cache: convert prune loop from recursive invocation to iterative #5636
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The prune logic would prune multiple times because one prune could cause more things to be capable of pruning and change the logic. This was done through a recursive invocation. Since go doesn't have support for function tail calls, this would result in a new stack entry for each loop. This unrolls the logic so the prune function is invoked iteratively rather than recursively. `prune` and `pruneOnce` have also had their names swapped. In general, `pruneOnce` implies that it runs a single prune while `prune` sounds like the top level function. The current code had this reversed and `pruneOnce` would call `prune` and `prune` would call itself recursively. I've also updated a section in the controller that invoked prune on each worker. In older versions of Go, the current version was correct because those versions of Go would reuse the location for each loop which would cause goroutines to all reference the same worker instead of different workers. Recent versions of Go have changed the behavior so this is no longer needed. Signed-off-by: Jonathan A. Sternberg <[email protected]>
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Jan 11, 2025
| return err | ||
| } | ||
| totalReleasedSize += releasedSize | ||
| totalReleasedCount += releasedCount |
| }) | ||
| } | ||
| for { | ||
| releasedSize, releasedCount, err := cm.pruneOnce(ctx, ch, popt) |
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releasedCount in here seems more like a bool indicating if anything was pruned (unless I'm missing some usage of totalReleasedCount).
| return nil | ||
| }) | ||
| }(w) | ||
| eg.Go(func() error { |
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I guess this is go1.22+ only
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The prune logic would prune multiple times because one prune could cause more things to be capable of pruning and change the logic. This was done through a recursive invocation.
Since go doesn't have support for function tail calls, this would result in a new stack entry for each loop. This unrolls the logic so the prune function is invoked iteratively rather than recursively.
pruneandpruneOncehave also had their names swapped. In general,pruneOnceimplies that it runs a single prune whileprunesounds like the top level function. The current code had this reversed andpruneOncewould callpruneandprunewould call itself recursively.I've also updated a section in the controller that invoked prune on each worker. In older versions of Go, the current version was correct because those versions of Go would reuse the location for each loop which would cause goroutines to all reference the same worker instead of different workers.
Recent versions of Go have changed the behavior so this is no longer needed.