[gecode-users] Propagator

[Christian Schulte]

Hi Jan,

there are the following catches:

a) propagators do not use destructors. Instead, when a propagator is
deleted, the dispose function is called. That in particular implies that for
any member of your propagator you have to explicitly call the member's
destructor (that is something that is done automatically inside a destructor
but not in the dispose function).

b) most likely you are under the assumption that when a space containing
your propagator is deleted, the dispose method of the propagator is called
such that memory possibly allocated by your propagator is freed. That is not
the case. In case your propagator requires the dispose method to be called
when a space is deleted, the propagator must register itself with its space
for deletion. For example, when home refers to the space, you have to
register the propagator by
	home.notice(*this, AP_DISPOSE);
and consequently in the dispose function you have to deregister
	home.ignore(*this, AP_DISPOSE);

The only exception is if your propagator has only allocated memory from the
space but not via malloc or something else. Then it does not be deleted when
its space is deleted.

Then, the behaviour you describe must have to do with something else as
there is really nothing special happening for NaryPropagator. Maybe you
could check your code again.

I think you are referring to the Gecode 2.* implementation of the
cumulatives propagator. That was actually nonsensical and has been changed
in 3.*. If no variables are modified by a propagator and the propagator says
ES_NOFIX, Gecode still knows that nothing has changed. So finding out
whether something has changed, and if yes reporting ES_NOFIX and ES_FIX
otherwise is exactly the same than reporting ES_NOFIX.

I hope that helps
Christian

--
Christian Schulte, www.ict.kth.se/~cschulte/


-----Original Message-----
From: users-bounces at gecode.org [mailto:users-bounces at gecode.org] On Behalf
Of Jan Kelbel
Sent: Monday, May 25, 2009 3:16 PM
To: users at gecode.org
Subject: [gecode-users] Propagator

Hello,

some months ago I implemented N-ary propagator (it is that edge-finder). 
When I used it to solve larger problem instances, I noticed that it 
consumes memory in rate of about 1MB/s.
I tested it in Gecode 2.2.0 (where it was even about 3MB/s) and in 
Gecode 3.1.0., using MS Visual C++ 2008.

This propagator is inherited from class NaryPropagator. In the propagate 
method, there is an array for sorting, which is created using the Region 
allocation.

When I changed the edge-finder to inherit directly from the class 
Propagator, the growing memory consumption disappeared.

My question is, are there some rules, what should be implemented in 
propagator inherited from NaryPropagator in order allocate/dealocate 
memory correctly?


My second question (set of questions) is related to Val propagator for 
cumulatives constrait, which is my study material for implementation of 
scheduling constraints.
1) in Val::propagate()  file cumulatives/val.hpp
at line 276 there is a test if all the variables are assigned. Is there 
a reason why in case of subsumed = true; the function ES_SUBSUMED() is 
called  as late as at line 386?

2) Why there is no ES_FIX return from the Val::propagate() method?
In the documentation is that when the propagator computes fixpoint, it 
should return ES_FIX.
Is the reason that checking whether fixpoint is reached is expensive, 
and the propagation scheduler arranges that the propagation is not 
executed too many times?

Thank you.

Regards, Jan




_______________________________________________
Gecode users mailing list
users at gecode.org
https://www.gecode.org/mailman/listinfo/gecode-users