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test_env_get_set_multithreaded fails with Miri on Windows #124411

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rust-lang/miri
#3517
@RalfJung

Description

@RalfJung
  0.117855   error: Undefined Behavior: Data race detected between (1) non-atomic write on thread `unnamed-4` and (2) non-atomic read on thread `unnamed-3` at alloc158665+0x8. (2) just happened here
  0.000062      --> /home/runner/work/miri-test-libstd/miri-test-libstd/rust-src-patched/library/std/src/sys/pal/windows/os.rs:299:28
  0.000011       |
  0.000008   299 |         |buf, sz| unsafe { c::GetEnvironmentVariableW(k.as_ptr(), buf, sz) },
  0.000006       |                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Data race detected between (1) non-atomic write on thread `unnamed-4` and (2) non-atomic read on thread `unnamed-3` at alloc158665+0x8. (2) just happened here
  0.000008       |
  0.000006   help: and (1) occurred earlier here
  0.000007      --> library/std/tests/env.rs:156:13
  0.000007       |
  0.000006   156 |             set_var("foo", "bar");
  0.000007       |             ^^^^^^^^^^^^^^^^^^^^^
  0.000009       = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
  0.000008       = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
  0.000006       = note: BACKTRACE (of the first span) on thread `unnamed-3`:
  0.000007       = note: inside closure at /home/runner/work/miri-test-libstd/miri-test-libstd/rust-src-patched/library/std/src/sys/pal/windows/os.rs:299:28: 299:75
  0.000007       = note: inside `std::sys::pal::windows::fill_utf16_buf::<{closure@std::sys::pal::windows::os::getenv::{closure#0}}, for<'a> fn(&'a [u16]) -> std::ffi::OsString {<std::ffi::OsString as std::os::windows::ffi::OsStringExt>::from_wide}, std::ffi::OsString>` at /home/runner/work/miri-test-libstd/miri-test-libstd/rust-src-patched/library/std/src/sys/pal/windows/mod.rs:260:27: 260:76
  0.000007       = note: inside `std::sys::pal::windows::os::getenv` at /home/runner/work/miri-test-libstd/miri-test-libstd/rust-src-patched/library/std/src/sys/pal/windows/os.rs:298:5: 301:6
  0.000006       = note: inside `std::env::_var_os` at /home/runner/work/miri-test-libstd/miri-test-libstd/rust-src-patched/library/std/src/env.rs:271:5: 271:24
  0.000007       = note: inside `std::env::var_os::<&str>` at /home/runner/work/miri-test-libstd/miri-test-libstd/rust-src-patched/library/std/src/env.rs:267:5: 267:26
  0.000007   note: inside closure
  0.000007      --> library/std/tests/env.rs:150:21
  0.000007       |
  0.000006   150 |             let _ = var_os("foo");
  0.000007       |                     ^^^^^^^^^^^^^
  0.000007   
  0.000007   note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
  0.000006   
  0.006593   error: aborting due to 1 previous error
  0.000035   
  0.005739   test test_env_get_set_multithreaded ... error: test failed, to rerun pass `--test env`

Now... I seem to remember something about the Windows API actually being thread-safe? So this is probably a bug in Miri, which not report data races from concurrent environment accesses on Windows? @ChrisDenton is that right?

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