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Stop locking every RegionImage pixel write - #616
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Scan workers write distinct pixels of a region image, and saves only start after every scan for the region has finished, so the lock in setPixel was only needed to allocate the pixel array. Allocate it with double-checked locking on a volatile field instead, and leave pixel writes unsynchronized.
jpenilla
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Oct 16, 2026
Scan workers write distinct pixels of a region image, and saves only start after every scan for the region has finished, so the lock in setPixel was only needed to allocate the pixel array. Allocate it with double-checked locking on a volatile field instead, and leave pixel writes unsynchronized.
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RegionImage.setPixelwassynchronized, so every pixel write from every scan worker took the same lock. The lock is now only taken to allocate the pixel array, using double-checked locking on avolatilefield, and pixel writes are unsynchronized.Two things make unsynchronized writes safe. Each chunk is scanned by only one worker, so no two workers write the same pixel. Saving only starts after every scan for the region has finished, which guarantees the save sees all the writes. Rendered tiles are byte-identical to master.
Performance