pantsbuild / pants
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coverage: 92.83% (-0.001%) from 92.831%
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Permit vfork fast-path within local `execute_process` (#23466)

Replaces use of `tokio::process::Command::pre_exec()` to establish a new
process group for the spawned child instead with
`tokio::proces::Command::process_group()`, as the former requires a
"slow" `fork -> (pre_exec closures)* -> exec` codepath, and the latter
permits a `vfork -> exec`-based fast-path.

This improves local build performance relative to both the resident set
size that the Pants process builds up (i.e. through in-memory caching of
rule results), and to the number of processes spawned through
`execute_process()`.

The "slow" path translates to underlying `clone()` syscalls without the
`CLONE_VFORK|CLONE_VM` flags, which suffer latency relative to the
parent process resident set size due to duplication of page tables for
the child, a cost which can become considerable for parent processes
(i.e., `pants`) that have allocated significant memory (e.g., cached
rule results), and can become meaningful for local Pants builds spawning
many processes.

This change permits the runtime to take the "fast" `vfork`-based path
(using `clone()` with `CLONE_VFORK|CLONE_VM`), which has ~constant
latency irrespective of parent memory allocation. "Permits", because
this code change alone does not ensure the fast path is taken;
minimally, the environment must also supply a glibc v2.29+, the earliest
version providing another required ingredient for taking the `vfork`
fast path (`posix_spawn_file_actions_addchdir_np()`).

93795 of 101040 relevant lines covered (92.83%)

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Source Files on main

Recent builds

Builds Branch Commit Type Ran Committer Via Coverage
28692728896 main Permit vfork fast-path within local `execute_process` (#23466) Replaces use of `tokio::process::Command::pre_exec()` to establish a new process group for the spawned child instead with `tokio::proces::Command::process_group()`, as the former requ... push web-flow github
92.83
28680877405 main Significantly reduce engine coroutine memory overhead (#23481) Easy wins that reduces peak engine memory by _a lot_. I've left comments at each site, as the choices may be non-obvious. ```console RUSTC_BOOTSTRAP=1 RUSTFLAGS=-Zprint-type-sizes c... push web-flow github
92.83
28679312469 main Upgrade pex to v2.97.0 (#23482) Changelogs: - https://github.com/pex-tool/pex/releases/tag/v2.97.0 - https://github.com/pex-tool/pex/releases/tag/v2.96.2 push web-flow github
92.83
28668849370 main drop support for EoL Python 3.9 in bundled lockfiles (#23464) Python 3.9 has been EoL for a while, and support has been removed from Pip. Based on the pattern in #22578 ; paves the way for a redux of #23440 push web-flow github
92.83
28620887565 main update bundled sqlfluff tool version to 4.x (#23462) The prior upper bounded version of sqlfluff doesn't work with the latest click (see among other issues https://github.com/sqlfluff/sqlfluff/issues/7960) so the next lockfile generation would ot... push web-flow github
92.83
28620848489 main preserve "pyside2" test in dedicated resolve (#23460) In https://github.com/pantsbuild/pants/issues/12390 we ended at "ignorance persists" so I want to be cautions about dropping any related tests, but pyside2 version used only supports the (now ... push web-flow github
92.83
28620729226 main drop python3.9 specific tests that use the bundled lockfiles (#23457) I think these "does black/mypy support Python syntax circa 2020?" tests have outlived their usefulness and removing them makes it easier to drop support for Python 3.9 (EoL sin... push web-flow github
92.83
28620681174 main add a resolve toggle for bundled lockfiles (#23445) This adds a `resolve` toggle to generate_builtin_lockfiles.py so we can split apart "switching to uv" from the next generation. Originally part of https://github.com/pantsbuild/pants/pull/23440 push web-flow github
92.83
28620007211 main provide an explicit shebang for the mypy shell script (#23479) So, I had looked at this a few times and been curious how it worked. The answer exposed by https://github.com/pantsbuild/pants/pull/23466 is that it only *accidentally* worked. To quo... push web-flow github
92.83
28619476844 main plumb thru --validate-entry-point as a field (#23474) Exposes --validate-entry-point from way back in https://github.com/pex-tool/pex/pull/521 as a field. Why? I have a repo with a combination of "vanilla" pex_binary targets as well as ones that... push web-flow github
92.96
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