Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:60807
Mailing-List: contact internals-help@lists.php.net; run by ezmlm
Received-SPF: pass (pb1.pair.com: domain gmail.com designates 74.125.82.54 as permitted sender)
Message-ID: <4FD7AF94.5000503@gmail.com>
Date: Tue, 12 Jun 2012 23:07:32 +0200
User-Agent: Thunderbird
MIME-Version: 1.0
To: Tom Boutell <tom@punkave.com>
CC: ab@php.net, Laruence <laruence@php.net>, 
 Nikita Popov <nikita.ppv@googlemail.com>,
 PHP internals <internals@lists.php.net>
References: <CAF+90c_47HtYHnMztUUb7Gd5_gKhpJYJN=G-KJFSmSt_=w2+Lw@mail.gmail.com> <CABBJUpdietc_cXVNjKZpnKrBqa13VTL2zAjCbehWsH9WNTHA5w@mail.gmail.com> <CABBJUpcLMUbqwo7XZupyEBpiymeFRhXnwcOrm09hipYk_uNhag@mail.gmail.com> <CABBJUpdkCe8reX6nw7nok-5GBJHEdKj8ix4yPmqY+NeK-YuRVA@mail.gmail.com> <18e2afd236c1f0c5901824fa6ab5e9f5.squirrel@webmail.klapt.com> <CAORXhG+X3QVbJY5WLpXqDCqztvnN+ciSFX9uie4xKfNvqN4yzw@mail.gmail.com>
In-Reply-To: <CAORXhG+X3QVbJY5WLpXqDCqztvnN+ciSFX9uie4xKfNvqN4yzw@mail.gmail.com>
Content-Type: text/plain; charset=windows-1252
Content-Transfer-Encoding: 7bit
Subject: Re: [PHP-DEV] Generators in PHP
From: keisial@gmail.com (=?windows-1252?Q?=C1ngel_Gonz=E1lez?=)

On 11/06/12 23:12, Tom Boutell wrote:
> Can you really use setjmp and longjmp in that way safely? I thought it
> was only safe to longjmp "back," not "forward" - you can use them to
> fake exception support but that's it because you'll smash the stack
> otherwise. Something like that...
My first reaction was also "How do you return to the mid-running function?"

However, given that the running function is in PHP-land, I think you could
(in non-zts, it's direct in zts), save EG() contents and replace with
new values,
and then continue the execution.
As it's treating "threads" non-preemtively, that should work.
The C code would also view a different thread, but because it is viewing
different globals (some extensions might need changes). Not really
involving
setjmp() / longjmp().

You could make userland context switches (adding arch-specific code) for
the C code by switching the stack under your ESP, but it's highly likely to
produce some obscure bugs by missing to keep a register...