ack/lang/occam/lib/channel.c

/* $Header$ */
/*	channel.c - basic channel handling routines */
#include <errno.h>
#include <signal.h>
#define __CHANNEL__
#ifdef __USG
#include <termio.h>
#else
#include <sgtty.h>
#endif
#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];
#ifdef __USG
		struct termio tty;
#else
		struct sgttyb tty;
#endif

		if ((v& ~0xff)==0)	/* Plain character */
			putc( (int) v, fp);
		else
		if (v==C_F_TEXT) {
#ifdef __USG
			ioctl(fileno(fp), TCGETA, &tty);
			tty.c_oflag |= (ONLCR);
			tty.c_iflag |= (ICRNL);
			tty.c_cc[VMIN] = 1;
			tty.c_cc[VTIME] = 0;
			tty.c_lflag |= (ECHO|ICANON);
			ioctl(fileno(fp), TCSETA, &tty);
#else
			gtty(fileno(fp), &tty);
			tty.sg_flags&= ~CBREAK;
			tty.sg_flags|= ECHO|CRMOD;
			stty(fileno(fp), &tty);
#endif
		} else
		if (v==C_F_RAW) {
#ifdef __USG
			ioctl(fileno(fp), TCGETA, &tty);
			tty.c_oflag &= ~(ONLCR);
			tty.c_iflag &= ~(ICRNL);
			tty.c_cc[VMIN] = 1;
			tty.c_cc[VTIME] = 0;
			tty.c_lflag &= ~(ECHO|ICANON);
			ioctl(fileno(fp), TCSETA, &tty);
#else
			gtty(fileno(fp),&tty);
			tty.sg_flags|= CBREAK;
			tty.sg_flags&= ~(ECHO|CRMOD);
			stty(fileno(fp), &tty);
#endif
		}
	}	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;
{
#ifdef __BSD4_2
#include <fcntl.h>
#ifndef O_NDELAY
#define O_NDELAY FNDELAY
#endif
	int flags;
#endif
	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 */

				/* Unfortunately, the mechanism that was used
				   here does not work on all Unix systems.
				   On BSD 4.2 and newer, the "read" is 
				   automatically restarted. Therefore, on
				   these systems, we try it with non-blocking
				   reads
				*/
#ifdef __BSD4_2
				flags = fcntl(fileno(fp), F_GETFL, 0);
				fcntl(fileno(fp), F_SETFL, flags | O_NDELAY);
				errno = 0;
				ch = getc(fp);
				fcntl(fileno(fp), F_SETFL, flags);
				if (errno == EWOULDBLOCK) {
					clearerr(fp);
					return 0;
				}
#else
				signal(SIGALRM, timeout);
				alarm(1);

				errno=0;
				ch=getc(fp);

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

				if (errno==EINTR) {
					clearerr(fp);
					return 0;
				}
#endif
				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();
}