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[PHP-DEV] [RFC] Fiber support (again)

Posted by Haitao Lv 
Haitao Lv
[PHP-DEV] [RFC] Fiber support (again)
February 08, 2018 02:10AM
Hi internals,

I propose to introduce the Fiber feature AGAIN.

The main purpose of the RFC is to introducing a lightweight stackful coroutine support for PHP and make it possible to write non-blocking code in the blocking style.

In this RFC, no new keyword is needed. So it will not break the PHP 7.3 release.

Please see the RFC https://wiki.php.net/rfc/fiber

Dmitry and I are working on the implementation at https://github.com/fiberphp/fiber-ext
And a series of usage demo can be found at https://github.com/fiberphp/fiber-demo

Please offer you comments.

Thank you.

---
Haitao Lv


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Aaron Piotrowski
Re: [PHP-DEV] [RFC] Fiber support (again)
February 08, 2018 05:20AM
> On Feb 7, 2018, at 7:05 PM, Haitao Lv <[email protected]> wrote:
>
> Hi internals,
>
> I propose to introduce the Fiber feature AGAIN.
>
> The main purpose of the RFC is to introducing a lightweight stackful coroutine support for PHP and make it possible to write non-blocking code in the blocking style.
>
> In this RFC, no new keyword is needed. So it will not break the PHP 7.3 release.
>
> Please see the RFC https://wiki.php.net/rfc/fiber
>
> Dmitry and I are working on the implementation at https://github.com/fiberphp/fiber-ext
> And a series of usage demo can be found at https://github.com/fiberphp/fiber-demo
>
> Please offer you comments.
>
> Thank you.
>
> ---
> Haitao Lv
>


Hi Haitao,

I'm very excited to see this sort of feature coming to PHP.

A couple of questions and thoughts:

- How do you determine when a fiber has returned? Looking at the source, it appears Fiber::status() must be used, comparing against constants. Separate methods similar to Generator would be better IMO. e.g.: Fiber::alive(), Fiber::suspended(), Fiber::running()

- What about throwing exceptions into a fiber?

- Using Fiber::resume() to initialize the fiber and resume feels awkward. Separate methods again would be better here, perhaps Fiber::init(...$args) and Fiber::resume($send).

- What happens if the sub1() function in the RFC is invoked outside of a fiber?

- I think a keyword here would be beneficial, even if it has a minor BC impact. Fibers could then be written like generators. `await` or `emit` as a keyword perhaps? This would be a less verbose API, feel less magical (a static method call that actually pauses execution feels out of place), and would allow Fibers to be returned from methods, named functions, etc with less boilerplate.

Thanks to you and Dmitry for working on this!

Aaron Piotrowski
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Haitao Lv
Re: [PHP-DEV] [RFC] Fiber support (again)
February 08, 2018 05:00PM
> On Feb 8, 2018, at 12:18, Aaron Piotrowski <[email protected]> wrote:
>
>>
>> On Feb 7, 2018, at 7:05 PM, Haitao Lv <[email protected]> wrote:
>>
>> Hi internals,
>>
>> I propose to introduce the Fiber feature AGAIN.
>>
>> The main purpose of the RFC is to introducing a lightweight stackful coroutine support for PHP and make it possible to write non-blocking code in the blocking style.
>>
>> In this RFC, no new keyword is needed. So it will not break the PHP 7.3 release.
>>
>> Please see the RFC https://wiki.php.net/rfc/fiber
>>
>> Dmitry and I are working on the implementation at https://github.com/fiberphp/fiber-ext
>> And a series of usage demo can be found at https://github.com/fiberphp/fiber-demo
>>
>> Please offer you comments.
>>
>> Thank you.
>>
>> ---
>> Haitao Lv
>>
>
>
> Hi Haitao,
>
> I'm very excited to see this sort of feature coming to PHP.
>
> A couple of questions and thoughts:
>
> - How do you determine when a fiber has returned? Looking at the source, it appears Fiber::status() must be used, comparing against constants. Separate methods similar to Generator would be better IMO. e.g.: Fiber::alive(), Fiber::suspended(), Fiber::running()

Offering methods like Fiber::alive, Fiber::running makes no difference to check the Fiber::status() return value. This is just a style issue. And as a language feature,
Fiber only offer the essential API and let other works to the user land.

