# gil.rs - source
Source of the Rust file `/home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/pyo3-0.13.2/src/gil.rs`.
Keywords: rust, rustlang, rust-lang

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    // Copyright (c) 2017-present PyO3 Project and Contributors

    //! Interaction with python's global interpreter lock

    use crate::{ffi, internal_tricks::Unsendable, Python};
    use parking_lot::{const_mutex, Mutex, Once};
    use std::cell::{Cell, RefCell};
    use std::{mem::ManuallyDrop, ptr::NonNull};

    static START: Once = Once::new();

    thread_local! {
        /// This is a internal counter in pyo3 monitoring whether this thread has the GIL.
        ///
        /// It will be incremented whenever a GILGuard or GILPool is created, and decremented whenever
        /// they are dropped.
        ///
        /// As a result, if this thread has the GIL, GIL_COUNT is greater than zero.
        ///
        /// pub(crate) because it is manipulated temporarily by Python::allow_threads
        pub(crate) static GIL_COUNT: Cell<usize> = Cell::new(0);

        /// Temporally hold objects that will be released when the GILPool drops.
        static OWNED_OBJECTS: RefCell<Vec<NonNull<ffi::PyObject>>> = RefCell::new(Vec::with_capacity(256));
    }

    /// Check whether the GIL is acquired.
    ///
    /// Note: This uses pyo3's internal count rather than PyGILState_Check for two reasons:
    ///  1) for performance
    ///  2) PyGILState_Check always returns 1 if the sub-interpreter APIs have ever been called,
    ///     which could lead to incorrect conclusions that the GIL is held.
    pub(crate) fn gil_is_acquired() -> bool {
        GIL_COUNT.try_with(|c| c.get() > 0).unwrap_or(false)
    }

    /// Prepares the use of Python in a free-threaded context.
    ///
    /// If the Python interpreter is not already initialized, this function
    /// will initialize it with disabled signal handling
    /// (Python will not raise the `KeyboardInterrupt` exception).
    /// Python signal handling depends on the notion of a 'main thread', which must be
    /// the thread that initializes the Python interpreter.
    ///
    /// If both the Python interpreter and Python threading are already initialized,
    /// this function has no effect.
    ///
    /// # Availability
    /// This function is only available when linking against Python distributions that contain a
    /// shared library.
    ///
    /// This function is not available on PyPy.
    ///
    /// # Panics
    /// - If the Python interpreter is initialized but Python threading is not,
    ///   a panic occurs.
    ///   It is not possible to safely access the Python runtime unless the main
    ///   thread (the thread which originally initialized Python) also initializes
    ///   threading.
    ///
    /// # Example
    /// ```rust
    /// use pyo3::prelude::*;
    ///
    /// # #[allow(clippy::needless_doctest_main)]
    /// fn main() {
    ///     pyo3::prepare_freethreaded_python();
    ///     Python::with_gil(|py| {
    ///         py.run("print('Hello World')", None, None)
    ///     });
    /// }
    /// ```
    #[cfg(all(Py_SHARED, not(PyPy)))]
    #[allow(clippy::clippy::collapsible_if)] // for if cfg!
    pub fn prepare_freethreaded_python() {
        // Protect against race conditions when Python is not yet initialized and multiple threads
        // concurrently call 'prepare_freethreaded_python()'. Note that we do not protect against
        // concurrent initialization of the Python runtime by other users of the Python C API.
        START.call_once_force(|_| unsafe {
            // Use call_once_force because if initialization panics, it's okay to try again.
            if ffi::Py_IsInitialized() != 0 {
                // If Python is already initialized, we expect Python threading to also be initialized,
                // as we can't make the existing Python main thread acquire the GIL.
                assert_ne!(ffi::PyEval_ThreadsInitialized(), 0);
            } else {
                ffi::Py_InitializeEx(0);

                // Changed in version 3.7: This function is now called by Py_Initialize(), so you don’t
                // have to call it yourself anymore.
                if cfg!(not(Py_3_7)) {
                    if ffi::PyEval_ThreadsInitialized() == 0 {
                        ffi::PyEval_InitThreads();
                    }
                }

