Disable inheritance of file descriptors created by Swift Testing by default. #1145
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…efault. This PR makes file descriptors created by Swift Testing `FD_CLOEXEC` by default (on Windows, `~HANDLE_FLAG_INHERIT`.) We then clear `FD_CLOEXEC` for specific file descriptors that should be inherited. On Darwin, this is effectively ignored because we use `POSIX_SPAWN_CLOEXEC_DEFAULT`, and on Windows we use `PROC_THREAD_ATTRIBUTE_HANDLE_LIST` which has much the same effect. (On non-Darwin POSIX platforms, there's no reliable way to ensure only one child process inherits a particular file descriptor.) This change is speculative. Resolves #1140.
grynspan
added
bug
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@swift-ci test |
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@swift-ci test |
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@swift-ci test |
grynspan
requested review from
stmontgomery,
briancroom and
suzannaratcliff
as code owners
stmontgomery
reviewed
Jun 9, 2025
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Confirmed that a swift-foundation branch with exit tests enabled successfully ran those exit tests with this swift-testing version on Ubuntu 20.04 (but failed previously) |
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@swift-ci test |
stmontgomery
approved these changes
Jun 9, 2025
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@swift-ci Please test |
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Relevant glibc change (non-portable and only on relatively recent glibc versions though.) https://sourceware.org/bugzilla/show_bug.cgi?id=23640 |
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FreeBSD also clears |
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Jun 10, 2025
On [FreeBSD](https://man.freebsd.org/cgi/man.cgi?query=posix_spawn_file_actions_adddup2), [OpenBSD](https://github.com/openbsd/src/blob/master/lib/libc/gen/posix_spawn.c#L155), [Android](https://android.googlesource.com/platform/bionic/+/master/libc/bionic/spawn.cpp#103), and [Glibc ≥ 2.29](https://sourceware.org/bugzilla/show_bug.cgi?id=23640), `posix_spawn_file_actions_adddup2()` automatically clears `FD_CLOEXEC` if the file descriptors passed to it are equal. Relying on this behaviour eliminates a race condition when spawning child processes. This functionality is standardized in [POSIX.1-2024](https://pubs.opengroup.org/onlinepubs/9799919799/) thanks to [Austin Group Defect #411](https://www.austingroupbugs.net/view.php?id=411). Some older Linuxes (Amazon Linux 2 in particular) don't have this functionality, so we do a runtime check of the Glibc version. This PR is a follow-up to #1145. Resolves #1140. ### Checklist: - [x] Code and documentation should follow the style of the [Style Guide](https://github.com/apple/swift-testing/blob/main/Documentation/StyleGuide.md). - [x] If public symbols are renamed or modified, DocC references should be updated.
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This PR makes file descriptors created by Swift Testing
FD_CLOEXECby default (on Windows,~HANDLE_FLAG_INHERIT.) We then clearFD_CLOEXECfor specific file descriptors that should be inherited. On Darwin, this is effectively ignored because we usePOSIX_SPAWN_CLOEXEC_DEFAULT, and on Windows we usePROC_THREAD_ATTRIBUTE_HANDLE_LISTwhich has much the same effect. (On non-Darwin POSIX platforms, there's no reliable way to ensure only one child process inherits a particular file descriptor.)This change is speculative. No additional unit tests are added because existing test coverage should be sufficient; the reported issue is on a platform (Ubuntu 20.04) where we don't have any CI jobs.
Resolves #1140.
Checklist: