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When Atomics.wait() is polyfilled, do not attempt to use it in _emscripten_thread_mailbox_await() #25853

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When Atomics.wait() is polyfilled, do not attempt to use it in _emscripten_thread_mailbox_await() #25853

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When Atomics.wait() is polyfilled, do not attempt to use it in _emscr…
juj Nov 22, 2025
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Add dependency
juj Nov 22, 2025
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juj Nov 22, 2025
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4 changes: 3 additions & 1 deletion src/lib/libatomic.js
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Original file line number Diff line number Diff line change
Expand Up @@ -22,7 +22,9 @@ addToLibrary({
// https://github.com/tc39/proposal-atomics-wait-async/blob/master/PROPOSAL.md
// This polyfill performs polling with setTimeout() to observe a change in the
// target memory location.
$polyfillWaitAsync__postset: `if (!Atomics.waitAsync || (globalThis.navigator?.userAgent && Number((navigator.userAgent.match(/Chrom(e|ium)\\/([0-9]+)\\./)||[])[2]) < 91)) {
$waitAsyncPolyfilled: `Atomics.waitAsyncPolyfilled = (!Atomics.waitAsync || (globalThis.navigator?.userAgent && Number((navigator.userAgent.match(/Chrom(e|ium)\\/([0-9]+)\\./)||[])[2]) < 91));`,
$polyfillWaitAsync__deps: ['$waitAsyncPolyfilled'],
$polyfillWaitAsync__postset: `if (Atomics.waitAsyncPolyfilled) {
let __Atomics_waitAsyncAddresses = [/*[i32a, index, value, maxWaitMilliseconds, promiseResolve]*/];
function __Atomics_pollWaitAsyncAddresses() {
let now = performance.now();
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4 changes: 2 additions & 2 deletions src/lib/libpthread.js
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Expand Up @@ -1261,9 +1261,9 @@ var LibraryPThread = {
}
}),

_emscripten_thread_mailbox_await__deps: ['$checkMailbox'],
_emscripten_thread_mailbox_await__deps: ['$checkMailbox', '$waitAsyncPolyfilled'],
_emscripten_thread_mailbox_await: (pthread_ptr) => {
if (Atomics.waitAsync) {
if (!Atomics.waitAsyncPolyfilled) {
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@sbc100 sbc100 Nov 22, 2025

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Why not just if (waitAsyncPolyfilled)? i.e. why modify the Atomics object at all?

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@juj juj Nov 22, 2025

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The idea was to make it look like a public API, if other code might need to check if the implementation was polyfilled or not. Changed to not modify the Atomics object.

// Wait on the pthread's initial self-pointer field because it is easy and
// safe to access from sending threads that need to notify the waiting
// thread.
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