path: root/utils/Timer.cc

/*
 *	CENA C++ Utilities
 *
 *	by Stephane Chatty
 *
 *	Copyright 1992
 *	Centre d'Etudes de la Navigation Aerienne (CENA)
 *
 *	timers
 *
 *	$Id$
 *	$CurLog$
 */

#include "Timer.h"
#include "Signal.h"
#include "List.h"

#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <sys/wait.h>
#include <sys/time.h>

/*?class CcuBaseTimer
The class \typ{CcuBaseTimer} is provided as a base class for timers.
It comes with a derived class \typ{CcuTimer} that can immediately be used.
A timer is created with a period expressed in milliseconds. It will then
periodically call the member function \fun{Handle}, which should be redefined
in derived classes.

Please note that timers use the signal \var{SIGALRM} and the interval timers
provided by UNIX.
Using them concurrently with system calls such as \fun{sleep} yields
unexpected results.

The member function \fun{Handle} has a time parameter: it is passed the
current (absolute) time when the signal was received from the system. However,
several timers may be triggered at the same time.
If one of them has a slow \fun{Handle}, the time passed to the next ones no more
corrresponds to the current time. If you want to know the exact time, and you are
not sure of the behaviour of the other timers, it is preferable to use a \typ{CcuTimeStamp}.
?*/

/*!class CcuBaseTimer
The implementation of CcuBaseTimer is a bit tricky, because it tries to be fast.
Here is the basic idea: active timers are stored in a list, sorted by increasing time-out
times. When a signal occurs, all timers whose time-out time is smaller than the current
time are notified and removed from the list, then they are inserted again.
Then, the optimizations. First, we distinguish the first active timer from the others.
It is not in the list, but has a pointer of its own. Second, we do not remove timers
from the list when they are stopped, but rather flag them as inactive. It means that
we have to test a flag when extracting timers from the list. It also means that we can
have many occurences of the same timer in the list, only one being in the right place.
Even worse, when such a timer is inserted again in the list, there is no way of knowing
that the other occurences are wrong: it is the same object, and it no longer flagged as
inactive. However, if we remove all encountered inactive timers when inserting one,
and if we make sure that a timer is flagged as inactive when we insert it, all wrong
occurences before the right one will be removed. 
!*/

CcuSignalHandler* CcuBaseTimer::TimeOutHandler = 0;
CcuBaseTimer* CcuBaseTimer::FirstActive = 0;
#ifndef CPLUS_BUG19
CcuListOf <CcuBaseTimer>* CcuBaseTimer::OtherActive = 0;
#else
CcuList* CcuBaseTimer::OtherActive = 0;
#endif

/*?nodoc?*/
void
CcuBaseTimer :: ClassInit ()
{
	TimeOutHandler = new CcuSignalHandler (SigAlrm, &CcuBaseTimer::HandleSignal);
#ifndef CPLUS_BUG19
	OtherActive = new CcuListOf <CcuBaseTimer>;
#else
	OtherActive = new CcuList;
#endif
}

/*?hidden?*/
void
CcuBaseTimer :: StopAlarm ()
{
	struct itimerval itval;
	timerclear (&itval.it_value);
	timerclear (&itval.it_interval);
	setitimer (ITIMER_REAL, &itval, 0);
}

/*?hidden?*/
void
CcuBaseTimer :: SetAlarm (Millisecond delay)
{
	if (delay <= 0) {
		StopAlarm ();
		kill (getpid (), SigAlrm);
		return;
	}

	struct itimerval itval;
	timerclear (&itval.it_interval);
	itval.it_value.tv_sec = delay / 1000;
	itval.it_value.tv_usec = 1000 * (delay % 1000);
	setitimer (ITIMER_REAL, &itval, 0);
}

/*!
Remove and return the first active timer in the active timer list.
Timers in that list can actually be inactive.
!*/
/*?hidden?*/
CcuBaseTimer*
CcuBaseTimer :: ExtractNextActive ()
{
	CcuBaseTimer* t;

	/* all entries of OtherActive are valid pointers,
	    hence t == 0 iff OtherActive is empty */
#ifndef CPLUS_BUG19
	while ((t = OtherActive->RemoveFirst ()) && (t->Status != Active))
#else
	while ((t = (CcuBaseTimer*) OtherActive->RemoveFirst ()) && (t->Status != Active))
#endif
		;
	return t;
}

#ifndef CPLUS_BUG19

/*?hidden?*/
int
CcuBaseTimer :: IsInactive (CcuBaseTimer* t)
{
	return (t->Status != Active);
}

#else

/*?hidden?*/
int
CcuBaseTimer :: IsInactive (CcuListItem* t)
{
	return (((CcuBaseTimer*) t)->Status != Active);
}

#endif	/* CPLUS_BUG19 */


/*!
This function is called by the signal handler. The first active timer is expired
and scheduled again. Then all the timers whose expiration time is earlier
that the current time are removed from the list, expired and scheduled again.
The first non-expired timer, if any, is removed from the list and saved 
as the first active timer. 
Finally, the alarm is set up to expire at the expiration time of the new first
active timer.
!*/
/*?hidden?*/
void
CcuBaseTimer :: HandleSignal (int)
{
	CcuTimeStamp now;

	/* Handle the first timer */
	FirstActive->Reschedule ();
	FirstActive->Handle (now);

	/* handle all other expired timers. */
	CcuBaseTimer* t;
	while (t = ExtractNextActive ()) {
		/* Problem : if one Handle () is long, "now"  will then be wrong. */
		if (t->NextDate > now)
			break;
		t->Reschedule ();
		t->Handle (now);
	}