                // Release the GIL.
                ffi::PyEval_SaveThread();
            }
        });
    }

    /// Executes the provided closure with an embedded Python interpreter.
    ///
    /// This function intializes the Python interpreter, executes the provided closure, and then
    /// finalizes the Python interpreter.
    ///
    /// After execution all Python resources are cleaned up, and no further Python APIs can be called.
    /// Because many Python modules implemented in C do not support multiple Python interpreters in a
    /// single process, it is not safe to call this function more than once. (Many such modules will not
    /// initialize correctly on the second run.)
    ///
    /// # Availability
    /// This function is only available when linking against Python distributions that contain a shared
    /// library.
    ///
    /// This function is not available on PyPy.
    ///
    /// # Panics
    /// - If the Python interpreter is already initalized before calling this function.
    ///
    /// # Safety
    /// - This function should only ever be called once per process (usually as part of the `main`
    ///   function). It is also not thread-safe.
    /// - No Python APIs can be used after this function has finished executing.
    /// - The return value of the closure must not contain any Python value, _including_ `PyResult`.
    ///
    /// # Example
    /// ```rust
    /// use pyo3::prelude::*;
    ///
    /// # #[allow(clippy::needless_doctest_main)]
    /// fn main() {
    ///     unsafe {
    ///         pyo3::with_embedded_python_interpreter(|py| {
    ///             py.run("print('Hello World')", None, None)
    ///         });
    ///     }
    /// }
    /// ```
    #[cfg(all(Py_SHARED, not(PyPy)))]
    #[allow(clippy::clippy::collapsible_if)] // for if cfg!
    pub unsafe fn with_embedded_python_interpreter<F, R>(f: F) -> R
    where
        F: for<'p> FnOnce(Python<'p>) -> R,
    {
        assert_eq!(
            ffi::Py_IsInitialized(),
            0,
            "called `with_embedded_python_interpreter` but a Python interpreter is already running."
        );

        ffi::Py_InitializeEx(0);

        // Changed in version 3.7: This function is now called by Py_Initialize(), so you don’t have to
        // call it yourself anymore.
        if cfg!(not(Py_3_7)) {
            if ffi::PyEval_ThreadsInitialized() == 0 {
                ffi::PyEval_InitThreads();
            }
        }

        // Safe: the GIL is already held because of the Py_IntializeEx call.
        let pool = GILPool::new();

        // Import the threading module - this ensures that it will associate this thread as the "main"
        // thread, which is important to avoid an `AssertionError` at finalization.
        pool.python().import("threading").unwrap();

        // Execute the closure.
        let result = f(pool.python());

        // Drop the pool before finalizing.
        drop(pool);

        // Finalize the Python interpreter.
        ffi::Py_Finalize();

        result
    }

    /// RAII type that represents the Global Interpreter Lock acquisition. To get hold of a value of
    /// this type, see [`Python::acquire_gil`](struct.Python.html#method.acquire_gil).
    ///
    /// # Example
    /// ```
    /// use pyo3::Python;
    ///
    /// {
    ///     let gil_guard = Python::acquire_gil();
    ///     let py = gil_guard.python();
    /// } // GIL is released when gil_guard is dropped
    /// ```
    #[must_use]
    pub struct GILGuard {
        gstate: ffi::PyGILState_STATE,
        pool: ManuallyDrop<Option<GILPool>>,
    }

    impl GILGuard {
        /// Retrieves the marker type that proves that the GIL was acquired.
        #[inline]
        pub fn python(&self) -> Python {
            unsafe { Python::assume_gil_acquired() }
        }

