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Commit b91c82d

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hborchardtjkrems
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fix(@angular/build): avoid race condition in sass importer
On slow systems, a race condition can lead to the sass worker thread being notified to wake up before a message is posted. This causes the build to be aborted because the searched file is not found. Waiting twice for a non-zero number in the signal handles this race correctly, and the second wait should be a noop in the usual case. Fixes #27167 (cherry picked from commit 5f473af)
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‎packages/angular/build/src/tools/sass/worker.ts‎

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@@ -80,6 +80,25 @@ export default async function renderSassStylesheet(request: RenderRequestMessage
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containingUrl: containingUrl ? fileURLToPath(containingUrl) : null,
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},
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});
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// Wait for the main thread to set the signal to 1 and notify, which tells
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// us that a message can be received on the port.
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// If the main thread is fast, the signal will already be set to 1, and no
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// sleep/notify is necessary.
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// However, there can be a race condition here:
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// - the main thread sets the signal to 1, but does not get to the notify instruction yet
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// - the worker does not pause because the signal is set to 1
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// - the worker very soon enters this method again
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// - this method sets the signal to 0 and sends the message
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// - the signal is 0 and so the `Atomics.wait` call blocks
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// - only now the main thread runs the `notify` from the first invocation, so the
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// worker continues.
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// - but there is no message yet in the port, because the thread should not have been
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// waken up yet.
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// To combat this, wait for a non-0 value _twice_.
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// Almost every time, this immediately continues with "not-equal", because
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// the signal is still set to 1, except during the race condition, when the second
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// wait will wait for the correct notify.
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Atomics.wait(importerChannel.signal, 0, 0);
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Atomics.wait(importerChannel.signal, 0, 0);
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const result = receiveMessageOnPort(importerChannel.port)?.message as string | null;

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