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fix(@angular/build): avoid race condition in sass importer

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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
This commit is contained in:
hborchardt 2024-10-14 23:01:07 +02:00 committed by Jan Olaf Martin
parent d8ab36bf7d
commit 5f473affcf
1 changed files with 19 additions and 0 deletions
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19
packages/angular/build/src/tools/sass/worker.ts
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@ -106,6 +106,25 @@ export default async function renderSassStylesheet(
containingUrl: containingUrl ? fileURLToPath(containingUrl) : null,
},
});
// Wait for the main thread to set the signal to 1 and notify, which tells
// us that a message can be received on the port.
// If the main thread is fast, the signal will already be set to 1, and no
// sleep/notify is necessary.
// However, there can be a race condition here:
// - the main thread sets the signal to 1, but does not get to the notify instruction yet
// - the worker does not pause because the signal is set to 1
// - the worker very soon enters this method again
// - this method sets the signal to 0 and sends the message
// - the signal is 0 and so the `Atomics.wait` call blocks
// - only now the main thread runs the `notify` from the first invocation, so the
// worker continues.
// - but there is no message yet in the port, because the thread should not have been
// waken up yet.
// To combat this, wait for a non-0 value _twice_.
// Almost every time, this immediately continues with "not-equal", because
// the signal is still set to 1, except during the race condition, when the second
// wait will wait for the correct notify.
Atomics.wait(importerChannel.signal, 0, 0);
Atomics.wait(importerChannel.signal, 0, 0);
const result = receiveMessageOnPort(importerChannel.port)?.message as string | null;