| commit | cc182f23010571ffa8ebce38d1e8456661ce3b14 | [log] [tgz] |
|---|---|---|
| author | nharmata <nharmata@google.com> | Wed May 04 08:30:39 2022 -0700 |
| committer | Copybara-Service <copybara-worker@google.com> | Wed May 04 08:32:08 2022 -0700 |
| tree | 1f74a26ef919ac470dadce1b6a89a0a540a47ce2 | |
| parent | c30ffb071ac415138b8c033f2ba2d7df226e6102 [diff] |
Micro-optimize `Iterable` usage in `ActionExecutionFunction#addDiscoveredInputs`. Problem: In practice, the implementation of `Environment#getOrderedValuesAndExceptions` iterates over its given `Iterable` 3 times. For the call in `ActionExecutionFunction#addDiscoveredInputs`, this `Iterable` is a lazy transformation of the one from `InputDiscoveryState#filterKnownDiscoveredInputs` which itself is a lazy filter using `ActionInputMap#getMetadata`. When there are a lot of inputs, this wasteful repeated work adds up. Solution: Create a temporary `ImmutableList` formed by doing `InputDiscoveryState#filterKnownDiscoveredInputs` once, and use that for the call to `Environment#getOrderedValuesAndExceptions`. The theoretical downside is we potentially increase our peak heap usage. On a benchmark of extreme build with lots of actions with lots of input files, this approach consistently saves 2% CPU but has no significant impact on peak heap usage. Alternatives considered: Refactor `Environment#getOrderedValuesAndExceptions` to reduce the number of iterations over the given `Iterable`. But given that both aggregate and specific CPU profiles show the heavy hitter source of the problem is `ActionExecutionFunction#addDiscoveredInputs` and also a general refactor might not reduce the number of iterations as well as this CL here, I decided against this approach. PiperOrigin-RevId: 446464608
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