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Merged
youknowone merged 2 commits into from
Jul 10, 2025
Merged

fix(itertools): add re-entrancy guard to tee object #5931

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aaf1805
fix(itertools): add re-entrancy guard to tee object
ever0de Jul 10, 2025
17011c4
apply feedback PyRwLock -> PyMutex & remove AtomicCell<bool> lock field
ever0de Jul 10, 2025
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fix(itertools): add re-entrancy guard to tee object
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@ever0de
ever0de committed Jul 10, 2025
commit aaf18058f825c6a9328b9d62f2eb70b0674d2285
2 changes: 0 additions & 2 deletions Lib/test/test_itertools.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1761,8 +1761,6 @@ def test_tee_del_backward(self):
del forward, backward
raise

# TODO: RUSTPYTHON
@unittest.expectedFailure
def test_tee_reenter(self):
class I:
first = True
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14 changes: 12 additions & 2 deletions vm/src/stdlib/itertools.rs
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Expand Up @@ -1185,21 +1185,31 @@ mod decl {
struct PyItertoolsTeeData {
iterable: PyIter,
values: PyRwLock<Vec<PyObjectRef>>,
locked: AtomicCell<bool>,
}

impl PyItertoolsTeeData {
fn new(iterable: PyIter, _vm: &VirtualMachine) -> PyResult<PyRc<Self>> {
Ok(PyRc::new(Self {
iterable,
values: PyRwLock::new(vec![]),
locked: AtomicCell::new(false),
}))
}

fn get_item(&self, vm: &VirtualMachine, index: usize) -> PyResult<PyIterReturn> {
if self.values.read().len() == index {
let result = raise_if_stop!(self.iterable.next(vm)?);
self.values.write().push(result);
if self.locked.swap(true) {
return Err(vm.new_runtime_error("cannot re-enter the tee iterator"));
}

let result = self.iterable.next(vm);
self.locked.store(false);

let obj = raise_if_stop!(result?);
self.values.write().push(obj);
}

Comment on lines 1199 to +1207
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@youknowone youknowone Jul 10, 2025

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While traditional locks prefer to lock the code, Rust locks prefer to lock the data.
After changing PyRwLock to PyMutex, this approach will work

Suggested change
if self.values.read().len() == index {
let result = raise_if_stop!(self.iterable.next(vm)?);
self.values.write().push(result);
if self.locked.swap(true) {
return Err(vm.new_runtime_error("cannot re-enter the tee iterator"));
}
let result = self.iterable.next(vm);
self.locked.store(false);
let obj = raise_if_stop!(result?);
self.values.write().push(obj);
}
let Some(values) = self.values.try_lock() else {
return Err(vm.new_runtime_error("cannot re-enter the tee iterator"));
};
if values.len() == index {
let obj = raise_if_stop!(self.iterable.next(vm)?);
values.push(obj);
}
Ok(PyIterReturn::Return(values[index].clone()))

Ok(PyIterReturn::Return(self.values.read()[index].clone()))
}
}
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