Intent to Extend Experiment: Shared Array Buffers, Atomics and Futex APIs

[Chromestatus]

Contact emails

va...@chromium.org, cl...@chromium.org

Explainer

No information provided

Specification

https://tc39.github.io/ecma262/#sec-sharedarraybuffer-objects

Design docs

No information provided
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer

Summary

Adds the JavaScript type SharedArrayBuffer gated behind COOP/COEP. The concept of a SharedArrayBuffer is that a message to a worker, is posted but instead of copying the content of the array just a reference to it is shared. The Atomic API provides atomic loads and stores and Read/Modify/Write accesses to SharedArrayBuffers. The Atomic.wait provides the ability for a worker to wait for another worker to signal it, without having to spinlock.

Blink component

Blink>JavaScript

Web Feature ID

No information provided

Search tags

SharedArrayBuffer, SAB

TAG review

https://github.com/w3ctag/design-reviews/issues/471

TAG review status

Pending

Origin Trial Name

SharedArrayBuffers in non-isolated pages on Desktop platforms

Chromium Trial Name

UnrestrictedSharedArrayBuffer

Link to origin trial feedback summary

https://bugs.chromium.org/p/chromium/issues/entry?components=Internals%3ESandbox%3ESiteIsolation

Origin Trial documentation link

https://developer.chrome.com/blog/enabling-shared-array-buffer/

Risks

Interoperability and Compatibility

No information provided

Gecko: Shipped/Shipping (https://bugzilla.mozilla.org/show_bug.cgi?id=1312446)

WebKit: Shipped/Shipping (https://developer.apple.com/library/content/releasenotes/General/WhatsNewInSafari/Articles/Safari_10_1.html)

Web developers: Positive

Other signals:

WebView application risks

Does this intent deprecate or change behavior of existing APIs, such that it has potentially high risk for Android WebView-based applications?

No information provided

Goals for experimentation

No information provided

Reason this experiment is being extended

This is a deprecation trial, and we're giving more time to websites to stop using the deprecated behavior.

Reason this experiment is being extended

The release of DocumentIsolationPolicy in M137 is helping developers adopt crossOriginIsolation as a way out of this reverse Origin Trial. However, it will still take time for developers to adopt. We would like to extend the OT as the final extension and give developers 6 milestones to get out of this reverse Origin Trial. Once this is approved and developers have requested their token, we will close this trial so that no further origins adopt the deprecated behavior.

Reason this experiment is being extended

We still have one of the historic users of ungated SharedArrayBuffers which has not managed to transition to cross-origin isolation (Google Earth). They are in the process of deploying COEP and asked us for an extension of the reverse origin trial until M146, when they believe they will be done with COEP deployment. Once the extension is approved, we'll close the Origin Trial to ensure no new users can register.

Ongoing technical constraints

No information provided

Debuggability

DevTools warning in case SAB is used in none COI context is in place

Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, ChromeOS, Android, and Android WebView)?

No

Is this feature fully tested by web-platform-tests?

Yes
https://source.chromium.org/chromium/chromium/src/+/master:third_party/blink/web_tests/external/wpt/html/infrastructure/safe-passing-of-structured-data/shared-array-buffers/no-coop-coep.https.any.js https://github.com/tc39/test262/tree/master/test/built-ins/SharedArrayBuffer https://github.com/tc39/test262/tree/master/test/built-ins/Atomics

Flag name on about://flags

No information provided

Finch feature name

No information provided

Non-finch justification

No information provided

Requires code in //chrome?

False

Tracking bug

https://bugs.chromium.org/p/chromium/issues/detail?id=709179

Launch bug

https://bugs.chromium.org/p/chromium/issues/detail?id=1138860

Estimated milestones

Origin trial desktop first	92
Origin trial desktop last	131
Origin trial extension 1 end milestone	109
Origin trial extension 2 end milestone	131
Origin trial extension 3 end milestone	124
Origin trial extension 4 end milestone	136
Origin trial extension 5 end milestone	142
Origin trial extension 6 end milestone	146
DevTrial on desktop	60
DevTrial on Android	88

Link to entry on the Chrome Platform Status

https://chromestatus.com/feature/4570991992766464?gate=5932856039833600

Links to previous Intent discussions

Intent to Experiment: https://groups.google.com/a/chromium.org/g/blink-dev/c/1NKvbIj3dq4
Intent to Extend Experiment 1: https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAH0ixBN2JhcYtpT4UYKcAfHt1e0Wz_Uxz0CkXcAntguhbmyNCA%40mail.gmail.com
Intent to Extend Experiment 2: https://groups.google.com/u/1/a/chromium.org/g/blink-dev/c/4tDmckQLZLQ
Intent to Extend Experiment 3: https://groups.google.com/a/chromium.org/g/blink-dev/c/UospzV3lZMk/m/X9K0k8kuAQAJ
Intent to Extend Experiment 4: https://groups.google.com/a/chromium.org/g/blink-dev/c/A4CR6MIVzds/m/rpsWnzq6AAAJ?e=48417069
Intent to Extend Experiment 5: https://groups.google.com/a/chromium.org/d/msgid/blink-dev/681b67ca.170a0220.4750a.028e.GAE%40google.com
Intent to Ship: https://groups.google.com/a/chromium.org/g/blink-dev/c/1NKvbIj3dq4

This intent message was generated by Chrome Platform Status.

[Mike Taylor]

When this was renewed last year, we discussed closing new registrations and only allowing exiting registrations to renew. Was this ever set up? (if so, it seems to have regressed, from what I can tell).

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[Camille Lamy]

No unfortunately we did not do it at the time. Now it's clear we really need to do it.

[Camille Lamy]

[Mike Taylor]

Camille and I met yesterday to discuss this intent.

LGTM to extend to M146, contingent on the fact that we set up a renewal flow that only allows renewals for existing participants. However, Camille will be out for ~2 weeks, so let's extend this now on the backend and set up the registration approval flow when she gets back (I am happy to help, having done this once before). Another option would also be to ask the OT team to close new registrations in ~2 weeks (this may not be a supported workflow, dunno).

On 11/14/25 11:20 a.m., Camille Lamy wrote:

On Tue, Nov 11, 2025 at 5:34 PM Camille Lamy <cl...@google.com> wrote:

No unfortunately we did not do it at the time. Now it's clear we really need to do it.

Reason this experiment is being extended

The release of DocumentIsolationPolicy in M137 is helping developers adopt crossOriginIsolation as a way out of this reverse Origin Trial. However, it will still take time for developers to adopt. We would like to extend the OT as the final extension and give developers 6 milestones to get out of this reverse Origin Trial. Once this is approved and developers have requested their token, we will close this trial so that no further origins adopt the deprecated behavior.

Reason this experiment is being extended

We still have one of the historic users of ungated SharedArrayBuffers which has not managed to transition to cross-origin isolation (Google Earth). They are in the process of deploying COEP and asked us for an extension of the reverse origin trial until M146, when they believe they will be done with COEP deployment. Once the extension is approved, we'll close the Origin Trial to ensure no new users can register.