path: root/comm/Scheduler.cc

/*
 *	Ivy League
 *
 *	Channel sets, or multiplexers, or schedulers
 *
 *	Copyright 1990-2000
 *	Laboratoire de Recherche en Informatique (LRI)
 *	Centre d'Etudes de la Navigation Aerienne (CENA)
 *
 *	original code by Michel Beaudouin-Lafon,
 *	heavily modified by Stephane Chatty and Stephane Sire
 *
 *	$Id$
 *
 */

#include "Scheduler.h"
#include "TimeOut.h"
#include "SignalHandler.h"

#include <signal.h>	// for NSIG
#include <sys/errno.h>
#include <sys/time.h>
#include <sys/socket.h>

#include <stdlib.h>
#include <stdio.h>
#include <memory.h>
#include <setjmp.h>

#if defined(__hpux) && !defined(__GNUG__)
#define FD_SET_TYPE(x) ((int*) x)
#else
#define FD_SET_TYPE(x) (x)
#endif

#ifdef __osf__
extern "C" int select (int, fd_set*, fd_set*, fd_set*, struct timeval*);
#endif

extern int errno;

IvlBaseScheduler* IvlScd = 0;

#ifndef FD_SET
#ifndef NFDBITS
#define	FD_SET(n, p)	((p)->fds_bits[0] |= (1 << (n)))
#define	FD_CLR(n, p)	((p)->fds_bits[0] &= ~(1 << (n)))
#define	FD_ISSET(n, p)	((p)->fds_bits[0] & (1 << (n)))
#define	FD_ZERO(p)	((p)->fds_bits[0] = 0)
#else
#define	FD_SET(n, p)	((p)->fds_bits[(n)/NFDBITS] |= (1 << ((n) % NFDBITS)))
#define	FD_CLR(n, p)	((p)->fds_bits[(n)/NFDBITS] &= ~(1 << ((n) % NFDBITS)))
#define	FD_ISSET(n, p)	((p)->fds_bits[(n)/NFDBITS] & (1 << ((n) % NFDBITS)))
#define	FD_ZERO(p)	memset((char *)(p), 0, sizeof(*(p)))
#endif
#endif

/*?class IvlBaseScheduler
Schedulers make it possible to handle several communication channels at the
same time; their implementation is based on the Unix \com{select} system call
or similar mechanisms. Schedulers are also able to implement safe (ie. not
interruption-based) timers and signal handlers.

Some of the channels in the set are active, others can be inactive.  A
multiplexer can be scanned so that the functions \fun{HandleRead} and
\fun{HandleWrite} are called for every active channel that is ready to
read or write.

If a channel needs to perform a background task or buffer input/output,
it can add a hook on the multiplexer with \fun{AddHook} which will be
called before actually scanning. For example that's the case for a connection
with the X server, when some pending events have been buffered into the
client by the previous \fun{HandleRead} call and need to be processed.

Schedulers may have different implementations, depending on the
environment.  When no other library is involved, they are simply
implemented on top of Unix.  But if \uch\ channels have to be mixed
with the X Toolkit for instance, the implementation uses the
mechanisms provided by the X Toolkit to add new channels.  The same
holds for Tcl/Tk or other environments. Every such implentation
corresponds to a derived class of \typ{IvlBaseScheduler}, which
offers a uniform interface that hides the implementation
differences. See the class \typ{IvlScheduler} for a ``pure \uch''
implementation of multiplexers.

Note that the functions that take an integer file descriptor as
argument can be passed a \typ{IvlFd} or a \typ{IvlChannel} because
the corresponding conversion operators are defined.

The way to Add/Remove a channel from a multiplexer is to call
\fun{Add} and \fun{Remove} of the channel with the multiplexer as an
argument for the first one.

