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sbt/notes/2.0.0/parallel-dependency-resolution.md
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BrianHotoppandClaude Opus 4.8 0ee7323110 [2.x] fix: Parallelize dependency resolution when no progress bar is rendered (#9270)
update held a process-global lock around coursier resolution and artifact
fetching whenever a logger was set OR coursier was not in fallback mode. That
lock exists only to serialize coursier's interactive progress bar, which is
rendered solely when no custom logger is supplied and coursier is not in
fallback mode. The loggerOpt.nonEmpty clause therefore over-serialized the
common non-interactive case (IntelliJ re-imports, CI, any non-TTY run, where
sbt supplies a quiet debug-only logger), making update scale with the number
of modules rather than the number of distinct artifacts.

Fixes #5508.

Co-authored-by: Claude Opus 4.8 (1M context) <[email protected]>
2026-05-28 15:31:38 -04:00

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### `update` resolves modules in parallel
Dependency resolution (`update`) no longer holds a process-global lock while
coursier is *not* rendering its interactive progress bar -- that is, whenever a
custom `csrLogger` is set, or coursier is in fallback display mode (the default
under IntelliJ, CI, and any non-TTY environment, or with `COURSIER_PROGRESS=false`).
Previously the lock was taken even for sbt's quiet default logger, so `update`
processed one module at a time and its duration grew with the number of modules
rather than the number of distinct artifacts. Large multi-module builds and
IDE/CI re-imports could spend minutes serializing resolution.
The lock is still held while coursier draws its live per-module progress bars in
an interactive terminal, because that renderer is not safe to drive concurrently;
to parallelize there as well, run with `COURSIER_PROGRESS=false`. Fully parallel
resolution *with* live progress bars is tracked by [#5627][i5627].
This addresses [#5508][i5508].
[i5508]: https://github.com/sbt/sbt/issues/5508
[i5627]: https://github.com/sbt/sbt/issues/5627