> - What about throwing exceptions into a fiber?

Currently does not support throw exception into the fiber. User land code could check
the value of Fiber::yield and throw exception themselves. The Ruby's Fiber and Lua's
coroutine also does not support such api as well.

>
> - Using Fiber::resume() to initialize the fiber and resume feels awkward. Separate methods again would be better here, perhaps Fiber::init(...$args) and Fiber::resume($send).

All Fiber created with a suspended status. So make resume to do both the init and resume
do make sense.

Please see Ruby Fiber API https://ruby-doc.org/core-2.2.0/Fiber.html.

>
> - What happens if the sub1() function in the RFC is invoked outside of a fiber?

You will get a Fatal Error like
Fatal error: Uncaught Error: Cannot call Fiber::yield out of Fiber

> - I think a keyword here would be beneficial, even if it has a minor BC impact. Fibers could then be written like generators. `await` or `emit` as a keyword perhaps? This would be a less verbose API, feel less magical (a static method call that actually pauses execution feels out of place), and would allow Fibers to be returned from methods, named functions, etc with less boilerplate.

Wishing this to be accepted by the community in the PHP 7.3, so no keyword is accepted.
And if the community cannot accept, the Fiber can be still distributed as a standalone
extension. So we cannot depend on a new keyword.

> Thanks to you and Dmitry for working on this!
>
> Aaron Piotrowski
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Niklas Keller
Re: [PHP-DEV] [RFC] Fiber support (again)
February 08, 2018 11:30PM
>
> > - How do you determine when a fiber has returned? Looking at the source,
> it appears Fiber::status() must be used, comparing against constants.
> Separate methods similar to Generator would be better IMO. e.g.:
> Fiber::alive(), Fiber::suspended(), Fiber::running()
>
> Offering methods like Fiber::alive, Fiber::running makes no difference to
> check the Fiber::status() return value. This is just a style issue. And as
> a language feature,
> Fiber only offer the essential API and let other works to the user land.


The language should offer a sane API, not the absolute minimum required to
work for these things.


> > - What about throwing exceptions into a fiber?
>
> Currently does not support throw exception into the fiber. User land code
> could check
> the value of Fiber::yield and throw exception themselves. The Ruby's Fiber
> and Lua's
> coroutine also does not support such api as well.


And throw the exception where? That means async code with fibers can't
really handle errors?


>
> >
> > - Using Fiber::resume() to initialize the fiber and resume feels
> awkward. Separate methods again would be better here, perhaps
> Fiber::init(...$args) and Fiber::resume($send).
>
> All Fiber created with a suspended status. So make resume to do both the
> init and resume
> do make sense.
>

It does't make sense to me. Reading the example in the README and
understanding why the first resume() takes two arguments instead of one
took me quite some minutes.


> Please see Ruby Fiber API https://ruby-doc.org/core-2.2.0/Fiber.html.
>
> >
> > - What happens if the sub1() function in the RFC is invoked outside of a
> fiber?
>
> You will get a Fatal Error like
> Fatal error: Uncaught Error: Cannot call Fiber::yield out of Fiber
>
> > - I think a keyword here would be beneficial, even if it has a minor BC
> impact. Fibers could then be written like generators. `await` or `emit` as
> a keyword perhaps? This would be a less verbose API, feel less magical (a
> static method call that actually pauses execution feels out of place), and
> would allow Fibers to be returned from methods, named functions, etc with
> less boilerplate.
>
> Wishing this to be accepted by the community in the PHP 7.3, so no keyword
> is accepted.
> And if the community cannot accept, the Fiber can be still distributed as
> a standalone
> extension. So we cannot depend on a new keyword.


Right, if it's a standalone extension it can't use a new keyword, but as a
language feature it totally can.

Looking at the current README, there are two issues that must be completely
solved IMO before accepting this:

> Each Fiber has a separate 4k stack. You can use the fiber.stack_size ini
option to change the default stack size. You can also use the second
argument of Fiber::__construct to set the stack size on fly.

