Add PidFd::{kill, wait, try_wait}

[the8472]

#117957 changed Child kill/wait/try_wait to use its pidfd instead of the pid, when one is available.
This PR extracts those implementations and makes them available on PidFd directly.

The PidFd implementations differ significantly from the corresponding Child methods:

• the methods can be called after the child has been reaped, which will result in an error but will be safe. This state is not observable in Child unless something stole the zombie child
• the ExitStatus is not kept, meaning that only the first time a wait succeeds it will be returned
• wait does not close stdin
• wait only requires &self instead of &mut self since there is no state to maintain and subsequent calls are safe

Tracking issue: #82971

[rustbot]

r? @cuviper

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[cuviper]

If you call child.pidfd().wait() (or with take_pidfd()), doesn't that break child.wait()?

[the8472]

Good point. It shouldn't break it immediately since the pid won't be recycled until the fd is dropped (not confident, haven't tested this). But once one does drop it, yeah it'd become an issue.

But people do want to take out pidfds, e.g. for process management in tokio.
So either we have to make it take_pidfd(self) so it consumes the child or try_clone the fd instead so the child can hold onto its own copy.

[the8472]

I've replaced take_pidfd with into_pidfd which consumes the child.

[cuviper]

OK, into_pidfd() is better to make sure we avoid pid reuse on the child, but there's still an issue with the saved status. That is, child.pidfd().wait() cannot save the status, so it's lost from child.wait(). (Ditto try_wait())

At the very least, this should be an unresolved question on the tracking issue. Apart from that, r=me.

[the8472]

Yes it'll be lost but in those cases calling Child::wait will return an error as PidFd::wait would, not an incorrect value.
This is indeed new behavior, but any code using PidFd will also be new.

I'll note it in the tracking issue.

@bors r=cuviper rollup

[bors]

📌 Commit 210400a has been approved by cuviper

It is now in the queue for this repository.

[matthiaskrgr]

@bors r- #126775 (comment)

[workingjubilee]

@bors rollup=iffy

[the8472]

fixed the import, docs build for x86_64-pc-windows-gnu

@bors r=cuviper

[bors]

📌 Commit 8abf149 has been approved by cuviper

It is now in the queue for this repository.

[bors]

⌛ Testing commit 8abf149 with merge 06c6b72...

[rust-log-analyzer]

The job x86_64-msvc failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

failures:

