Clean up yield inheritance (#115)

Clean up yield inheritance:

 1. Key the scheduling state based on the {{Scheduler}} to prevent
    leaking it across (potentially cross-origin) windows. This changes
    the event loop's continuation state to be a small wrapper around a
    map. The continuation state is propagated in the same way, but the
    scheduler state is unique to the scheduler and not shared. In
    practice there will only be one entry in this map (a task or
    microtask can only have originated from one task), but the mechanism
    is generic enough to support other use cases, implementations
    can optimize this, and the key/value mapping hopefully makes the
    isolation clear.

 2. Propagate the current scheduling state in "queue a microtask",
    unless coming from JavaScript, in which case the propagation is
    handled by the abstract job closure. Previously, the state would be
    inherited only if it wasn't reset by another microtask or after the
    postTask callback ran. This fixes the inconsistency, making directly
    scheduled microtasks match microtasks originating from JavaScript.

Author: shaseley

spec/patches.md

@@ -32,8 +32,30 @@ determine task execution order across [=scheduler task queues=] of the same {{Ta
 all {{Scheduler}}s associated with the same [=event loop=]. A timestamp would also suffice as long
 as it is guaranteed to be strictly increasing and unique.
 
-Add: An [=event loop=] has a <dfn for="event loop">current scheduling state</dfn> (a [=scheduling
-state=] or null), which is initialized to null.
+Add: An [=event loop=] has a <dfn for="event loop">current continuation state</dfn> (a
+[=continuation state=] or null), which is initially null.
+
+Add the following algorithms:
+
+<div algorithm>
+  To <dfn>set the continuation state value</dfn> for |key| to |value| given an |eventLoop| (an
+  [=event loop=]):
+
+  1. If |eventLoop|'s [=event loop/current continuation state=] is null, then set |eventLoop|'s
+     [=event loop/current continuation state=] to a new [=continuation state=].
+  1. Let |continuationState| be |eventLoop|'s [=event loop/current continuation state=].
+  1. Assert: |continuationState|'s [=continuation state/state map=][|key|] does not [=map/exist=].
+  1. Set |continuationState|'s [=continuation state/state map=][|key|] to |value|.
+</div>
+
+<div algorithm>
+  To <dfn>get the continuation state value</dfn> for |key| given an |eventLoop| (an [=event loop=]):
+
+  1. Let |continuationState| be |eventLoop|'s [=event loop/current continuation state=].
+  1. If |continuationState| is not null and |continuationState|'s
+     [=continuation state/state map=][|key|] [=map/exists=], then return |continuationState|'s
+     [=continuation state/state map=][|key|], otherwise return null.
+</div>
 
 ### <a href="https://html.spec.whatwg.org/multipage/webappapis.html#event-loop-processing-model">Event loop: processing model</a> ### {#sec-patches-html-event-loop-processing}
 
@@ -80,33 +102,59 @@ Issue: The |taskQueue| in this step will either be a [=set=] of [=tasks=] or a [
 *roughly* compatible. Ideally, there would be a common task queue interface that supports a `pop()`
 method that would return a plain [=task=], but that would involve a fair amount of refactoring.
 
+### <a href="https://html.spec.whatwg.org/#queuing-tasks">Event Loop: Queuing Tasks</a> ### {#sec-patches-html-queuing-tasks}
+
+Change the <a href="https://html.spec.whatwg.org/#queue-a-microtask">To queue a microtask</a>
+algorithm to accept an optional boolean |ignoreContinuationState| (default false).
+
+Change Step 5 to the following:
+
+  1. Let |continuationState| be null.
+  1. If |ignoreContinuationState| is false and |eventLoop|'s
+     [=event loop/current continuation state=] is not null, then set |continuationState| to the
+     result of [=list/cloning=] |event loop|'s [=event loop/current continuation state=].
+  1. Set <var ignore=''>microtask</var>'s <a attribute for="task">steps</a> to the following:
+    1. If |ignoreContinuationState| is false, then set |eventLoop|'s
+       [=event loop/current continuation state=] to |continuationState|.
+    1. Run <var ignore=''>steps</var>.
+    1. If |ignoreContinuationState| is false, then set |eventLoop|'s
+       [=event loop/current continuation state=] to null.
+
 ### <a href="https://html.spec.whatwg.org/multipage/webappapis.html#hostmakejobcallback">HostMakeJobCallback(callable)</a> ### {#sec-patches-html-hostmakejobcallback}
 
