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Editorial: clarify worker lifetime definitions
The previous definitions relied on long prose sentences with lots of conjunctions and disjunctions. Change them to algorithms that return true or false. These algorithms also operate on the well-defined concept of a WorkerGlobalScope object, instead of the ill-defined concept of a "worker". Rearrange the order to be actively needed, then protected, then permissible, since these are ever-widening definitions. Add a clarifying note summarizing how these terms are used, and their relationship to each other, and their relationship to bfcache. Add a definition, and clarifying note, for the "between-loads shared worker timeout", to make it more prominent.
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@@ -122199,8 +122199,8 @@ interface <dfn interface>BroadcastChannel</dfn> : <span>EventTarget</span> {
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<code>Document</code></span> is <span>fully active</span>, or</p></li>
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<li><p>a <code>WorkerGlobalScope</code> object whose <span
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data-x="dom-WorkerGlobalScope-closing">closing</span> flag is false and whose
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<span>worker</span> is not a <span>suspendable worker</span>.</p></li>
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data-x="dom-WorkerGlobalScope-closing">closing</span> flag is false and is not <span
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data-x="suspendable worker">suspendable</span>.</p></li>
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</ul>
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<p>The <dfn method for="BroadcastChannel"><code
@@ -123081,35 +123081,132 @@ interface <dfn interface>SharedWorkerGlobalScope</dfn> : <span>WorkerGlobalScope
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<hr>
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<p>A worker is said to be a <dfn>permissible worker</dfn> if its <code>WorkerGlobalScope</code>'s
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<span>owner set</span> is not <span data-x="list is empty">empty</span> or:</p>
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<p>A user agent has an <span>implementation-defined</span> value, the <dfn>between-loads shared
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worker timeout</dfn>, which is some small amount of time. This represents how long the user agent
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allows shared workers to survive while a page is loading, in case that page is going to contact
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the shared worker again. Setting this value to greater than zero lets user agents avoid the cost
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of restarting a shared worker used by a site when the user is navigating from page to page within
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that site.</p>
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<ul class=brief>
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<li>its <span>owner set</span> has been <span data-x="list is empty">empty</span> for no more
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than a short <span>implementation-defined</span> timeout value,</li>
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<li>its <code>WorkerGlobalScope</code> object is a <code>SharedWorkerGlobalScope</code> object
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(i.e., the worker is a shared worker), and</li>
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<li>the user agent has a <span>navigable</span> whose <span data-x="nav-document">active
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document</span> is not <span>completely loaded</span>.</li>
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</ul>
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<p class="note">A typical value for the <span>between-loads shared worker timeout</span> might be
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5 seconds.</p>
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<hr>
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<p>A <code>WorkerGlobalScope</code> <var>global</var> is <dfn data-x="active needed
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worker">actively needed</dfn> if the following algorithm returns true:</p>
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<ol>
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<li>
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<p><span data-x="list iterate">For each</span> <var>owner</var> of <var>global</var>'s
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<span>owner set</span>:</p>
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<ol>
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<li><p>If <var>owner</var> is a <code>Document</code>, and <var>owner</var> is <span>fully
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active</span>, then return true.</p></li>
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<li><p>If <var>owner</var> is a <code>WorkerGlobalScope</code> that is <span data-x="active
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needed worker">actively needed</span>, then return true.</p></li>
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</ol>
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</li>
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<li><p>Return false.</p></li>
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</ol>
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<p>A <code>WorkerGlobalScope</code> <var>global</var> is <dfn data-x="protected
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worker">protected</dfn> if the following algorithm returns true:</p>
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<ol>
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<li><p>If <var>global</var> is not <span data-x="active needed worker">actively needed</span>,
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then return false.</p></li>
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<li><p>If <var>global</var> is a <code>SharedWorkerGlobalScope</code>, then return true.</p></li>
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<li><p>If <var>global</var>'s <span>the worker's ports</span> is not <span data-x="list is
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empty">empty</span>, then return true.</p></li>
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<li><p>If <var>global</var> has outstanding timers, database transactions, or network
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connections, then return true.</p></li>
