Issue #387: Monitoring algo takes pending request to start into account (#392)

tidoust · markafoltz · commit 0c800c5c5bee · 2016-12-21T11:39:31.000-08:00
* Issue #387: Monitoring algo now takes pending request to start into account Main changes: - Prose similar to that used in the Web Bluetooth spec used for the garbage collection note for the "presentation display availability" to clarify the intent. We may want to adjust this text in #391. - Notion of "presentation availability promise" dropped. That promise is now referenced in `getAvailability` as "an unsettled Promise from a previous call to `getAvailability` on `presentationRequest`". This avoids having to be explicit about garbage collection rules. - Step that instructs the UA to run the monitoring algorithm no longer runs "in parallel" (see #381) - Note added next to that step to clarify that the monitoring algorithm needs to run again even if it is still running - The monitoring algorithm now starts by making a shallow copy of the "set of presentation availability objects" which gets completed with the right tuple if there is a pending call to `start` (note there can be at most one such pending call per controlling browsing context) - Steps that update the `value` property adjusted to set the value directly for `PresentationAvailability` objects that have not yet been exposed to ECMAScript object. This is triggered by the following (new) problem: the `getAvailibility` promise gets resolved with a `PresentationAvailability` object as soon as the monitoring algorithm is done running, but the monitoring algorithm "queued a task" to update the `value` property of `PresentationAvailability` objects. The `value` property of the returned `PresentationAvailability` object would always have been the initial value (`false` in most cases), even if the monitoring algorithm had found an available display. Also, we probably do not want to fire `change` events for properties that JS code has not yet been given any chance to read. Here as well, we may want to adjust this text in #391. - The initial `value` of newly created `PresentationAvailability` objects is now always `false`. There should be no need to set it to `true` given that the monitoring algorithm refreshes that value right after that (and given the previous fix). - I added a note next to the monitoring algorithm to clarify that a user agent may interrupt and re-run the algorithm to group requests, which seems like a possible optimization. * Issue #387: Use availabilitySet in the monitoring algorithm The variable is obviously useless if it is not referenced. This should have been part of previous commit. * Issue #387: drop "exposed to JS" and allow monitoring aggregation This commit drops the fuzzy "exposed to ECMAScript" wording in the monitoring algorithm, and replaces it with a more common "initialized" concept. The notion is clarified in an editorial note next to the step that uses it. The editorial note that follows the monitoring algorithm was also complete to mention that user agents may aggregate monitoring activities across browsing contexts. * Issue #387: Update notes with @mfoltzgoogle suggestions
diff --git a/index.html b/index.html
@@ -1126,10 +1126,10 @@ <h4>
             abort these steps.
             </li>
             <li>If there is already an unsettled <a>Promise</a> from a previous
-            call to <code>start</code> on any <code>PresentationRequest</code>
-            in the same <a>controlling browsing context</a>, return a new
-            <a>Promise</a> rejected with an <a>OperationError</a> exception and
-            abort all remaining steps.
+            call to <a for="PresentationRequest">start</a> on any
+            <a>PresentationRequest</a> in the same <a>controlling browsing
+            context</a>, return a new <a>Promise</a> rejected with an
+            <a>OperationError</a> exception and abort all remaining steps.
             </li>
             <li>Let <var>P</var> be a new <a>Promise</a>.
             </li>
@@ -1551,6 +1551,11 @@ <h3>
           any <a>available presentation display</a> for at least one of the
           <a>presentation request URLs</a> of the request.
         </p>
+        <p>
+          The <a>presentation display availability</a> for a presentation
+          request is eligible for garbage collection when no ECMASCript code
+          can observe the <code>PresentationAvailability</code> object.
+        </p>
         <p>
           If the <a>controlling user agent</a> can <a>monitor the list of
           available presentation displays</a> in the background (without a
@@ -1561,8 +1566,9 @@ <h3>
         </p>
         <p>
           The <dfn for="PresentationAvailability">value</dfn> attribute MUST
-          return the last value it was set to. The value is updated by the
-          <a>monitor the list of available presentation displays</a> algorithm.
