Reduce lock contention caused by regen pattern

[SirYwell]

Overview

Description

SingleThreadQueueExtent#getFullBlock calls SingleThreadQueueExtent#getOrCreateChunk every time. As this method contains a lock, that can cause some significant contention. If we process an edit chunk-wise, we can remember the chunk instead and have a cheaper access pattern. In my tests I'm seeing a ~15% improvement in edit duration.

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