May 24, 2012 Destructor nonsense on dlang.org | ||||
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Hi, http://dlang.org/class.html#Destructor "The garbage collector is not guaranteed to run the destructor for all unreferenced objects." What the *hell*? So resources are allowed to arbitrarily leak and the programmer has to actually expect this to happen? I really, really hope that this is a documentation error or early design decision that has since been rectified but with lack of documentation updates. -- Alex Rønne Petersen alex@lycus.org http://lycus.org |
May 24, 2012 Re: Destructor nonsense on dlang.org | ||||
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Posted in reply to Alex Rønne Petersen | On Thursday, 24 May 2012 at 12:21:02 UTC, Alex Rønne Petersen wrote:
> Hi,
>
> http://dlang.org/class.html#Destructor
>
> "The garbage collector is not guaranteed to run the destructor for all unreferenced objects."
>
> What the *hell*? So resources are allowed to arbitrarily leak and the programmer has to actually expect this to happen?
>
> I really, really hope that this is a documentation error or early design decision that has since been rectified but with lack of documentation updates.
use "clear", or "scope (exit)" or "structs" or scoped!... etc.
There could always be a false reference... so you cannot depend on automatically releasing resources in a class destructor.
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May 24, 2012 Re: Destructor nonsense on dlang.org | ||||
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Posted in reply to Thor | On 24-05-2012 14:33, Thor wrote: > On Thursday, 24 May 2012 at 12:21:02 UTC, Alex Rønne Petersen wrote: >> Hi, >> >> http://dlang.org/class.html#Destructor >> >> "The garbage collector is not guaranteed to run the destructor for all >> unreferenced objects." >> >> What the *hell*? So resources are allowed to arbitrarily leak and the >> programmer has to actually expect this to happen? >> >> I really, really hope that this is a documentation error or early >> design decision that has since been rectified but with lack of >> documentation updates. > > use "clear", or "scope (exit)" or "structs" or scoped!... etc. I know. > > There could always be a false reference... so you cannot depend on > automatically releasing resources in a class destructor. > False pointers have nothing to do with it. The GC should free and finalize all objects on shutdown, meaning the finalizer runs *sooner or later*. If this is the case (which I do believe it is), then the docs are very wrong. -- Alex Rønne Petersen alex@lycus.org http://lycus.org |
May 24, 2012 Re: Destructor nonsense on dlang.org | ||||
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Posted in reply to Alex Rønne Petersen | On 2012-05-24 12:21:01 +0000, Alex Rønne Petersen <alex@lycus.org> said: > Hi, > > http://dlang.org/class.html#Destructor > > "The garbage collector is not guaranteed to run the destructor for all unreferenced objects." > > What the *hell*? So resources are allowed to arbitrarily leak and the programmer has to actually expect this to happen? > > I really, really hope that this is a documentation error or early design decision that has since been rectified but with lack of documentation updates. I think it means that objects not collected when the program terminates will never be, and thus the destructor will not be called. There's also the issue of false pointers that can prevent some objects from being collected. More generally, you can't really count on the destructor being called because the GC is free to decide when to recycle memory. An implementation that never collects and always allocate new memory is a perfectly valid GC implementation, even though it might not be very practical in most cases. -- Michel Fortin michel.fortin@michelf.com http://michelf.com/ |
May 24, 2012 Re: Destructor nonsense on dlang.org | ||||
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Posted in reply to Alex Rønne Petersen | On Thursday, 24 May 2012 at 12:38:45 UTC, Alex Rønne Petersen wrote:
> On 24-05-2012 14:33, Thor wrote:
>> On Thursday, 24 May 2012 at 12:21:02 UTC, Alex Rønne Petersen wrote:
>>> Hi,
>>>
>>> http://dlang.org/class.html#Destructor
>>>
>>> "The garbage collector is not guaranteed to run the destructor for all
>>> unreferenced objects."
>>>
>>> What the *hell*? So resources are allowed to arbitrarily leak and the
>>> programmer has to actually expect this to happen?
>>>
>>> I really, really hope that this is a documentation error or early
>>> design decision that has since been rectified but with lack of
>>> documentation updates.
>>
>> use "clear", or "scope (exit)" or "structs" or scoped!... etc.
>
> I know.
>
>>
>> There could always be a false reference... so you cannot depend on
>> automatically releasing resources in a class destructor.
>>
>
> False pointers have nothing to do with it. The GC should free and finalize all objects on shutdown, meaning the finalizer runs *sooner or later*. If this is the case (which I do believe it is), then the docs are very wrong.
__gshared uint my_false_ptr;
even if we are shutting down, the static references doesn't disappear... or did I miss something?
