Further clarify worker lifetime relationships

After e9ccb97, the specification contained an incorrect statement in the non-normative note stating that every worker that is actively needed is protected. This is not correct (see also #11598). This commit expands the non-normative note with more details and examples on the relationships between actively needed, protected, and permissible.

Author: domenic

source

@@ -130479,6 +130479,46 @@ interface <dfn interface>SharedWorkerGlobalScope</dfn> : <span>WorkerGlobalScope
   </ol>
   </div>
 
+  <div class="note" id="note-worker-lifetime-terminology-relationships">
+   <p>The following relationships hold between these terms:</p>
+
+   <ul>
+    <li><p>Every <code>WorkerGlobalScope</code> that is <span data-x="active needed worker">actively
+    needed</span> or <span data-x="protected worker">protected</span> is <span data-x="permissible
+    worker">permissible</span>.</p></li>
+
+    <li><p>Every <code>WorkerGlobalScope</code> that is <span data-x="protected
+    worker">protected</span> is <span data-x="active needed worker">actively needed</span>.</p></li>
+   </ul>
+
+   <p>However, the converses do not always hold:</p>
+
+   <ul>
+    <li><p>A <code>WorkerGlobalScope</code> can be <span data-x="active needed worker">actively
+    needed</span> but not <span data-x="protected worker">protected</span>, if it's a dedicated
+    worker with no outstanding async work that is still performing computation on behalf of a fully
+    active owner, but whose corresponding <code>Worker</code> object has been garbage collected. <a
+    href="#ports-and-garbage-collection">Because of the garbage collection</a>, the <span
+    data-x="the worker's ports">ports</span> collection is empty, so it is no longer protected.
+    However, its event loop has not yet yielded to <a
+    href="#step-empty-worker-global-scope-owner-set">empty its owner set</a>, so it is still
+    actively needed.</p></li>
+
+    <li><p>A <code>WorkerGlobalScope</code> can be <span data-x="permissible
+    worker">permissible</span> but not <span data-x="protected worker">protected</span> or <span
+    data-x="active needed worker">actively needed</span>, if all the <code>Document</code>s in its
+    transitive set of owners are in <a href="#note-bfcache">bfcache</a>, or if it's a
+    <code>SharedWorkerGlobalScope</code> with no current owners being kept alive for the duration of
+    the <span>between-loads shared worker timeout</span>.</p></li>
+   </ul>
+  </div>
+
+  <p class="note" id="note-between-loads-shared-worker-timeout-lifetime">The <span>between-loads
+  shared worker timeout</span> only influences the definition of <span data-x="permissible
+  worker">permissible</span>, not <span data-x="protected worker">protected</span>, and so
+  implementations are not required to keep shared workers alive for that duration. Rather, they are
+  required to close shared workers after the timeout is reached.</p>
+
   <div algorithm>
   <p>A <code>WorkerGlobalScope</code> <var>global</var> is <dfn data-x="suspendable
   worker">suspendable</dfn> if the following algorithm returns true:</p>
@@ -130503,33 +130543,15 @@ interface <dfn interface>SharedWorkerGlobalScope</dfn> : <span>WorkerGlobalScope
     they stop being <span data-x="protected worker">protected</span> and when they stop being <span
     data-x="permissible worker">permissible</span>.</p></li>
 
-    <li><p>Workers get <a href="#step-suspending-workers">suspended or un-suspended</a> based on
-    whether they are <span data-x="suspendable worker">suspendable</span>.</p></li>
-
     <li><p>Workers that have been closed, but keep executing, <a
     href="#terminate-rampant-workers">can be terminated</a> at the user agent's discretion, once
     they stop being <span data-x="active needed worker">actively needed</span>.</p></li>
-   </ul>
 
-   <p>Note that every <code>WorkerGlobalScope</code> that is <span data-x="active needed
-   worker">actively needed</span> is <span data-x="protected worker">protected</span>, and every
-   <code>WorkerGlobalScope</code> that is <span data-x="protected worker">protected</span> is <span
-   data-x="permissible worker">permissible</span>. (But the converses do not hold.)</p>
-
-   <p>An important difference between <span data-x="protected worker">protected</span> and <span
-   data-x="permissible worker">permissible</span> is that a <code>WorkerGlobalScope</code> is <span
-   data-x="protected worker">protected</span> only if its transitive set of owners contains at least
-   one <span>fully active</span> <code>Document</code>, whereas a <code>WorkerGlobalScope</code> can
-   be <span data-x="permissible worker">permissible</span> even if all the <code>Document</code>s in
-   its transitive set of owners are in <a href="#note-bfcache">bfcache</a>.</p>
+    <li><p>Workers get <a href="#step-suspending-workers">suspended or un-suspended</a> based on
+    whether they are <span data-x="suspendable worker">suspendable</span>.</p></li>
+   </ul>
   </div>
 
-  <p class="note" id="note-between-loads-shared-worker-timeout-lifetime">The <span>between-loads
-  shared worker timeout</span> only influences the definition of <span data-x="permissible
-  worker">permissible</span>, not <span data-x="protected worker">protected</span>, and so
-  implementations are not required to keep shared workers alive for that duration. Rather, they are
-  required to close shared workers after the timeout is reached.</p>
-
 
   <h4 id="worker-processing-model"><span id="processing-model-10"></span>Processing model</h4>
 
@@ -130824,11 +130846,8 @@ interface <dfn interface>SharedWorkerGlobalScope</dfn> : <span>WorkerGlobalScope
       <p>Disentangle all the ports in the list of <span>the worker's ports</span>.</p>
      </li>
 
-     <li>
-      <!-- this has no normative impact but makes it clearer that the worker is irrelevant now, and
-      doesn't have to survive until its Documents all die off too --> <p><span data-x="list
-      empty">Empty</span> <var>worker global scope</var>'s <span>owner set</span>.</p>
-     </li>
+     <li id="step-empty-worker-global-scope-owner-set"><p><span data-x="list empty">Empty</span>
+     <var>worker global scope</var>'s <span>owner set</span>.</p></li>
     </ol>
    </li>
   </ol>