Microtask scheduling

Calvin Metcalf calvin.metcalf at gmail.com
Mon Jun 26 17:48:48 UTC 2017

One of the big use cases for process.nextTick is throwing errors outside
the current stack, either to avoid preventing cleanup or to avoid being
caught in try/catch blocks or promise chains so using a promise directly
isn't very useful.  This came up in the browserify/webpack shim for

On Mon, Jun 26, 2017 at 12:29 PM C. Scott Ananian <ecmascript at cscott.net>

> Promise dispatch should actually simplify to this in certain common
> cases.  I meant to write up a document describing the typical dispatch
> optimizations high-performance Promise libraries do, based on my
> experiences writing https://github.com/cscott/babybird (although
> Optimization Notes in the README of that package contains the basic
> details).  Assuming the Promise implementation is fast, then
> Promise#then0(...) should basically give you direct access to the internal
> `asap`-like dispatcher.
>   --scott
> On Mon, Jun 26, 2017 at 8:20 AM, Calvin Metcalf <calvin.metcalf at gmail.com>
> wrote:
>> Kris, you're conflating macrotasks and microtasks [1]. This has come up a
>> couple times before and there have been issues raised by browser
>> venders[2][3].
>> 1. https://github.com/YuzuJS/setImmediate#macrotasks-and-microtasks
>> 2. https://bugzilla.mozilla.org/show_bug.cgi?id=686201
>> 3.
>> https://groups.google.com/a/chromium.org/forum/#!msg/blink-dev/Hn3GxRLXmR0/XP9xcY_gBPQJ
>> On Mon, Jun 26, 2017 at 2:51 AM Kris Siegel <krissiegel at gmail.com> wrote:
>>> This seems more like a platform-level feature versus something that
>>> needs to be part of the ECMAScript standard. Also, keep in mind it's rarely
>>> a good idea to explicitly call nextTick() in node as it executes the code
>>> immediately after the current code is finished and before the next,
>>> scheduled code (this can cause issues with processing I/O if you're doing
>>> it too frequently).
>>> In a browser you can sorta emulate similar behavior through IE's
>>> setImmediate(), using postMessage() or even the requestAnimationFrame().
>>> Granted none of those are exactly like nextTick() and I wouldn't mind
>>> seeing something like setImmediate() become more of a standard but this
>>> isn't for the ECMAScript group.
>>> On Wed, Jun 21, 2017 at 2:10 PM, Isiah Meadows <isiahmeadows at gmail.com>
>>> wrote:
>>>> It's a relatively low-level operation, but in performance-sensitive
>>>> async code and polyfills, there's still a strong need for raw
>>>> microtask scheduling, at a much lower level than promises. In
>>>> particular, there's two very frequently used modules providing a
>>>> wrapper for this specific thing:
>>>> 1. next-tick: A browser polyfill for Node's `process.nextTick`, with
>>>> over 2M downloads last month and 88 direct dependents.
>>>> 2. asap: A microtask scheduler that avoids blocking Node's I/O loop,
>>>> with over 7M downloads last month and 88 direct dependents.
>>>> In addition, several libraries like Bluebird have to implement their
>>>> own wrappers to gain similar functionality without assuming another
>>>> dependency.
>>>> Any chance something like Node's `process.nextTick` could be added,
>>>> maybe something like `Promise.schedule(func, thisArg, ...args)`?
>>>> -----
>>>> Isiah Meadows
>>>> me at isiahmeadows.com
>>>> Looking for web consulting? Or a new website?
>>>> Send me an email and we can get started.
>>>> www.isiahmeadows.com
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