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worker: prevent event loop starvation through MessagePorts #29315

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56d0e4a
worker: prevent event loop starvation through MessagePorts
addaleax Jun 2, 2019
fab5d00
fixup! worker: prevent event loop starvation through MessagePorts
addaleax Sep 7, 2019
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fixup! worker: prevent event loop starvation through MessagePorts
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@addaleax
addaleax committed Sep 7, 2019
commit fab5d00d7d8178a02bacf253676c6f0a1d64b16b
13 changes: 9 additions & 4 deletions src/node_messaging.cc
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Expand Up @@ -604,21 +604,26 @@ void MessagePort::OnMessage() {
HandleScope handle_scope(env()->isolate());
Local<Context> context = object(env()->isolate())->CreationContext();

ssize_t processing_limit;
size_t processing_limit;
{
Mutex::ScopedLock(data_->mutex_);
processing_limit = data_->incoming_messages_.size();
processing_limit = std::max(data_->incoming_messages_.size(),
static_cast<size_t>(1000));
}

// data_ can only ever be modified by the owner thread, so no need to lock.
// However, the message port may be transferred while it is processing
// messages, so we need to check that this handle still owns its `data_` field
// on every iteration.
while (data_) {
if (--processing_limit < 0) {
if (processing_limit-- == 0) {
// Prevent event loop starvation by only processing those messages without
// interruption that were already present when the OnMessage() call was
// first triggered.
// first triggered, but at least 1000 messages because otherwise the
// overhead of repeatedly triggering the uv_async_t instance becomes
// noticable, at least on Windows.
// (That might require more investigation by somebody more familiar with
// Windows.)
TriggerAsync();
return;
}
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2 changes: 2 additions & 0 deletions test/parallel/test-worker-message-port-infinite-message-loop.js
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Expand Up @@ -24,4 +24,6 @@ port1.on('message', () => {

port2.postMessage(0);

// This is part of the test -- the event loop should be available and not stall
// out due to the recursive .postMessage() calls.
setTimeout(common.mustCall(), 0);