 Add the following before step 5:
 
   1. Let |event loop| be <var ignore=''>incumbent settings<var>'s
      [=environment settings object/realm=]'s [=realm/agent=]'s [=agent/event loop=].
-  1. Let |state| be |event loop|'s [=event loop/current scheduling state=].
+  1. Let |state| be the result of [=list/cloning=] |event loop|'s
+     [=event loop/current continuation state=] if [=event loop/current continuation state=] is not
+     null, or otherwise null.
 
 Modify step 5 to read:
 
  1. Return the <span>JobCallback Record</span> { \[[Callback]]: <var ignore=''>callable</var>,
     \[[HostDefined]]: { \[[IncumbentSettings]]: <var ignore=''>incumbent settings</var>,
     \[[ActiveScriptContext]]: <var ignore=''>script execution context</var>,
-    \[[SchedulingState]]: |state| } }.
+    \[[ContinuationState]]: |state| } }.
 
 ### <a href="https://html.spec.whatwg.org/multipage/webappapis.html#hostcalljobcallback">HostCallJobCallback(callback, V, argumentsList)</a> ### {#sec-patches-html-hostcalljobcallback}
 
 Add the following steps before step 5:
 
   1. Let |event loop| be <var ignore=''>incumbent settings<var>'s
      [=environment settings object/realm=]'s [=realm/agent=]'s [=agent/event loop=].
-  1. Set |event loop|'s [=event loop/current scheduling state=] to
-     <var ignore=''>callback</var>.\[[HostDefined]].\[[SchedulingState]].
+  1. Set |event loop|'s [=event loop/current continuation state=] to
+     <var ignore=''>callback</var>.\[[HostDefined]].\[[ContinuationState]].
 
 Add the following after step 7:
 
-  1. Set |event loop|'s [=event loop/current scheduling state=] to null.
+  1. Set |event loop|'s [=event loop/current continuation state=] to null.
+
+### <a href="https://html.spec.whatwg.org/multipage/webappapis.html#hostenqueuepromisejob">HostEnqueuePromiseJob(job, realm)</a> ### {#sec-patches-html-hostenqueuepromisejob}
+
+Change step 2 to:
+
+ 1. Queue a microtask to perform the following steps with |ignoreContinuationState| set to true:
 
 ## <a href="https://w3c.github.io/requestidlecallback/">`requestIdleCallback()`</a> ## {#sec-patches-requestidlecallback}
 
@@ -118,9 +166,9 @@ Add the following step before step 3.3:
   1. Let |state| be a new [=scheduling state=].
   1. Set |state|'s [=scheduling state/priority source=] to the result of [=creating a fixed priority
      unabortable task signal=] given "{{TaskPriority/background}}" and |realm|.
-  1. Let |event loop| be |realm|'s [=realm/agent=]'s [=agent/event loop=].
-  1. Set |event loop|'s [=event loop/current scheduling state=] to |state|.
+  1. Let |scheduler| be the {{Scheduler}} whose [=relevant realm=] is |realm|.
+  1. [=Set the current scheduling state=] for |scheduler| to |state|.
 
 Add the following after step 3.3:
 
-  1. Set |event loop|'s [=event loop/current scheduling state=] to null.
+  1. Set |event loop|'s [=event loop/current continuation state=] to null.

spec/scheduling-tasks.md

@@ -175,12 +175,22 @@ A <dfn>scheduler task queue</dfn> is a [=struct=] with the following [=struct/it
 A <dfn>scheduling state</dfn> is a [=struct=] with the following [=struct/items=]:
 
 : <dfn for="scheduling state">abort source</dfn>
-:: An {{AbortSignal}} object or, initially null.
+:: An {{AbortSignal}} object or null, initially null.
 : <dfn for="scheduling state">priority source</dfn>
 :: A {{TaskSignal}} object or null, initially null.
 
