On Darwin, lock access to the environ block.
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This PR adds calls to Darwin's internal libc functions `environ_lock_np()` and `environ_unlock_np()` when directly accessing the `environ` block (via the CRT function `_NSGetEnviron()`.) These calls are necessary because direct access to `environ` is not thread-safe by default. The standard library guards accesses to `getenv()` and `setenv()`, but `environ` is a global variable and neither it nor `_NSGetEnviron()` can be made thread-safe internally. This change does not prevent data races when using the result of `getenv()`, but short of a new `copyenv_np()` or `getenv_r()` function, there's not much we can do about it. This change has no effect on Linux since it doesn't have these non-portable functions, but if equivalents are added in the future, we can add support too. Windows' `GetEnvironmentStringsW()` API returns a copy of the environment block, so it doesn't need a lock. Compare Foundation's use [here](https://github.com/apple/swift-foundation/blob/main/Sources/_CShims/platform_shims.c).
grynspan
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bug
grynspan
requested review from
stmontgomery,
dennisweissmann,
briancroom,
SeanROlszewski and
suzannaratcliff
as code owners
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@swift-ci please test |
stmontgomery
approved these changes
May 7, 2024
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@swift-ci please test |
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This PR adds calls to Darwin's internal libc functions
environ_lock_np()andenviron_unlock_np()when directly accessing theenvironblock (via the CRT function_NSGetEnviron().)These calls are necessary because direct access to
environis not thread-safe by default. The standard library guards accesses togetenv()andsetenv(), butenvironis a global variable and neither it nor_NSGetEnviron()can be made thread-safe internally.This change does not prevent data races when using the result of
getenv(), but short of a newcopyenv_np()orgetenv_r()function, there's not much we can do about it. This change has no effect on Linux since it doesn't have these non-portable functions, but if equivalents are added in the future, we can add support too. Windows'GetEnvironmentStringsW()API returns a copy of the environment block, so it doesn't need a lock.Compare Foundation's use here.
Checklist: