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Add AbortSignal.any()
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- This implements an optimization that puts all children on
  non-dependent signals (i.e., those associated with a controller).
  This allows "intermediate" nodes (e.g., B in A follows B follows C)
  to be garbage collected if they are being kept alive to propagate
  aborts.

- This removes the follow algorithm, so callsites will need to be
  updated.

- The "create a composite abort signal" algorithm takes an interface so
  that TaskSignal.any() can easily hook into it, but create a 
  TaskSignal.

- Some algorithms that invoke "follow" create an AbortSignal in a 
  particular realm. This enables doing that, but borrows some language 
  from elsewhere in the spec w.r.t. doing the default thing. Neither of
  the other two static members specify a realm.

Follow-up PRs:

- whatwg/fetch#1646
- w3c/ServiceWorker#1678
- whatwg/streams#1277

This also sets the stage to make AbortSignal's "signal abort" fully 
internal. #1194 tracks the remainder.

Tests: web-platform-tests/wpt#37434 and web-platform-tests/wpt#39785.

Fixes #920.
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@shaseley
shaseley authored May 17, 2023
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Original file line number Diff line number Diff line change
Expand Up @@ -30,6 +30,7 @@ type: interface
urlPrefix: https://tc39.es/ecma262/#; spec: ECMASCRIPT
text: Construct; url: sec-construct; type: abstract-op
type: dfn
text: current realm; url: current-realm
text: realm; url: realm
text: surrounding agent; url: surrounding-agent
urlPrefix: https://w3c.github.io/hr-time/#; spec: HR-TIME
Expand Down Expand Up @@ -1768,6 +1769,7 @@ interface AbortController {
<p>An {{AbortController}} object has an associated <dfn for=AbortController>signal</dfn> (an
{{AbortSignal}} object).

<div algorithm>
<p>The
<dfn constructor for=AbortController lt="AbortController()"><code>new AbortController()</code></dfn>
constructor steps are:
Expand All @@ -1777,13 +1779,22 @@ constructor steps are:

<li><p>Set <a>this</a>'s <a for=AbortController>signal</a> to <var>signal</var>.
</ol>
</div>

<p>The <dfn attribute for=AbortController><code>signal</code></dfn> getter steps are to return
<a>this</a>'s <a for=AbortController>signal</a>.

<div algorithm>
<p>The <dfn method for=AbortController><code>abort(<var>reason</var>)</code></dfn> method steps are
to <a for=AbortSignal>signal abort</a> on <a>this</a>'s <a for=AbortController>signal</a> with
<var>reason</var> if it is given.
to <a for=AbortController>signal abort</a> on <a>this</a> with <var>reason</var> if it is given.
</div>

<div algorithm>
<p>To <dfn export for=AbortController>signal abort</dfn> on an {{AbortController}}
<var>controller</var> with an optional <var>reason</var>, <a for=AbortSignal>signal abort</a> on
<var>controller</var>'s <a for=AbortController>signal</a> with <var>reason</var> if it is given.
</div>


<h3 id=interface-AbortSignal>Interface {{AbortSignal}}</h3>

Expand All @@ -1792,6 +1803,7 @@ to <a for=AbortSignal>signal abort</a> on <a>this</a>'s <a for=AbortController>s
interface AbortSignal : EventTarget {
[NewObject] static AbortSignal abort(optional any reason);
[Exposed=(Window,Worker), NewObject] static AbortSignal timeout([EnforceRange] unsigned long long milliseconds);
[NewObject] static AbortSignal _any(sequence&lt;AbortSignal> signals);

readonly attribute boolean aborted;
readonly attribute any reason;
Expand All @@ -1805,6 +1817,11 @@ interface AbortSignal : EventTarget {
<dd>Returns an {{AbortSignal}} instance whose <a for=AbortSignal>abort reason</a> is set to
<var>reason</var> if not undefined; otherwise to an "{{AbortError!!exception}}" {{DOMException}}.

<dt><code>AbortSignal . <a method for=AbortSignal lt=any(signals)>any</a>(<var>signals</var>)</code>
<dd>Returns an {{AbortSignal}} instance which will be aborted once any of <var>signals</var> is
aborted. Its <a for=AbortSignal>abort reason</a> will be set to whichever one of <var>signals</var>
caused it to be aborted.

<dt><code>AbortSignal . <a method for=AbortSignal lt=timeout(milliseconds)>timeout</a>(<var>milliseconds</var>)</code>
<dd>Returns an {{AbortSignal}} instance which will be aborted in <var>milliseconds</var>
milliseconds. Its <a for=AbortSignal>abort reason</a> will be set to a
Expand All @@ -1821,35 +1838,32 @@ interface AbortSignal : EventTarget {
{{AbortController}} has signaled to abort; otherwise, does nothing.
</dl>

<p>An {{AbortSignal}} object has an associated <dfn export for=AbortSignal>abort reason</dfn>, which is a
JavaScript value. It is undefined unless specified otherwise.

