Re: [Vala] use weak and var together
On Sat, 2009-01-10 at 23:48 +0100, Hans Vercammen wrote: Why do this manually? Don't you need to chain the dispose handlers throughout the hierarchy to make it usable somehow? As far as I understand the GObject dispose mechanism, it doesn't prevent the cyclic references from not being cleaned up. But it allows you to manually break them if they exist. Perhaps it would be a good idea to dispose the member references in the GObject dispose handler by default instead of the finalize handler. In this case the user could build a custom object management system on top of vala and call the dispose handler explicitly when required. Of course this could cause various side-effects when not used carefully. On the other hand so do raw pointers and preventing these memory leaks is as far as know only possible by using weak references. The issue is that freeing everything already in dispose is not always correct, it could lead to crashes if referenced objects access other objects while being disposed. However, dispose is available as a virtual method in Vala and overriding it should provide you with the means necessary to support the GObject dispose mechanism. When you make sure that there are no cycles by using weak references, this is not necessary. Jürg ___ Vala-list mailing list Vala-list@gnome.org http://mail.gnome.org/mailman/listinfo/vala-list
Re: [Vala] use weak and var together
On Sat, 2009-01-10 at 01:04 -0500, Yu Feng wrote: On Fri, 2008-12-12 at 08:08 +0100, Jürg Billeter wrote: On Thu, 2008-12-11 at 23:56 -0500, Yu Feng wrote: Talking about circular references, is it possible to have a circular ref breaker mechanism like the one in GTK for vala fundamental classes? I don't think we should always add a dispose mechanism to fundamental classes. However, if someone wants to use that, it should still be possible to implement this with a bit of extra Vala code. I suddenly realized it is impossible to write dispose mechanism with extra vala code because one can not override the hidden unref method, therefore one can not do the cycle detection/breaking at the right time. unref methods are never virtual in GObject. However, you can override the dispose method in Vala. Is this what you meant or can you explain what exactly you want to achieve? Jürg ___ Vala-list mailing list Vala-list@gnome.org http://mail.gnome.org/mailman/listinfo/vala-list
Re: [Vala] use weak and var together
On Sat, 2009-01-10 at 09:24 +0100, Jürg Billeter wrote: On Sat, 2009-01-10 at 01:04 -0500, Yu Feng wrote: On Fri, 2008-12-12 at 08:08 +0100, Jürg Billeter wrote: On Thu, 2008-12-11 at 23:56 -0500, Yu Feng wrote: Talking about circular references, is it possible to have a circular ref breaker mechanism like the one in GTK for vala fundamental classes? I don't think we should always add a dispose mechanism to fundamental classes. However, if someone wants to use that, it should still be possible to implement this with a bit of extra Vala code. I suddenly realized it is impossible to write dispose mechanism with extra vala code because one can not override the hidden unref method, therefore one can not do the cycle detection/breaking at the right time. unref methods are never virtual in GObject. However, you can override the dispose method in Vala. Is this what you meant or can you explain what exactly you want to achieve? No. We were talking about GTypeInstance fundamental classes in that mail. They don't have a 'dispose' method to be overriden. Jürg ___ Vala-list mailing list Vala-list@gnome.org http://mail.gnome.org/mailman/listinfo/vala-list
Re: [Vala] use weak and var together
On Sat, 2009-01-10 at 19:36 +0100, Jürg Billeter wrote:
On Sat, 2009-01-10 at 13:07 -0500, Yu Feng wrote:
On Sat, 2009-01-10 at 18:35 +0100, Jürg Billeter wrote:
Right, but I'm not sure that you need to change anything in the unref
function to get dispose functionality working. Can you explain more
specifically what you can't get working with the current possibilities?
Yes I can do this:
class Object {
Object ref_to_there;
Object ref_to_here;
private disposed = false;
public virtual void dispose() {
/*release references here*/
ref_to_there = null;
ref_to_here = null;
}
private void run_dispose() {
if(disposed) return;
disposed = true;
dispose();
}
public void destroy() {
Object holder = this;
/*needed if invoked from a weak reference of this*/
run_dispose();
holder = null;
}
}
Then Object.destroy can be used to manifestly break any cycle
references.
I was thinking about auto-cycle-breaking but it is unfortunately beyond
my knowledge.
Unfortunately, there is no magic trick to break reference cycles
automatically in a simple way. In general, this requires an additional
garbage or cycle collector which scans stack and heap.
