, which is why I
have the shared variable of how many events are currently occuring
(modem_in_use).  When I run this program, I'm always getting an error
about the modem being locked by pid XXX, so it's never being closed. 
Anyone have any experience with this kinda thing?

Chuck

-- 
Chuck Haines
chaines@gmail.com
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WPI Class of 2005
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