[gecode-users] Propagator

[Jan Kelbel]

Hi Christian,

thank you for the answer. From the things you described (and I already 
tried, though I not really knew what it is doing), it must be something 
else. The propagator has one array created in propagate() method using 
Region allocator, that should be freed automatically when the 
propagate() returns, and one SharedArray that is shared among all the 
copies of one propagator.

Regards, Jan


Christian Schulte napsal(a):
> 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
> 
> 
> 
> 
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