+          return the last value it was set to. The value is initialized and
+          updated by the <a>monitor the list of available presentation
+          displays</a> algorithm.
         </p>
         <p>
           The <dfn for="PresentationAvailability">onchange</dfn> attribute is
@@ -1573,15 +1579,6 @@ <h3>
           <h4>
             The set of presentation availability objects
           </h4>
-          <p>
-            Each <code>PresentationRequest</code> has a <a>presentation
-            availability promise</a> and a <a>presentation display
-            availability</a>, which are initially set to <code>null</code>. The
-            <dfn>presentation availability promise</dfn> for a
-            <code>PresentationRequest</code> is a <code>Promise</code> object
-            that <a data-lt="resolve">resolves</a> to the <a>presentation
-            display availability</a> for the request.
-          </p>
           <p>
             The <a>user agent</a> MUST keep track of the <dfn>set of
             presentation availability objects</dfn> created by the
@@ -1686,19 +1683,15 @@ <h4>
                 </li>
               </ol>
             </li>
-            <li>If the <a>presentation availability promise</a> for
-            <code>presentationRequest</code> is not <code>null</code>, return
-            the <code>presentationRequest</code> object's <a>presentation
-            availability promise</a> and abort these steps.
+            <li>If there is an unsettled <a>Promise</a> from a previous call to
+            <a for="PresentationRequest">getAvailability</a> on
+            <code>presentationRequest</code>, return that <a>Promise</a> and
+            abort these steps.
             </li>
-            <li>Otherwise, set the <code>presentationRequest</code> object's
-            <a>presentation availability promise</a> to a newly created <code>
-              Promise</code> object and set <var>P</var> to this
-              <code>Promise</code>.
+            <li>Otherwise, let <var>P</var> be a new <a>Promise</a>.
             </li>
-            <li>Return the <code>presentationRequest</code> object's
-            <a>presentation availability promise</a>, but continue running
-            these steps <a>in parallel</a>.
+            <li>Return <var>P</var>, but continue running these steps <a>in
+            parallel</a>.
             </li>
             <li>If the user agent is unable to continuously <a>monitor the list
             of available presentation displays</a> in the background, but can
@@ -1726,34 +1719,20 @@ <h4>
             </li>
             <li>Set the <a>presentation display availability</a> for
             <var>presentationRequest</var> to a newly created
-            <code>PresentationAvailability</code> object, and let <var>A</var>
-            be that object.
-            </li>
-            <li>Set the <code>value</code> property of <var>A</var> as follows:
-              <ol>
-                <li>
-                  <code>false</code> if the <a>list of available presentation
-                  displays</a> is empty.
-                </li>
-                <li>
-                  <code>true</code> if there is at least one <a>available
-                  presentation display</a> for some member of
-                  <var>presentationUrls</var>. That is, there is an entry
-                  <var>(presentationUrl, display)</var> in the <a>list of
-                  available presentation displays</a> for some
-                  <var>presentationUrl</var> in <var>presentationUrls</var>.
-                </li>
-                <li>
-                  <code>false</code> otherwise.
-                </li>
-              </ol>
+            <a>PresentationAvailability</a> object, and let <var>A</var> be
+            that object.
             </li>
             <li>Create a tuple <em>(<var>A</var>,
             <var>presentationUrls</var>)</em> and add it to the <a>set of
             presentation availability objects</a>.
             </li>
             <li>Run the algorithm to <a>monitor the list of available
-            presentation displays</a> <a>in parallel</a>.
+            presentation displays</a>.
+              <div class="note">
+                The monitoring algorithm must be run at least one more time
+                after the previous step to pick up the tuple that was added to
+                the <a>set of presentation availability objects</a>.
+              </div>
             </li>
             <li>
               <a>Resolve</a> <var>P</var> with <var>A</var>.
@@ -1770,11 +1749,28 @@ <h4>
             "PresentationRequest" data-lt="start">select a presentation
             display</a>, the <a>user agent</a> MUST <dfn>monitor the list of
             available presentation displays</dfn> by running the following
-            steps.