        /// PyO3 internal API for acquiring the GIL. The public API is Python::acquire_gil.
        ///
        /// If PyO3 does not yet have a `GILPool` for tracking owned PyObject references, then this new
        /// `GILGuard` will also contain a `GILPool`.
        pub(crate) fn acquire() -> GILGuard {
            // Maybe auto-initialize the GIL:
            //  - If auto-initialize feature set and supported, try to initalize the interpreter.
            //  - If the auto-initialize feature is set but unsupported, emit hard errors only when the
            //    extension-module feature is not activated - extension modules don't care about
            //    auto-initialize so this avoids breaking existing builds.
            //  - Otherwise, just check the GIL is initialized.
            cfg_if::cfg_if! {
                if #[cfg(all(feature = "auto-initialize", Py_SHARED, not(PyPy)))] {
                    prepare_freethreaded_python();
                } else if #[cfg(all(feature = "auto-initialize", not(feature = "extension-module"), not(Py_SHARED), not(__pyo3_ci)))] {
                    compile_error!(concat!(
                        "The `auto-initialize` feature is not supported when linking Python ",
                        "statically instead of with a shared library.\n\n",
                        "Please disable the `auto-initialize` feature, for example by entering the following ",
                        "in your cargo.toml:\n\n",
                        "    pyo3 = { version = \"",
                        env!("CARGO_PKG_VERSION"),
                        "\", default-features = false }\n\n",
                        "Alternatively, compile PyO3 using a Python distribution which contains a shared ",
                        "libary."
                    ));
                } else if #[cfg(all(feature = "auto-initialize", not(feature = "extension-module"), PyPy, not(__pyo3_ci)))] {
                    compile_error!(concat!(
                        "The `auto-initialize` feature is not supported by PyPy.\n\n",
                        "Please disable the `auto-initialize` feature, for example by entering the following ",
                        "in your cargo.toml:\n\n",
                        "    pyo3 = { version = \"",
                        env!("CARGO_PKG_VERSION"),
                        "\", default-features = false }\n\n",
                    ));
                } else {
                    // extension module feature enabled and PyPy or static linking
                    // OR auto-initialize feature not enabled
                    START.call_once_force(|_| unsafe {
                        // Use call_once_force because if there is a panic because the interpreter is
                        // not initialized, it's fine for the user to initialize the interpreter and
                        // retry.
                        assert_ne!(
                            ffi::Py_IsInitialized(),
                            0,
                            "The Python interpreter is not initalized and the `auto-initialize` feature is not enabled."
                        );
                        assert_ne!(
                            ffi::PyEval_ThreadsInitialized(),
                            0,
                            "Python threading is not initalized and the `auto-initialize` feature is not enabled."
                        );
                    });
                }
            }

            let gstate = unsafe { ffi::PyGILState_Ensure() }; // acquire GIL

            // If there's already a GILPool, we should not create another or this could lead to
            // incorrect dangling references in safe code (see #864).
            let pool = if !gil_is_acquired() {
                Some(unsafe { GILPool::new() })
            } else {
                // As no GILPool was created, need to update the gil count manually.
                increment_gil_count();
                None
            };

            GILGuard {
                gstate,
                pool: ManuallyDrop::new(pool),
            }
        }
    }

    /// The Drop implementation for `GILGuard` will release the GIL.
    impl Drop for GILGuard {
        fn drop(&mut self) {
            // First up, try to detect if the order of destruction is correct.
            let _ = GIL_COUNT.try_with(|c| {
                if self.gstate == ffi::PyGILState_STATE::PyGILState_UNLOCKED && c.get() != 1 {
                    // XXX: this panic commits to leaking all objects in the pool as well as
                    // potentially meaning the GIL never releases. Perhaps should be an abort?
                    // Unfortunately abort UX is much worse than panic.
                    panic!("The first GILGuard acquired must be the last one dropped.");
                }
            });

            // If this GILGuard doesn't own a pool, then need to decrease the count after dropping
            // all objects from the pool.
            let should_decrement = self.pool.is_none();

            // Drop the objects in the pool before attempting to release the thread state
            unsafe {
                ManuallyDrop::drop(&mut self.pool);
            }

            if should_decrement {
                decrement_gil_count();
            }

            unsafe {
                ffi::PyGILState_Release(self.gstate);
            }
        }
    }

