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Date: Tue, 20 Dec 2005 21:27:30 +0100
Reply-To: Marcus Boerger <helly@php.net>
Message-ID: <1583077781.20051220212730@marcus-boerger.de>
To: Daine Mamacos <scuzzy@reverseorder.net>
Cc: Alan Pinstein <apinstein@mac.com>, PHP <internals@lists.php.net>
In-Reply-To: <20051220171533.M69638@reverseorder.net>
References: <20051216141608.M76819@reverseorder.net>
	<124842700.20051216203820@marcus-boerger.de>
	<20051219100552.M48206@reverseorder.net>
	<1649362906.20051219201607@marcus-boerger.de>
	<20051220134857.M91845@reverseorder.net>
	<6E2D0033-4F34-42D2-9C2B-EF59C62B83B6@mac.com>
	<20051220171533.M69638@reverseorder.net>
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Subject: Re: [PHP-DEV] exceptions in the destructor
From: helly@php.net (Marcus Boerger)

Hello Daine,


a) i didn't contradict myself - you obviously didn't really follow
   what i wrote

b) you can force calling the destructor by using unset() or = null;
   but only if reference count is 1.
c) exceptions are 'thrown' not called, maybe you didn't use throw new
   exception here or you were just writing a bit weired?
d) as said already several times (not only to you) exceptions *can*
   be thrown in destructors

e) this doesn't belong in internals@

regards
marcus

Tuesday, December 20, 2005, 6:22:31 PM, you wrote:

> I agree completely...
> I think the GC should be better documented.
> I also would like someone to tell me why exceptions cannot be called in the
> destructor? Since they can't, this means the reliability of a destructor is
> uncontrolled and nothing can be done to see if this completes successfully.

> This in some way or another, renders them completely useless if you require
> them to complete an operation and at least have the peace of mind that you
> will be able to deal with errors rather than the application throwing a fatal
> error.


> On Tue, 20 Dec 2005 11:38:34 -0500, Alan Pinstein wrote
>> > Your last post also indicates, that because the destructors are  
>> > only called
>> > after script termination, the scope of an object is global, always.
>> > Is this true?
>> 
>> This isn't true, at least empirically. Destructors are called when  
>> the GC frees the object.
>> 
>> For many objects, this is at script termination. But if you null out 
>>  the ref to an object, it will occur immediately.
>> 
>> $a = new A();
>> $a = null; // destructor called just after this line
>> 
>> I am not certain that this should be considered *predictable*  
>> behavior, as the behavior of the GC is not well/publicly documented  
>> to my knowledge, and thus this is a reasonable question for the  
>> internals list.
>> 
>> Personally I would like to see more documentation of how GC works so 
>>  that we as developers can depend on it a little better for OO 
>> cleanup  activities. I have another thread going that still remains 
>> unanswered  about how to prevent circular references to objects that 
>> deadlock the  GC.
>> 
>> Alan
>> 
>> > Also, I've called fwrite in a destructor before, so clearly not all  
>> > IO is
>> > terminated before the destructor is called.
>> > When you refer to output facility, what are you talking about?
>> >
>> > Many thanks
>> > Daine Mamacos.
>> >
>> >
>> > On Mon, 19 Dec 2005 20:16:07 +0100, Marcus Boerger wrote
>> >> Hello Daine,
>> >>
>> >>   you still don't get it. Your problem is the way php works. You
>> >> cannot put any output functionality in destructors because they are
>> >> called *after* your scipt is being terminted (to be precise after
>> >> the output facility has been shutdown on script termination).
>> >>
>> >> This is btw a question the general php list.
>> >>
>> >> marcus
>> >>
>> >> Monday, December 19, 2005, 11:07:53 AM, you wrote:
>> >>
>> >>> While you're example works, mine doesn't, it has to do with the  
>> >>> class
>> >>> assignment. If you actually bother to do anything with the class, it
>> > doesn't work.
>> >>
>> >>> $ php -r 'class blah { function __destruct() { throw new Exception 
>> >>> ("exception
>> >>> thrown"); } } $blah = new blah();'
>> >>
>> >>> give that a try and see what happens
>> >>> (;
>> >>> also http://bugs.php.net/bug.php?id=33598 clearly states that  
>> >>> they cannoy be
>> >>> thrown in the destructor.
>> >>> Errrr... *shrug*
>> >>
>> >>> On Fri, 16 Dec 2005 20:38:20 +0100, Marcus Boerger wrote
>> >>>> Hello Daine,
>> >>>>
>> >>>> marcus@zaphod /usr/src/PHP_5_1 $ php -r 'class A{function
>> >>>> __destruct(){throw new Exception("A");}} new A;' make:
>> >>>> `sapi/cli/php' is up to date.
>> >>>>
>> >>>> Fatal error: Uncaught exception 'Exception' with message 'A' in
>> >>>> Command line code:1 Stack trace:
>> >>>> #0 Command line code(1): A::__destruct()
>> >>>> #1 {main}
>> >>>>   thrown in Command line code on line 1
>> >>>>
>> >>>> As the code above clearly show, exceptions can be thrown.
>> >>>>
>> >>>> marcus
>> >>>>
>> >>>> Friday, December 16, 2005, 3:17:54 PM, you wrote:
>> >>>>
>> >>>>> Is there any reason why one is not allowed to throw an  
>> >>>>> exception in the
>> >>>>> destructor of a class?
>> >>>>> I mean, it makes sense, considering this is not always the  
>> >>>>> final step
>> > of code,
>> >>>>> and it is usually used for finalising things, and it would be a  
>> >>>>> good
>> > idea to
>> >>>>> know if anything goes wrong at that stage.
>> >>>>> Otherwise is there any compromise one can use to "emulate" this  
>> >>>>> feature?
>> >>>>
>> >>>>> Daine Mamacos.
>> >>>>
>> >>>>> --
>> >>>>> random signature
>> >>>>
>> >>>> Best regards,
>> >>>>  Marcus
>> >>>>
>> >>>> -- 
>> >>>> PHP Internals - PHP Runtime Development Mailing List
>> >>>> To unsubscribe, visit: http://www.php.net/unsub.php
>> >>
>> >>> --
>> >>> random signature
>> >>
>> >> -- 
>> >> Best regards,
>> >>  Marcus                            mailto:mail@marcus-boerger.de
>> >
>> >
>> > --
>> > random signature
>> >
>> > -- 
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>> >
>> 
>> -- 
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> --
> random signature




Best regards,
 Marcus