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Define agents and agent clusters
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Define the infrastructure for SharedArrayBuffer. This also clarifies
along which boundaries a browser implementation can use processes and
threads.

shaky foundation. Because of that, similar-origin window agents are
the best place to store state that would formerly go on unit of
related similar-origin browsing contexts.

tc39/ecma262#882 is follow-up to define
agents in more detail; in particular make their implicit realms slot
explicit. w3c/css-houdini-drafts#224 is
follow-up to define worklet ownership better which is needed to
define how they relate to agent (sub)clusters.

Fixes part of #2260. Fixes
w3c/ServiceWorker#1115. Fixes most of
w3c/css-houdini-drafts#380 (no tests and no
nice grouping of multiple realms in a single agent as that is not
needed).
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annevk committed Apr 16, 2017
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<ul class="brief">
<li><dfn data-x-href="https://tc39.github.io/ecma262/#active-function-object">active function object</dfn></li>
<li><dfn data-x-href="https://tc39.github.io/ecma262/#sec-agents">agent</dfn> and
<dfn data-x-href="https://tc39.github.io/ecma262/#sec-agent-clusters">agent cluster</dfn></li>
<li><dfn data-x-href="https://tc39.github.io/ecma262/#sec-automatic-semicolon-insertion">automatic semicolon insertion</dfn></li>
<li>The <dfn data-x-href="https://tc39.github.io/ecma262/#current-realm">current Realm Record</dfn></li>
<li><dfn data-x-href="https://tc39.github.io/ecma262/#early-error-rule">early error</dfn></li>
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<li>The <dfn data-x="js-abstract-equality" data-x-href="https://tc39.github.io/ecma262/#sec-abstract-equality-comparison">Abstract Equality Comparison</dfn> algorithm</li>
<li>The <dfn data-x="js-strict-equality" data-x-href="https://tc39.github.io/ecma262/#sec-strict-equality-comparison">Strict Equality Comparison</dfn> algorithm</li>
<li>The <dfn data-x-href="https://tc39.github.io/ecma262/#sec-date-objects"><code>Date</code></dfn> class</li>
<li>The <dfn data-x-href="https://tc39.github.io/ecma262/#sec-sharedarraybuffer-objects"><code>SharedArrayBuffer</code></dfn> class</li>
<li>The <dfn data-x-href="https://tc39.github.io/ecma262/#sec-native-error-types-used-in-this-standard-typeerror"><code>TypeError</code></dfn> class</li>
<li>The <dfn data-x="js-RangeError" data-x-href="https://tc39.github.io/ecma262/#sec-native-error-types-used-in-this-standard-rangeerror"><code>RangeError</code></dfn> class</li>
<li>The <dfn data-x="js-typeof" data-x-href="https://tc39.github.io/ecma262/#sec-typeof-operator"><code>typeof</code></dfn> operator</li>
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<li><dfn data-x-href="https://w3c.github.io/ServiceWorker/#dfn-serviceworker-link">serviceworker link</dfn></li>
<li><dfn data-x-href="https://w3c.github.io/ServiceWorker/#serviceworker"><code>ServiceWorker</code></dfn> interface</li>
<li><dfn data-x-href="https://w3c.github.io/ServiceWorker/#serviceworkercontainer"><code>ServiceWorkerContainer</code></dfn> interface</li>
<li><dfn data-x-href="https://w3c.github.io/ServiceWorker/#serviceworkerglobalscope"><code>ServiceWorkerGlobalScope</code></dfn> interface</li>
<li><dfn data-x-href="https://w3c.github.io/ServiceWorker/#dfn-use-cache">use cache</dfn></li>
</ul>

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</ul>
</dd>

<dt>Worklets</dt>

<dd>
<p>The following feature is defined in the <cite>Worklets</cite> specification: <ref
spec=WORKLETS></p>

<ul class="brief">
<li><dfn data-x-href="https://drafts.css-houdini.org/worklets/#workletglobalscope"><code>WorkletGlobalScope</code></dfn></li>
</ul>
</dd>

</dl>

<hr>
Expand Down Expand Up @@ -88419,6 +88434,139 @@ import "https://example.com/foo/../module2.js";</pre>
data-x="concept-module-script-module-record">module record</span>.</p></li>
</ol>

<h5>Integration with the JavaScript agent formalism</h5>

<p>JavaScript defines the concept of an <span>agent</span>. Until such a time that this standard
has a better handle on lifetimes, we define five types of <span data-x="agent">agents</span> that
user agents must allocate at the appropriate time.</p>

<p class="note">In the future, when this specification has a better handle on lifetimes, we hope
to define exactly when <span data-x="agent">agents</span> and <span data-x="agent cluster">agent
clusters</span> are created.</p>

<dl>
<dt><dfn data-export="">Similar-origin window agent</dfn></dt>
<dd>
<p>An <span>agent</span> whose [[CanBlock]] is false and whose set of <span
data-x="JavaScript realm">realms</span> consists of all <span
data-x="concept-global-object-realm">realms</span> of <code>Window</code> objects whose
<span>relevant settings object</span>'s <span>responsible browsing context</span> is in the same
<span>unit of related similar-origin browsing contexts</span>.</p>

<p class="note">Two <code>Window</code> objects that are <span>same origin</span> can be in
different <span data-x="similar-origin window agent">similar-origin window agents</span>, for
instance iif they are each in their own <span>top-level browsing context</span>.</p>
</dd>

<dt><dfn data-export="">Dedicated worker agent</dfn></dt>
<dd><p>An <span>agent</span> whose [[CanBlock]] is true and whose set of <span data-x="JavaScript
realm">realms</span> consists of a single <code>DedicatedWorkerGlobalScope</code> object's <span
data-x="concept-global-object-realm">Realm</span>.</p></dd>