Resizing of the stack should happen automatically, just like generators
resize automatically.

> Fiber::yield cannot be used in internal callback

This also seems problematic and will make fibers quite less useful,
especially as these yields can happen anywhere down the stack.

Regards, Niklas
Haitao Lv
Re: [PHP-DEV] [RFC] Fiber support (again)
February 09, 2018 01:20AM
> On Feb 9, 2018, at 06:22, Niklas Keller <[email protected]> wrote:
>
>>
>>> - How do you determine when a fiber has returned? Looking at the source,
>> it appears Fiber::status() must be used, comparing against constants.
>> Separate methods similar to Generator would be better IMO. e.g.:
>> Fiber::alive(), Fiber::suspended(), Fiber::running()
>>
>> Offering methods like Fiber::alive, Fiber::running makes no difference to
>> check the Fiber::status() return value. This is just a style issue. And as
>> a language feature,
>> Fiber only offer the essential API and let other works to the user land.
>
>
> The language should offer a sane API, not the absolute minimum required to
> work for these things.

The Ruby's Fiber do offer a live? method but does not have a getStatus method.
The Lua's coroutine only offer a status method.

So do we really need to offer three additional helper method? Or what is your
advice about these API?

>
>>> - What about throwing exceptions into a fiber?
>>
>> Currently does not support throw exception into the fiber. User land code
>> could check
>> the value of Fiber::yield and throw exception themselves. The Ruby's Fiber
>> and Lua's
>> coroutine also does not support such api as well.
>
>
> And throw the exception where? That means async code with fibers can't
> really handle errors?

Actually you can transfer any thing to Fiber by the resume method. And you can
check the return value of Fiber::yield to handle error.

Fiber is designed as a primitive, low level, and lightweight feature. User land
code seldom not need to use them directly in your normal code.
So the following is not a big problem,

$a = Fiber::yield(...);
if ($a === false) {
throw new Exception(...);
}

And both the Ruby and Lua does not offer such API as well.
>
>>
>>>
>>> - Using Fiber::resume() to initialize the fiber and resume feels
>> awkward. Separate methods again would be better here, perhaps
>> Fiber::init(...$args) and Fiber::resume($send).
>>
>> All Fiber created with a suspended status. So make resume to do both the
>> init and resume
>> do make sense.
>>
>
> It does't make sense to me. Reading the example in the README and
> understanding why the first resume() takes two arguments instead of one
> took me quite some minutes.

This Ruby's Fiber and Lua's coroutine using one resume API to init and resume
the coroutine. I do not think a dedicate is really required.

The generator cannot be init by it's send method. And if you want to implement
coroutine feature(without stack) by it, you have to write code

function run() {
if ($this->beforeFirstYield) {
$this->beforeFirstYield = false;
return $this->coroutine->current();
} else {
$retval = $this->coroutine->send($this->sendValue);
$this->sendValue = null;
return $retval;
}
}

It is verbose.

See https://nikic.github.io/2012/12/22/Cooperative-multitasking-using-coroutines-in-PHP.html

>
>> Please see Ruby Fiber API https://ruby-doc.org/core-2.2.0/Fiber.html.
>>
>>>
>>> - What happens if the sub1() function in the RFC is invoked outside of a
>> fiber?
>>
>> You will get a Fatal Error like
>> Fatal error: Uncaught Error: Cannot call Fiber::yield out of Fiber
>>
>>> - I think a keyword here would be beneficial, even if it has a minor BC
>> impact. Fibers could then be written like generators. `await` or `emit` as
>> a keyword perhaps? This would be a less verbose API, feel less magical (a
>> static method call that actually pauses execution feels out of place), and
>> would allow Fibers to be returned from methods, named functions, etc with
>> less boilerplate.
>>
>> Wishing this to be accepted by the community in the PHP 7.3, so no keyword
>> is accepted.
>> And if the community cannot accept, the Fiber can be still distributed as
>> a standalone
>> extension. So we cannot depend on a new keyword.
>
>
> Right, if it's a standalone extension it can't use a new keyword, but as a
> language feature it totally can.

In my opinion, using a keyword or call a method is just a coding style problem.
Introducing a new keyword does not offer any benefit by makes a minor BC.