    /// Thread-safe storage for objects which were inc_ref / dec_ref while the GIL was not held.
    struct ReferencePool {
        pointers_to_incref: Mutex<Vec<NonNull<ffi::PyObject>>>,
        pointers_to_decref: Mutex<Vec<NonNull<ffi::PyObject>>>,
    }

    impl ReferencePool {
        const fn new() -> Self {
            Self {
                pointers_to_incref: const_mutex(Vec::new()),
                pointers_to_decref: const_mutex(Vec::new()),
            }
        }

        fn register_incref(&self, obj: NonNull<ffi::PyObject>) {
            self.pointers_to_incref.lock().push(obj)
        }

        fn register_decref(&self, obj: NonNull<ffi::PyObject>) {
            self.pointers_to_decref.lock().push(obj)
        }

        fn update_counts(&self, _py: Python) {
            macro_rules! swap_vec_with_lock {
                // Get vec from one of ReferencePool's mutexes via lock, swap vec if needed, unlock.
                ($cell:expr) => {{
                    let mut locked = $cell.lock();
                    let mut out = Vec::new();
                    if !locked.is_empty() {
                        std::mem::swap(&mut out, &mut *locked);
                    }
                    drop(locked);
                    out
                }};
            }

            // Always increase reference counts first - as otherwise objects which have a
            // nonzero total reference count might be incorrectly dropped by Python during
            // this update.
            for ptr in swap_vec_with_lock!(self.pointers_to_incref) {
                unsafe { ffi::Py_INCREF(ptr.as_ptr()) };
            }

            for ptr in swap_vec_with_lock!(self.pointers_to_decref) {
                unsafe { ffi::Py_DECREF(ptr.as_ptr()) };
            }
        }
    }

    unsafe impl Sync for ReferencePool {}

    static POOL: ReferencePool = ReferencePool::new();

    /// A RAII pool which PyO3 uses to store owned Python references.
    pub struct GILPool {
        /// Initial length of owned objects and anys.
        /// `Option` is used since TSL can be broken when `new` is called from `atexit`.
        start: Option<usize>,
        no_send: Unsendable,
    }

    impl GILPool {
        /// Create a new `GILPool`. This function should only ever be called with the GIL.
        ///
        /// It is recommended not to use this API directly, but instead to use `Python::new_pool`, as
        /// that guarantees the GIL is held.
        ///
        /// # Safety
        /// As well as requiring the GIL, see the notes on `Python::new_pool`.
        #[inline]
        pub unsafe fn new() -> GILPool {
            increment_gil_count();
            // Update counts of PyObjects / Py that have been cloned or dropped since last acquisition
            POOL.update_counts(Python::assume_gil_acquired());
            GILPool {
                start: OWNED_OBJECTS.try_with(|o| o.borrow().len()).ok(),
                no_send: Unsendable::default(),
            }
        }

        /// Get the Python token associated with this `GILPool`.
        pub fn python(&self) -> Python {
            unsafe { Python::assume_gil_acquired() }
        }
    }

    impl Drop for GILPool {
        fn drop(&mut self) {
            if let Some(obj_len_start) = self.start {
                let dropping_obj = OWNED_OBJECTS.with(|holder| {
                    // `holder` must be dropped before calling Py_DECREF, or Py_DECREF may call
                    // `GILPool::drop` recursively, resulting in invalid borrowing.
                    let mut holder = holder.borrow_mut();
                    if obj_len_start < holder.len() {
                        holder.split_off(obj_len_start)
                    } else {
                        Vec::new()
                    }
                });
                for obj in dropping_obj {
                    unsafe {
                        ffi::Py_DECREF(obj.as_ptr());
                    }
                }
            }
            decrement_gil_count();
        }
    }

    /// Register a Python object pointer inside the release pool, to have reference count increased
    /// next time the GIL is acquired in pyo3.
    ///
    /// If the GIL is held, the reference count will be increased immediately instead of being queued
    /// for later.
    ///
    /// # Safety
    /// The object must be an owned Python reference.
    pub unsafe fn register_incref(obj: NonNull<ffi::PyObject>) {
        if gil_is_acquired() {
            ffi::Py_INCREF(obj.as_ptr())
        } else {
            POOL.register_incref(obj);
        }
    }

