Array.shift() causing bad perf when there are lots of tasks

[jtarchie]

tl;dr - Chrome doesn't handle Array#shift in an efficient manner for large arrays. Causing workerQueue to not handle lots of events in a quick manner.

Our application uses EventSource to stream output from an external process. The EventSource is modeled as a subscription, with each event triggering a new message.

On some streams, we can received hundreds of thousands of events, which creates a new process for each event on the elm process queue. On Google Chrome, the process queue does not get processed in a timely manner. On Firefox, however, it is near instantaneous. We were able to find with the Performance developer tool in Chrome that a lot of time is spent in work.

We've been able to find that Array.shift in Javascript is inefficient in Google Chrome for large arrays. This causes workQueue to choke on a large amount of processes.

With @zwilias help there is a SSCCE example. It doesn't use EventSource, but does demostrate the slow processing of a large number of processes. Try it in Chrome and then FF. Such wow, amaze!

[process-bot]

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[process-bot]

Thanks for the issue! Make sure it satisfies this checklist. My human colleagues will appreciate it!

Here is what to expect next, and if anyone wants to comment, keep these things in mind.

[zwilias]

For reference, a fairly simple fifo queue implementation that only has enqueue and dequeue operations like this one make performance on chrome manageable. (It basically cheats by acting as if dequeued elements are no longer in the array, periodically slicing the start off in a batch.)

[zwilias]

For reference, a fairly simple fifo queue implementation that only has enqueue and dequeue operations like this one make performance on chrome manageable. (It basically cheats by acting as if dequeued elements are no longer in the array, periodically slicing the start off in a batch.)