Both Ruby's Fiber and Lua's coroutine does not required a dedicate keyword.

> Looking at the current README, there are two issues that must be completely
> solved IMO before accepting this:
>
>> Each Fiber has a separate 4k stack. You can use the fiber.stack_size ini
> option to change the default stack size. You can also use the second
> argument of Fiber::__construct to set the stack size on fly.
>
> Resizing of the stack should happen automatically, just like generators
> resize automatically.

This size is the init stack size. It means when a Fiber created, it will get a
dedicate stack of 4k size. When the fiber use all the stack space, zend vm will
allocate additional space for feature call frame, automatically.

The default size is 4k means that every fiber requires at least 4k memory to use
as there own stack. But user can change this by php.ini and the construct argument
to reduce the memory footprint.

>
>> Fiber::yield cannot be used in internal callback
>
> This also seems problematic and will make fibers quite less useful,
> especially as these yields can happen anywhere down the stack.
>

This do be a problem. But not so much big problem.

You cannot use Fiber::yield like

$f = new Fiber(function () {
array_map(function ($i) {
Fiber::yield($i);
}, [1, 2, 3]);
});
$f->resume();
$f->resume();

Because when zend execute the array_map, it will push a new frame onto the c stack.
When zend execute Fiber::yield, it only backup it's php stack, and it's c stack
will be overwrites.

However, you can use Fiber::yield like

$f = new Fiber(function () {
Fiber::yield(1); // will cause by resume, by an internal callback
});

ExtEventLoop::onRead($fd, function () { // this is an internal call
$f->resume();
});

> Regards, Niklas




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S.A.N
Re: [PHP-DEV] [RFC] Fiber support (again)
February 09, 2018 11:10AM
This has already been discussed in github

Fiber::resume()
https://github.com/fiberphp/fiber-ext/issues/7

Fiber::throw()
https://github.com/fiberphp/fiber-ext/issues/6

Keywords - async/await
https://github.com/fiberphp/fiber-ext/issues/10

I believe that current API is normal for the Pecl ext, but to become
semantics of PHP language, the API needs to be improved

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Niklas Keller
Re: [PHP-DEV] [RFC] Fiber support (again)
February 09, 2018 12:50PM
>
> > The language should offer a sane API, not the absolute minimum required
> to
> > work for these things.
>
> The Ruby's Fiber do offer a live? method but does not have a getStatus
> method.
> The Lua's coroutine only offer a status method.
>
> So do we really need to offer three additional helper method? Or what is
> your
> advice about these API?


What's the downside?

>
> >>> - What about throwing exceptions into a fiber?
> >>
> >> Currently does not support throw exception into the fiber. User land
> code
> >> could check
> >> the value of Fiber::yield and throw exception themselves. The Ruby's
> Fiber
> >> and Lua's
> >> coroutine also does not support such api as well.
> >
> >
> > And throw the exception where? That means async code with fibers can't
> > really handle errors?
>
> Actually you can transfer any thing to Fiber by the resume method. And you
> can
> check the return value of Fiber::yield to handle error.
>
> Fiber is designed as a primitive, low level, and lightweight feature. User
> land
> code seldom not need to use them directly in your normal code.
> So the following is not a big problem,
>
> $a = Fiber::yield(...);
> if ($a === false) {
> throw new Exception(...);
> }
>
> And both the Ruby and Lua does not offer such API as well.
>

We have started building a PoC library on top of Fibers, see
https://github.com/amphp/green-thread/blob/7bd3470e7986169372d5e9c39500f3652091b512/src/functions.php
..

We'd like to avoid the additional `await()` function and rather directly
couple Fibers with promises in the PHP core.

Using `await` (the keyword) instead of `Fiber::yield()` feels way better
and avoids the need for any wrapping libraries for what should be a core
feature.

`async` can be added to create a new Fiber and Fiber can implement Promise.


