Serializing and deserializing SharedArrayBuffer

Fixes #2260 (by being the last in a set of fixes). Closes
tc39/proposal-ecmascript-sharedmem#144 and closes
tc39/proposal-ecmascript-sharedmem#65.

Author: domenic

source

@@ -495,6 +495,13 @@
   be thought of as completely serializing the execution of all scripts in all <span data-x="browsing
   context">browsing contexts</span>.</p>
 
+  <p>The exception to this general design principle is the JavaScript <code>SharedArrayBuffer</code>
+  class. Using <code>SharedArrayBuffer</code>s, it can in fact be observed that scripts in other
+  <span data-x="event loop">event loops</span> are executing simultaneously. Furthermore, due to the
+  JavaScript memory model, there are situations which not only are un-representable via serialized
+  <em>script</em> execution, but also un-representable via serialized <em>statement</em> execution
+  among those scripts.</p>
+
   </div>
 
 
@@ -2912,6 +2919,7 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
      <li>The <dfn data-x-href="https://tc39.github.io/ecma262/#sec-isconstructor">IsConstructor</dfn> abstract operation</li>
      <li>The <dfn data-x-href="https://tc39.github.io/ecma262/#sec-isdatadescriptor">IsDataDescriptor</dfn> abstract operation</li>
      <li>The <dfn data-x-href="https://tc39.github.io/ecma262/#sec-isdetachedbuffer">IsDetachedBuffer</dfn> abstract operation</li>
+     <li>The <dfn data-x-href="https://tc39.github.io/ecma262/#sec-issharedarraybuffer">IsSharedArrayBuffer</dfn> abstract operation</li>
      <li>The <dfn data-x="js-NewObjectEnvironment" data-x-href="https://tc39.github.io/ecma262/#sec-newobjectenvironment">NewObjectEnvironment</dfn> abstract operation</li>
      <!-- the next set of Ordinary* abstract operations are in order of appearance -->
      <li>The <dfn data-x-href="https://tc39.github.io/ecma262/#sec-ordinarygetprototypeof">OrdinaryGetPrototypeOf</dfn> abstract operation</li>
@@ -7858,23 +7866,36 @@ interface <dfn>DOMStringList</dfn> {
     <p>Otherwise, if <var>value</var> has an [[ArrayBufferData]] internal slot, then:</p>
 
     <ol>
-     <li><p>If <span>IsDetachedBuffer</span>(<var>value</var>) is true, then throw a
-     <span>"<code>DataCloneError</code>"</span> <code>DOMException</code>.</p></li>
-
      <li><p>Let <var>size</var> be <var>value</var>.[[ArrayBufferByteLength]].</p></li>
 
+     <li><p>If <span>IsSharedArrayBuffer</span>(<var>value</var>) is true, then set
+     <var>serialized</var> to { [[Type]]: "SharedArrayBuffer", [[ArrayBufferData]]:
+     <var>value</var>.[[ArrayBufferData]], [[ArrayBufferByteLength]]: <var>size</var>,
+     [[EventLoop]]: <span>current Realm Record</span>'s <span
+     data-x="concept-realm-settings-object">settings object</span>'s <span>responsible event
+     loop</span> }.</p></li>
+
      <li>
-      <p>Let <var>dataCopy</var> be ? <span>CreateByteDataBlock</span>(<var>size</var>).</p>
+      <p>Otherwise:</p>
 
-      <p class="note">This can throw a <code data-x="js-RangeError">RangeError</code> exception upon
-      allocation failure.</p>
-     </li>
+      <ol>
+       <li><p>If <span>IsDetachedBuffer</span>(<var>value</var>) is true, then throw a
+       <span>"<code>DataCloneError</code>"</span> <code>DOMException</code>.</p></li>
+
+       <li>
+        <p>Let <var>dataCopy</var> be ? <span>CreateByteDataBlock</span>(<var>size</var>).</p>
 
