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Save errno inside allow_threads in semaphore acquire by youknowone · Pull Request #7391 · RustPython/RustPython · GitHub

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Save errno inside allow_threads in semaphore acquire #7391

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Merged
youknowone merged 1 commit into from
Mar 10, 2026
Conversation 3 Commits 1 Checks 12 Files changed
Merged

Save errno inside allow_threads in semaphore acquire #7391

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83 changes: 65 additions & 18 deletions crates/stdlib/src/multiprocessing.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -706,41 +706,69 @@ mod _multiprocessing {

// if (res < 0 && errno == EAGAIN && blocking)
if res < 0 && Errno::last() == Errno::EAGAIN && blocking {
// Couldn't acquire immediately, need to block
// Couldn't acquire immediately, need to block.
//
// Save errno inside the allow_threads closure, before
// attach_thread() runs — matches CPython which saves
// `err = errno` before Py_END_ALLOW_THREADS.

#[cfg(not(target_vendor = "apple"))]
{
let mut saved_errno;
loop {
let sem_ptr = self.handle.as_ptr();
// Py_BEGIN_ALLOW_THREADS / Py_END_ALLOW_THREADS
res = if let Some(ref dl) = deadline {
vm.allow_threads(|| unsafe { libc::sem_timedwait(sem_ptr, dl) })
let (r, e) = if let Some(ref dl) = deadline {
vm.allow_threads(|| {
let r = unsafe { libc::sem_timedwait(sem_ptr, dl) };
(
r,
if r < 0 {
Errno::last()
} else {
Errno::from_raw(0)
},
)
})
} else {
vm.allow_threads(|| unsafe { libc::sem_wait(sem_ptr) })
vm.allow_threads(|| {
let r = unsafe { libc::sem_wait(sem_ptr) };
(
r,
if r < 0 {
Errno::last()
} else {
Errno::from_raw(0)
},
)
})
};
res = r;
saved_errno = e;

if res >= 0 {
break;
}
let err = Errno::last();
if err == Errno::EINTR {
if saved_errno == Errno::EINTR {
vm.check_signals()?;
continue;
}
break;
}
if res < 0 {
return handle_wait_error(vm, saved_errno);
}
}
#[cfg(target_vendor = "apple")]
{
// macOS: use polled fallback since sem_timedwait is not available
if let Some(ref dl) = deadline {
match sem_timedwait_polled(self.handle.as_ptr(), dl, vm) {
Ok(()) => res = 0,
Ok(()) => {}
Err(SemWaitError::Timeout) => {
// Timeout occurred - return false directly
return Ok(false);
}
Err(SemWaitError::SignalException(exc)) => {
// Propagate the original exception (e.g., KeyboardInterrupt)
return Err(exc);
}
Err(SemWaitError::OsError(e)) => {
Expand All @@ -749,31 +777,42 @@ mod _multiprocessing {
}
} else {
// No timeout: use sem_wait (available on macOS)
let mut saved_errno;
loop {
let sem_ptr = self.handle.as_ptr();
res = vm.allow_threads(|| unsafe { libc::sem_wait(sem_ptr) });
let (r, e) = vm.allow_threads(|| {
let r = unsafe { libc::sem_wait(sem_ptr) };
(
r,
if r < 0 {
Errno::last()
} else {
Errno::from_raw(0)
},
)
});
res = r;
saved_errno = e;
if res >= 0 {
break;
}
let err = Errno::last();
if err == Errno::EINTR {
if saved_errno == Errno::EINTR {
vm.check_signals()?;
continue;
}
break;
}
if res < 0 {
return handle_wait_error(vm, saved_errno);
}
}
}
}

// result handling:
if res < 0 {
} else if res < 0 {
// Non-blocking path failed, or blocking=false
let err = Errno::last();
match err {
Errno::EAGAIN | Errno::ETIMEDOUT => return Ok(false),
Errno::EINTR => {
// EINTR should be handled by the check_signals() loop above
// If we reach here, check signals again and propagate any exception
return vm.check_signals().map(|_| false);
}
_ => return Err(os_error(vm, err)),
Expand Down Expand Up @@ -1081,6 +1120,14 @@ mod _multiprocessing {
CString::new(full).map_err(|_| vm.new_value_error("embedded null character"))
}

fn handle_wait_error(vm: &VirtualMachine, saved_errno: Errno) -> PyResult<bool> {
match saved_errno {
Errno::EAGAIN | Errno::ETIMEDOUT => Ok(false),
Errno::EINTR => vm.check_signals().map(|_| false),
_ => Err(os_error(vm, saved_errno)),
}
}

fn os_error(vm: &VirtualMachine, err: Errno) -> PyBaseExceptionRef {
// _PyMp_SetError maps to PyErr_SetFromErrno
let exc_type = match err {
Expand Down
4 changes: 3 additions & 1 deletion crates/vm/src/builtins/tuple.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -108,7 +108,9 @@ impl PyPayload for PyTuple {

#[inline]
unsafe fn freelist_push(obj: *mut PyObject) -> bool {
let len = unsafe { &*(obj as *const crate::Py<PyTuple>) }.elements.len();
let len = unsafe { &*(obj as *const crate::Py<PyTuple>) }
.elements
.len();
if len == 0 || len > TupleFreeList::MAX_SAVE_SIZE {
return false;
}
Expand Down
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