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<!-- TODO: would be nice to make the above rigorous. -->
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<li><p>Return false.</p></li>
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</ol>
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<p>A <code>WorkerGlobalScope</code> <var>global</var> is <dfn data-x="permissible
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worker">permissible</dfn> if the following algorithm returns true:</p>
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<ol>
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<li><p>If <var>global</var>'s <span>owner set</span> is not <span data-x="list is
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empty">empty</span>, then return true.</p></li>
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<li>
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<p>If all of the following are true:</p>
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<p class="note">The second part of this definition allows a shared worker to survive for a short
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time while a page is loading, in case that page is going to contact the shared worker again. This
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can be used by user agents as a way to avoid the cost of restarting a shared worker used by a site
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when the user is navigating from page to page within that site.</p>
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<ul>
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<li><p><var>global</var> is a <code>SharedWorkerGlobalScope</code>;</p></li>
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<li><p><var>global</var>'s <span>owner set</span> has been <span data-x="list is
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empty">empty</span> for no more than the user agent's <span>between-loads shared worker
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timeout</span>; and</p>
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<li><p>the user agent has a <span>navigable</span> whose <span data-x="nav-document">active
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document</span> is not <span>completely loaded</span>,</p></li>
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</ul>
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<p>then return true.</p>
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</li>
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<li><p>Return false.</p></li>
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</ol>
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<p>A worker is said to be an <dfn>active needed worker</dfn> if any of its <span data-x="owner
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set">owners</span> are either <code>Document</code> objects that are <span>fully active</span> or
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<span data-x="active needed worker">active needed workers</span>.</p>
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<p>A <code>WorkerGlobalScope</code> <var>global</var> is <dfn data-x="suspendable
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worker">suspendable</dfn> if the following algorithm returns true:</p>
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<p>A worker is said to be a <dfn>protected worker</dfn> if it is an <span>active needed
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worker</span> and either it has outstanding timers, database transactions, or network connections,
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or its list of <span>the worker's ports</span> is not empty, or its <code>WorkerGlobalScope</code>
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is actually a <code>SharedWorkerGlobalScope</code> object (i.e., the worker is a shared
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worker).</p>
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<ol>
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<li><p>If <var>global</var> is <span data-x="active needed worker">actively needed</span>, then
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return false.</p></li>
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<p>A worker is said to be a <dfn>suspendable worker</dfn> if it is not an <span>active needed
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worker</span> but it is a <span>permissible worker</span>.</p>
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<li><p>If <var>global</var> is <span data-x="permissible worker">permissible</span>, then return
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true.</p></li>
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<li><p>Return false.</p></li>
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</ol>
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<div class="note" id="note-worker-lifetime-terminology">
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<p>These concepts are used elsewhere in the specification's normative requirements as
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follows:</p>
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<ul>
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<li><p>Workers get <a href="#step-closing-orphan-workers">closed as orphans</a> between when
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they stop being <span data-x="protected worker">protected</span> and when they stop being <span
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data-x="permissible worker">permissible</span>.</p></li>
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<li><p>Workers get <a href="#step-suspending-workers">suspended or un-suspended</a> based on
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whether they are <span data-x="suspendable worker">suspendable</span>.</p></li>
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<li><p>Workers that have been closed, but keep executing, <a
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href="#terminate-rampant-workers">can be terminated</a> at the user agent's discretion, once
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they stop being <span data-x="active needed worker">actively needed</span>.</p></li>
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</ul>
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<p>Note that every <code>WorkerGlobalScope</code> that is <span data-x="active needed
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worker">actively needed</span> is <span data-x="protected worker">protected</span>, and every
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<code>WorkerGlobalScope</code> that is <span data-x="protected worker">protected</span> is <span