?*/

/*?
Create an empty channel set.
?*/
IvlBaseScheduler :: IvlBaseScheduler ()
: IvlBaseMultiplexer (),
  Channels (new (IvlChannel*) [NFILE]),
  Timers (),
  ReadCount (0),
  WriteCount (0),
  SelectCount (0),
  SigFired (false),
  Handlers (new IvlBaseScheduledHandler* [NSIG]),
  NbSignals (new int [NSIG])
{	
	memset (Handlers, 0, NSIG * sizeof (IvlBaseScheduledHandler*));
	memset (NbSignals, 0, NSIG * sizeof (int));
	memset (Channels, 0, NFILE * sizeof (IvlChannel*));
}

/*?nodoc?*/
IvlBaseScheduler :: ~IvlBaseScheduler ()
{
#ifdef CPLUS_BUG4
	delete [NFILE] Channels;
	delete [NSIG] NbSignals;
	delete [NSIG] Handlers;
#else
	delete [] Channels;
	delete [] NbSignals;
	delete [] Handlers;
#endif
	Channels = 0;
}

/*?
This array operator returns a pointer to the channel corresponding to file descriptor \var{fd}.
If there is no such channel in this channel set, the operator returns NIL.
?*/
IvlChannel*
IvlBaseScheduler :: operator [] (int fd)
{
	return (fd < 0 || fd >= NFILE) ? 0 : Channels [fd];
}

/*?
Add a channel to the multiplexer. No copy is made by this
function.  If a channel with the same file descriptor as the one being
added is already in the set, the old channel is first removed. That
means that for a given file descriptor, there can be only one channel
working on it at a time.
?*/
bool
IvlBaseScheduler :: Add (IvlChannel* chan)
{
	int fd = chan->GetFd ();
	if (fd < 0 || fd >= NFILE)
		return false;
	IvlChannel* ochan = Channels [fd];
	if (ochan)
		ochan->Remove ();
	Channels [fd] = chan;
	SetMasks (fd, chan->IOMode ());
	return true;
}

/*?
Remove a channel from the set. This function can be passed a \var{IvlChannel}.
?*/
bool
IvlBaseScheduler :: Remove (int fd)
{
	if (fd < 0 || fd >= NFILE)
		return false;
	IvlChannel* ch = Channels [fd];
	if (ch) {
		SetMasks (fd, IONone);
		Channels [fd] = 0;
	}
	return true;
}

/*?
Remove all channels from this channel set.
This function calls \fun{Remove} for all channels of the set.
This is a way of exiting from \fun{LoopScan}.
?*/
void
IvlBaseScheduler :: RemoveAll ()
{
	for (int fd = 0; fd < NFILE; fd++) {
		IvlChannel* ch = Channels [fd];
		if (ch) 
			ch->Remove ();    // Calls IvlBaseMultiplexer::Remove
	}
}

/*?
Change the mode of a channel in the set.
Mode \var{IONone} makes the channel inactive (without removing it).
This function can be passed a \var{IvlChannel}.
?*/
void
IvlBaseScheduler :: SetMode (int fd, IOMODE mode)
{
	if (fd < 0)
		return;
	
	SetMasks (fd, mode);
	Channels [fd] -> SetMode (mode);
}

/*!
This function is called by IvlScheduledHandlers when a signal is
received. It just stores the signal for future (and safe) handling.
!*/
/*?hidden?*/
void
IvlBaseScheduler :: HandleSignal (IvlBaseScheduledHandler& h)
{
	if (!SigFired)
		AddSignalHook ();
	SigFired = true;
	int sig = h.GetSignal () - 1;
	/* We have to work with arrays, because we are in a signal
	   handler, and we cannot use lists */
	Handlers [sig] = &h;
	NbSignals [sig]++;

}

/*!
This virtual function is called the first time when a signal is received by a
signal handler associated to the multiplexer. It makes it possible
to call implementation-dependant functions that defer the handling to
safer times.
!*/
/*
Does not need to be defined in IvlScheduler, because
they use the flag SigFired.
*/
/*?hidden?*/
void
IvlBaseScheduler :: AddSignalHook ()
{
}

/*!
This function triggers the handling of all deferred signals. It should be
called when \fun{AddSignalHook} has been called and the times are safe.
!*/
/*?hidden?*/
void
IvlBaseScheduler :: HandleDeferredSignals ()
{
	IvlSignalBlocker b (AllSigs);
	int c;
	for (int i = 0; i < NSIG; ++i)
		if (c = NbSignals [i]) {
			Handlers [i]->DeferredHandle (c);
			NbSignals [i] = 0;
			Handlers [i] = 0;
		}
}

