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Racing condition between input event and page switching #38621

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Racing condition between input event and page switching#38621
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A-webdriver
@PotatoCP

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@PotatoCP
PotatoCP
opened on Aug 12, 2025

Consider this tests

servo/tests/wpt/tests/webdriver/tests/classic/perform_actions/navigation.py

Lines 26 to 37 in b397843

def test_key(session, inline, key_chain):
session.url = inline(f"""
<input onkeydown="window.location = '{inline(PAGE_CONTENT)}'"/>
<script>
const input = document.querySelector("input");
input.focus();
</script>
""")
key_chain \
.key_down("1") \
.key_up("1") \

After key down action is sent, servo will change the document. Unfortunately, we have no synchronization with how key up action is dispatched here.

From manual logging, what I found is that here

servo/components/script/script_thread.rs

Lines 3604 to 3609 in b397843

fn handle_input_event(&self, pipeline_id: PipelineId, event: ConstellationInputEvent) {
let Some(document) = self.documents.borrow().find_document(pipeline_id) else {
warn!("Compositor event sent to closed pipeline {pipeline_id}.");
return;
};

when we finally process the pending input, the key up will never be processed, since for its pipeline we will not call below function.

servo/components/script/script_thread.rs

Lines 1053 to 1057 in b397843

fn process_pending_input_events(&self, pipeline_id: PipelineId, can_gc: CanGc) {
let Some(document) = self.documents.borrow().find_document(pipeline_id) else {
warn!("Processing pending compositor events for closed pipeline {pipeline_id}.");
return;
};

Because between handling the event and processing the pending input, we will mark the document as inactive due to the page being switch.

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