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Split InterpreterFrame hot/cold fields into FrameColdData #8433

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Split InterpreterFrame hot/cold fields into FrameColdData #8433

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69b0c12
Factor with_iframe into enter_iframe/exit_iframe helpers
youknowone Aug 1, 2026
f5c5a9e
Allocate InterpreterFrame and LocalsPlus together on the datastack
youknowone Aug 1, 2026
be300a8
Implement trampoline loop for Python-to-Python calls
youknowone Aug 1, 2026
0e666bb
Optimize trampoline: skip recursion check, avoid temporary_refs mutex…
youknowone Aug 1, 2026
895a53a
Use UnsafeCell for pending_tailcall_refs
youknowone Aug 1, 2026
1bea35f
Remove .claude/settings.json from tracking
youknowone Aug 1, 2026
b874b75
Replace SendPtr with Option<SendNonNull> for type-safe pending tailcall
youknowone Aug 2, 2026
fcc9e6f
Restrict PendingFrame to private, expose only set/take methods
youknowone Aug 2, 2026
b84cbfd
Restore C-stack overflow check in trampoline enter_iframe_unchecked
youknowone Aug 2, 2026
df72972
Address code review: entry frame double-free, panic safety, cleanup
youknowone Aug 2, 2026
212d9c1
Split InterpreterFrame hot/cold fields into FrameColdData
youknowone Aug 2, 2026
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Use UnsafeCell for pending_tailcall_refs 
The VM is per-thread so RefCell's runtime borrow checking is
unnecessary overhead. Replace with UnsafeCell for direct access.

Assisted-by: Claude
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@youknowone
youknowone committed Aug 2, 2026
commit 895a53a15eafb7c74d25575673b28d44097cfee9
4 changes: 2 additions & 2 deletions crates/vm/src/frame.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -10665,7 +10665,7 @@ impl ExecutingFrame<'_> {
// the VM side channel, avoiding a per-frame mutex lock on
// temporary_refs.
let callable = self.pop_value();
vm.pending_tailcall_refs.borrow_mut().push(callable);
unsafe { &mut *vm.pending_tailcall_refs.get() }.push(callable);

vm.pending_tailcall_frame
.set(crate::vm::SendPtr(callee_iframe as *mut InterpreterFrame));
Expand Down Expand Up @@ -10720,7 +10720,7 @@ impl ExecutingFrame<'_> {
fastlocals[0] = Some(bound_self);

// Transfer ownership to the trampoline via the VM side channel.
let mut refs = vm.pending_tailcall_refs.borrow_mut();
let refs = unsafe { &mut *vm.pending_tailcall_refs.get() };
refs.push(bound_function);
refs.push(callable);

Expand Down
25 changes: 16 additions & 9 deletions crates/vm/src/vm/mod.rs
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Expand Up @@ -113,9 +113,9 @@ pub struct VirtualMachine {
pub(crate) pending_tailcall_frame: Cell<SendPtr<crate::frame::InterpreterFrame>>,
/// Owned references that keep callee raw pointers valid during TailCall.
/// Set by `tailcall_prepare_frame`, drained by the trampoline into
/// its local `owned_refs` Vec. This avoids per-frame mutex lock on
/// `temporary_refs`.
pub(crate) pending_tailcall_refs: RefCell<Vec<PyObjectRef>>,
/// its local `owned_refs` Vec. Uses UnsafeCell because the VM is
/// per-thread and this field is only accessed on the owning thread.
pub(crate) pending_tailcall_refs: core::cell::UnsafeCell<Vec<PyObjectRef>>,
}

/// Non-owning frame pointer for the non-unix threading frames stack.
Expand Down Expand Up @@ -949,7 +949,7 @@ impl VirtualMachine {
callable_cache: CallableCache::default(),
audit_hooks: RefCell::new(vec![]),
pending_tailcall_frame: Cell::new(SendPtr::null()),
pending_tailcall_refs: RefCell::new(Vec::with_capacity(2)),
pending_tailcall_refs: core::cell::UnsafeCell::new(Vec::with_capacity(2)),
};

if vm.state.hash_secret.hash_str("")
Expand Down Expand Up @@ -1443,7 +1443,9 @@ impl VirtualMachine {
debug_assert!(!initial_ptr.is_null());
self.pending_tailcall_frame.set(SendPtr::null());
// Drain the refs that keep the initial callee's raw pointers alive.
let initial_refs = self.pending_tailcall_refs.borrow_mut().drain(..).collect();
let initial_refs = unsafe { &mut *self.pending_tailcall_refs.get() }
.drain(..)
.collect();
frame_stack.push(SuspendedFrame {
iframe: iframe as *mut crate::frame::InterpreterFrame,
entry_state,
Expand All @@ -1460,7 +1462,9 @@ impl VirtualMachine {
let result = crate::frame::run_iframe(callee, self);
match result {
Ok(ExecutionResult::TailCall) => {
let refs = self.pending_tailcall_refs.borrow_mut().drain(..).collect();
let refs = unsafe { &mut *self.pending_tailcall_refs.get() }
.drain(..)
.collect();
frame_stack.push(SuspendedFrame {
iframe: callee_ptr,
entry_state: callee_entry,
Expand Down Expand Up @@ -1509,7 +1513,9 @@ impl VirtualMachine {
let result = crate::frame::run_iframe(caller_iframe, self);
match result {
Ok(ExecutionResult::TailCall) => {
let refs = self.pending_tailcall_refs.borrow_mut().drain(..).collect();
let refs = unsafe { &mut *self.pending_tailcall_refs.get() }
.drain(..)
.collect();
drop(_caller_refs);
frame_stack.push(SuspendedFrame {
iframe: caller_iframe_ptr,
Expand Down Expand Up @@ -1565,8 +1571,9 @@ impl VirtualMachine {
let result = crate::frame::run_iframe(caller_iframe, self);
match result {
Ok(ExecutionResult::TailCall) => {
let refs =
self.pending_tailcall_refs.borrow_mut().drain(..).collect();
let refs = unsafe { &mut *self.pending_tailcall_refs.get() }
.drain(..)
.collect();
drop(_caller_refs);
frame_stack.push(SuspendedFrame {
iframe: caller_iframe_ptr,
Expand Down
2 changes: 1 addition & 1 deletion crates/vm/src/vm/thread.rs
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Expand Up @@ -1023,7 +1023,7 @@ impl VirtualMachine {
callable_cache: self.callable_cache.clone(),
audit_hooks: RefCell::new(vec![]),
pending_tailcall_frame: Cell::new(super::SendPtr::null()),
pending_tailcall_refs: RefCell::new(Vec::with_capacity(2)),
pending_tailcall_refs: core::cell::UnsafeCell::new(Vec::with_capacity(2)),
};
ThreadedVirtualMachine { vm }
}
Expand Down