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Subject: Re: Reusing main VM stack for generators
From: dmitry@zend.com (Dmitry Stogov)

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On 01/22/2016 10:29 PM, Bob Weinand wrote:
>> Am 22.01.2016 um 15:43 schrieb Dmitry Stogov <dmitry@zend.com 
>> <mailto:dmitry@zend.com>>:
>>
>>
>> Hi,
>>
>> Could you please, take a look into the PoC.
>> It's incomplete, but may be you get ideas how to fix this.
>>
>> https://gist.github.com/dstogov/285024375d15cacf2a9b
>>
>> Few tests are failed, because YIELD may be used as expression in 
>> nested calls (between INIT_FCALL/DO_FCALL), and the caller function 
>> restores EG(vm_stack_top), loosing and overwriting that active frame.
>>
>> <?php
>> function gen() {
>>     var_dump(yield 1);
>> }
>>
>> for ($gen = gen(); $gen->valid(); $gen->send(0)) {
>>     var_dump($gen->current());
>> }
>> ?>
>>
>> Thanks. Dmitry.
>
> Hey, that's pretty similar to what I did 
> https://github.com/php/php-src/commit/0f0471a9893230918084798d4e35db37d7b4519d 
> <https://github.com/php/php-src/compare/master...bwoebi:stackless_generators> in 
> that old patch, which you rejected because we hadn't found any 
> solution for that issue with yield inside calls.

yes, this is similar.

>
> We basically need a way to properly first fetch the args (beware: 
> func_arg fetches...) before instantiating the call frame, an issue 
> which for example could be solved if we applied my 
> vm_stack_restructuring patch (because it only installs call frames 
> after all args were fetched).

I thought about that approach, but the amount of changes doesn't worth 
the result. Doing this only for generators doesn't make a lot of sense.

>
> I believe this patch won't work without significant refactoring (like 
> vm_stack_refactoring branch) … so, either we bite the bullet and look 
> at that patch again, or we can forget this idea too.

most probably, you are right.

Thanks. Dmitry.

>
> Thanks,
> Bob


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