-     <li><p>Perform ! <span>CopyDataBlockBytes</span>(<var>dataCopy</var>, 0,
-     <var>value</var>.[[ArrayBufferData]], 0, <var>size</var>).</p></li>
+        <p class="note">This can throw a <code data-x="js-RangeError">RangeError</code> exception
+        upon allocation failure.</p>
+       </li>
+
+       <li><p>Perform ! <span>CopyDataBlockBytes</span>(<var>dataCopy</var>, 0,
+       <var>value</var>.[[ArrayBufferData]], 0, <var>size</var>).</p></li>
 
-     <li><p>Set <var>serialized</var> to { [[Type]]: "ArrayBuffer", [[ArrayBufferData]]:
-     <var>dataCopy</var>, [[ArrayBufferByteLength]]: <var>size</var> }.</p></li>
+       <li><p>Set <var>serialized</var> to { [[Type]]: "ArrayBuffer", [[ArrayBufferData]]:
+       <var>dataCopy</var>, [[ArrayBufferByteLength]]: <var>size</var> }.</p></li>
+      </ol>
+     </li>
     </ol>
    </li>
 
@@ -8261,11 +8282,30 @@ o.myself = o;</pre>
    <var>serialized</var>.[[OriginalFlags]].</p></li>
 
    <li>
-    <p>Otherwise, if <var>serialized</var>.[[Type]] is "ArrayBuffer", then set <var>value</var> to a new ArrayBuffer
-    object in <var>targetRealm</var> whose [[ArrayBufferData]] internal slot value is
-    <var>serialized</var>.[[ArrayBufferData]], and whose [[ArrayBufferByteLength]] internal slot
+    <p>Otherwise, if <var>serialized</var>.[[Type]] is "SharedArrayBuffer", then:</p>
+
+    <ol>
+     <li><p>If <var>targetRealm</var>'s <span data-x="concept-realm-settings-object">settings
+     object</span>'s <span>responsible event loop</span> is not in the same <span>unit of
+     share-within-able event loops</span> as <var>serialized</var>.[[EventLoop]], then then throw a
+     <span>"<code>DataCloneError</code>"</span> <code>DOMException</code>.</p></li>
+
+     <li><p>Otherwise, set <var>value</var> to a new SharedArrayBuffer object in
+     <var>targetRealm</var> whose [[ArrayBufferData]] internal slot value is
+     <var>serialized</var>.[[ArrayBufferData]] and whose [[ArrayBufferByteLength]] internal slot
+     value is <var>serialized</var>.[[ArrayBufferByteLength]].</p></li>
+    </ol>
+   </li>
+
+   <li>
+    <p>Otherwise, if <var>serialized</var>.[[Type]] is "ArrayBuffer", then set <var>value</var> to a
+    new ArrayBuffer object in <var>targetRealm</var> whose [[ArrayBufferData]] internal slot value
+    is <var>serialized</var>.[[ArrayBufferData]], and whose [[ArrayBufferByteLength]] internal slot
     value is <var>serialized</var>.[[ArrayBufferByteLength]].</p>
 
+    <p>If this throws an exception, then throw a <span>"<code>DataCloneError</code>"</span>
+    <code>DOMException</code>.</p>
+
     <p class="note">This step might throw an exception if there is not enough memory available to
     create such an ArrayBuffer object.</p>
    </li>
@@ -8474,7 +8514,8 @@ o.myself = o;</pre>
      <span>[[Detached]]</span> internal slot, then throw a
      <span>"<code>DataCloneError</code>"</span> <code>DOMException</code>.</p></li>
 
-     <li><p>If <var>transferable</var> has an [[ArrayBufferData]] internal slot and !
+     <li><p>If <var>transferable</var> has an [[ArrayBufferData]] internal slot and either !
+     <span>IsSharedArrayBuffer</span>(<var>transferable</var>) is true or !
      <span>IsDetachedBuffer</span>(<var>transferable</var>) is true, then throw a
      <span>"<code>DataCloneError</code>"</span> <code>DOMException</code>.</p></li>