    /// Register a Python object pointer inside the release pool, to have reference count decreased
    /// next time the GIL is acquired in pyo3.
    ///
    /// If the GIL is held, the reference count will be decreased immediately instead of being queued
    /// for later.
    ///
    /// # Safety
    /// The object must be an owned Python reference.
    pub unsafe fn register_decref(obj: NonNull<ffi::PyObject>) {
        if gil_is_acquired() {
            ffi::Py_DECREF(obj.as_ptr())
        } else {
            POOL.register_decref(obj);
        }
    }

    /// Register an owned object inside the GILPool.
    ///
    /// # Safety
    /// The object must be an owned Python reference.
    pub unsafe fn register_owned(_py: Python, obj: NonNull<ffi::PyObject>) {
        debug_assert!(gil_is_acquired());
        // Ignores the error in case this function called from `atexit`.
        let _ = OWNED_OBJECTS.try_with(|holder| holder.borrow_mut().push(obj));
    }

    /// Increment pyo3's internal GIL count - to be called whenever GILPool or GILGuard is created.
    #[inline(always)]
    fn increment_gil_count() {
        // Ignores the error in case this function called from `atexit`.
        let _ = GIL_COUNT.try_with(|c| c.set(c.get() + 1));
    }

    /// Decrement pyo3's internal GIL count - to be called whenever GILPool or GILGuard is dropped.
    #[inline(always)]
    fn decrement_gil_count() {
        // Ignores the error in case this function called from `atexit`.
        let _ = GIL_COUNT.try_with(|c| {
            let current = c.get();
            debug_assert!(
                current > 0,
                "Negative GIL count detected. Please report this error to the PyO3 repo as a bug."
            );
            c.set(current - 1);
        });
    }

    /// Ensure the GIL is held, used in the implementation of Python::with_gil
    pub(crate) fn ensure_gil() -> EnsureGIL {
        if gil_is_acquired() {
            EnsureGIL(None)
        } else {
            EnsureGIL(Some(GILGuard::acquire()))
        }
    }

    /// Struct used internally which avoids acquiring the GIL where it's not necessary.
    pub(crate) struct EnsureGIL(Option<GILGuard>);

    impl EnsureGIL {
        /// Get the GIL token.
        ///
        /// # Safety
        /// If `self.0` is `None`, then this calls [Python::assume_gil_acquired].
        /// Thus this method could be used to get access to a GIL token while the GIL is not held.
        /// Care should be taken to only use the returned Python in contexts where it is certain the
        /// GIL continues to be held.
        pub unsafe fn python(&self) -> Python {
            match &self.0 {
                Some(gil) => gil.python(),
                None => Python::assume_gil_acquired(),
            }
        }
    }

    #[cfg(test)]
    mod test {
        use super::{gil_is_acquired, GILPool, GIL_COUNT, OWNED_OBJECTS, POOL};
        use crate::{ffi, gil, AsPyPointer, IntoPyPointer, PyObject, Python, ToPyObject};
        use std::ptr::NonNull;

        fn get_object(py: Python) -> PyObject {
            // Convenience function for getting a single unique object, using `new_pool` so as to leave
            // the original pool state unchanged.
            let pool = unsafe { py.new_pool() };
            let py = pool.python();

            let obj = py.eval("object()", None, None).unwrap();
            obj.to_object(py)
        }

        fn owned_object_count() -> usize {
            OWNED_OBJECTS.with(|holder| holder.borrow().len())
        }

        #[test]
        fn test_owned() {
            let gil = Python::acquire_gil();
            let py = gil.python();
            let obj = get_object(py);
            let obj_ptr = obj.as_ptr();
            // Ensure that obj does not get freed
            let _ref = obj.clone_ref(py);

            unsafe {
                {
                    let pool = py.new_pool();
                    gil::register_owned(pool.python(), NonNull::new_unchecked(obj.into_ptr()));

                    assert_eq!(owned_object_count(), 1);
                    assert_eq!(ffi::Py_REFCNT(obj_ptr), 2);
                }
                {
                    let _pool = py.new_pool();
                    assert_eq!(owned_object_count(), 0);
                    assert_eq!(ffi::Py_REFCNT(obj_ptr), 1);
                }
            }
        }

