fix(stdune): preserve Windows flock handles and errors#15528
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Handle_val dereferences an OCaml custom block and must not be evaluated after releasing the runtime. Reacquiring the runtime can also overwrite the thread-local Windows last-error value from LockFileEx or UnlockFileEx. Extract each handle while holding the runtime and save GetLastError immediately after a failed system call. Signed-off-by: Rudi Grinberg <me@rgrinberg.com>
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@nojb could you double check that this makes sense? It looks plausible to me, but I don't have enough winapi experience to make a judgement. |
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Jul 18, 2026
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LGTM, but I don't think it is necessary to preserve GetLastError() (it should already be preserved by caml_acquire_runtime_system(), same as errno.
| ok = LockFileEx(fd, dwFlags, 0, MAXDWORD, MAXDWORD, &overlapped); | ||
| if (!ok) { | ||
| error = GetLastError(); | ||
| } |
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I believe caml_acquire_runtime_system() expressively preserves errno/GetLastError(), so there is no need for this pirouette. See ocaml/ocaml#10220.
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Good to know, thanks. |
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Note that the other change, moving |
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Handle_val dereferences an OCaml custom block and must not be evaluated
after releasing the runtime. Reacquiring the runtime can also overwrite
the thread-local Windows last-error value from LockFileEx or
UnlockFileEx.
Extract each handle while holding the runtime and save GetLastError
immediately after a failed system call.