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run microtasks before ticks #51267

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run microtasks before ticks #51267

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14 changes: 14 additions & 0 deletions doc/api/cli.md
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Original file line number Diff line number Diff line change
Expand Up @@ -863,6 +863,20 @@ Use this flag to generate a blob that can be injected into the Node.js
binary to produce a [single executable application][]. See the documentation
about [this configuration][`--experimental-sea-config`] for details.


### `--experimental-task-ordering`

<!-- YAML
added: REPLACEME
-->

> Stability: 1 - Experimental

Enable experimental task ordering. Always drain micro task queue
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Suggested change
Enable experimental task ordering. Always drain micro task queue
Enable experimental task ordering. Always drain Microtasks queue

It would also be useful to link to a doc like https://developer.mozilla.org/en-US/docs/Web/API/HTML_DOM_API/Microtask_guide#microtasks here.

before running `process.nextTick` to avoid unintuitive behavior
and unexpected logical deadlocks when mixing async callback and
event API's with `Promise`, `async`/`await`` and `queueMicroTask`.
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Can you provide some examples? Without examples I doubt how many users would be able to recognize whether this can be useful for them and pick up this option.

Also note that we have a section in process.md saying..

every time the "next tick queue" is drained, the microtask queue
is drained immediately after.

I think that should be updated to mention this option.


### `--experimental-shadow-realm`

<!-- YAML
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13 changes: 12 additions & 1 deletion lib/internal/process/task_queues.js
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Expand Up @@ -41,6 +41,7 @@ const {

const { AsyncResource } = require('async_hooks');

let experimentalTaskOrdering;
// *Must* match Environment::TickInfo::Fields in src/env.h.
const kHasTickScheduled = 0;

Expand All @@ -65,8 +66,16 @@ function runNextTicks() {
}

function processTicksAndRejections() {
if (experimentalTaskOrdering === undefined) {
const { getOptionValue } = require('internal/options');
experimentalTaskOrdering = getOptionValue('--experimental-task-ordering');
}

let tock;
do {
if (experimentalTaskOrdering) {
runMicrotasks();
}
while ((tock = queue.shift()) !== null) {
const asyncId = tock[async_id_symbol];
emitBefore(asyncId, tock[trigger_async_id_symbol], tock);
Expand All @@ -92,7 +101,9 @@ function processTicksAndRejections() {

emitAfter(asyncId);
}
runMicrotasks();
if (!experimentalTaskOrdering) {
runMicrotasks();
}
} while (!queue.isEmpty() || processPromiseRejections());
setHasTickScheduled(false);
setHasRejectionToWarn(false);
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