        #[test]
        fn test_owned_nested() {
            let gil = Python::acquire_gil();
            let py = gil.python();
            let obj = get_object(py);
            // Ensure that obj does not get freed
            let _ref = obj.clone_ref(py);
            let obj_ptr = obj.as_ptr();

            unsafe {
                {
                    let _pool = py.new_pool();
                    assert_eq!(owned_object_count(), 0);

                    gil::register_owned(py, NonNull::new_unchecked(obj.into_ptr()));

                    assert_eq!(owned_object_count(), 1);
                    assert_eq!(ffi::Py_REFCNT(obj_ptr), 2);
                    {
                        let _pool = py.new_pool();
                        let obj = get_object(py);
                        gil::register_owned(py, NonNull::new_unchecked(obj.into_ptr()));
                        assert_eq!(owned_object_count(), 2);
                    }
                    assert_eq!(owned_object_count(), 1);
                }
                {
                    assert_eq!(owned_object_count(), 0);
                    assert_eq!(ffi::Py_REFCNT(obj_ptr), 1);
                }
            }
        }

        #[test]
        fn test_pyobject_drop_with_gil_decreases_refcnt() {
            let gil = Python::acquire_gil();
            let py = gil.python();
            let obj = get_object(py);
            // Ensure that obj does not get freed
            let _ref = obj.clone_ref(py);
            let obj_ptr = obj.as_ptr();

            unsafe {
                {
                    assert_eq!(owned_object_count(), 0);
                    assert_eq!(ffi::Py_REFCNT(obj_ptr), 2);
                }

                // With the GIL held, obj can be dropped immediately
                drop(obj);
                assert_eq!(ffi::Py_REFCNT(obj_ptr), 1);
            }
        }

        #[test]
        fn test_pyobject_drop_without_gil_doesnt_decrease_refcnt() {
            let gil = Python::acquire_gil();
            let py = gil.python();
            let obj = get_object(py);
            // Ensure that obj does not get freed
            let _ref = obj.clone_ref(py);
            let obj_ptr = obj.as_ptr();

            unsafe {
                {
                    assert_eq!(owned_object_count(), 0);
                    assert_eq!(ffi::Py_REFCNT(obj_ptr), 2);
                }

                // Without the GIL held, obj cannot be dropped until the next GIL acquire
                drop(gil);
                drop(obj);
                assert_eq!(ffi::Py_REFCNT(obj_ptr), 2);

                {
                    // Next time the GIL is acquired, the object is released
                    let _gil = Python::acquire_gil();
                    assert_eq!(ffi::Py_REFCNT(obj_ptr), 1);
                }
            }
        }

        #[test]
        fn test_gil_counts() {
            // Check GILGuard and GILPool both increase counts correctly
            let get_gil_count = || GIL_COUNT.with(|c| c.get());

            assert_eq!(get_gil_count(), 0);
            let gil = Python::acquire_gil();
            assert_eq!(get_gil_count(), 1);

            assert_eq!(get_gil_count(), 1);
            let pool = unsafe { GILPool::new() };
            assert_eq!(get_gil_count(), 2);

            let pool2 = unsafe { GILPool::new() };
            assert_eq!(get_gil_count(), 3);

            drop(pool);
            assert_eq!(get_gil_count(), 2);

            let gil2 = Python::acquire_gil();
            assert_eq!(get_gil_count(), 3);

            drop(gil2);
            assert_eq!(get_gil_count(), 2);

            drop(pool2);
            assert_eq!(get_gil_count(), 1);

            drop(gil);
            assert_eq!(get_gil_count(), 0);
        }

        #[test]
        fn test_allow_threads() {
            // allow_threads should temporarily release GIL in PyO3's internal tracking too.
            let gil = Python::acquire_gil();
            let py = gil.python();

            assert!(gil_is_acquired());

            py.allow_threads(move || {
                assert!(!gil_is_acquired());

                let gil = Python::acquire_gil();
                assert!(gil_is_acquired());

                drop(gil);
                assert!(!gil_is_acquired());
            });

            assert!(gil_is_acquired());
        }

        #[test]
        fn dropping_gil_does_not_invalidate_references() {
            // Acquiring GIL for the second time should be safe - see #864
            let gil = Python::acquire_gil();
            let py = gil.python();
            let obj;

            let gil2 = Python::acquire_gil();
            obj = py.eval("object()", None, None).unwrap();
            drop(gil2);