Is it basically to maintain a list of all pointers to the object? With
some extension to vala compiler at AssignmentBinding perhaps we can have
this list at a relatively cheap cost without scanning stacks and heaps.
Jürg
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Re: [Vala] use weak and var together
In addition to keeping a list of pointers to the object, you'll need to
traverse them in some way to find cycles and free storage with cycles, but not
pointed to by any non-cycles. That pass should not be done every time you
break a pointer link because it can be very expensive, just as garbage
collection is. You could do it periodically, maybe every so many allocations
or so many seconds -- but if you do that, you've basically written a garbage
collector.
Remember that an object can be part of more than one cycle, and you have to
know how many of those refs are cyclic refs, and how many (if any) aren't
from cycles. That's non-local knowledge. What I'm saying is that it's not an
easy think to calculate, and there's a reason that garbage collectors tend to
be slow :-)
--- On Sat, 1/10/09, Yu Feng rainwood...@gmail.com wrote:
From: Yu Feng rainwood...@gmail.com
Subject: Re: [Vala] use weak and var together
To: Jürg Billeter j...@bitron.ch
Cc: vala-list@gnome.org
Date: Saturday, January 10, 2009, 12:45 PM
On Sat, 2009-01-10 at 19:36 +0100, Jürg Billeter wrote:
On Sat, 2009-01-10 at 13:07 -0500, Yu Feng wrote:
On Sat, 2009-01-10 at 18:35 +0100, Jürg Billeter
wrote:
Right, but I'm not sure that you need to
change anything in the unref
function to get dispose functionality
working. Can you explain more
specifically what you can't get working
with the current possibilities?
Yes I can do this:
class Object {
Object ref_to_there;
Object ref_to_here;
private disposed = false;
public virtual void dispose() {
/*release references here*/
ref_to_there = null;
ref_to_here = null;
}
private void run_dispose() {
if(disposed) return;
disposed = true;
dispose();
}
public void destroy() {
Object holder = this;
/*needed if invoked from a weak reference
of this*/
run_dispose();
holder = null;
}
}
Then Object.destroy can be used to manifestly
break any cycle
references.
I was thinking about auto-cycle-breaking but it
is unfortunately beyond
my knowledge.
Unfortunately, there is no magic trick to break
reference cycles
automatically in a simple way. In general, this
requires an additional
garbage or cycle collector which scans stack and heap.
Is it basically to maintain a list of all pointers to the
object? With
some extension to vala compiler at AssignmentBinding
perhaps we can have
this list at a relatively cheap cost without scanning
stacks and heaps.
Jürg
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Re: [Vala] use weak and var together
On Sat, 2009-01-10 at 13:07 -0500, Yu Feng wrote:
On Sat, 2009-01-10 at 18:35 +0100, Jürg Billeter wrote:
On Sat, 2009-01-10 at 12:19 -0500, Yu Feng wrote:
On Sat, 2009-01-10 at 09:24 +0100, Jürg Billeter wrote:
On Sat, 2009-01-10 at 01:04 -0500, Yu Feng wrote:
On Fri, 2008-12-12 at 08:08 +0100, Jürg Billeter wrote:
On Thu, 2008-12-11 at 23:56 -0500, Yu Feng wrote:
Talking about circular references, is it possible to have a
circular ref
breaker mechanism like the one in GTK for vala fundamental
classes?
I'm not very familiar with the inner workings. But don't they explicitly
destroy the objects instead of simply unreffing like vala does?
I don't think we should always add a dispose mechanism to
fundamental
classes. However, if someone wants to use that, it should still be
possible to implement this with a bit of extra Vala code.
I suddenly realized it is impossible to write dispose mechanism with
extra vala code because one can not override the hidden unref method,
therefore one can not do the cycle detection/breaking at the right
time.
unref methods are never virtual in GObject. However, you can override
the dispose method in Vala. Is this what you meant or can you explain
what exactly you want to achieve?
No. We were talking about GTypeInstance fundamental classes in that
mail. They don't have a 'dispose' method to be overriden.
Right, but I'm not sure that you need to change anything in the unref
function to get dispose functionality working. Can you explain more
specifically what you can't get working with the current possibilities?