---- [ui] tests\ui\lto\lto-duplicate-symbols.rs stdout ----

error: auxiliary build of "C:\\a\\rust\\rust\\tests\\ui\\lto\\auxiliary\\lto-duplicate-symbols1.rs" failed to compile: 
status: exit code: 1
command: PATH="C:\a\rust\rust\build\x86_64-pc-windows-msvc\stage2\bin;C:\Program Files (x86)\Windows Kits\10\bin\x64;C:\Program Files (x86)\Windows Kits\10\bin\10.0.22621.0\x64;C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.40.33807\bin\HostX64\x64;C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.40.33807\bin\HostX64\x64;C:\a\rust\rust\build\x86_64-pc-windows-msvc\stage0-bootstrap-tools\x86_64-pc-windows-msvc\release\deps;C:\a\rust\rust\build\x86_64-pc-windows-msvc\stage0\bin;C:\Program Files\PowerShell\7;C:\a\_temp\msys64\mingw64\bin;C:\a\_temp\msys64\usr\local\bin;C:\a\_temp\msys64\usr\bin;C:\a\_temp\msys64\usr\bin;C:\a\rust\rust\ninja;C:\a\rust\rust\sccache;C:\a\_temp\setup-msys2;C:\Program Files\MongoDB\Server\5.0\bin;C:\aliyun-cli;C:\vcpkg;C:\Program Files (x86)\NSIS;C:\tools\zstd;C:\Program Files\Mercurial;C:\hostedtoolcache\windows\stack\2.15.7\x64;C:\cabal\bin;C:\ghcup\bin;C:\mingw64\bin;C:\Program Files\dotnet;C:\Program Files\MySQL\MySQL Server 8.0\bin;C:\Program Files\R\R-4.4.0\bin\x64;C:\SeleniumWebDrivers\GeckoDriver;C:\SeleniumWebDrivers\EdgeDriver;C:\SeleniumWebDrivers\ChromeDriver;C:\Program Files (x86)\sbt\bin;C:\Program Files (x86)\GitHub CLI;C:\Program Files\Git\bin;C:\Program Files (x86)\pipx_bin;C:\npm\prefix;C:\hostedtoolcache\windows\go\1.21.11\x64\bin;C:\hostedtoolcache\windows\Python\3.9.13\x64\Scripts;C:\hostedtoolcache\windows\Python\3.9.13\x64;C:\hostedtoolcache\windows\Ruby\3.0.7\x64\bin;C:\Program Files\OpenSSL\bin;C:\tools\kotlinc\bin;C:\hostedtoolcache\windows\Java_Temurin-Hotspot_jdk\8.0.412-8\x64\bin;C:\Program Files\ImageMagick-7.1.1-Q16-HDRI;C:\Program Files\Microsoft SDKs\Azure\CLI2\wbin;C:\ProgramData\kind;C:\ProgramData\docker-compose;C:\ProgramData\Chocolatey\bin;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0;C:\Windows\System32\OpenSSH;C:\Program Files\dotnet;C:\Program Files\PowerShell\7;C:\Program Files\Microsoft\Web Platform Installer;C:\Program Files\TortoiseSVN\bin;C:\Program Files\Microsoft SQL Server\Client SDK\ODBC\170\Tools\Binn;C:\Program Files\Microsoft SQL Server\150\Tools\Binn;C:\Program Files (x86)\Windows Kits\10\Windows Performance Toolkit;C:\Program Files (x86)\WiX Toolset v3.14\bin;C:\Program Files\Microsoft SQL Server\130\DTS\Binn;C:\Program Files\Microsoft SQL Server\140\DTS\Binn;C:\Program Files\Microsoft SQL Server\150\DTS\Binn;C:\Program Files\Microsoft SQL Server\160\DTS\Binn;C:\Strawberry\c\bin;C:\Strawberry\perl\site\bin;C:\Strawberry\perl\bin;C:\ProgramData\chocolatey\lib\pulumi\tools\Pulumi\bin;C:\Program Files\CMake\bin;C:\ProgramData\chocolatey\lib\maven\apache-maven-3.8.7\bin;C:\Program Files\Microsoft Service Fabric\bin\Fabric\Fabric.Code;C:\Program Files\Microsoft SDKs\Service Fabric\Tools\ServiceFabricLocalClusterManager;C:\Program Files\nodejs;C:\Program Files\Git\cmd;C:\Program Files\Git\mingw64\bin;C:\Program Files\Git\usr\bin;C:\Program Files\GitHub CLI;C:\tools\php;C:\Program Files (x86)\sbt\bin;C:\Program Files\Amazon\AWSCLIV2;C:\Program Files\Amazon\SessionManagerPlugin\bin;C:\Program Files\Amazon\AWSSAMCLI\bin;C:\Program Files\Microsoft SQL Server\130\Tools\Binn;C:\Program Files\LLVM\bin;C:\Users\runneradmin\.dotnet\tools;C:\Users\runneradmin\.cargo\bin;C:\Users\runneradmin\AppData\Local\Microsoft\WindowsApps;C:\a\_temp\msys64\usr\bin\site_perl;C:\a\_temp\msys64\usr\bin\vendor_perl;C:\a\_temp\msys64\usr\bin\core_perl" "C:\\a\\rust\\rust\\build\\x86_64-pc-windows-msvc\\stage2\\bin\\rustc.exe" "C:\\a\\rust\\rust\\tests\\ui\\lto\\auxiliary\\lto-duplicate-symbols1.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=C:\\Users\\runneradmin\\.cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=C:\\a\\rust\\rust\\vendor" "--sysroot" "C:\\a\\rust\\rust\\build\\x86_64-pc-windows-msvc\\stage2" "--target=x86_64-pc-windows-msvc" "--check-cfg" "cfg(FALSE)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--out-dir" "C:\\a\\rust\\rust\\build\\x86_64-pc-windows-msvc\\test\\ui\\lto\\lto-duplicate-symbols\\auxiliary" "-A" "internal_features" "-Crpath" "-Cdebuginfo=0" "-Lnative=C:\\a\\rust\\rust\\build\\x86_64-pc-windows-msvc\\native\\rust-test-helpers" "-L" "C:\\a\\rust\\rust\\build\\x86_64-pc-windows-msvc\\test\\ui\\lto\\lto-duplicate-symbols\\auxiliary"
--- stderr -------------------------------
--- stderr -------------------------------
error: couldn't create a temp dir: Access is denied. (os error 5) at path "C:\\a\\_temp\\msys64\\tmp\\rustcMwb8Le"
error: aborting due to 1 previous error
------------------------------------------


---
test result: FAILED. 16875 passed; 1 failed; 250 ignored; 0 measured; 2 filtered out; finished in 379.97s

Some tests failed in compiletest suite=ui mode=ui host=x86_64-pc-windows-msvc target=x86_64-pc-windows-msvc
Build completed unsuccessfully in 0:40:48
make: *** [Makefile:102: ci-msvc-ps1] Error 1
  network time: Sat, 22 Jun 2024 00:38:20 GMT
##[error]Process completed with exit code 2.
Post job cleanup.
[command]"C:\Program Files\Git\bin\git.exe" version

[bors]

💔 Test failed - checks-actions

[cuviper]

@bors retry

[bors]

⌛ Testing commit 8abf149 with merge 10e1f5d...

[bors]

☀️ Test successful - checks-actions
Approved by: cuviper
Pushing 10e1f5d to master...

[rust-timer]

Finished benchmarking commit (10e1f5d): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.3%	[-0.3%, -0.3%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.3%	[-0.3%, -0.3%]	1

Max RSS (memory usage)

This benchmark run did not return any relevant results for this metric.

Cycles

This benchmark run did not return any relevant results for this metric.

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 693.147s -> 695.587s (0.35%)
Artifact size: 326.88 MiB -> 326.88 MiB (0.00%)