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Track deque mutations and release removed items outside locks #8847

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Merged
youknowone merged 1 commit into from
Sep 27, 2026
Merged

Track deque mutations and release removed items outside locks #8847

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145 changes: 99 additions & 46 deletions crates/vm/src/stdlib/_collections.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -183,21 +183,27 @@ mod _collections {
let max_len = self.maxlen;
let mut elements: Vec<PyObjectRef> = iterable.try_to_value(vm)?;
elements.reverse();

if let Some(max_len) = max_len {
if max_len > elements.len() {
let mut deque = self.borrow_deque_mut();
let truncate_until = max_len - elements.len();
deque.truncate(truncate_until);
} else {
self.borrow_deque_mut().clear();
elements.truncate(max_len);
}
elements.truncate(max_len);
}
if elements.is_empty() {
return Ok(());
}
let mut created = VecDeque::from(elements);
let mut borrowed = self.borrow_deque_mut();
created.append(&mut borrowed);
core::mem::swap(&mut created, &mut borrowed);
let discarded = {
let mut deque = self.borrow_deque_mut();
let discarded = if let Some(max_len) = max_len {
let retained = (max_len - created.len()).min(deque.len());
deque.split_off(retained)
} else {
VecDeque::new()
};
created.append(&mut deque);
core::mem::swap(&mut created, &mut deque);
self.state.fetch_add(1);
discarded
};
drop(discarded);
Ok(())
}

Expand Down Expand Up @@ -268,19 +274,37 @@ mod _collections {
}

#[pymethod]
fn remove(&self, value: PyObjectRef, vm: &VirtualMachine) -> PyResult {
fn remove(&self, value: PyObjectRef, vm: &VirtualMachine) -> PyResult<()> {
let start_state = self.state.load();
let index = self.mut_index(vm, &value)?;

if start_state != self.state.load() {
Err(vm.new_index_error("deque mutated during remove()."))
} else if let Some(index) = index.into() {
let mut deque = self.borrow_deque_mut();
self.state.fetch_add(1);
Ok(deque.remove(index).unwrap())
} else {
Err(vm.new_value_error("deque.remove(x): x not in deque"))
let len = self.borrow_deque().len();
let mutated = || vm.new_index_error("deque mutated during iteration");
for index in 0..len {
let item = self
.borrow_deque()
.get(index)
.cloned()
.ok_or_else(mutated)?;
let equal = item.rich_compare_bool(&value, PyComparisonOp::Eq, vm)?;
// Releasing the comparison reference can also run a finalizer.
drop(item);
if start_state != self.state.load() {
return Err(mutated());
}
if equal {
let removed = {
let mut deque = self.borrow_deque_mut();
if start_state != self.state.load() {
return Err(mutated());
}
let removed = deque.remove(index).ok_or_else(mutated)?;
self.state.fetch_add(1);
removed
};
drop(removed);
return Ok(());
}
}
Err(vm.new_value_error("deque.remove(x): x not in deque"))
}

#[pymethod]
Expand Down Expand Up @@ -333,10 +357,18 @@ mod _collections {
}

fn __delitem__(&self, idx: isize, vm: &VirtualMachine) -> PyResult<()> {
let mut deque = self.borrow_deque_mut();
idx.wrapped_at(deque.len())
.and_then(|i| deque.remove(i).map(drop))
.ok_or_else(|| vm.new_index_error("deque index out of range"))
let removed = {
let mut deque = self.borrow_deque_mut();
let removed = idx
.wrapped_at(deque.len())
.and_then(|i| deque.remove(i))
.ok_or_else(|| vm.new_index_error("deque index out of range"))?;
self.state.fetch_add(1);
removed
};
// Finalizers can mutate the deque, so release the lock first.
drop(removed);
Ok(())
}

fn __contains__(&self, needle: &PyObject, vm: &VirtualMachine) -> PyResult<bool> {
Expand Down Expand Up @@ -381,8 +413,16 @@ mod _collections {
}

fn __imul__(zelf: PyRef<Self>, n: isize, vm: &VirtualMachine) -> PyResult<PyRef<Self>> {
let mul_deque = zelf._mul(n, vm)?;
*zelf.borrow_deque_mut() = mul_deque;
if n == 1 || zelf.borrow_deque().is_empty() {
return Ok(zelf);
}
let mut mul_deque = zelf._mul(n, vm)?;
{
let mut deque = zelf.borrow_deque_mut();
core::mem::swap(&mut *deque, &mut mul_deque);
zelf.state.fetch_add(1);
}
drop(mul_deque);
Ok(zelf)
}

Expand Down Expand Up @@ -490,36 +530,49 @@ mod _collections {
None
};

// retrieve elements first to not to make too huge lock
let elements = iterable
.into_option()
.map(|iter| {
let mut elements: Vec<PyObjectRef> = iter.try_to_value(vm)?;
if let Some(maxlen) = maxlen {
elements.drain(..elements.len().saturating_sub(maxlen));
}
Ok(elements)
})
.transpose()?;

// SAFETY: This is hacky part for read-only field
// Because `maxlen` is only mutated from __init__. We can abuse the lock of deque to ensure this is locked enough.
// If we make a single lock of deque not only for extend but also for setting maxlen, it will be safe.
{
let removed = {
let mut deque = zelf.borrow_deque_mut();
// Clear any previous data present.
deque.clear();
unsafe {
// `maxlen` is better to be defined as UnsafeCell in common practice,
// but then more type works without any safety benefits
let unsafe_maxlen =
&zelf.maxlen as *const _ as *const core::cell::UnsafeCell<Option<usize>>;
*(*unsafe_maxlen).get() = maxlen;
}
if let Some(elements) = elements {
deque.extend(elements);
let removed = core::mem::take(&mut *deque);
if !removed.is_empty() {
zelf.state.fetch_add(1);
}
removed
};
// Release old elements before iterating; their finalizers can add new ones.
drop(removed);

let Some(iterable) = iterable.into_option() else {
return Ok(());
};
let maxlen = zelf.maxlen;
let mut elements: Vec<PyObjectRef> = iterable.try_to_value(vm)?;
if let Some(maxlen) = maxlen {
elements.drain(..elements.len().saturating_sub(maxlen));
}
if elements.is_empty() {
return Ok(());
}
let discarded = {
let mut deque = zelf.borrow_deque_mut();
let discard_until = maxlen.map_or(0, |maxlen| {
deque.len().saturating_sub(maxlen - elements.len())
});
let discarded: Vec<_> = deque.drain(..discard_until).collect();
deque.extend(elements);
zelf.state.fetch_add(1);
discarded
};
drop(discarded);

Ok(())
}
Expand Down
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