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Fix deadlock in c-api when a thread enters a stop_the_world #8355

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Merged
youknowone merged 2 commits into from
Jul 23, 2026
+21 −9
Merged

Fix deadlock in c-api when a thread enters a stop_the_world #8355

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2e71298
Fix deadlock in c-api when a thread enters a stop_the_world
bschoenmaeckers Jul 23, 2026
5fafa89
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bschoenmaeckers Jul 23, 2026
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7 changes: 6 additions & 1 deletion crates/capi/src/lib.rs
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Original file line number Diff line number Diff line change
@@ -1,7 +1,8 @@
#![allow(clippy::missing_safety_doc)]

use crate::pyerrors::init_exception_statics;
use crate::pylifecycle::MAIN_INTERP;
use crate::pylifecycle::{MAIN_INTERP, MAIN_INTERP_PTR};
use core::sync::atomic::Ordering;
pub use rustpython_vm::PyObject;
use rustpython_vm::{Context, Interpreter};
use std::sync::MutexGuard;
Expand Down Expand Up @@ -61,4 +62,8 @@ pub fn init_main_interpreter(interpreter: Interpreter) {
// Safety: Interpreter was not initialized before, so we can safely assume the statics are not used
unsafe { init_exception_statics(&Context::genesis().exceptions) };
*interp = Some(interpreter);
MAIN_INTERP_PTR.store(
interp.as_ref().unwrap() as *const _ as *mut _,
Ordering::Release,
);
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}
8 changes: 7 additions & 1 deletion crates/capi/src/pylifecycle.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@ use crate::pyerrors::init_exception_statics;
use crate::pystate::ensure_thread_has_vm_attached;
use alloc::ffi::CString;
use core::ffi::{c_char, c_int, c_ulong};
use core::sync::atomic::{AtomicPtr, Ordering};
use rustpython_vm::common::rc::PyRc;
use rustpython_vm::stdlib::sys;
use rustpython_vm::version::{MAJOR, MICRO, MINOR, RUSTPYTHON_BUILD_INFO, VERSION_HEX};
Expand All @@ -11,6 +12,7 @@ use rustpython_vm::{Context, Interpreter};
use std::sync::{LazyLock, Mutex};

pub(crate) static MAIN_INTERP: Mutex<Option<Interpreter>> = Mutex::new(None);
pub(crate) static MAIN_INTERP_PTR: AtomicPtr<Interpreter> = AtomicPtr::new(core::ptr::null_mut());

/// Request a thread local vm from the main interpreter
pub(crate) fn request_vm_from_interpreter() -> ThreadedVirtualMachine {
Expand All @@ -25,7 +27,7 @@ pub static Py_Version: c_ulong = VERSION_HEX as c_ulong;

#[unsafe(no_mangle)]
pub extern "C" fn Py_IsInitialized() -> c_int {
get_main_interpreter().is_some() as c_int
!MAIN_INTERP_PTR.load(Ordering::Acquire).is_null() as c_int
}

#[unsafe(no_mangle)]
Expand All @@ -52,6 +54,10 @@ pub extern "C" fn Py_InitializeEx(_initsigs: c_int) {
})
.build()
.into();
MAIN_INTERP_PTR.store(
interp.as_ref().unwrap() as *const _ as *mut _,
Ordering::Release,
);
drop(interp);
ensure_thread_has_vm_attached();
}
Expand Down
15 changes: 8 additions & 7 deletions crates/capi/src/pystate.rs
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Original file line number Diff line number Diff line change
@@ -1,7 +1,7 @@
use crate::get_main_interpreter;
use crate::pylifecycle::request_vm_from_interpreter;
use crate::pylifecycle::{MAIN_INTERP_PTR, request_vm_from_interpreter};
use crate::util::FfiResult;
use core::ffi::c_int;
use core::sync::atomic::Ordering;
use rustpython_vm::vm::thread::{
CurrentVmAttachState, SavedThreadState, attach_current_thread, release_current_thread,
restore_current_thread, save_current_thread, with_current_vm,
Expand Down Expand Up @@ -67,11 +67,12 @@ pub unsafe extern "C" fn PyEval_RestoreThread(state: *mut PyThreadState) {

#[unsafe(no_mangle)]
pub extern "C" fn PyInterpreterState_Get() -> *mut PyInterpreterState {
get_main_interpreter()
.as_ref()
.map(|interp| interp as *const PyInterpreterState)
.expect("PyInterpreterState_Get called but no main interpreter was found")
.cast_mut()
let ptr = MAIN_INTERP_PTR.load(Ordering::Acquire);
assert!(
!ptr.is_null(),
"PyInterpreterState_Get() called but the interpreter is not initialized"
);
ptr
}

#[unsafe(no_mangle)]
Expand Down
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