+            steps:
           </p>
           <ol link-for="PresentationAvailability">
-            <li>Set the <a>list of available presentation displays</a> to the
-            empty list.
+            <li>Let <var>availabilitySet</var> be a shallow copy of the <a>set
+            of presentation availability objects</a>.
+            </li>
+            <li>If there is a pending request to <a for="PresentationRequest"
+            data-lt="start">select a presentation display</a> for a
+            <a>PresentationRequest</a> and if the <a>PresentationRequest</a>'s
+            <a>presentation display availability</a> is <code>null</code>, then
+            run the following substeps:
+              <ol>
+                <li>Let <var>A</var> be a newly created
+                <a>PresentationAvailability</a> object.
+                </li>
+                <li>Create a tuple <em>(<var>A</var>,
+                <var>presentationUrls</var>)</em> where
+                <var>presentationUrls</var> is the <a>PresentationRequest</a>'s
+                <a>presentation request URLs</a> and add it to
+                <var>availabilitySet</var>.
+                </li>
+              </ol>
             </li>
             <li>Let <var>newDisplays</var> be an empty list.
             </li>
@@ -1785,9 +1781,12 @@ <h4>
             <li>Retrieve <a>presentation displays</a> (using an implementation
             specific mechanism) and set <var>newDisplays</var> to this list.
             </li>
+            <li>Set the <a>list of available presentation displays</a> to the
+            empty list.
+            </li>
             <li>For each member <em>(<var>A</var>,
-            <var>availabilityUrls</var>)</em> of the <a>set of presentation
-            availability objects</a>, run the following steps:
+            <var>availabilityUrls</var>)</em> of <var>availabilitySet</var>,
+            run the following steps:
               <ol>
                 <li>Set <var>previousAvailability</var> to the value of
                 <var>A</var>'s <a>value</a> property.
@@ -1814,6 +1813,10 @@ <h4>
                     </li>
                   </ol>
                 </li>
+                <li>If <var>A</var>'s <a>value</a> property has not yet been
+                initialized, then set <var>A</var>'s <a>value</a> property to
+                <var>newAvailability</var> and skip the following step.
+                </li>
                 <li>If <var>previousAvailability</var> is not equal to
                 <var>newAvailability</var>, then <a>queue a task</a> to run the
                 following steps:
@@ -1830,15 +1833,26 @@ <h4>
               </ol>
             </li>
           </ol>
+          <div class="note">
+            The <a>controlling user agent</a> may choose how often to
+            <a>monitor the list of available presentation displays</a>,
+            including grouping requests from <a for=
+            "PresentationRequest">start</a> and <a for=
+            "PresentationRequest">getAvailability</a>, and aggregating them
+            across <a data-lt="browsing context">browsing contexts</a>.
+          </div>
           <p>
-            When a <a>PresentationAvailability</a> object is no longer alive
-            (i.e., is eligible for garbage collection), the <a>user agent</a>
-            SHOULD run the following steps:
+            When a <a>presentation display availability</a> object is eligible
+            for garbage collection, the <a>user agent</a> SHOULD run the
+            following steps:
           </p>
           <ol>
+            <li>Let <var>A</var> be the newly deceased
+            <a>PresentationAvailability</a> object
+            </li>
             <li>Find and remove any entry <em>(<var>A</var>,
             <var>availabilityUrl</var>)</em> in the <a>set of presentation
-            availability objects</a> for the newly deceased <var>A</var>.
+            availability objects</a>.
             </li>
             <li>If the <a>set of presentation availability objects</a> is now
             empty and there is no pending request to <a for=

-Original file line number
+Diff line change
             abort these steps.
             li>
             <li>If there is already an unsettled <a>Promisea> from a previous
 -            call to <code>startcode> on any <code>PresentationRequestcode>
 -            in the same <a>controlling browsing contexta>, return a new
 -            <a>Promise</a> rejected with an <a>OperationErrora> exception and
 -            abort all remaining steps.