	CcuTimeStamp then;	
	if (t)
		SetAlarm (t->NextDate - then);


	FirstActive = t;
}


/*?
Create a timer that will send a signal every \var{period} milliseconds, \var{pulses} times.
If \var{pulses} is negative, the timer will send signals forever.
Timers are activated at creation time. They are disactivated, but not destroyed, after
their last signal.
?*/
CcuBaseTimer :: CcuBaseTimer (Millisecond period, int pulses)
: Status (Active),
  Period (period),
  PulsesLeft (pulses)
{
	CcuSignalBlocker b (SigAlrm);

	if (!TimeOutHandler)
		ClassInit ();
	if (PulsesLeft != 0)
		Activate ();
}


/*?hidden?*/
CcuBaseTimer :: ~CcuBaseTimer ()
{
	/* stop it */
	if (Status == Active)
		Stop ();

	/* Remove all entries pointing to inactive timers, including this one */
	OtherActive->Remove (IsInactive, CcuList::All);
}

/*?
Change the period of a timer. The new period will not be taken into account
before the next time-out.
?*/
void
CcuBaseTimer :: ChangePeriod  (Millisecond period)
{
	CcuSignalBlocker b (SigAlrm);
	Period = period;
}

/*?
Stop this timer if it was running, then start it with its current period.
This function can be used to reset a timer to the beginning of a period.
?*/
void
CcuBaseTimer :: Restart ()
{
	if (PulsesLeft == 0)
		return;

	/* this function could be optimized: sometimes SetAlarm is called twice. */
	CcuSignalBlocker b (SigAlrm);
	if (Status == Active)
		Stop ();
	Activate ();
}

/*!
This function sets up a timer that was previously inactive.
The timer is inserted in the list of active timers, and if it is the
first one, the alarm is updated.
!*/
/*?hidden?*/
void
CcuBaseTimer :: Activate ()
{
	CcuTimeStamp now;
	NextDate = now + Period;
	
	if (!FirstActive) {
		FirstActive = this;
		SetAlarm (Period);
	} else if (NextDate < FirstActive->NextDate ) {
		SetAlarm (Period);
		OtherActive->Prepend (FirstActive);
		FirstActive = this;
	} else
		Schedule (NextDate);
	Status = Active;
}

/*?hidden?*/
void
CcuBaseTimer :: Reschedule ()
{
	if (PulsesLeft == 0)	// this should not happen...
		return;

	if (PulsesLeft > 0)
		if (--PulsesLeft == 0)
			return;

	Schedule (NextDate + Period);
}

/*?hidden?*/
void
CcuBaseTimer :: Schedule (Millisecond when)
{
	NextDate = when;

	/* temporarily set status to inactive so that obsolete entries
	    in OtherActive pointing to this timer can be removed */
	Status = Inactive;

#ifndef CPLUS_BUG19
	CcuListIterOf <CcuBaseTimer> li (*OtherActive);
	CcuListIterOf <CcuBaseTimer> lj (*OtherActive);
#else
	CcuListIter li (*OtherActive);
	CcuListIter lj (*OtherActive);
#endif

	while (++li) {
		/* while we're at it, remove inactive timers from the list */
#ifndef CPLUS_BUG19
		CcuBaseTimer* cur = *li;
#else
		CcuBaseTimer* cur = (CcuBaseTimer*) *li;
#endif
		if (cur->Status != Active) {
			OtherActive->RemoveAfter (lj);
			li = lj;
		} else if (cur->NextDate < NextDate)
			++lj;
		else
			break;
	}
	OtherActive->InsertAfter (lj, this);
	Status = Active;
}

/*?
Stop a timer.
This timer will not deliver any signal until \fun{Restart} is called.
?*/
void
CcuBaseTimer :: Stop ()
{
	if (Status != Active)
		return;

	CcuSignalBlocker b (SigAlrm);
	
	Status = Inactive;

	/* if this timer was the first active one, find another one to replace it */
	if (this == FirstActive) {
		FirstActive = ExtractNextActive ();
		if (FirstActive == 0)
			StopAlarm ();
		else {
			CcuTimeStamp now;
			SetAlarm (FirstActive->NextDate -now);
		}
	}
}

/*?
Wait for this timer to expire. If it is stopped, return immediately.
?*/
void
CcuBaseTimer :: Wait ()
{
	if (Status != Active)
		return;

	Millisecond next_date = NextDate;
	for (;;) {
		if (wait (0) >= 0)	// not an interrupt
			continue;
		if (Status != Active || next_date != NextDate)
			return;
	}
}

/*?hidden?*/
void
CcuBaseTimer :: Handle (Millisecond)
{
}

/*?class CcuTimer
The class \typ{CcuTimer} is a derived class of \typ{CcuBaseTimer} that
can be used without deriving a new class.
Each \typ{CcuTimer} holds a pointer to a function which is called when the timer
expires. This function, which is passed to the constructor, must
take a \typ{Millisecond} argument and return \typ{void}.
?*/

/*?
Create a timer that will expire every \var{period} milliseconds and call
the function \var{handler}.
?*/
CcuTimer :: CcuTimer (Millisecond period, void (*handler) (Millisecond), int pulses)
: CcuBaseTimer (period, pulses),
  Handler (handler)
{
}

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

/*?nodoc?*/
void
CcuTimer :: Handle (Millisecond ref)
{
	(*Handler) (ref);
}