<p>An {{AbortSignal}} object is <dfn export for="AbortSignal">aborted</dfn> when its
[=AbortSignal/abort reason=] is not undefined.

<p>An {{AbortSignal}} object has associated <dfn for=AbortSignal>abort algorithms</dfn>, which is a
<a for=/>set</a> of algorithms which are to be executed when it is [=AbortSignal/aborted=]. Unless
specified otherwise, its value is the empty set.

<p>To <dfn export for=AbortSignal>add</dfn> an algorithm <var>algorithm</var> to an {{AbortSignal}}
object <var>signal</var>, run these steps:

<ol>
<li><p>If <var>signal</var> is [=AbortSignal/aborted=], then return.

<li><p><a for=set>Append</a> <var>algorithm</var> to <var>signal</var>'s
<a for=AbortSignal>abort algorithms</a>.
</ol>
<p>An {{AbortSignal}} object has an associated <dfn export for=AbortSignal>abort reason</dfn> (a
JavaScript value), which is initially undefined.

<p>To <dfn export for=AbortSignal>remove</dfn> an algorithm <var>algorithm</var> from an
{{AbortSignal}} <var>signal</var>, <a for=set>remove</a> <var>algorithm</var> from
<var>signal</var>'s <a for=AbortSignal>abort algorithms</a>.
<p>An {{AbortSignal}} object has associated <dfn for=AbortSignal>abort algorithms</dfn>, (a
<a for=/>set</a> of algorithms which are to be executed when it is [=AbortSignal/aborted=]),
which is initially empty.

<p class=note>The [=AbortSignal/abort algorithms=] enable APIs with complex
requirements to react in a reasonable way to {{AbortController/abort()}}. For example, a given API's
[=AbortSignal/abort reason=] might need to be propagated to a cross-thread environment, such as a
service worker.

<p>An {{AbortSignal}} object has a <dfn for="AbortSignal">dependent</dfn> (a boolean), which is
initially false.

<p>An {{AbortSignal}} object has associated <dfn for=AbortSignal>source signals</dfn> (a weak
<a for=/>set</a> of {{AbortSignal}} objects that the object is dependent on for its
[=AbortSignal/aborted=] state), which is initially empty.

<p>An {{AbortSignal}} object has associated <dfn for=AbortSignal>dependent signals</dfn> (a weak
<a for=/>set</a> of {{AbortSignal}} objects that are dependent on the object for their
[=AbortSignal/aborted=] state), which is initially empty.

<hr>

<div algorithm>
<p>The static <dfn method for=AbortSignal><code>abort(<var>reason</var>)</code></dfn> method steps
are:

Expand All @@ -1861,7 +1875,9 @@ are:

<li>Return <var>signal</var>.
</ol>
</div>

<div algorithm>
<p>The static <dfn method for=AbortSignal><code>timeout(<var>milliseconds</var>)</code></dfn> method
steps are:

Expand All @@ -1886,6 +1902,13 @@ steps are:

<li><p>Return <var>signal</var>.
</ol>
</div>

<div algorithm>
<p>The static <dfn method for=AbortSignal><code>any(<var>signals</var>)</code></dfn> method
steps are to return the result of <a>creating a dependent abort signal</a> from <var>signals</var>
using {{AbortSignal}} and the <a>current realm</a>.
</div>

<p>The <dfn attribute for=AbortSignal>aborted</dfn> getter steps are to return true if <a>this</a>
is [=AbortSignal/aborted=]; otherwise false.
Expand Down Expand Up @@ -1924,46 +1947,114 @@ is [=AbortSignal/aborted=]; otherwise false.
<dfn event for=AbortSignal><code>abort</code></dfn>.

<p class=note>Changes to an {{AbortSignal}} object represent the wishes of the corresponding
{{AbortController}} object, but an API observing the {{AbortSignal}} object can chose to ignore
{{AbortController}} object, but an API observing the {{AbortSignal}} object can choose to ignore
them. For instance, if the operation has already completed.

<hr>

<p>An {{AbortSignal}} object is <dfn export for="AbortSignal">aborted</dfn> when its
[=AbortSignal/abort reason=] is not undefined.

<div algorithm>
<p>To <dfn export for=AbortSignal>add</dfn> an algorithm <var>algorithm</var> to an {{AbortSignal}}
object <var>signal</var>:

<ol>
<li><p>If <var>signal</var> is [=AbortSignal/aborted=], then return.

<li><p><a for=set>Append</a> <var>algorithm</var> to <var>signal</var>'s
<a for=AbortSignal>abort algorithms</a>.
</ol>
</div>

<div algorithm>
<p>To <dfn export for=AbortSignal>remove</dfn> an algorithm <var>algorithm</var> from an
{{AbortSignal}} <var>signal</var>, <a for=set>remove</a> <var>algorithm</var> from
<var>signal</var>'s <a for=AbortSignal>abort algorithms</a>.
</div>

<div algorithm>
<p>To <dfn export for=AbortSignal>signal abort</dfn>, given an {{AbortSignal}} object
<var>signal</var> and an optional <var>reason</var>, run these steps:
<var>signal</var> and an optional <var>reason</var>:

<ol>
<li><p>If <var>signal</var> is [=AbortSignal/aborted=], then return.