Yes I can do this:
class Object {
Object ref_to_there;
Object ref_to_here;
private disposed = false;
public virtual void dispose() {
/*release references here*/
ref_to_there = null;
ref_to_here = null;
}
private void run_dispose() {
if(disposed) return;
disposed = true;
dispose();
}
public void destroy() {
Object holder = this;
/*needed if invoked from a weak reference of this*/
run_dispose();
holder = null;
}
}
Then Object.destroy can be used to manifestly break any cycle
references.
Why do this manually? Don't you need to chain the dispose handlers
throughout the hierarchy to make it usable somehow?
As far as I understand the GObject dispose mechanism, it doesn't prevent
the cyclic references from not being cleaned up. But it allows you to
manually break them if they exist.
Perhaps it would be a good idea to dispose the member references in the
GObject dispose handler by default instead of the finalize handler. In
this case the user could build a custom object management system on top
of vala and call the dispose handler explicitly when required. Of course
this could cause various side-effects when not used carefully. On the
other hand so do raw pointers and preventing these memory leaks is as
far as know only possible by using weak references.
Hans
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Re: [Vala] use weak and var together
On Sat, 2009-01-10 at 13:16 -0800, Noah Gibbs wrote: In addition to keeping a list of pointers to the object, you'll need to traverse them in some way to find cycles and free storage with cycles, but not pointed to by any non-cycles. That pass should not be done every time you break a pointer link because it can be very expensive, just as garbage collection is. You could do it periodically, maybe every so many allocations or so many seconds -- but if you do that, you've basically written a garbage collector. I agree. However, cyclic references are basically a trademark for reference counting. It's relatively fast and easy to implement, but you probably don't want use this in combination with a garbage collector as the reference count other than zero is of no meaning to the collector. Remember that an object can be part of more than one cycle, and you have to know how many of those refs are cyclic refs, and how many (if any) aren't from cycles. That's non-local knowledge. What I'm saying is that it's not an easy think to calculate, and there's a reason that garbage collectors tend to be slow :-) There are actually rather fast garbage collection algorithms out there. The main reason I can think of why they still appear to be slow is that in most cases they have to stop the world to do their processing. Hans ___ Vala-list mailing list Vala-list@gnome.org http://mail.gnome.org/mailman/listinfo/vala-list
Re: [Vala] use weak and var together
On Sun, 2009-01-11 at 01:23 +0100, Thomas Chust wrote: Hans Vercammen wrote: On Sat, 2009-01-10 at 13:16 -0800, Noah Gibbs wrote: [...] Remember that an object can be part of more than one cycle, and you have to know how many of those refs are cyclic refs, and how many (if any) aren't from cycles. That's non-local knowledge. What I'm saying is that it's not an easy think to calculate, and there's a reason that garbage collectors tend to be slow :-) There are actually rather fast garbage collection algorithms out there. The main reason I can think of why they still appear to be slow is that in most cases they have to stop the world to do their processing. [...] Hello, there are also real-time garbage collectors that never need to stop the program for more than a few microseconds and can run concurrently with the main program on a separate thread. Garbage collection isn't necessarily slow, if it's implemented well. The trick is to make the extra work happen concurrently with the main program and / or at convenient points in time. Especially if you have a lot of memory and can afford to just allocate objects, deferring cleanup until the main program is idle, garbage collection is usually faster than manual memory management or reference counting which incurs more calls to the allocator at inconvenient points in time. I'm not sure what the actual benefit would be that way. In general I would agree, but if you mean running the garbage collector in a different thread; it would imply more synchronization mechanisms, which would also slow down the process significantly. Not all programs have a main idle loop or are multi-threaded by default. The main idea of reference counting is to take care of the object life-cycle immediately without prosponing it to a different process/thread. Hans ___ Vala-list mailing list Vala-list@gnome.org http://mail.gnome.org/mailman/listinfo/vala-list
Re: [Vala] use weak and var together
On Sat, 2009-01-10 at 23:48 +0100, Hans Vercammen wrote:
On Sat, 2009-01-10 at 13:07 -0500, Yu Feng wrote:
On Sat, 2009-01-10 at 18:35 +0100, Jürg Billeter wrote:
On Sat, 2009-01-10 at 12:19 -0500, Yu Feng wrote:
On Sat, 2009-01-10 at 09:24 +0100, Jürg Billeter wrote:
On Sat, 2009-01-10 at 01:04 -0500, Yu Feng wrote:
On Fri, 2008-12-12 at 08:08 +0100, Jürg Billeter wrote:
On Thu, 2008-12-11 at 23:56 -0500, Yu Feng wrote:
Talking about circular references, is it possible to have a
circular ref
breaker mechanism like the one in GTK for vala fundamental
classes?