/*?hidden?*/
void
IvlBaseScheduler :: SetMasks (int, IOMODE)
{
}

static jmp_buf reset_run;

class IvlMpxAborter : public IvlBaseScheduledHandler {
public:
	IvlMpxAborter (IvlBaseScheduler& m, int s) : IvlBaseScheduledHandler (m, s) {}
	void	DeferredHandle (int)	{ MyScd.Abort (); }
};

/*?
Run a multiplexer: make it repeatedly scan its channels, and take the
appropriate actions. This function will exit under a number of
circumstances, reflected by its return value.
\small
\begin{tabular}{ll}
\var{isMpxTerminated}&the method \fun{Close} has been called.\\
\var{isMpxEmpty}&there are no more channels in the set.\\
\var{isMpxAborted}&the method \fun{Abort} has been called,
or signals SIGINT or SIGTERM were received.\\
\var{isMpxError}&an error has occured.
\end{tabular}
?*/
MPX_RES
IvlBaseScheduler :: Run ()
{
	if (setjmp (reset_run))
		return isMpxAborted;

	IvlMpxAborter h1 (*this, SigTerm);
	IvlMpxAborter h2 (*this, SigInt);

	return Loop ();
}

/*?
Remove all channels from the multiplexer, thus stopping it if running.
?*/
void
IvlBaseScheduler :: Close ()
{
	RemoveAll ();
	Looping = false;
}

/*?
Stop the multiplexer, without cleaning it.
?*/
void
IvlBaseScheduler :: Abort ()
{
	if (Looping)
		longjmp (reset_run, 1);
}

/*?class IvlScheduler
The class \typ{IvlScheduler} is the default implementation of multiplexers,
used when there are no compatibility needs. For historical reasons, it offers
a number of additional methods.
?*/

/*?
Build an empty multiplexer.
?*/
IvlScheduler :: IvlScheduler ()
: IvlBaseScheduler (),
  TimeOut (-1),
  Looping (false),
  Hooks ()

{
	FD_ZERO (&ReadMask);
	FD_ZERO (&WriteMask);
	FD_ZERO (&SelectMask);
}

/*?nodoc?*/
IvlScheduler :: ~IvlScheduler ()
{
}

// update the masks when channel fd changes its mode
//
/*?hidden?*/
void
IvlScheduler :: SetMasks (int fd, IOMODE mode)
{
	if (mode & IORead) {
		if (! FD_ISSET (fd, &ReadMask)) {
			ReadCount++;
			FD_SET (fd, &ReadMask);
		}
	} else {
		if (FD_ISSET (fd, &ReadMask)) {
			FD_CLR (fd, &ReadMask);
			ReadCount--;
		}
	}
	
	if (mode & IOWrite) {
		if (! FD_ISSET (fd, &WriteMask)) {
			WriteCount++;
			FD_SET (fd, &WriteMask);
		}
	} else {
		if (FD_ISSET (fd, &WriteMask)) {
			FD_CLR (fd, &WriteMask);
			WriteCount--;
		}
	}
	
	if (mode & IOSelect) {
		if (! FD_ISSET (fd, &SelectMask)) {
			SelectCount++;
			FD_SET (fd, &SelectMask);
		}
	} else {
		if (FD_ISSET (fd, &SelectMask)) {
			FD_CLR (fd, &SelectMask);
			SelectCount--;
		}
	}
	
}

#if 0
/*?
This function calls the select handler of each channel of the set in select mode.
It returns true as soon as one select handler returns true,
else it returns false when the select handlers have been called.
?*/
bool
IvlScheduler :: HandleSelect ()
{
	int	fd, nfd;
	
	if (fd0 >= NFILE)
		fd0 = 0;
	for (fd = fd0++, nfd = SelectCount; nfd; (fd < NFILE) ? fd++ : (fd = 0)) {
		if (! FD_ISSET (fd, &SelectMask))
			continue;
		if (Channels [fd] -> HandleSelect ())
			return true;
		nfd--;
		if (! Looping)
			return false;
	}
	return false;
}

