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digitalmars.D.learn - Destructor order

reply Temtaime <temtaime gmail.com> writes:
Hi !
I wonder if i can rely on this code :

http://dpaste.dzfl.pl/745cc5b1cdfb

There's two questions:
1) Is dtors always called in reverse order ?
2) Is all the dtors always called when i call destroy ?

Thanks for a reply !
Mar 18 2016
parent reply Nicholas Wilson <iamthewilsonator hotmail.com> writes:
On Friday, 18 March 2016 at 10:20:40 UTC, Temtaime wrote:

 Hi !
 I wonder if i can rely on this code :

 http://dpaste.dzfl.pl/745cc5b1cdfb

 There's two questions:
 1) Is dtors always called in reverse order ?


yes

 2) Is all the dtors always called when i call destroy ?


yes. destroy calls __dtor() which recursively call __dtor() on 
its members


 Thanks for a reply !
Mar 18 2016
parent reply Steven Schveighoffer <schveiguy yahoo.com> writes:
On 3/18/16 7:44 AM, Nicholas Wilson wrote:

 On Friday, 18 March 2016 at 10:20:40 UTC, Temtaime wrote:

 Hi !
 I wonder if i can rely on this code :

 http://dpaste.dzfl.pl/745cc5b1cdfb

 There's two questions:
 1) Is dtors always called in reverse order ?


 yes

 2) Is all the dtors always called when i call destroy ?


 yes. destroy calls __dtor() which recursively call __dtor() on its members


I think technically not true. If you call __dtor directly, it does not 
recurse. But this is an implementation detail.

-Steve
Mar 18 2016
parent reply Andrea Fontana <nospam example.com> writes:
On Friday, 18 March 2016 at 14:53:20 UTC, Steven Schveighoffer 
wrote:

 On 3/18/16 7:44 AM, Nicholas Wilson wrote:

 On Friday, 18 March 2016 at 10:20:40 UTC, Temtaime wrote:

 Hi !
 I wonder if i can rely on this code :

 http://dpaste.dzfl.pl/745cc5b1cdfb

 There's two questions:
 1) Is dtors always called in reverse order ?


 yes

 2) Is all the dtors always called when i call destroy ?


 yes. destroy calls __dtor() which recursively call __dtor() on 
 its members


 I think technically not true. If you call __dtor directly, it 
 does not recurse. But this is an implementation detail.

 -Steve


Why doesn't this print ~B ~A?
http://dpaste.dzfl.pl/0bef0a4316b7

It raises a bug on my code because dtor are called in "wrong" 
order.
b holds a ref to a, why a is desctructed before b?

Andrea
Mar 18 2016
parent reply Steven Schveighoffer <schveiguy yahoo.com> writes:
On 3/18/16 10:58 AM, Andrea Fontana wrote:

 On Friday, 18 March 2016 at 14:53:20 UTC, Steven Schveighoffer wrote:

 On 3/18/16 7:44 AM, Nicholas Wilson wrote:

 On Friday, 18 March 2016 at 10:20:40 UTC, Temtaime wrote:

 Hi !
 I wonder if i can rely on this code :

 http://dpaste.dzfl.pl/745cc5b1cdfb

 There's two questions:
 1) Is dtors always called in reverse order ?


 yes

 2) Is all the dtors always called when i call destroy ?


 yes. destroy calls __dtor() which recursively call __dtor() on its
 members


 I think technically not true. If you call __dtor directly, it does not
 recurse. But this is an implementation detail.


 Why doesn't this print ~B ~A?
 http://dpaste.dzfl.pl/0bef0a4316b7

 It raises a bug on my code because dtor are called in "wrong" order.
 b holds a ref to a, why a is desctructed before b?


Structs are contained completely within the class instance memory block 
(e.g. the OP's code). Classes are references. They are not destroyed 
when you destroy the holder, that is left up to the GC, which can 
destroy in any order. And in fact, it's a programming error to destroy 
any GC-allocated memory inside your dtor, because it may already be gone!

