| commit | 52adf0b3d14d4af60ece33c95b94be058bafb41b | [log] [tgz] |
|---|---|---|
| author | Googler <leba@google.com> | Thu Apr 25 08:11:49 2024 -0700 |
| committer | Copybara-Service <copybara-worker@google.com> | Thu Apr 25 08:13:29 2024 -0700 |
| tree | 6a0ff2bb90657981af001a15fb205665b90dbe98 | |
| parent | 83cfbe845529a270b89185129eaf2a3c2e71989b [diff] |
Fix a race condition in IncrementalPackageRoots. Consider the following scenario: - Top level targets `A` and `B` - To execute actions in `A`, we need to plant symlinks for `NestedSet<Package>: [A1, C1, [D1]]`, - To execute actions in `B`, we need to plant symlinks for `NestedSet<Package>: [B1, C1, [D1]]` In the end, we expect to see symlinks to `A1`, `B1`, `C1` and `D1`. **What went wrong** With the current code, there are 2 possible race conditions: 1. Transitive NestedSet level: - Start to plant symlinks for `A` - `NestedSet [D1]` added to `handledPackageNestedSets`. _No symlink planted yet_. - Start to plant symlinks for `B` - `NestedSet [D1]` seen as "handled" and immediately skipped. Planted `B1` and `C1`. `B` moves on to execution. => actions from `B` that requires `D1` would fail (no such file or directory). 2. Individual symlink level: - Start to plant symlinks for `A` - `C1` added to `lazilyPlantedSymlinks`. _No symlink planted yet_. - Start to plant symlinks for `B` - `C1` already seen in `lazilyPlantedSymlinks` and immediately skipped. Planted `B1` and `D1`. `B` moves on to execution. => actions from `B` that requires `C1` would fail (no such file or directory). **The Solution** In order to prevent this race condition, we can plant the symlinks for top level targets `A` and `B` sequentially. This gives us the guarantee that: for an action `foo` under a top level target `A`, `foo` is only executed when all the necessary symlinks for `A` are already planted. The above scenario would look like: - Start to plant symlinks for `A` - The `TopLevelTargetReadyForSymlinkPlanting` event for `B` arrived and is held in the sequential event queue - Plant all symlinks. `lazilyPlantedSymlinks: [A1, C1, D1]`. `A` moves on to execution. - Start to plant symlinks for `B` - `NestedSet [D1]` already seen in `handledPackageNestedSets` and immediately skipped. - `C1` already seen in `lazilyPlantedSymlinks` and immediately skipped. - Planted `B1`. `B` moves on to execution. As an (hopefully not premature) optimization, the symlinks under a single top level target are planted in parallel. Fixes #22073 Verified locally with something similar to the repro in https://github.com/bazelbuild/bazel/issues/22073#issue-2256831560. PiperOrigin-RevId: 628080361 Change-Id: Ic6c1a6606d26400c46aa98bfeddc844abd075d0a
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