> >
> >>
> >>>
> >>> - Using Fiber::resume() to initialize the fiber and resume feels
> >> awkward. Separate methods again would be better here, perhaps
> >> Fiber::init(...$args) and Fiber::resume($send).
> >>
> >> All Fiber created with a suspended status. So make resume to do both the
> >> init and resume
> >> do make sense.
> >>
> >
> > It does't make sense to me. Reading the example in the README and
> > understanding why the first resume() takes two arguments instead of one
> > took me quite some minutes.
>
> This Ruby's Fiber and Lua's coroutine using one resume API to init and
> resume
> the coroutine. I do not think a dedicate is really required.
>
> The generator cannot be init by it's send method. And if you want to
> implement
> coroutine feature(without stack) by it, you have to write code
>
> function run() {
> if ($this->beforeFirstYield) {
> $this->beforeFirstYield = false;
> return $this->coroutine->current();
> } else {
> $retval = $this->coroutine->send($this->sendValue);
> $this->sendValue = null;
> return $retval;
> }
> }
>
> It is verbose.
>

That's why we directly prime coroutines on creation, see
https://github.com/amphp/amp/blob/4a742beb59615f36ed998e2dc210e36576e44c44/lib/Coroutine.php#L36-L52


> See https://nikic.github.io/2012/12/22/Cooperative-
> multitasking-using-coroutines-in-PHP.html
>
> >
> >> Please see Ruby Fiber API https://ruby-doc.org/core-2.2.0/Fiber.html.
> >>
> >>>
> >>> - What happens if the sub1() function in the RFC is invoked outside of
> a
> >> fiber?
> >>
> >> You will get a Fatal Error like
> >> Fatal error: Uncaught Error: Cannot call Fiber::yield out of Fiber
> >>
> >>> - I think a keyword here would be beneficial, even if it has a minor BC
> >> impact. Fibers could then be written like generators. `await` or `emit`
> as
> >> a keyword perhaps? This would be a less verbose API, feel less magical
> (a
> >> static method call that actually pauses execution feels out of place),
> and
> >> would allow Fibers to be returned from methods, named functions, etc
> with
> >> less boilerplate.
> >>
> >> Wishing this to be accepted by the community in the PHP 7.3, so no
> keyword
> >> is accepted.
> >> And if the community cannot accept, the Fiber can be still distributed
> as
> >> a standalone
> >> extension. So we cannot depend on a new keyword.
> >
> >
> > Right, if it's a standalone extension it can't use a new keyword, but as
> a
> > language feature it totally can.
>
> In my opinion, using a keyword or call a method is just a coding style
> problem.
> Introducing a new keyword does not offer any benefit by makes a minor BC.
>

It makes code way easier to write IMO.


> Both Ruby's Fiber and Lua's coroutine does not required a dedicate keyword.
>
> > Looking at the current README, there are two issues that must be
> completely
> > solved IMO before accepting this:
> >
> >> Each Fiber has a separate 4k stack. You can use the fiber.stack_size ini
> > option to change the default stack size. You can also use the second
> > argument of Fiber::__construct to set the stack size on fly.
> >
> > Resizing of the stack should happen automatically, just like generators
> > resize automatically.
>
> This size is the init stack size. It means when a Fiber created, it will
> get a
> dedicate stack of 4k size. When the fiber use all the stack space, zend vm
> will
> allocate additional space for feature call frame, automatically.
>
> The default size is 4k means that every fiber requires at least 4k memory
> to use
> as there own stack. But user can change this by php.ini and the construct
> argument
> to reduce the memory footprint.


That's good to hear! Any reason why these need to be configureable? They're
not for generators either. IMO a sane default would probably be enough.


>
> >
> >> Fiber::yield cannot be used in internal callback
> >
> > This also seems problematic and will make fibers quite less useful,
> > especially as these yields can happen anywhere down the stack.
> >
>
> This do be a problem. But not so much big problem.
>
> You cannot use Fiber::yield like
>
> $f = new Fiber(function () {
> array_map(function ($i) {
> Fiber::yield($i);
> }, [1, 2, 3]);
> });
> $f->resume();
> $f->resume();
>
> Because when zend execute the array_map, it will push a new frame onto the
> c stack.
> When zend execute Fiber::yield, it only backup it's php stack, and it's c
> stack
> will be overwrites.
>
> However, you can use Fiber::yield like
>
> $f = new Fiber(function () {
> Fiber::yield(1); // will cause by resume, by an internal callback
> });
>
> ExtEventLoop::onRead($fd, function () { // this is an internal call
> $f->resume();
> });


The issue here is not using it directly within array_map, but rather
somewhere down the stack, which a user can never know.