 +            call to <a for="PresentationRequest">starta> on any
 +            <a>PresentationRequesta> in the same <a>controlling browsing
 +            context</a>, return a new <a>Promisea> rejected with an
 +            <a>OperationErrora> exception and abort all remaining steps.
             li>
             <li>Let <var>Pvar> be a new <a>Promisea>.
             li>
           any <a>available presentation displaya> for at least one of the
           <a>presentation request URLsa> of the request.
         p>
 +        <p>
 +          The <a>presentation display availabilitya> for a presentation
 +          request is eligible for garbage collection when no ECMASCript code
 +          can observe the <code>PresentationAvailabilitycode> object.
 +        p>
         <p>
           If the <a>controlling user agenta> can <a>monitor the list of
           available presentation displaysa> in the background (without a
         p>
         <p>
           The <dfn for="PresentationAvailability">valuedfn> attribute MUST
 -          return the last value it was set to. The value is updated by the
 -          <a>monitor the list of available presentation displaysa> algorithm.
 +          return the last value it was set to. The value is initialized and
 +          updated by the <a>monitor the list of available presentation
 +          displaysa> algorithm.
         p>
         <p>
           The <dfn for="PresentationAvailability">onchangedfn> attribute is
           <h4>
             The set of presentation availability objects
           h4>
 -          <p>
 -            Each <code>PresentationRequestcode> has a <a>presentation
 -            availability promisea> and a <a>presentation display
 -            availabilitya>, which are initially set to <code>nullcode>. The
 -            <dfn>presentation availability promisedfn> for a
 -            <code>PresentationRequestcode> is a <code>Promisecode> object
 -            that <a data-lt="resolve">resolvesa> to the <a>presentation
 -            display availabilitya> for the request.
 -          p>
           <p>
             The <a>user agenta> MUST keep track of the <dfn>set of
             presentation availability objectsdfn> created by the
                 li>
               ol>
             li>
 -            <li>If the <a>presentation availability promisea> for
 -            <code>presentationRequestcode> is not <code>nullcode>, return
 -            the <code>presentationRequestcode> object's <a>presentation
 -            availability promisea> and abort these steps.
 +            <li>If there is an unsettled <a>Promisea> from a previous call to
 +            <a for="PresentationRequest">getAvailabilitya> on
 +            <code>presentationRequestcode>, return that <a>Promisea> and
 +            abort these steps.
             li>
 -            <li>Otherwise, set the <code>presentationRequestcode> object's
 -            <a>presentation availability promisea> to a newly created <code>
 -              Promisecode> object and set <var>Pvar> to this
 -              <code>Promisecode>.
 +            <li>Otherwise, let <var>Pvar> be a new <a>Promisea>.
             li>
 -            <li>Return the <code>presentationRequestcode> object's
 -            <a>presentation availability promisea>, but continue running
 -            these steps <a>in parallela>.
 +            <li>Return <var>Pvar>, but continue running these steps <a>in
 +            parallela>.
             li>
             <li>If the user agent is unable to continuously <a>monitor the list
             of available presentation displaysa> in the background, but can
             li>
             <li>Set the <a>presentation display availabilitya> for
             <var>presentationRequestvar> to a newly created
 -            <code>PresentationAvailabilitycode> object, and let <var>Avar>
 -            be that object.
 -            li>
 -            <li>Set the <code>valuecode> property of <var>Avar> as follows:
 -              <ol>
 -                <li>
 -                  <code>falsecode> if the <a>list of available presentation
 -                  displaysa> is empty.
 -                li>
 -                <li>
 -                  <code>truecode> if there is at least one <a>available
 -                  presentation displaya> for some member of
 -                  <var>presentationUrlsvar>. That is, there is an entry
 -                  <var>(presentationUrl, display)var> in the <a>list of
 -                  available presentation displaysa> for some
 -                  <var>presentationUrlvar> in <var>presentationUrlsvar>.
 -                li>
 -                <li>
 -                  <code>falsecode> otherwise.
 -                li>
 -              ol>
 +            <a>PresentationAvailabilitya> object, and let <var>Avar> be
 +            that object.
             li>
             <li>Create a tuple <em>(<var>Avar>,
             <var>presentationUrlsvar>)em> and add it to the <a>set of
             presentation availability objectsa>.
             li>
             <li>Run the algorithm to <a>monitor the list of available
 -            presentation displaysa> <a>in parallela>.
