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[WTF] Add ThreadSafeLazyUniquePtr#64619

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Constellation:eng/WTF-Add-ThreadSafeLazyUniquePtr
May 11, 2026
Merged

[WTF] Add ThreadSafeLazyUniquePtr#64619
webkit-commit-queue merged 1 commit into
WebKit:mainfrom
Constellation:eng/WTF-Add-ThreadSafeLazyUniquePtr

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@Constellation Constellation commented May 9, 2026 •
edited by webkit-early-warning-system
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1661ae2

[WTF] Add ThreadSafeLazyUniquePtr
https://bugs.webkit.org/show_bug.cgi?id=314487
rdar://176696158

Reviewed by Keith Miller.

Point of this class is adding handy class which uses the pattern,

    if (oldValue)
        return oldValue;

    newValue = factory();
    if (oldValue = Strong-CAS-with-release(oldValue, nullptr, newValue)) {
        destroy newValue;
        return oldValue;
    }
    return newValue;

This removes necessity of locking to publish a new value to the other
thread. We speculatively create a new value and attempt to publish it,
if it failed, we use the already published one. But otherwise, we
install a newly created one. This is ownership wrapped version of
Atomics.h's ensurePointer.

This is something similar to standard C++'s
`std::atomic<std::shared_ptr<T>>`. But it does not offer
`std::atomic<std::unique_ptr<T>>`, so this is why this class exists.

We use this class for IPIntSharedBytecode in RTT. We also remove
storeStoreFence() since now we use "release" to publish a value via strong-CAS.

* Source/JavaScriptCore/wasm/WasmTypeDefinition.cpp:
(JSC::Wasm::RTT::ensureArgumINTBytecode const):
(JSC::Wasm::RTT::ensureUINTBytecode const):
(JSC::Wasm::RTT::ensureCallBytecode const):
(JSC::Wasm::RTT::ensureTailCallBytecode const):
* Source/JavaScriptCore/wasm/WasmTypeDefinition.h:
* Source/WTF/WTF.xcodeproj/project.pbxproj:
* Source/WTF/wtf/CMakeLists.txt:
* Source/WTF/wtf/ThreadSafeLazyUniquePtr.h: Added.

Canonical link: https://commits.webkit.org/313019@main

bf3fa09

Misc iOS, visionOS, tvOS & watchOS macOS Linux Windows Apple Internal
✅ 🧪 style ✅ 🛠 ios   🛠 mac ✅ 🛠 wpe ⏳ 🛠 win ⏳ 🛠 ios-apple
✅ 🛠 ios-sim ✅ 🛠 mac-AS-debug   🧪 wpe-wk2 ⏳ 🧪 win-tests ⏳ 🛠 mac-apple
✅ 🧪 webkitperl   🧪 ios-wk2   🧪 api-mac   🧪 api-wpe ⏳ 🛠 vision-apple
⏳ 🧪 ios-wk2-wpt ⏳ 🧪 api-mac-debug   🛠 gtk3-libwebrtc
loading 🛠 🧪 jsc ⏳ 🧪 api-ios   🧪 mac-wk1 ✅ 🛠 gtk
loading 🛠 🧪 jsc-debug-arm64   🛠 ios-safer-cpp   🧪 mac-wk2   🧪 gtk-wk2
✅ 🛠 vision ⏳ 🧪 mac-AS-debug-wk2   🧪 api-gtk
✅ 🛠 vision-sim   🧪 mac-wk2-stress ✅ 🛠 playstation
✅ 🛠 🧪 unsafe-merge   🧪 vision-wk2   🧪 mac-intel-wk2 ✅ 🛠 jsc-armv7
✅ 🛠 tv   🛠 mac-safer-cpp   🧪 jsc-armv7-tests
✅ 🛠 tv-sim
✅ 🛠 watch
  🛠 watch-sim

@Constellation Constellation requested a review from a team as a code owner May 9, 2026 19:07
@Constellation Constellation self-assigned this May 9, 2026
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webkit-early-warning-system commented May 9, 2026 •
edited
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EWS run on previous version of this PR (hash f31a772)

