add test which is broken with gevent

pytests/pyproject.toml

@@ -20,6 +20,7 @@ classifiers = [
 
 [project.optional-dependencies]
 dev = [
+    "gevent>=23.9.1",
     "hypothesis>=3.55",
     "pytest-asyncio>=0.21",
     "pytest-benchmark>=3.4",

pytests/src/misc.rs

@@ -1,4 +1,4 @@
-use pyo3::prelude::*;
+use pyo3::{prelude::*, types::PyDict};
 use std::borrow::Cow;
 
 #[pyfunction]
@@ -17,10 +17,24 @@ fn accepts_bool(val: bool) -> bool {
     val
 }
 
+#[pyfunction]
+fn get_item_and_run_callback(dict: Bound<'_, PyDict>, callback: Bound<'_, PyAny>) -> PyResult<()> {
+    // This function gives the opportunity to run a pure-Python callback so that
+    // gevent can instigate a context switch. This had problematic interactions
+    // with PyO3's removed "GIL Pool".
+    // For context, see https://github.com/PyO3/pyo3/issues/3668
+    let item = dict.get_item("key")?.expect("key not found in dict");
+    let string = item.to_string();
+    callback.call0()?;
+    assert_eq!(item.to_string(), string);
+    Ok(())
+}
+
 #[pymodule]
 pub fn misc(_py: Python<'_>, m: &PyModule) -> PyResult<()> {
     m.add_function(wrap_pyfunction!(issue_219, m)?)?;
     m.add_function(wrap_pyfunction!(get_type_full_name, m)?)?;
     m.add_function(wrap_pyfunction!(accepts_bool, m)?)?;
+    m.add_function(wrap_pyfunction!(get_item_and_run_callback, m)?)?;
     Ok(())
 }

pytests/tests/test_misc.py

@@ -2,6 +2,7 @@
 import platform
 import sys
 
+import gevent
 import pyo3_pytests.misc
 import pytest
 
@@ -64,3 +65,39 @@ def test_accepts_numpy_bool():
     assert pyo3_pytests.misc.accepts_bool(False) is False
     assert pyo3_pytests.misc.accepts_bool(numpy.bool_(True)) is True
     assert pyo3_pytests.misc.accepts_bool(numpy.bool_(False)) is False
+
+
+class ArbitraryClass:
+    worker_id: int
+    iteration: int
+
+    def __init__(self, worker_id: int, iteration: int):
+        self.worker_id = worker_id
+        self.iteration = iteration
+
+    def __repr__(self):
+        return f"ArbitraryClass({self.worker_id}, {self.iteration})"
+
+    def __del__(self):
+        print("del", self.worker_id, self.iteration)
+
+
+def test_gevent():
+    def worker(worker_id: int) -> None:
+        for iteration in range(2):
+            d = {"key": ArbitraryClass(worker_id, iteration)}
+
+            def arbitrary_python_code():
+                # remove the dictionary entry so that the class value can be
+                # garbage collected
+                del d["key"]
+                print("gevent sleep", worker_id, iteration)
+                gevent.sleep(0)
+                print("after gevent sleep", worker_id, iteration)
+
+            print("start", worker_id, iteration)
+            pyo3_pytests.misc.get_item_and_run_callback(d, arbitrary_python_code)
+            print("end", worker_id, iteration)
+
+    workers = [gevent.spawn(worker, i) for i in range(2)]
+    gevent.joinall(workers)