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Add note to indicate why priority queue callbacks may be undefined #28337

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merged 6 commits into from
Feb 10, 2021
Merged

Add note to indicate why priority queue callbacks may be undefined #28337

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5b3e1c0
Check that waitingList callbacks are defined before calling to preven…
Jan 20, 2021
af40466
switch to typeof as jest.fn does not seem to be an instance of Function
Jan 20, 2021
af38a18
Add debugging to try and track down reason for undefined callback
Feb 4, 2021
9c562dc
Remove debugging
Feb 9, 2021
99bc2ac
Instead of checking for undefined callback check that the element has…
Feb 10, 2021
54426a7
Switch to just adding a comment to highlight cause of issue
Feb 10, 2021
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6 changes: 5 additions & 1 deletion packages/priority-queue/src/index.js
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Original file line number Diff line number Diff line change
Expand Up @@ -96,7 +96,11 @@ export const createQueue = () => {
const callback = /** @type {WPPriorityQueueCallback} */ ( elementsMap.get(
nextElement
) );
callback();

if ( typeof callback === 'function' ) {
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another option would be a try/catch here instead, with a warning for isDev on catch so at least there is an indication that something is going through the queue without a callback

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in which case the callback won't be a valid function?

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@youknowriad It turns out that in some cases if the callBack in runWaitingList takes a while to complete, the element can be added back to the waitList before elementsMap.delete is called. It then gets called before the new element in the waitingList goes through runWaitingList, so when it does there is no matching element in the elementsMap and the exception happens.

Screen Shot 2021-02-10 at 2 53 34 PM

I added some extra debugging in this PR, and you can see above callback being called for waitingList item 82, but then item 83 being added before the delete from element map happens for 82.

I have changed this PR to handle this situation by check that an element has not been added back to the waitList before deleting it from the element map, and this seems to fix the issue in the gallery refactor PR, but not sure if there are any other implications to handling this way.

callback();
}

elementsMap.delete( nextElement );
} while ( hasTimeRemaining() );

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