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May 24, 2012 Re: Destructor nonsense on dlang.org | ||||
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Posted in reply to Alex Rønne Petersen | On Thursday, 24 May 2012 at 12:21:02 UTC, Alex Rønne Petersen wrote:
> Hi,
>
> http://dlang.org/class.html#Destructor
>
> "The garbage collector is not guaranteed to run the destructor for all unreferenced objects."
>
> What the *hell*? So resources are allowed to arbitrarily leak and the programmer has to actually expect this to happen?
>
> I really, really hope that this is a documentation error or early design decision that has since been rectified but with lack of documentation updates.
I'm pretty sure it's the same in Java.
Finalizers (a.k.a. class destructors) are practically useless.
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May 24, 2012 Re: Destructor nonsense on dlang.org | ||||
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Posted in reply to Peter Alexander | On Thu, 24 May 2012 08:54:45 -0400, Peter Alexander <peter.alexander.au@gmail.com> wrote:
> On Thursday, 24 May 2012 at 12:21:02 UTC, Alex Rønne Petersen wrote:
>> Hi,
>>
>> http://dlang.org/class.html#Destructor
>>
>> "The garbage collector is not guaranteed to run the destructor for all unreferenced objects."
>>
>> What the *hell*? So resources are allowed to arbitrarily leak and the programmer has to actually expect this to happen?
>>
>> I really, really hope that this is a documentation error or early design decision that has since been rectified but with lack of documentation updates.
>
> I'm pretty sure it's the same in Java.
>
> Finalizers (a.k.a. class destructors) are practically useless.
From Java spec:
"The Java programming language does not specify how soon a finalizer will be invoked, except to say that it will happen before the storage for the object is reused"
So yeah, there is no guarantee when a finalizer will be invoked.
However, I'd tend to believe Java implementations will attempt to invoke all finalizers of objects left on the heap at program shutdown.
I think D is the same too, as long as termination is normal (i.e. not from throwing an Error).
-Steve
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May 24, 2012 Re: Destructor nonsense on dlang.org | ||||
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Posted in reply to Peter Alexander | Le 24/05/2012 14:54, Peter Alexander a écrit :
> On Thursday, 24 May 2012 at 12:21:02 UTC, Alex Rønne Petersen wrote:
>> Hi,
>>
>> http://dlang.org/class.html#Destructor
>>
>> "The garbage collector is not guaranteed to run the destructor for all
>> unreferenced objects."
>>
>> What the *hell*? So resources are allowed to arbitrarily leak and the
>> programmer has to actually expect this to happen?
>>
>> I really, really hope that this is a documentation error or early
>> design decision that has since been rectified but with lack of
>> documentation updates.
>
> I'm pretty sure it's the same in Java.
>
> Finalizers (a.k.a. class destructors) are practically useless.
Java finalizer is a pretty bad design decision. Let's not reproduce error made in Java in D's destructors.
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May 24, 2012 Re: Destructor nonsense on dlang.org | ||||
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Posted in reply to deadalnix | On Thu, 24 May 2012 09:47:23 -0400, deadalnix <deadalnix@gmail.com> wrote:
> Le 24/05/2012 14:54, Peter Alexander a écrit :
>> On Thursday, 24 May 2012 at 12:21:02 UTC, Alex Rønne Petersen wrote:
>>> Hi,
>>>
>>> http://dlang.org/class.html#Destructor
>>>
>>> "The garbage collector is not guaranteed to run the destructor for all
>>> unreferenced objects."
>>>
>>> What the *hell*? So resources are allowed to arbitrarily leak and the
>>> programmer has to actually expect this to happen?
>>>
>>> I really, really hope that this is a documentation error or early
>>> design decision that has since been rectified but with lack of
>>> documentation updates.
>>
>> I'm pretty sure it's the same in Java.
>>
>> Finalizers (a.k.a. class destructors) are practically useless.
>
> Java finalizer is a pretty bad design decision. Let's not reproduce error made in Java in D's destructors.
You actually need a finalizer if you want to have resources that aren't GC allocated.
-Steve
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May 24, 2012 Re: Destructor nonsense on dlang.org | ||||
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Posted in reply to Steven Schveighoffer | On 2012-05-24 13:38:01 +0000, "Steven Schveighoffer" <schveiguy@yahoo.com> said: > However, I'd tend to believe Java implementations will attempt to invoke > all finalizers of objects left on the heap at program shutdown. In Java you can call System.runFinalizersOnExit(true), but the default is false and this method has been deprecated because unsafe in multithreaded environments. <http://docs.oracle.com/javase/6/docs/api/java/lang/System.html#runFinalization()> -- Michel Fortin michel.fortin@michelf.com http://michelf.com/ |
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