This might result in subtle BC breaks. It means that a Fiber::yield() can
never be added to code without breaking BC. I guess we need to rewrite all
functions that accept user-defined callbacks for it to work.

IMO PHP's main() function should be a Fiber, too, which makes it impossible
to use Fiber::yield() outside a Fiber and enables top-level await().

Regards, Niklas
Björn Larsson
Re: [PHP-DEV] [RFC] Fiber support (again)
February 09, 2018 10:00PM
Den 2018-02-09 kl. 12:48, skrev Niklas Keller:
>
> We have started building a PoC library on top of Fibers, see
> https://github.com/amphp/green-thread/blob/7bd3470e7986169372d5e9c39500f3652091b512/src/functions.php
> .
>
> We'd like to avoid the additional `await()` function and rather directly
> couple Fibers with promises in the PHP core.
>
> Using `await` (the keyword) instead of `Fiber::yield()` feels way better
> and avoids the need for any wrapping libraries for what should be a core
> feature.
>
> `async` can be added to create a new Fiber and Fiber can implement Promise.
>
Regarding these potential new keywords await & async.
Any need to look into how Hacklang uses these keywords?
Could there be portability aspects on the functionality in
itself?

Regards //Björn Larsson

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Niklas Keller
Re: [PHP-DEV] [RFC] Fiber support (again)
February 10, 2018 08:40AM
2018-02-09 21:53 GMT+01:00 Björn Larsson <[email protected]>:
> Regarding these potential new keywords await & async.
> Any need to look into how Hacklang uses these keywords?
> Could there be portability aspects on the functionality in
> itself?

No, there's no need to look at Hacklang and be compatible. They do
their own thing.

Regards, Niklas

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Haitao Lv
Re: [PHP-DEV] [RFC] Fiber support (again)
February 10, 2018 11:00AM
Hi, all,

I have updated the RFC https://wiki.php.net/rfc/fiber

changes list:

- introduce the `throw(Exception $exceptin)` API
- record issues discussed

> On Feb 9, 2018, at 08:12, Haitao Lv <[email protected]> wrote:
>
>>
>> On Feb 9, 2018, at 06:22, Niklas Keller <[email protected]> wrote:
>>
>>>
>>>> - How do you determine when a fiber has returned? Looking at the source,
>>> it appears Fiber::status() must be used, comparing against constants.
>>> Separate methods similar to Generator would be better IMO. e.g.:
>>> Fiber::alive(), Fiber::suspended(), Fiber::running()
>>>
>>> Offering methods like Fiber::alive, Fiber::running makes no difference to
>>> check the Fiber::status() return value. This is just a style issue. And as
>>> a language feature,
>>> Fiber only offer the essential API and let other works to the user land.
>>
>>
>> The language should offer a sane API, not the absolute minimum required to
>> work for these things.
>
> The Ruby's Fiber do offer a live? method but does not have a getStatus method.
> The Lua's coroutine only offer a status method.
>
> So do we really need to offer three additional helper method? Or what is your
> advice about these API?
>
>>
>>>> - What about throwing exceptions into a fiber?
>>>
>>> Currently does not support throw exception into the fiber. User land code
>>> could check
>>> the value of Fiber::yield and throw exception themselves. The Ruby's Fiber
>>> and Lua's
>>> coroutine also does not support such api as well.
>>
>>
>> And throw the exception where? That means async code with fibers can't
>> really handle errors?
>
> Actually you can transfer any thing to Fiber by the resume method. And you can
> check the return value of Fiber::yield to handle error.
>
> Fiber is designed as a primitive, low level, and lightweight feature. User land
> code seldom not need to use them directly in your normal code.
> So the following is not a big problem,
>
> $a = Fiber::yield(...);
> if ($a === false) {
> throw new Exception(...);
> }
>
> And both the Ruby and Lua does not offer such API as well.
>>
>>>
>>>>
>>>> - Using Fiber::resume() to initialize the fiber and resume feels
>>> awkward. Separate methods again would be better here, perhaps
>>> Fiber::init(...$args) and Fiber::resume($send).
>>>
>>> All Fiber created with a suspended status. So make resume to do both the
>>> init and resume
>>> do make sense.
>>>
>>
>> It does't make sense to me. Reading the example in the README and
>> understanding why the first resume() takes two arguments instead of one
>> took me quite some minutes.
>
> This Ruby's Fiber and Lua's coroutine using one resume API to init and resume
> the coroutine. I do not think a dedicate is really required.
>
> The generator cannot be init by it's send method. And if you want to implement
> coroutine feature(without stack) by it, you have to write code
>
> function run() {
> if ($this->beforeFirstYield) {
> $this->beforeFirstYield = false;
> return $this->coroutine->current();
> } else {
> $retval = $this->coroutine->send($this->sendValue);
> $this->sendValue = null;
> return $retval;
> }
> }
>
> It is verbose.
>
> See https://nikic.github.io/2012/12/22/Cooperative-multitasking-using-coroutines-in-PHP.html
>
>>
>>> Please see Ruby Fiber API https://ruby-doc.org/core-2.2.0/Fiber.html.
>>>
>>>>
>>>> - What happens if the sub1() function in the RFC is invoked outside of a
>>> fiber?
>>>
>>> You will get a Fatal Error like
>>> Fatal error: Uncaught Error: Cannot call Fiber::yield out of Fiber
>>>
>>>> - I think a keyword here would be beneficial, even if it has a minor BC
>>> impact. Fibers could then be written like generators. `await` or `emit` as
>>> a keyword perhaps? This would be a less verbose API, feel less magical (a
>>> static method call that actually pauses execution feels out of place), and
>>> would allow Fibers to be returned from methods, named functions, etc with
>>> less boilerplate.
>>>
>>> Wishing this to be accepted by the community in the PHP 7.3, so no keyword
>>> is accepted.
>>> And if the community cannot accept, the Fiber can be still distributed as
>>> a standalone
>>> extension. So we cannot depend on a new keyword.
>>
>>
>> Right, if it's a standalone extension it can't use a new keyword, but as a
>> language feature it totally can.
>
> In my opinion, using a keyword or call a method is just a coding style problem.
> Introducing a new keyword does not offer any benefit by makes a minor BC.
>
> Both Ruby's Fiber and Lua's coroutine does not required a dedicate keyword.
>
>> Looking at the current README, there are two issues that must be completely
>> solved IMO before accepting this:
>>
>>> Each Fiber has a separate 4k stack. You can use the fiber.stack_size ini
>> option to change the default stack size. You can also use the second
>> argument of Fiber::__construct to set the stack size on fly.
>>
>> Resizing of the stack should happen automatically, just like generators
>> resize automatically.
>
> This size is the init stack size. It means when a Fiber created, it will get a
> dedicate stack of 4k size. When the fiber use all the stack space, zend vm will
> allocate additional space for feature call frame, automatically.
>
> The default size is 4k means that every fiber requires at least 4k memory to use
> as there own stack. But user can change this by php.ini and the construct argument
> to reduce the memory footprint.
>
>>
>>> Fiber::yield cannot be used in internal callback
>>
>> This also seems problematic and will make fibers quite less useful,
>> especially as these yields can happen anywhere down the stack.
>>
>
> This do be a problem. But not so much big problem.
>
> You cannot use Fiber::yield like
>
> $f = new Fiber(function () {
> array_map(function ($i) {
> Fiber::yield($i);
> }, [1, 2, 3]);
> });
> $f->resume();
> $f->resume();
>
> Because when zend execute the array_map, it will push a new frame onto the c stack.
> When zend execute Fiber::yield, it only backup it's php stack, and it's c stack
> will be overwrites.
>
> However, you can use Fiber::yield like
>
> $f = new Fiber(function () {
> Fiber::yield(1); // will cause by resume, by an internal callback
> });
>
> ExtEventLoop::onRead($fd, function () { // this is an internal call
> $f->resume();
> });
>
>> Regards, Niklas
>
>
>
>
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Niklas Keller
Re: [PHP-DEV] [RFC] Fiber support (again)
February 10, 2018 04:00PM
> Hi, all,
>
> I have updated the RFC https://wiki.php.net/rfc/fiber
>
> changes list:
>
> - introduce the `throw(Exception $exceptin)` API
> - record issues discussed

What about my suggestion of making PHP's main() automatically a Fiber,
which avoids Fiber::yield() being used outside of a Fiber, because
everything is a Fiber?