 <br/>
 
+A <dfn>continuation state</dfn> is a [=struct=] with the following [=struct/items=]:
+
+: <dfn for="continuation state">state map</dfn>
+:: An initially empty [=map=].
+
+Note: The [=continuation state/state map=] can be implemented as weak map if its keys are
+implemented as garbage collected objects.
+
+<br/>
+
 A <dfn>task handle</dfn> is a [=struct=] with the following [=struct/items=]:
 
 : <dfn for="task handle">task</dfn>
@@ -289,6 +299,25 @@ A <dfn>task handle</dfn> is a [=struct=] with the following [=struct/items=]:
 
 ### Scheduling Tasks and Continuations ### {#sec-scheduler-alg-scheduling-tasks-and-continuations}
 
+<div algorithm>
+  To <dfn>set the current scheduling state</dfn> for |scheduler| (a {{Scheduler}}) to |state| (a
+  [=scheduling state=]):
+
+  1. Let |eventLoop| be |scheduler|'s [=relevant agent=]'s [=agent/event loop=].
+  1. [=Set the continuation state value=] for |scheduler| to |state| given |eventLoop|.
+
+  Note: Any key can be used for the [=continuation state/state map=] as long as it is unique to the
+  {{Scheduler}}.
+</div>
+
+<div algorithm>
+  To <dfn>get the current scheduling state</dfn> for |scheduler| (a {{Scheduler}}):
+
+  1. Let |eventLoop| be |scheduler|'s [=relevant agent=]'s [=agent/event loop=].
+  1. Return the result of [=getting the continuation state value=] for |scheduler| given
+     |eventLoop|.
+</div>
+
 <div algorithm>
   To <dfn>schedule a postTask task</dfn> for {{Scheduler}} |scheduler| given a
   {{SchedulerPostTaskCallback}} |callback| and {{SchedulerPostTaskOptions}} |options|:
@@ -316,12 +345,12 @@ A <dfn>task handle</dfn> is a [=struct=] with the following [=struct/items=]:
        for |scheduler| given |state|'s [=scheduling state/priority source=] and false.
     1. [=Schedule a task to invoke an algorithm=] for |scheduler| given |handle| and the following
        steps:
-      1. Let |event loop| be the |scheduler|'s [=relevant agent=]'s [=agent/event loop=].
-      1. Set |event loop|'s [=event loop/current scheduling state=] to |state|.
+      1. Let |eventLoop| be the |scheduler|'s [=relevant agent=]'s [=agent/event loop=].
+      1. [=Set the current scheduling state=] for |scheduler| to |state|.
       1. Let |callbackResult| be the result of [=invoking=] |callback| with « » and "`rethrow`".
          If that threw an exception, then [=reject=] |result| with that. Otherwise, [=resolve=]
          |result| with |callbackResult|.
-      1. Set |event loop|'s [=event loop/current scheduling state=] to null.
+      1. Set |eventLoop|'s [=event loop/current continuation state=] to null.
   1. Let |delay| be |options|["{{SchedulerPostTaskOptions/delay}}"].
   1. If |delay| is greater than 0, then [=run steps after a timeout=] given |scheduler|'s [=relevant
      global object=], "`scheduler-postTask`", |delay|, and the following steps:
@@ -340,8 +369,7 @@ Issue: [=Run steps after a timeout=] doesn't necessarily account for suspension;
   To <dfn>schedule a yield continuation</dfn> for {{Scheduler}} |scheduler|:
 
   1. Let |result| be [=a new promise=].
-  1. Let |inheritedState| be the |scheduler|'s [=relevant agent=]'s [=agent/event loop=]'s
-     [=event loop/current scheduling state=].
+  1. Let |inheritedState| be the result of [=getting the current scheduling state=] for |scheduler|.
   1. Let |abortSource| be |inheritedState|'s [=scheduling state/abort source=] if |inheritedState|
      is not null, or otherwise null.
   1. If |abortSource| is not null and |abortSource| is [=AbortSignal/aborted=], then [=reject=]