I'm not very familiar with the inner workings. But don't they explicitly
destroy the objects instead of simply unreffing like vala does?
Neither am I. GTKObject has a destroy signal to do the magic with
g_ojbect_run_dispose. Cycle references are automatically resolved. the
relavent code are in gtk/gtkobject.c but I didn't have time to study it
carefully.
I don't think we should always add a dispose mechanism to
fundamental
classes. However, if someone wants to use that, it should still be
possible to implement this with a bit of extra Vala code.
I suddenly realized it is impossible to write dispose mechanism with
extra vala code because one can not override the hidden unref
method,
therefore one can not do the cycle detection/breaking at the right
time.
unref methods are never virtual in GObject. However, you can override
the dispose method in Vala. Is this what you meant or can you explain
what exactly you want to achieve?
No. We were talking about GTypeInstance fundamental classes in that
mail. They don't have a 'dispose' method to be overriden.
Right, but I'm not sure that you need to change anything in the unref
function to get dispose functionality working. Can you explain more
specifically what you can't get working with the current possibilities?
Yes I can do this:
class Object {
Object ref_to_there;
Object ref_to_here;
private disposed = false;
public virtual void dispose() {
/*release references here*/
ref_to_there = null;
ref_to_here = null;
}
private void run_dispose() {
if(disposed) return;
disposed = true;
dispose();
}
public void destroy() {
Object holder = this;
/*needed if invoked from a weak reference of this*/
run_dispose();
holder = null;
}
}
Then Object.destroy can be used to manifestly break any cycle
references.
Why do this manually? Don't you need to chain the dispose handlers
throughout the hierarchy to make it usable somehow?
But this is not a GObject. It's about implementing two stage disposal
and ref breaking with GTypeInstance classes.
As far as I understand the GObject dispose mechanism, it doesn't prevent
the cyclic references from not being cleaned up. But it allows you to
manually break them if they exist.
Perhaps it would be a good idea to dispose the member references in the
GObject dispose handler by default instead of the finalize handler. In
this case the user could build a custom object management system on top
of vala and call the dispose handler explicitly when required. Of course
this could cause various side-effects when not used carefully. On the
other hand so do raw pointers and preventing these memory leaks is as
far as know only possible by using weak references.
Hans
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Re: [Vala] use weak and var together
On Sat, 2009-01-10 at 21:12 -0500, Yu Feng wrote:
On Sat, 2009-01-10 at 23:48 +0100, Hans Vercammen wrote:
On Sat, 2009-01-10 at 13:07 -0500, Yu Feng wrote:
On Sat, 2009-01-10 at 18:35 +0100, Jürg Billeter wrote:
On Sat, 2009-01-10 at 12:19 -0500, Yu Feng wrote:
On Sat, 2009-01-10 at 09:24 +0100, Jürg Billeter wrote:
On Sat, 2009-01-10 at 01:04 -0500, Yu Feng wrote:
On Fri, 2008-12-12 at 08:08 +0100, Jürg Billeter wrote:
On Thu, 2008-12-11 at 23:56 -0500, Yu Feng wrote:
Talking about circular references, is it possible to have a
circular ref
breaker mechanism like the one in GTK for vala fundamental
classes?
I'm not very familiar with the inner workings. But don't they explicitly
destroy the objects instead of simply unreffing like vala does?
Neither am I. GTKObject has a destroy signal to do the magic with
g_ojbect_run_dispose. Cycle references are automatically resolved. the
relavent code are in gtk/gtkobject.c but I didn't have time to study it
carefully.
As far as I can tell they use the gtk_widget_destroy function. Which in
turn explicitly calls g_object_run_dispose.
I don't think we should always add a dispose mechanism to
fundamental
classes. However, if someone wants to use that, it should still
be
possible to implement this with a bit of extra Vala code.
I suddenly realized it is impossible to write dispose mechanism
with
extra vala code because one can not override the hidden unref
method,
therefore one can not do the cycle detection/breaking at the
right time.
unref methods are never virtual in GObject. However, you can
override
the dispose method in Vala. Is this what you meant or can you
explain
what exactly you want to achieve?