This would require another continuation mechanism, as nothing has
access to the automatically created main()-Fiber otherwise.

There would also need to be something that stops the script execution
as soon as there's no non-suspended Fiber anymore.

Regarding the internal calls: A core dump / segfault in case of
Fiber::yield() inside an internal function is unacceptable. It doesn't
give the user any clue what's wrong. Instead, an exception could be
thrown from Fiber::yield(), which just bubbles up then. Full support
for internal functions could be added at a later point then.

Regards, Niklas


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吕海涛
Re: [PHP-DEV] [RFC] Fiber support (again)
February 10, 2018 04:10PM
> On Feb 10, 2018, at 22:49, Niklas Keller <[email protected]> wrote:
>
>> Hi, all,
>>
>> I have updated the RFC https://wiki.php.net/rfc/fiber
>>
>> changes list:
>>
>> - introduce the `throw(Exception $exceptin)` API
>> - record issues discussed
>
> What about my suggestion of making PHP's main() automatically a Fiber,
> which avoids Fiber::yield() being used outside of a Fiber, because
> everything is a Fiber?
>
> This would require another continuation mechanism, as nothing has
> access to the automatically created main()-Fiber otherwise.
>
> There would also need to be something that stops the script execution
> as soon as there's no non-suspended Fiber anymore.

As you pointed out, the main process cannot be a Fiber because it need to
schedule other fibers.

>
> Regarding the internal calls: A core dump / segfault in case of
> Fiber::yield() inside an internal function is unacceptable. It doesn't
> give the user any clue what's wrong. Instead, an exception could be
> thrown from Fiber::yield(), which just bubbles up then. Full support
> for internal functions could be added at a later point then.

It is impossible to solve this issue before we get a pure stackless Zend VM.

If this feature can be merged into PHP 7.3, we could introduce a new counter
to record the zend vm nested level. Every time you enter an internal call,
let zend increment the counter, and decrement it when out.

When we create a fiber, we remember current vm nested level. When zend execute
Fiber::yield,it will throw an error if the current vm nested level is not
equal to the original one.

This feature cannot be implemented without changing the zend vm code base.

Maybe we could get a stackless zend vm in the feature. like the stackless python

https://github.com/stackless-dev/stackless

>
> Regards, Niklas




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Niklas Keller
Re: [PHP-DEV] [RFC] Fiber support (again)
February 10, 2018 04:50PM
>> There would also need to be something that stops the script execution
>> as soon as there's no non-suspended Fiber anymore.
>
> As you pointed out, the main process cannot be a Fiber because it need to
> schedule other fibers.

The conclusion is wrong. There just needs to be a way to access this
fiber, e.g. Fiber::getMain().

>>
>> Regarding the internal calls: A core dump / segfault in case of
>> Fiber::yield() inside an internal function is unacceptable. It doesn't
>> give the user any clue what's wrong. Instead, an exception could be
>> thrown from Fiber::yield(), which just bubbles up then. Full support
>> for internal functions could be added at a later point then.
>
> It is impossible to solve this issue before we get a pure stackless Zend VM.
>
> If this feature can be merged into PHP 7.3, we could introduce a new counter
> to record the zend vm nested level. Every time you enter an internal call,
> let zend increment the counter, and decrement it when out.
>
> When we create a fiber, we remember current vm nested level. When zend execute
> Fiber::yield,it will throw an error if the current vm nested level is not
> equal to the original one.
>
> This feature cannot be implemented without changing the zend vm code base.

You're proposing this as language feature, not as an external
extension, so that is entirely fine and actually the reason why this
should be in core instead of an external extension.

Regards, Niklas

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