<dt><dfn data-export="">Shared worker agent</dfn></dt>
<dd><p>An <span>agent</span> whose [[CanBlock]] is true and whose set of <span data-x="JavaScript
realm">realms</span> consists a single <code>SharedWorkerGlobalScope</code> object's <span
data-x="concept-global-object-realm">Realm</span>.</p></dd>

<dt><dfn data-export="">Service worker agent</dfn></dt>
<dd><p>An <span>agent</span> whose [[CanBlock]] is false and whose set of <span data-x="JavaScript
realm">realms</span> consists of a single <code>ServiceWorkerGlobalScope</code> object's <span
data-x="concept-global-object-realm">Realm</span>.</p></dd>

<dt><dfn data-export="">Worklet agent</dfn></dt>
<dd>
<p>An <span>agent</span> whose [[CanBlock]] is false and whose set of <span
data-x="JavaScript realm">realms</span> consists of a single <code>WorkletGlobalScope</code>
object's <span data-x="concept-global-object-realm">Realm</span>.</p>

<p class="note">While conceptually it might be cleaner for worklets that end up with multiple
realms to put all those in the same agent, it is not observable in practice.</p>
</dd>
</dl>

<p>For convenience in what follows, for all <span data-x="agent">agents</span> that are not <span
data-x="similar-origin window agent">similar-origin window agents</span>, we define <dfn
data-x="concept-agent-realm">the agent's realm</dfn> to be the single <span data-x="JavaScript
realm">realm</span> in its set of realms, and <dfn data-x="concept-agent-global">the agent's
global object</dfn> to be <span data-x="concept-agent-realm">the agent's realm</span>'s <span
data-x="concept-realm-global">global object</span>.</p>

<p>To determine the manifestation of JavaScript's <span>agent cluster</span> concept in user
agents, we first define an <dfn>agent subcluster</dfn> for a given <span>agent</span>
<var>agent</var>, based on its type:</p>

<dl class="switch">
<dt><span>Similar-origin window agent</span></dt>
<dd><p>The set containing <var>agent</var> and any <span>dedicated worker agent</span> whose
<span data-x="concept-agent-global">global object</span>'s <span>owner set</span> contains a
<code>Document</code> object whose <span data-x="concept-relevant-realm">relevant Realm</span>
belongs to <var>agent</var>.</p></dd>

<dt><span>Dedicated worker agent</span></dt>
<dd>
<p>The set containing:

<ul>
<li><var>agent</var>,</li>
<li>any <span>agent</span> with a <span data-x="JavaScript realm">realm</span> whose <span
data-x="concept-realm-global">global object</span> is in <var>agent</var>'s <span
data-x="concept-agent-global">global object</span>'s <span>owner set</span>, and</li>
<li>any <span>dedicated worker agent</span> whose <span data-x="concept-agent-global">global
object</span> is in <var>agent</var>'s <span data-x="concept-agent-global">global
object</span>'s <span>worker set</span>.
</ul>
</dd>

<dt><span>Worklet agent</span></dt>
<dd><p class="&#x0058;&#x0058;&#x0058;">Currently worklets have no clearly defined owner, see: <a
href="https://github.com/w3c/css-houdini-drafts/issues/224">w3c/css-houdini-drafts issue
#224</a>.</p></dd>

<dt><span>Shared worker agent</span></dt>
<dt><span>Service worker agent</span></dt>
<dd><p>The set containing <var>agent</var> and any <span>dedicated worker agent</span> whose
<span data-x="concept-agent-global">global object</span> is in <var>agent</var>'s <span
data-x="concept-agent-global">global object</span>'s <span>worker set</span>.</p></dd>
</dl>

<p>Then, the transitive closure of <span data-x="agent subcluster">agent subclusters</span> is an
<span>agent cluster</span>.</p>

<p class="note">The <span>agent cluster</span> concept is crucial for defining the JavaScript
memory model, and in particular among which <span data-x="agent">agents</span> the backing data of
<code>SharedArrayBuffer</code> objects can be shared.</p>

<div class="example">
<p>The following pairs of global objects are each within the same <span>agent cluster</span>, and
thus can use <code>SharedArrayBuffer</code> instances to share memory with each other:</p>

<ul class="brief">
<li>A <code>Window</code> and a dedicated worker that it created</li>

<li>A worker (of any type) and a dedicated worker it creates</li>

<li>A <code>Window</code> and the <code>Window</code> of an <code>iframe</code> element that
could be <span>same origin-domain</span></li>

<li>A <code>Window</code> and the <code>Window</code> that opened it</li>
</ul>

<p>The following pairs of global objects are <em>not</em> within the same <span>agent
cluster</span>, and thus cannot share memory:</p>

<ul class="brief">
<li>A <code>Window</code> and a shared worker it creates</li>

<li>A worker (of any type) and a shared worker it creates</li>

<li>A <code>Window</code> and a service worker it creates</li>

<li>A <code>Window</code> and the <code>Window</code> of an <code>iframe</code> element that
cannot be <span>same origin-domain</span></li>
</ul>

</div>

</div>


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<dt id="refsWHATWGWIKI">[WHATWGWIKI]</dt>
<dd><cite><a href="https://wiki.whatwg.org/">The WHATWG Wiki</a></cite>. WHATWG.</dd>

<dt id="refsWORKLETS">[WORKLETS]</dt>
<dd><cite><a href="https://drafts.css-houdini.org/worklets/">Worklets</a></cite>. I. Kilpatrick. W3C.</dd>

<dt id="refsWSP">[WSP]</dt>
<dd><cite><a href="https://tools.ietf.org/html/rfc6455">The WebSocket protocol</a></cite>, I. Fette, A. Melnikov. IETF.</dd>

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