#endif

////// should add signal handling
////// Hooks are probably badly handled
////// Scan should disappear anyway. Only use is in Xtv.
/*?nextdoc?*/
int
IvlScheduler :: Scan (bool nointr, bool poll)
{
	fd_set rmsk, wmsk;
	int nfd, ret = -1;
	register int fd;
	struct timeval tv;
	struct timeval* timeout = 0;
	
	if (poll) {
		timeout = &tv;
		tv.tv_sec = tv.tv_usec = 0;
	}

	while (ret <= 0) {
		if (ReadCount == 0 && WriteCount == 0 && SelectCount == 0) {
			ExecHooks (true);
			return 0;
		}
		ExecHooks (false);
	
		rmsk = ReadMask;
		wmsk = WriteMask;

		/* let's fiddle with ret to skip select if we are late with timers */
		ret = -1;
		if (!poll && TimeOut != -1) {
			IvlTimeStamp now;
			Millisecond delay = TimeOut - now;
			/* if delay < 0, select is unhappy */
			if (delay < 0)
				ret = 0;
			tv.tv_sec = delay / 1000;
			tv.tv_usec = 1000 * (delay % 1000);
			timeout = &tv;
		}

		/* skipping select is a trick to avoid problems with timers. However,
		    something more general should be done to:
			- manage priorities (I'm not sure the current situation is sound)
			- handle situations when we are late.
		*/
		/* Call select, except if late with timers */
		if (ret != 0)
			ret = select (NFILE, FD_SET_TYPE(&rmsk),  FD_SET_TYPE(&wmsk), 0, timeout);

		/* Handle time out */
		if (ret == 0) {
			if (TimeOut != -1)
				/* Fire might be called without reason if polling is on. Too bad... */
				IvlCoreTimer::Fire (&Timers);
			else if (!poll)
				fprintf (stderr, "select returned 0 without reason!\n");
			return 0;

		/* Handle errors */
		} else if (ret < 0) {
			if (nointr && ret == -1 && errno == EINTR)
				continue;
			else {
				ExecHooks (true);
				return ret;
			}
		}
	}

	/* Finally, handle pending input and output */
	for (fd = 0, nfd = ret; nfd; fd++) {
		if (FD_ISSET (fd, &wmsk)) {
			nfd--;
			IvlChannel* ch = Channels [fd];
			if (ch)
				ch->HandleWrite ();
		}
		if (FD_ISSET (fd, &rmsk)) {
			nfd--;
			IvlChannel* ch = Channels [fd];
			if (ch)
				ch->HandleRead ();
		}
	}
	
	return ret;
}

/*?
Scan the channels in the set and call the channel's handlers.
First the select handler (\fun{IvlChannel::HandleSelect}) of each channel with mode
\var{IOSelect} is called.
If it returns true, \fun{Scan} exits immediately, while \fun{LoopScan} loops immediately.
If no select handler returns true, the system call \fun{select} is used to poll or
wait for the channels that are ready.
When the select returns normally, the write handlers \fun{HandleWrite} of the
channels in mode \var{IOWrite} that are ready to write are called, and 
the read handlers (\fun{HandleRead}) of the channels in mode \fun{IORead}
that are ready to read are called.
If \var{nointr} is true, ignore the interrupted system calls, else return an error
whenever the \fun{select} system call is interrupted.
If \var{poll} is true, the call is non-blocking, else it is blocking.
\fun{Scan} calls \fun{select} only once;
it returns -2 if a select handler returns, it returns 0 if the channel set has no active channels,
else it returns the return code of \fun{select}.
\fun{LoopScan} calls \fun{select} repeatedly until \var{Stop} is called, or
an error occurs, the channel set has no more active channel
This can occur because the select, read or write handler of a channel may remove
the channel or change its mode.
This is usually done when the read handler detects an end of file.
\fun{LoopScan} returns \var{isMpxEmpty} when there are no more active channel in the set,
it returns \var{isMpxError} when an error occured (the code is in \var{errno}),
and it returns \var{isMpxTerminated} if \fun{Stop} or \fun{Close} was called.
?*/
MPX_RES
IvlScheduler :: LoopScan (bool nointr)
{
	fd_set rmsk, wmsk;
	register int nb_pending_fd, fd, fd0;
	Looping = true;

	for (fd0 = 0; Looping; fd0 < NFILE ? fd0++ : (fd0 = 0)) {
		
		/* First, handle signals */
		if (SigFired)
			HandleDeferredSignals ();

