Refactor WorkerThread runloop; avoid pathological starvation of pollers
#4247
+252
−241
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armanbilge
commented
Jan 21, 2025
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| def lookForWork(): Unit = { | ||
| var state = 0 | ||
| while (!done.get()) { | ||
| (state: @switch) match { | ||
| case 0 => | ||
| // Check the external queue after a failed dequeue from the local | ||
| // queue (due to the local queue being empty). |
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Actually, we could lift case 0 out of the loop. It's always guaranteed to run exactly once, and never again. The loop just transitions between cases 1 and 2.
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Fixes #4228.
At a high level, a
WorkerThreadis always in one of the following three states:Previously, (3) was a separate
parkLoop(), but (1) and (2) were entangled in the top-level runloop. Now, (2) is refactored into a separatelookForWork()loop. Thus, the top-level runloop is only responsible for tracking "ticks", such that polling runs every 64 ticks.