Details

Misc iOS, visionOS, tvOS & watchOS macOS Linux Windows Apple Internal
✅ 🧪 style ✅ 🛠 ios   🛠 mac   🛠 wpe ✅ 🛠 win ⏳ 🛠 ios-apple
✅ 🛠 ios-sim ✅ 🛠 mac-AS-debug   🧪 wpe-wk2   🧪 win-tests ⏳ 🛠 mac-apple
✅ 🧪 webkitperl   🧪 ios-wk2   🧪 api-mac   🧪 api-wpe ⏳ 🛠 vision-apple
  🧪 ios-wk2-wpt   🧪 api-mac-debug ✅ 🛠 gtk3-libwebrtc
  🛠 🧪 jsc   🧪 api-ios   🧪 mac-wk1   🛠 gtk
✅ 🛠 🧪 jsc-debug-arm64 ✅ 🛠 ios-safer-cpp   🧪 mac-wk2   🧪 gtk-wk2
✅ 🛠 vision   🧪 mac-AS-debug-wk2   🧪 api-gtk
✅ 🛠 vision-sim   🧪 mac-wk2-stress   🛠 playstation
  🧪 vision-wk2   🧪 mac-intel-wk2 ✅ 🛠 jsc-armv7
✅ 🛠 tv   🛠 mac-safer-cpp   🧪 jsc-armv7-tests
✅ 🛠 tv-sim
✅ 🛠 watch
✅ 🛠 watch-sim

@Constellation Constellation force-pushed the eng/WTF-Add-ThreadSafeLazyUniquePtr branch from f31a772 to a0282ad Compare May 9, 2026 19:08
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webkit-early-warning-system commented May 9, 2026 •
edited
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EWS run on previous version of this PR (hash a0282ad)

Details

Misc iOS, visionOS, tvOS & watchOS macOS Linux Windows Apple Internal
✅ 🧪 style ✅ 🛠 ios   🛠 mac ✅ 🛠 wpe   🛠 win ⏳ 🛠 ios-apple
✅ 🛠 ios-sim ✅ 🛠 mac-AS-debug   🧪 wpe-wk2   🧪 win-tests ⏳ 🛠 mac-apple
✅ 🧪 webkitperl   🧪 ios-wk2   🧪 api-mac   🧪 api-wpe ⏳ 🛠 vision-apple
  🧪 ios-wk2-wpt   🧪 api-mac-debug   🛠 gtk3-libwebrtc
✅ 🛠 🧪 jsc   🧪 api-ios   🧪 mac-wk1 ✅ 🛠 gtk
✅ 🛠 🧪 jsc-debug-arm64 ✅ 🛠 ios-safer-cpp   🧪 mac-wk2   🧪 gtk-wk2
✅ 🛠 vision   🧪 mac-AS-debug-wk2   🧪 api-gtk
✅ 🛠 vision-sim   🧪 mac-wk2-stress ✅ 🛠 playstation
  🧪 vision-wk2   🧪 mac-intel-wk2   🛠 jsc-armv7
✅ 🛠 tv   🛠 mac-safer-cpp   🧪 jsc-armv7-tests
✅ 🛠 tv-sim
✅ 🛠 watch
✅ 🛠 watch-sim

@Constellation Constellation force-pushed the eng/WTF-Add-ThreadSafeLazyUniquePtr branch from a0282ad to 1c1a141 Compare May 9, 2026 19:12
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webkit-early-warning-system commented May 9, 2026 •
edited
Loading

EWS run on previous version of this PR (hash 1c1a141)

Details

Misc iOS, visionOS, tvOS & watchOS macOS Linux Windows Apple Internal
✅ 🧪 style ✅ 🛠 ios ✅ 🛠 mac ✅ 🛠 wpe ✅ 🛠 win ✅ 🛠 ios-apple
✅ 🛠 ios-sim ✅ 🛠 mac-AS-debug ✅ 🧪 wpe-wk2 ❌ 🧪 win-tests ✅ 🛠 mac-apple
✅ 🧪 webkitperl ✅ 🧪 ios-wk2 ❌ 🧪 api-mac ✅ 🧪 api-wpe ✅ 🛠 vision-apple
✅ 🧪 ios-wk2-wpt ✅ 🧪 api-mac-debug ✅ 🛠 gtk3-libwebrtc
✅ 🛠 🧪 jsc ✅ 🧪 api-ios ✅ 🧪 mac-wk1 ✅ 🛠 gtk
✅ 🛠 🧪 jsc-debug-arm64 ✅ 🛠 ios-safer-cpp ✅ 🧪 mac-wk2 ✅ 🧪 gtk-wk2
✅ 🛠 vision ✅ 🧪 mac-AS-debug-wk2 ✅ 🧪 api-gtk
✅ 🛠 vision-sim ✅ 🧪 mac-wk2-stress ✅ 🛠 playstation
✅ 🧪 vision-wk2 ✅ 🧪 mac-intel-wk2 ✅ 🛠 jsc-armv7
✅ 🛠 tv ✅ 🛠 mac-safer-cpp ✅ 🧪 jsc-armv7-tests
✅ 🛠 tv-sim
✅ 🛠 watch
✅ 🛠 watch-sim

kmiller68
kmiller68 approved these changes May 11, 2026
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r=me

kmiller68
kmiller68 reviewed May 11, 2026
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Comment thread Source/WTF/wtf/ThreadSafeLazyUniquePtr.h
Comment on lines +52 to +53
template<typename Func>
T& ensure(NOESCAPE const Func& func) const
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Nit: Might be worth a comment along the lines of "In general there is no need to fence in func the compareExchangeStrong will ensure any stores to initialize the value will happen before the new pointer becomes visible."