#if 0
		/* Then, timers */
		IvlCoreTimer::Fire (&Timers);
#endif	
		/* Then, check I/Os */
		if (ReadCount == 0 && WriteCount == 0 && SelectCount == 0) {
			ExecHooks (true);
			return isMpxEmpty;
		}

		/* Then other hooks */
		ExecHooks (false);

		/* Lets get ready for calling select: set masks and compute next time out.
		    We fiddle with nb_pending_fd to skip select if we are late with timers */
		nb_pending_fd = -1;
		rmsk = ReadMask;
		wmsk = WriteMask;
		struct timeval tv;
		struct timeval* timeout = 0;
		if (TimeOut != -1) {
			IvlTimeStamp now;
			Millisecond delay = TimeOut - now;
			if (delay < 0)
				nb_pending_fd = 0;
			tv.tv_sec = delay / 1000;
			tv.tv_usec = 1000 * (delay % 1000);
			timeout = &tv;
		}

		/* Call select, except if late with timers */
		if (nb_pending_fd != 0)
			nb_pending_fd = select (NFILE, FD_SET_TYPE(&rmsk), FD_SET_TYPE(&wmsk), 0, timeout);
		/* Handle time out */
		if (nb_pending_fd == 0) {
			if (TimeOut != -1)
				IvlCoreTimer::Fire (&Timers);
			else
				fprintf (stderr, "select returned 0 without reason!\n");
			continue;

		/* Handle errors */
		} else if (nb_pending_fd < 0) {
			if (nointr && nb_pending_fd == -1 && errno == EINTR)
				continue;
			else {
				ExecHooks (true);
				return isMpxError;
			}
		}

		/* Finally, handle pending input and output */
		for (fd = fd0; nb_pending_fd; (fd < NFILE) ? fd++ : (fd = 0)) {
			if (FD_ISSET (fd, &wmsk)) {
				nb_pending_fd--;
				Channels[fd]->HandleWrite ();
				if (! Looping) {
					ExecHooks (true);
					return isMpxTerminated;
				}
			}
			if (FD_ISSET (fd, &rmsk)) {
				nb_pending_fd--;
				Channels[fd]->HandleRead ();
				if (! Looping) {
					ExecHooks (true);
					return isMpxTerminated;
				}
			}
		}
	}

	ExecHooks (true);
	return isMpxTerminated;
}

/*?nodoc?*/
char*
IvlScheduler :: StrRepr (char* buf)
{
	sprintf (buf, "R:%ux W:%ux", ReadMask, WriteMask);
	return buf;
}

/*?hidden?*/
void
IvlScheduler :: SetTimeOut (Millisecond delay)
{
	IvlTimeStamp now;
	TimeOut = now + delay;
}

/*?hidden?*/
void
IvlScheduler :: SuppressTimeOut ()
{
	TimeOut = -1;
}

/*?hidden?*/
MPX_RES
IvlScheduler :: Loop ()
{
	return LoopScan ();
}

void
IvlScheduler :: Stop ()
{
	Looping = false;
}

void
IvlScheduler :: AddHook (IvlMpxHook* h, bool final)
{
	Hooks.Append ((void*) h);
	if (final)
		FinalHooks.Append ((void*) h);
}

void
IvlScheduler :: RemoveHook (IvlMpxHook* h, bool final)
{
	Hooks.Remove ((void*) h);
	if (final)
		FinalHooks.Remove ((void*) h);
}

void
IvlScheduler :: AddFinalHook (IvlMpxHook* h)
{
	FinalHooks.Append ((void*) h);
}

void
IvlScheduler :: RemoveFinalHook (IvlMpxHook* h)
{
	FinalHooks.Remove ((void*) h);
}

void
IvlScheduler :: ExecHooks (bool final)
{
	IvlList* hooks = final ? &FinalHooks : &Hooks;
	IvlListIter li = *hooks;
	while (++li) {
		IvlMpxHook* h = (IvlMpxHook*) *li;
		(*h)();
	}
}

void
IvlOpen (IvlBaseScheduler* m)
{
	IvlScd = m ? m : new IvlScheduler;
	IvlMpx = IvlScd;
}

#if 0 /* rendu inutile par la fusion avec DNN ? */
MPX_RES
IvlLoop ()
{
	return IvlScd->Loop ();
}

void
IvlStop ()
{
	IvlScd->Stop ();
}
#endif