-Steve
Mar 18 2016
parent reply Andrea Fontana <nospam example.com> writes:
On Friday, 18 March 2016 at 15:03:14 UTC, Steven Schveighoffer 
wrote:

 On 3/18/16 10:58 AM, Andrea Fontana wrote:

 On Friday, 18 March 2016 at 14:53:20 UTC, Steven Schveighoffer 
 wrote:

 On 3/18/16 7:44 AM, Nicholas Wilson wrote:

 On Friday, 18 March 2016 at 10:20:40 UTC, Temtaime wrote:

 Hi !
 I wonder if i can rely on this code :

 http://dpaste.dzfl.pl/745cc5b1cdfb

 There's two questions:
 1) Is dtors always called in reverse order ?


 yes

 2) Is all the dtors always called when i call destroy ?


 yes. destroy calls __dtor() which recursively call __dtor() 
 on its
 members


 I think technically not true. If you call __dtor directly, it 
 does not
 recurse. But this is an implementation detail.


 Why doesn't this print ~B ~A?
 http://dpaste.dzfl.pl/0bef0a4316b7

 It raises a bug on my code because dtor are called in "wrong" 
 order.
 b holds a ref to a, why a is desctructed before b?


 Structs are contained completely within the class instance 
 memory block (e.g. the OP's code). Classes are references. They 
 are not destroyed when you destroy the holder, that is left up 
 to the GC, which can destroy in any order. And in fact, it's a 
 programming error to destroy any GC-allocated memory inside 
 your dtor, because it may already be gone!

 -Steve


Not the case. I'm writing a binding for a library. Class A and B 
wrap c-struct and on d-tor I have to free underlying c object 
calling c-library destroyer. I'm not destroying any 
d/GC-allocated object. But of course i have to destroy c object 
in the correct order... How to?
Mar 18 2016
next sibling parent Jeremy DeHaan <dehaan.jeremiah gmail.com> writes:
On Friday, 18 March 2016 at 15:07:53 UTC, Andrea Fontana wrote:

 On Friday, 18 March 2016 at 15:03:14 UTC, Steven Schveighoffer 
 wrote:

 On 3/18/16 10:58 AM, Andrea Fontana wrote:

 On Friday, 18 March 2016 at 14:53:20 UTC, Steven 
 Schveighoffer wrote:

 On 3/18/16 7:44 AM, Nicholas Wilson wrote:

 [...]


 I think technically not true. If you call __dtor directly, 
 it does not
 recurse. But this is an implementation detail.


 Why doesn't this print ~B ~A?
 http://dpaste.dzfl.pl/0bef0a4316b7

 It raises a bug on my code because dtor are called in "wrong" 
 order.
 b holds a ref to a, why a is desctructed before b?


 Structs are contained completely within the class instance 
 memory block (e.g. the OP's code). Classes are references. 
 They are not destroyed when you destroy the holder, that is 
 left up to the GC, which can destroy in any order. And in 
 fact, it's a programming error to destroy any GC-allocated 
 memory inside your dtor, because it may already be gone!

 -Steve


 Not the case. I'm writing a binding for a library. Class A and 
 B wrap c-struct and on d-tor I have to free underlying c object 
 calling c-library destroyer. I'm not destroying any 
 d/GC-allocated object. But of course i have to destroy c object 
 in the correct order... How to?


You can't rely on classes to have their destructors call in any 
particular order. My guess is that the GC is going through and 
deallocating them in the order they appear on the heap.

If you need destructors called in a reliable manner, use structs 
instead of classes or call destroy on your objects manually.
Mar 18 2016
prev sibling parent Steven Schveighoffer <schveiguy yahoo.com> writes:
On 3/18/16 11:07 AM, Andrea Fontana wrote:

 On Friday, 18 March 2016 at 15:03:14 UTC, Steven Schveighoffer wrote:

 Structs are contained completely within the class instance memory
 block (e.g. the OP's code). Classes are references. They are not
 destroyed when you destroy the holder, that is left up to the GC,
 which can destroy in any order. And in fact, it's a programming error
 to destroy any GC-allocated memory inside your dtor, because it may
 already be gone!


 Not the case. I'm writing a binding for a library. Class A and B wrap
 c-struct and on d-tor I have to free underlying c object calling
 c-library destroyer. I'm not destroying any d/GC-allocated object. But
 of course i have to destroy c object in the correct order... How to?


Then you need to reorganize how they are related. Even though class B 
wraps a C resource, it's still stored on the heap, and can be destroyed 
in any order.

I'd recommend ensuring the dependency requirement is implemented within 
one object. Either make B a struct member, or have the destruction done 
by a third object.

-Steve
Mar 18 2016