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data-x="permissible worker">permissible</span>. (But the converses do not hold.)</p>
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<p>An important difference between <span data-x="protected worker">protected</span> and <span
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data-x="permissible worker">permissible</span> is that a <code>WorkerGlobalScope</code> is <span
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data-x="protected worker">protected</span> only if its transitive set of owners contains at least
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one <span>fully active</span> <code>Document</code>, whereas a <code>WorkerGlobalScope</code> can
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be <span data-x="permissible worker">permissible</span> even if all the <code>Document</code>s in
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its transitive set of owners are in <a href="#note-bfcache">bfcache</a>.</p>
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</div>
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<p class="note" id="note-between-loads-shared-worker-timeout-lifetime">The <span>between-loads
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shared worker timeout</span> only influences the definition of <span data-x="permissible
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worker">permissible</span>, not <span data-x="protected worker">protected</span>, and so
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implementations are not required to keep shared workers alive for that duration. Rather, they are
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required to close shared workers after the timeout is reached.</p>
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<h4 id="worker-processing-model"><span id="processing-model-10"></span>Processing model</h4>
@@ -123333,21 +123430,19 @@ interface <dfn interface>SharedWorkerGlobalScope</dfn> : <span>WorkerGlobalScope
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<li><p>Create a new <code>WorkerLocation</code> object and associate it with <var>worker global
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scope</var>.</p>
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<li>
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<p><i>Closing orphan workers</i>: Start monitoring the worker such that no sooner than
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it stops being a <span>protected worker</span>, and no later than it stops being a
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<span>permissible worker</span>, <var>worker global scope</var>'s <span
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data-x="dom-WorkerGlobalScope-closing">closing</span> flag is set to true.</p>
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</li>
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<li id="step-closing-orphan-workers"><p><i>Closing orphan workers</i>: Start monitoring
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<var>worker global scope</var> such that no sooner than it stops being <span data-x="protected
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worker">protected</span>, and no later than it stops being <span data-x="permissible
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worker">permissible</span>, <var>worker global scope</var>'s <span
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data-x="dom-WorkerGlobalScope-closing">closing</span> flag is set to true.</p></li>
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<li>
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<p><i>Suspending workers</i>: Start monitoring the worker, such that whenever
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<var>worker global scope</var>'s <span data-x="dom-WorkerGlobalScope-closing">closing</span>
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flag is false and the worker is a <span>suspendable worker</span>, the user agent suspends
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execution of script in that worker until such time as either the <span
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data-x="dom-WorkerGlobalScope-closing">closing</span> flag switches to true or the worker stops
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being a <span>suspendable worker</span>.</p>
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</li>
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<li id="step-suspending-workers"><p><i>Suspending workers</i>: Start monitoring <var>worker
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global scope</var>, such that whenever <var>worker global scope</var>'s <span
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data-x="dom-WorkerGlobalScope-closing">closing</span> flag is false and it is <span
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data-x="suspendable worker">suspendable</span>, the user agent suspends execution of script in
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<var>worker global scope</var> until such time as either the <span
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data-x="dom-WorkerGlobalScope-closing">closing</span> flag switches to true or <var>worker
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global scope</var> stops being <span data-x="suspendable worker">suspendable</span>.</p></li>
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<li><p>Set <var>inside settings</var>'s <span
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data-x="concept-environment-execution-ready-flag">execution ready flag</span>.</p></li>
@@ -123439,8 +123534,9 @@ interface <dfn interface>SharedWorkerGlobalScope</dfn> : <span>WorkerGlobalScope
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entangled with.</p></li>
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</ol>
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<p>User agents may invoke the <span>terminate a worker</span> algorithm when a worker stops being
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an <span>active needed worker</span> and the worker continues executing even after its <span
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<p id="terminate-rampant-workers">User agents may invoke the <span>terminate a worker</span>
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algorithm when a worker stops being <span data-x="active needed worker">actively needed</span> and
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the worker continues executing even after its <span
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data-x="dom-WorkerGlobalScope-closing">closing</span> flag was set to true.</p>
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</div>

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