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Date: Sat, 9 Sep 2017 06:29:11 +0000 (UTC)
To: Rowan Collins <rowan.collins@gmail.com>, Haitao Lv <i@lvht.net>
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Subject: Re: [PHP-DEV] add Fiber (sackful coroutine) support
From: hufeng1987@gmail.com (zixu mo)

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the best corotine . must be golang go and chan. very easy to use. non blocking. 




On Sat, Sep 9, 2017 at 2:28 PM +0800, "Haitao Lv" <i@lvht.net> wrote:











> On 2 Sep 2017, at 20:19, Rowan Collins  wrote:
> 
> On 1 September 2017 14:02:29 BST, Haitao Lv  wrote:
>> 
>> Fiber is a lightweight thread. Please see
>> https://en.wikipedia.org/wiki/Fiber_(computer_science)
>> And ruby support Fiber. Please see
>> https://ruby-doc.org/core-2.4.1/Fiber.html
> 
> Ah, thanks, that makes more sense now.
> 
> I note that the examples there all implement it not as a keyword, but as a library function, which maybe makes more sense: whereas "yield" turns a function declaration into a generator declaration, "Fiber\yield", as we might call it, is just a function call which can happen anywhere and manipulates some global state.

As the Zend Engine does not offer API to pause execution, I cannot implement the await without
introducing a new keyword (just like yield).

> The choice of "await" also feels odd: you're not awaiting the thing on the right-hand side of the keyword, you're sending it somewhere and awaiting something else.

await is chosen because we cannot reuse the `yield` keyword. Maybe we can choose a more proper keyword.

>> You can see the await as a resumable return. The value after it
>> will be returned and the function
>> will be paused.
> 
> Again, this explanation doesn't make sense if you can call foo() without any Fiber code. If there isn't an active Fiber to pause, the "await" line can't "return" anything; it will presumably throw an error of some sort.
> 
> function foo($x) {
>     $y = Fiber\yield($x);
>     return $x + $y;
> }
> echo foo(1);
> 
> The 1 isn't "returned" to the echo, it's passed off to a global function for further processing. This makes much more sense to me than implying that foo() is no longer a normal function.

await is not yield. It need a separate vm stack to work. So call the foo function without a Fiber will
throw a runtime error exception.

> 
>>> Your ->resume() doesn't seem to do anything a normal generator can't,
>> except that the yield is nested deeper.
>> 
>> The await is a nested deeper yield!
> 
> Yes, I understand that, but that seems to be completely unrelated to the API design of having resume() act as start, continue, and final result all rolled into one. As I say, I didn't entirely follow the reasoning for allowing return in generators, but if Fibers are used for the same purpose, I would expect the same concerns to arise.
> 
> However, I think the comparison to generators may be more distracting than useful, as they seem to be very different solutions to the same or related problems.

If fiber were implemented, the generator would be a special fiber.




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