 +            presentation displaysa>.
 +              <div class="note">
 +                The monitoring algorithm must be run at least one more time
 +                after the previous step to pick up the tuple that was added to
 +                the <a>set of presentation availability objectsa>.
 +              div>
             li>
             <li>
               <a>Resolvea> <var>Pvar> with <var>Avar>.
             "PresentationRequest" data-lt="start">select a presentation
             displaya>, the <a>user agenta> MUST <dfn>monitor the list of
             available presentation displaysdfn> by running the following
 -            steps.
 +            steps:
           p>
           <ol link-for="PresentationAvailability">
 -            <li>Set the <a>list of available presentation displaysa> to the
 -            empty list.
 +            <li>Let <var>availabilitySetvar> be a shallow copy of the <a>set
 +            of presentation availability objectsa>.
 +            li>
 +            <li>If there is a pending request to <a for="PresentationRequest"
 +            data-lt="start">select a presentation displaya> for a
 +            <a>PresentationRequesta> and if the <a>PresentationRequesta>'s
 +            <a>presentation display availabilitya> is <code>nullcode>, then
 +            run the following substeps:
 +              <ol>
 +                <li>Let <var>Avar> be a newly created
 +                <a>PresentationAvailabilitya> object.
 +                li>
 +                <li>Create a tuple <em>(<var>Avar>,
 +                <var>presentationUrlsvar>)em> where
 +                <var>presentationUrlsvar> is the <a>PresentationRequesta>'s
 +                <a>presentation request URLsa> and add it to
 +                <var>availabilitySetvar>.
 +                li>
 +              ol>
             li>
             <li>Let <var>newDisplaysvar> be an empty list.
             li>
             <li>Retrieve <a>presentation displaysa> (using an implementation
             specific mechanism) and set <var>newDisplaysvar> to this list.
             li>
 +            <li>Set the <a>list of available presentation displaysa> to the
 +            empty list.
 +            li>
             <li>For each member <em>(<var>Avar>,
 -            <var>availabilityUrlsvar>)em> of the <a>set of presentation
 -            availability objectsa>, run the following steps:
 +            <var>availabilityUrlsvar>)em> of <var>availabilitySetvar>,
 +            run the following steps:
               <ol>
                 <li>Set <var>previousAvailabilityvar> to the value of
                 <var>Avar>'s <a>valuea> property.
                     li>
                   ol>
                 li>
 +                <li>If <var>Avar>'s <a>valuea> property has not yet been
 +                initialized, then set <var>Avar>'s <a>valuea> property to
 +                <var>newAvailabilityvar> and skip the following step.
 +                li>
                 <li>If <var>previousAvailabilityvar> is not equal to
                 <var>newAvailabilityvar>, then <a>queue a taska> to run the
                 following steps:
               ol>
             li>
           ol>
 +          <div class="note">
 +            The <a>controlling user agenta> may choose how often to
 +            <a>monitor the list of available presentation displaysa>,
 +            including grouping requests from <a for=
 +            "PresentationRequest">starta> and <a for=
 +            "PresentationRequest">getAvailabilitya>, and aggregating them
 +            across <a data-lt="browsing context">browsing contextsa>.
 +          div>
           <p>
 -            When a <a>PresentationAvailabilitya> object is no longer alive
 -            (i.e., is eligible for garbage collection), the <a>user agenta>
 -            SHOULD run the following steps:
 +            When a <a>presentation display availabilitya> object is eligible
 +            for garbage collection, the <a>user agenta> SHOULD run the
 +            following steps:
           p>
           <ol>
 +            <li>Let <var>Avar> be the newly deceased
 +            <a>PresentationAvailabilitya> object
 +            li>
             <li>Find and remove any entry <em>(<var>Avar>,
             <var>availabilityUrlvar>)em> in the <a>set of presentation
 -            availability objectsa> for the newly deceased <var>Avar>.
 +            availability objectsa>.
             li>
             <li>If the <a>set of presentation availability objectsa> is now
             empty and there is no pending request to <a for=