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Sounds good!

@Constellation Constellation force-pushed the eng/WTF-Add-ThreadSafeLazyUniquePtr branch from 1c1a141 to bf3fa09 Compare May 11, 2026 18:27
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webkit-early-warning-system commented May 11, 2026 •
edited
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EWS run on current version of this PR (hash bf3fa09)

Details

Misc iOS, visionOS, tvOS & watchOS macOS Linux Windows Apple Internal
✅ 🧪 style ✅ 🛠 ios   🛠 mac ✅ 🛠 wpe ⏳ 🛠 win ⏳ 🛠 ios-apple
✅ 🛠 ios-sim ✅ 🛠 mac-AS-debug   🧪 wpe-wk2 ⏳ 🧪 win-tests ⏳ 🛠 mac-apple
✅ 🧪 webkitperl   🧪 ios-wk2   🧪 api-mac   🧪 api-wpe ⏳ 🛠 vision-apple
⏳ 🧪 ios-wk2-wpt ⏳ 🧪 api-mac-debug   🛠 gtk3-libwebrtc
loading 🛠 🧪 jsc ⏳ 🧪 api-ios   🧪 mac-wk1 ✅ 🛠 gtk
loading 🛠 🧪 jsc-debug-arm64   🛠 ios-safer-cpp   🧪 mac-wk2   🧪 gtk-wk2
✅ 🛠 vision ⏳ 🧪 mac-AS-debug-wk2   🧪 api-gtk
✅ 🛠 vision-sim   🧪 mac-wk2-stress ✅ 🛠 playstation
✅ 🛠 🧪 unsafe-merge   🧪 vision-wk2   🧪 mac-intel-wk2 ✅ 🛠 jsc-armv7
✅ 🛠 tv   🛠 mac-safer-cpp   🧪 jsc-armv7-tests
✅ 🛠 tv-sim
✅ 🛠 watch
  🛠 watch-sim

@Constellation Constellation added the unsafe-merge-queue Applied to send a pull request to merge-queue, but skip building and testing label May 11, 2026
@Constellation
[WTF] Add ThreadSafeLazyUniquePtr
1661ae2 
https://bugs.webkit.org/show_bug.cgi?id=314487
rdar://176696158

Reviewed by Keith Miller.

Point of this class is adding handy class which uses the pattern,

    if (oldValue)
        return oldValue;

    newValue = factory();
    if (oldValue = Strong-CAS-with-release(oldValue, nullptr, newValue)) {
        destroy newValue;
        return oldValue;
    }
    return newValue;

This removes necessity of locking to publish a new value to the other
thread. We speculatively create a new value and attempt to publish it,
if it failed, we use the already published one. But otherwise, we
install a newly created one. This is ownership wrapped version of
Atomics.h's ensurePointer.

This is something similar to standard C++'s
`std::atomic<std::shared_ptr<T>>`. But it does not offer
`std::atomic<std::unique_ptr<T>>`, so this is why this class exists.

We use this class for IPIntSharedBytecode in RTT. We also remove
storeStoreFence() since now we use "release" to publish a value via strong-CAS.

* Source/JavaScriptCore/wasm/WasmTypeDefinition.cpp:
(JSC::Wasm::RTT::ensureArgumINTBytecode const):
(JSC::Wasm::RTT::ensureUINTBytecode const):
(JSC::Wasm::RTT::ensureCallBytecode const):
(JSC::Wasm::RTT::ensureTailCallBytecode const):
* Source/JavaScriptCore/wasm/WasmTypeDefinition.h:
* Source/WTF/WTF.xcodeproj/project.pbxproj:
* Source/WTF/wtf/CMakeLists.txt:
* Source/WTF/wtf/ThreadSafeLazyUniquePtr.h: Added.

Canonical link: https://commits.webkit.org/313019@main
@webkit-commit-queue webkit-commit-queue force-pushed the eng/WTF-Add-ThreadSafeLazyUniquePtr branch from bf3fa09 to 1661ae2 Compare May 11, 2026 18:35
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webkit-commit-queue commented May 11, 2026

Committed 313019@main (1661ae2): https://commits.webkit.org/313019@main

Reviewed commits have been landed. Closing PR #64619 and removing active labels.

@webkit-commit-queue webkit-commit-queue merged commit 1661ae2 into WebKit:main May 11, 2026
@webkit-commit-queue webkit-commit-queue removed the unsafe-merge-queue Applied to send a pull request to merge-queue, but skip building and testing label May 11, 2026
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