            // After gil2 drops, obj should still have a reference count of one
            assert_eq!(obj.get_refcnt(), 1);
        }

        #[test]
        fn test_clone_with_gil() {
            let gil = Python::acquire_gil();
            let py = gil.python();

            let obj = get_object(py);
            let count = obj.get_refcnt(py);

            // Cloning with the GIL should increase reference count immediately
            #[allow(clippy::redundant_clone)]
            let c = obj.clone();
            assert_eq!(count + 1, c.get_refcnt(py));
        }

        #[test]
        fn test_clone_without_gil() {
            let gil = Python::acquire_gil();
            let py = gil.python();
            let obj = get_object(py);
            let count = obj.get_refcnt(py);

            // Cloning without GIL should not update reference count
            drop(gil);
            let c = obj.clone();
            assert_eq!(
                count,
                obj.get_refcnt(unsafe { Python::assume_gil_acquired() })
            );

            // Acquring GIL will clear this pending change
            let gil = Python::acquire_gil();
            let py = gil.python();

            // Total reference count should be one higher
            assert_eq!(count + 1, obj.get_refcnt(py));

            // Clone dropped
            drop(c);

            // Overall count is now back to the original, and should be no pending change
            assert_eq!(count, obj.get_refcnt(py));
        }

        #[test]
        fn test_clone_in_other_thread() {
            let gil = Python::acquire_gil();
            let py = gil.python();
            let obj = get_object(py);
            let count = obj.get_refcnt(py);

            // Move obj to a thread which does not have the GIL, and clone it
            let t = std::thread::spawn(move || {
                // Cloning without GIL should not update reference count
                #[allow(clippy::redundant_clone)]
                let _ = obj.clone();
                assert_eq!(
                    count,
                    obj.get_refcnt(unsafe { Python::assume_gil_acquired() })
                );

                // Return obj so original thread can continue to use
                obj
            });

            let obj = t.join().unwrap();
            let ptr = NonNull::new(obj.as_ptr()).unwrap();

            // The pointer should appear once in the incref pool, and once in the
            // decref pool (for the clone being created and also dropped)
            assert_eq!(&*POOL.pointers_to_incref.lock(), &vec![ptr]);
            assert_eq!(&*POOL.pointers_to_decref.lock(), &vec![ptr]);

            // Re-acquring GIL will clear these pending changes
            drop(gil);
            let gil = Python::acquire_gil();

            assert!(POOL.pointers_to_incref.lock().is_empty());
            assert!(POOL.pointers_to_decref.lock().is_empty());

            // Overall count is still unchanged
            assert_eq!(count, obj.get_refcnt(gil.python()));
        }

        #[test]
        fn test_update_counts_does_not_deadlock() {
            // update_counts can run arbitrary Python code during Py_DECREF.
            // if the locking is implemented incorrectly, it will deadlock.

            let gil = Python::acquire_gil();
            let obj = get_object(gil.python());

            unsafe {
                unsafe extern "C" fn capsule_drop(capsule: *mut ffi::PyObject) {
                    // This line will implicitly call update_counts
                    // -> and so cause deadlock if update_counts is not handling recursion correctly.
                    let pool = GILPool::new();

                    // Rebuild obj so that it can be dropped
                    PyObject::from_owned_ptr(
                        pool.python(),
                        ffi::PyCapsule_GetPointer(capsule, std::ptr::null()) as _,
                    );
                }

                let ptr = obj.into_ptr();
                let capsule = ffi::PyCapsule_New(ptr as _, std::ptr::null(), Some(capsule_drop));

                POOL.register_decref(NonNull::new(capsule).unwrap());

                // Updating the counts will call decref on the capsule, which calls capsule_drop
                POOL.update_counts(gil.python())
            }
        }
    }