add tests

pyo3-ffi/src/acquire_gil.c

@@ -1,6 +1,4 @@
 #if defined(_WIN32)
-#include <windows.h>
-#include <synchapi.h>
 #else
 #include <pthread.h>
 #include <unistd.h>
@@ -19,18 +17,9 @@ int gil_func_name(void);
 
 #if defined(_WIN32)
 int wrapped_func_name(void) {
-    // Do the equivalent of https://github.com/python/cpython/issues/87135 (included
-    // in Python 3.14) to avoid pthread_exit unwinding the current thread, which tends
-    // to cause undefined behavior in Rust.
-    //
-    // Unfortunately, I don't know of a way to do a catch(...) from Rust.
-    __try {
-        return gil_func_name();
-    } __catch(void) {
-        while(1) {
-            SleepEx(INFINITE, TRUE);
-        }
-    }
+    // In MSVC, PyThread_exit_thread calls _endthreadex(0), which does not use SEH. This can
+    // cause Rust-level UB if there is pinned memory, but AFAICT there's not much we can do about it.
+    return gil_func_name();
 }
 #else
 static void hang_thread(void *ignore) {

pytests/src/misc.rs

@@ -9,6 +9,25 @@ fn issue_219() {
     Python::with_gil(|_| {});
 }
 
+#[pyclass]
+struct LockHolder {
+    #[allow(unused)]
+    sender: std::sync::mpsc::Sender<()>,
+}
+
+// This will hammer the GIL once the retyrbed LockHolder is dropped.
+#[pyfunction]
+fn hammer_gil_in_thread() -> PyResult<LockHolder> {
+    let (sender, receiver) = std::sync::mpsc::channel();
+    std::thread::spawn(move || {
+        receiver.recv().ok();
+        loop {
+            Python::with_gil(|_py| ());
+        }
+    });
+    Ok(LockHolder { sender })
+}
+
 #[pyfunction]
 fn get_type_fully_qualified_name<'py>(obj: &Bound<'py, PyAny>) -> PyResult<Bound<'py, PyString>> {
     obj.get_type().fully_qualified_name()
@@ -35,6 +54,7 @@ fn get_item_and_run_callback(dict: Bound<'_, PyDict>, callback: Bound<'_, PyAny>
 #[pymodule(gil_used = false)]
 pub fn misc(m: &Bound<'_, PyModule>) -> PyResult<()> {
     m.add_function(wrap_pyfunction!(issue_219, m)?)?;
+    m.add_function(wrap_pyfunction!(hammer_gil_in_thread, m)?)?;
     m.add_function(wrap_pyfunction!(get_type_fully_qualified_name, m)?)?;
     m.add_function(wrap_pyfunction!(accepts_bool, m)?)?;
     m.add_function(wrap_pyfunction!(get_item_and_run_callback, m)?)?;

pytests/tests/test_hammer_gil_in_thread.py

@@ -0,0 +1,20 @@
+from pyo3_pytests import misc
+
+
+def make_loop():
+    # create a reference loop that will only be destroyed when the GC is called at the end
+    # of execution
+    start = []
+    cur = [start]
+    for _ in range(1000 * 1000 * 10):
+        cur = [cur]
+    start.append(cur)
+    return start
+
+
+# set a bomb that will explode when modules are cleaned up
+loopy = [make_loop()]
+
+
+def test_hammer_gil():
+    loopy.append(misc.hammer_gil_in_thread())