<li><p>Set <var>signal</var>'s [=AbortSignal/abort reason=] to <var>reason</var> if it is given;
otherwise to a new "{{AbortError!!exception}}" {{DOMException}}.

<li><p><a for=set>For each</a> <var>algorithm</var> in <var>signal</var>'s
<li><p><a for=set>For each</a> <var>algorithm</var> of <var>signal</var>'s
[=AbortSignal/abort algorithms=]: run <var>algorithm</var>.

<li><p><a for=set>Empty</a> <var>signal</var>'s <a for=AbortSignal>abort algorithms</a>.

<li><p>[=Fire an event=] named {{AbortSignal/abort}} at <var>signal</var>.

<li><p><a for=set>For each</a> <var>dependentSignal</var> of <var>signal</var>'s
[=AbortSignal/dependent signals=], [=AbortSignal/signal abort=] on <var>dependentSignal</var> with
<var>signal</var>'s [=AbortSignal/abort reason=].
</ol>
</div>

<p>A <var>followingSignal</var> (an {{AbortSignal}}) is made to
<dfn export for=AbortSignal>follow</dfn> a <var>parentSignal</var> (an {{AbortSignal}}) by running
these steps:
<div algorithm>
<p>To <dfn export>create a dependent abort signal</dfn> from a list of {{AbortSignal}} objects
<var>signals</var>, using <var>signalInterface</var>, which must be either {{AbortSignal}} or an
interface that inherits from it, and a <var>realm</var>:

<ol>
<li><p>If <var>followingSignal</var> is [=AbortSignal/aborted=], then return.
<li><p>Let <var>resultSignal</var> be a <a for=/>new</a> object implementing
<var>signalInterface</var> using <var>realm</var>.

<li><p>If <var>parentSignal</var> is [=AbortSignal/aborted=], then
<a for=AbortSignal>signal abort</a> on <var>followingSignal</var> with <var>parentSignal</var>'s
[=AbortSignal/abort reason=].
<li><p><a for=list>For each</a> <var>signal</var> of <var>signals</var>: if <var>signal</var> is
[=AbortSignal/aborted=], then set <var>resultSignal</var>'s [=AbortSignal/abort reason=] to
<var>signal</var>'s [=AbortSignal/abort reason=] and return <var>resultSignal</var>.

<li><p>Set <var>resultSignal</var>'s [=AbortSignal/dependent=] to true.

<li>
<p>Otherwise, <a for=AbortSignal lt=add>add the following abort steps</a> to
<var>parentSignal</var>:
<p><a for=list>For each</a> <var>signal</var> of <var>signals</var>:

<ol>
<li><p><a for=AbortSignal>Signal abort</a> on <var>followingSignal</var> with
<var>parentSignal</var>'s [=AbortSignal/abort reason=].
<li>
<p>If <var>signal</var>'s [=AbortSignal/dependent=] is false, then:

<ol>
<li><p><a for=set>Append</a> <var>signal</var> to <var>resultSignal</var>'s
[=AbortSignal/source signals=].

<li><p><a for=set>Append</a> <var>resultSignal</var> to <var>signal</var>'s
[=AbortSignal/dependent signals=].
</ol>

<li>
<p>Otherwise, <a for=list>for each</a> <var>sourceSignal</var> of <var>signal</var>'s
[=AbortSignal/source signals=]:

<ol>
<li><p>Assert: <var>sourceSignal</var> is not [=AbortSignal/aborted=] and not
[=AbortSignal/dependent=].

<li><p>If <var>resultSignal</var>'s [=AbortSignal/source signals=] <a for=set>contains</a>
<var>sourceSignal</var>, then <a for=iteration>continue</a>.

<li><p><a for=set>Append</a> <var>sourceSignal</var> to <var>resultSignal</var>'s
[=AbortSignal/source signals=].

<li><p><a for=set>Append</a> <var>resultSignal</var> to <var>sourceSignal</var>'s
[=AbortSignal/dependent signals=].
</ol>
</ol>

<li><p>Return <var>resultSignal</var>.
</ol>
</div>


<h4 id=abort-signal-garbage-collection>Garbage collection</h4>

<p>A non-[=AbortSignal/aborted=] [=AbortSignal/dependent=] {{AbortSignal}} object must not be
garbage collected while its [=AbortSignal/source signals=] is non-empty and it has registered event
listeners for its {{AbortSignal/abort}} event or its [=AbortSignal/abort algorithms=] is non-empty.


<h3 id=abortcontroller-api-integration>Using {{AbortController}} and {{AbortSignal}} objects in
Expand Down

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