No. We were talking about GTypeInstance fundamental classes in that
mail. They don't have a 'dispose' method to be overriden.
Right, but I'm not sure that you need to change anything in the unref
function to get dispose functionality working. Can you explain more
specifically what you can't get working with the current possibilities?
Yes I can do this:
class Object {
Object ref_to_there;
Object ref_to_here;
private disposed = false;
public virtual void dispose() {
/*release references here*/
ref_to_there = null;
ref_to_here = null;
}
private void run_dispose() {
if(disposed) return;
disposed = true;
dispose();
}
public void destroy() {
Object holder = this;
/*needed if invoked from a weak reference of this*/
run_dispose();
holder = null;
}
}
Then Object.destroy can be used to manifestly break any cycle
references.
Why do this manually? Don't you need to chain the dispose handlers
throughout the hierarchy to make it usable somehow?
But this is not a GObject. It's about implementing two stage disposal
and ref breaking with GTypeInstance classes.
Yes, I understand. But if you can't free/break the possible cyclic
references of the private members from the base class, there is
basically little use in providing a virtual/override system for a
dispose method (either GObject or non-GObject). So think providing a
class dispose method for the fundamental classes is a good idea :)
(considering member references would be freed in the dispose method in
both cases).
Hans
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Re: [Vala] use weak and var together
Hi Jurg, Sorry for digging such an old post but I discovered something. See the end of the message. On Fri, 2008-12-12 at 08:08 +0100, Jürg Billeter wrote: On Thu, 2008-12-11 at 23:56 -0500, Yu Feng wrote: On Thu, 2008-12-11 at 22:11 +0100, Jürg Billeter wrote: On Wed, 2008-12-03 at 14:05 +, Frédéric Gaudy wrote: I don't know if it' a bug or a feature. When I use weak and var keywords, I obtain a error: error: The type name `var' could not be found Code : weak var thread = Thread.create( this.process_thread, true); I haven't decided yet whether we should support that and if yes, what exact syntax to use. In addition to your example, just weak thread =... might also be a possibility. I tend to not support it at all at the moment and rather try to minimize the number of situations where 'weak' is needed. I am wondering why you dislike weak so much. It does usually mess stuff up but it is also good if one knows what she is doing. It not only saves a ref and unref, but also breaks circular references. var is only used for local variables and you never need to break circular references with local variables. I only dislike it if it's used to workaround issues with not reference-counted objects. weak is perfectly fine to break circular references, that's the main reason it exists. Talking about circular references, is it possible to have a circular ref breaker mechanism like the one in GTK for vala fundamental classes? I don't think we should always add a dispose mechanism to fundamental classes. However, if someone wants to use that, it should still be possible to implement this with a bit of extra Vala code. I suddenly realized it is impossible to write dispose mechanism with extra vala code because one can not override the hidden unref method, therefore one can not do the cycle detection/breaking at the right time. Yu Jürg ___ Vala-list mailing list Vala-list@gnome.org http://mail.gnome.org/mailman/listinfo/vala-list
Re: [Vala] use weak and var together
On Thu, 2008-12-11 at 23:56 -0500, Yu Feng wrote: On Thu, 2008-12-11 at 22:11 +0100, Jürg Billeter wrote: On Wed, 2008-12-03 at 14:05 +, Frédéric Gaudy wrote: I don't know if it' a bug or a feature. When I use weak and var keywords, I obtain a error: error: The type name `var' could not be found Code : weak var thread = Thread.create( this.process_thread, true); I haven't decided yet whether we should support that and if yes, what exact syntax to use. In addition to your example, just weak thread =... might also be a possibility. I tend to not support it at all at the moment and rather try to minimize the number of situations where 'weak' is needed. I am wondering why you dislike weak so much. It does usually mess stuff up but it is also good if one knows what she is doing. It not only saves a ref and unref, but also breaks circular references. var is only used for local variables and you never need to break circular references with local variables. I only dislike it if it's used to workaround issues with not reference-counted objects. weak is perfectly fine to break circular references, that's the main reason it exists. Talking about circular references, is it possible to have a circular ref breaker mechanism like the one in GTK for vala fundamental classes? I don't think we should always add a dispose mechanism to fundamental classes. However, if someone wants to use that, it should still be possible to implement this with a bit of extra Vala code. Jürg ___ Vala-list mailing list Vala-list@gnome.org http://mail.gnome.org/mailman/listinfo/vala-list
