ack/lang/occam/lib/channel.c

/*	channel.c - basic channel handling routines */
#include <errno.h>
#include <signal.h>
#include <sgtty.h>
#include "ocm_chan.h"

static void disaster();

void c_init(c, z) register chan *c; register unsigned z;
/* Initialise an array of interprocess channels declared as: CHAN c[z]. */
{
	do {
		c->type=C_T_CHAN;
		(c++)->c.synch=C_S_FREE;
	} while (--z!=0);
}

void chan_in(v, c) long *v; register chan *c;
/* Reads a value from channel c and returns it through v. */
{
	switch(c->type) {
	case C_T_FILE:
		if ((c->f.flgs&C_F_READAHEAD)!=0) {
			*v=(c->f.preread&0377);
			c->f.flgs&= ~C_F_READAHEAD;
		} else {
			register FILE *fp= unix_file[c->f.index];

			*v= feof(fp) ? C_F_EOF : getc(fp);
		}
		break;
	case C_T_CHAN:
		deadlock=0;		/* Wait for value to arrive */
		while (c->c.synch!=C_S_ANY) resumenext();

		*v=c->c.val;
		c->c.synch=C_S_ACK;	/* Acknowledge receipt */
		break;
	default:
		disaster();
	}
}

void chan_out(v, c) long v; register chan *c;
/* Send value v through channel c. */
{
	switch(c->type) {
	case C_T_FILE: {
		register FILE *fp= unix_file[c->f.index];
		struct sgttyb tty;

		if ((v& ~0xff)==0)	/* Plain character */
			putc( (int) v, fp);
		else
		if (v==C_F_TEXT) {
			gtty(fileno(fp), &tty);
			tty.sg_flags&= ~CBREAK;
			tty.sg_flags|= ECHO|CRMOD;
			stty(fileno(fp), &tty);
		} else
		if (v==C_F_RAW) {
			gtty(fileno(fp), &tty);
			tty.sg_flags|= CBREAK;
			tty.sg_flags&= ~(ECHO|CRMOD);
			stty(fileno(fp), &tty);
		}
	}	break;
	case C_T_CHAN:
		deadlock=0;		/* Wait until channel is free */
		while (c->c.synch!=C_S_FREE) resumenext();

		c->c.val=v;
		c->c.synch=C_S_ANY;	/* Channel has data */

		deadlock=0;		/* Wait for acknowledgement */
		while (c->c.synch!=C_S_ACK) resumenext();

		c->c.synch=C_S_FREE;	/* Back to normal */
		break;
	default:
		disaster();
	}
}

static int timeout();

int chan_any(c) register chan *c;
{
	switch (c->type) {
	case C_T_FILE:
		if ((c->f.flgs&C_F_READAHEAD)!=0)
			return 1;
		else {
			register FILE *fp= unix_file[c->f.index];
			
			if (feof(fp))
				return 1;
			else {
				extern int errno;
				register ch;

				deadlock=0;
					/* No deadlock while waiting for key */

				signal(SIGALRM, timeout);
				alarm(1);

				errno=0;
				ch=getc(fp);

				signal(SIGALRM, SIG_IGN);
				alarm(0);

				if (errno==EINTR)
					return 0;
				else {
					if (!feof(fp)) {
						c->f.flgs|=C_F_READAHEAD;
						c->f.preread=ch;
					}
					return 1;
				}
			}
		}
	case C_T_CHAN:
		return c->c.synch==C_S_ANY;
	default:
		disaster();
	}
}

/* The ch=getc(fp) in the above function calls read(2) to do its task, but if
 * there's no input on the file (pipe or terminal) then the read will block.
 * To stop this read from blocking, we use the fact that if the read is
 * interrupted by a signal that is caught by the program, then the read returns
 * error EINTR after the signal is processed. Thus we use a one second alarm
 * to interrupt the read with a trap to timeout(). But since the alarm signal
 * may occur *before* the read is called, it is continuously restarted in
 * timeout() to prevent it from getting lost.
 */

static int timeout(sig)
{
	signal(SIGALRM, timeout);
	alarm(1);
}

static void disaster()
{
	write(2, "Fatal error: Channel variable corrupted\n", 40);
	abort();
}