Intermittent TIMEOUT in /preload/modulepreload-sri-importmap.html and /preload/modulepreload-sri.html #43354

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1. yezhizhen

   added

   A-content/scriptRelated to the script threadRelated to the script thread

   on Mar 17, 2026
2. yezhizhen commented on Mar 17, 2026

   

   yezhizhen

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   cc @Gae24
3. yezhizhen

   added

   I-intermittentProblem reproduces intermittently.Problem reproduces intermittently.

   on Mar 17, 2026
4. jdm

   changed the title [-]Intermittent TIMEOUT in `/preload/modulepreload-sri-importmap.html`[/-] [+]Intermittent TIMEOUT in `/preload/modulepreload-sri-importmap.html` and `/preload/modulepreload-sri.html`[/+] on Mar 18, 2026
5. jdm commented on Mar 18, 2026

   

   jdm

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     ▶ TIMEOUT [expected OK] /preload/modulepreload-sri.html
     │ 
     │ [2026-03-18T00:51:39Z ERROR script::script_module] Fetching module script failed Subresource integrity validation failed
     │   ▶ TIMEOUT [expected PASS] Script should not be loaded if modulepreload's integrity is invalid
     └   └   → Test timed out
   
6. jdm commented on Mar 18, 2026

   

   jdm

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   I reproduced this in a debug build.
7. jdm commented on Mar 18, 2026

   

   jdm

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   The timeout occurs when

   servo/components/script/script_module.rs

   Line 660 in e61298e

   document.deferred_script_loaded(&script, load, can_gc);

   is called but we hit this early return:

   servo/components/script/dom/document.rs

   Lines 2716 to 2718 in e61298e

   	if self.ready_state.get() != DocumentReadyState::Interactive {
   	return;
   	}
8. jdm commented on Mar 18, 2026

   

   jdm

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   Relevant spec:

   • https://html.spec.whatwg.org/multipage/scripting.html#prepare-the-script-element 35.4
   • https://html.spec.whatwg.org/multipage/parsing.html#the-end:list-of-scripts-that-will-execute-when-the-document-has-finished-parsing step 4

   This timeout happens when the document is already incorrectly in the Complete ready state. We shouldn't reach that state while there are still deferred scripts pending.
9. jdm commented on Mar 18, 2026

   

   jdm

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   When this occurs, we see:

   1. the parser marks the document's ready state as Interactive
   2. the parser finishes parsing and mark the PageSource as finished
   3. this triggers a call to process_deferred_scripts
   4. but self.deferred_scripts.take_next_ready_to_be_executed() returns None since the fetch isn't complete
   5. the document sees no outstanding loads (??) and says it's time to move on to the next step

   I don't see any use of LoadBlocker in htmlscriptelement.rs, and there's

   servo/components/script/dom/html/htmlscriptelement.rs

   Lines 838 to 839 in e61298e

   	// TODO:
   	// Step 31.8. Set el's delaying the load event to true.

   which looks like a smoking gun.
10. jdm commented on Mar 18, 2026

    

    jdm

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    fetch_a_classic_script uses Document::fetch, which uses DocumentLoader::fetch_async_with_callback which adds a blocking load. fetch_a_single_module uses DocumentLoader::fetch_async_with_callback if the module owner is a script element, but modulepreload modules do not use a script element owner.
11. Gae24 commented on Mar 18, 2026

    

    Gae24

    on Mar 18, 2026

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    fetch_a_classic_script uses Document::fetch, which uses DocumentLoader::fetch_async_with_callback which adds a blocking load. fetch_a_single_module uses DocumentLoader::fetch_async_with_callback if the module owner is a script element, but modulepreload modules do not use a script element owner.

    I thought DocumentLoader::fetch_async_with_callback shouldn't be used because modulepreloads shouldn't delay the load event.
12. jdm commented on Mar 18, 2026

    

    jdm

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    Yes, I agree. The issue is that the script element loading the module needs to delay the load event, but when it sees there's already matching preload request that doesn't happen.
13. elomscansio commented on Apr 3, 2026

    

    elomscansio

    on Apr 3, 2026

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    This is fixed by #43741

    #43741 (comment)
14. jdm

    closed this as completedon Apr 3, 2026
15. yezhizhen

    reopened this on Apr 3, 2026
16. yezhizhen commented on Apr 3, 2026

    

    yezhizhen

    on Apr 3, 2026

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    Gonna open this as the PR not merged yet.
17. jdm commented on Apr 3, 2026

    

    jdm

    on Apr 3, 2026

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    @elomscansio Can you add a "Fixes #43354" to that PR's description in that case?

    👍React with 👍1Reacted by Emmanuel Paul Elom
18. github-merge-queue

    added a commit that references this issue on Apr 6, 2026

    script: implement render-blocking option for script fetch and load ev…

    ...

    This issue will close once commit a7bc4a6 is merged into the 'main' branch.

    a7bc4a6
19. Gae24

    closed this as completedin #43741on Apr 6, 2026