Bug 235880

Summary:

WeakRef deref can return null instead of undefined

Product:

WebKit

Reporter:

Stef Busking <stef.busking>

Component:

JavaScriptCore

Assignee:

Yusuke Suzuki <ysuzuki>

Status:

RESOLVED FIXED

Severity:

Normal

CC:

ashvayka, bfulgham, ews-watchlist, fpizlo, keith_miller, mark.lam, msaboff, saam, sam, tzagallo, webkit-bug-importer, ysuzuki

Priority:

Keywords:

InRadar

Version:

Safari 15

Hardware:

Unspecified

OS:

Unspecified

Attachments:

Description	Flags
Patch	none
Patch	ashvayka: review+

Stef Busking

Reported 2022-01-31 01:51:25 PST

Seen in Safari 15.1, 15.2 (macOS) and Epiphany 41.3 (Linux) According to the ECMAScript specification (https://tc39.es/ecma262/multipage/managing-memory.html#sec-weakrefderef), a WeakRef's deref method should either return the referenced object or `undefined`. This behaves as expected in Chrome, Firefox and Edge, but it seems that in WebKit browsers this method may return `null` instead. I've confirmed this behavior using the following in the dev tools console: ``` a = new WeakRef(new ArrayBuffer(10000000)) // wait a while to allow GC to clean up the ArrayBuffer a.deref() ``` I'm not sure if Webkit browsers have a way to force garbage collection, but waiting a while or using other tabs seems to work for triggering this issue most of the time. Firefox allows forcing GC on about:memory, Chrome and Edge provide a button for this on the Memory tab of their dev tools. Expected behavior: a.deref() returns undefined (happens in Chrome, Firefox and Edge) Actual behavior: a.deref() returns null in Safari and Epiphany

Attachments
Patch (2.69 KB, patch) 2022-02-04 17:04 PST, Yusuke Suzuki	no flags	Details Formatted Diff Diff
Patch (6.19 KB, patch) 2022-02-04 17:14 PST, Yusuke Suzuki	ashvayka: review+	Details Formatted Diff Diff
Show Obsolete (1) View All Add attachment proposed patch, testcase, etc.

Radar WebKit Bug Importer

Comment 1 2022-02-04 16:18:02 PST

<rdar://problem/88513359>

Yusuke Suzuki

Comment 2 2022-02-04 17:04:46 PST

Created attachment 450955 [details] Patch

Yusuke Suzuki

Comment 3 2022-02-04 17:14:24 PST

Created attachment 450956 [details] Patch

Alexey Shvayka

Comment 4 2022-02-04 17:26:52 PST

Comment on attachment 450956 [details] Patch View in context: https://bugs.webkit.org/attachment.cgi?id=450956&action=review > Source/JavaScriptCore/ChangeLog:8 > + WeakRef#deref should return undefined when a wrapped object is collected. nit: a spec link perhaps? https://tc39.es/ecma262/#sec-weakrefderef

Yusuke Suzuki

Comment 5 2022-02-04 17:27:18 PST

Thanks Sam and Alexey!

Yusuke Suzuki

Comment 6 2022-02-04 18:00:33 PST

Comment on attachment 450956 [details] Patch View in context: https://bugs.webkit.org/attachment.cgi?id=450956&action=review >> Source/JavaScriptCore/ChangeLog:8 >> + WeakRef#deref should return undefined when a wrapped object is collected. > > nit: a spec link perhaps? https://tc39.es/ecma262/#sec-weakrefderef Nice, done.

Yusuke Suzuki

Comment 7 2022-02-04 23:27:04 PST

Committed r289152 (246848@trunk): <https://commits.webkit.org/246848@trunk>

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