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 /*
     pybind11/gil.h: RAII helpers for managing the GIL
 
     Copyright (c) 2016 Wenzel Jakob <wenzel.jakob@epfl.ch>
 
     All rights reserved. Use of this source code is governed by a
     BSD-style license that can be found in the LICENSE file.
 */
 
 #pragma once
 
 #include "detail/common.h"
 
 #include <cassert>
 
 #if !defined(PYBIND11_SIMPLE_GIL_MANAGEMENT)
 #    include "detail/internals.h"
 #endif
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 
 PYBIND11_NAMESPACE_BEGIN(detail)
 
 // forward declarations
 PyThreadState *get_thread_state_unchecked();
 
 PYBIND11_NAMESPACE_END(detail)
 
 #if !defined(PYBIND11_SIMPLE_GIL_MANAGEMENT)
 
 /* The functions below essentially reproduce the PyGILState_* API using a RAII
  * pattern, but there are a few important differences:
  *
  * 1. When acquiring the GIL from an non-main thread during the finalization
  *    phase, the GILState API blindly terminates the calling thread, which
  *    is often not what is wanted. This API does not do this.
  *
  * 2. The gil_scoped_release function can optionally cut the relationship
  *    of a PyThreadState and its associated thread, which allows moving it to
  *    another thread (this is a fairly rare/advanced use case).
  *
  * 3. The reference count of an acquired thread state can be controlled. This
  *    can be handy to prevent cases where callbacks issued from an external
  *    thread would otherwise constantly construct and destroy thread state data
  *    structures.
  *
  * See the Python bindings of NanoGUI (http://github.com/wjakob/nanogui) for an
  * example which uses features 2 and 3 to migrate the Python thread of
  * execution to another thread (to run the event loop on the original thread,
  * in this case).
  */
 
 class gil_scoped_acquire {
 public:
     PYBIND11_NOINLINE gil_scoped_acquire() {
         auto &internals = detail::get_internals();
         tstate = (PyThreadState *) PYBIND11_TLS_GET_VALUE(internals.tstate);
 
         if (!tstate) {
             /* Check if the GIL was acquired using the PyGILState_* API instead (e.g. if
                calling from a Python thread). Since we use a different key, this ensures
                we don't create a new thread state and deadlock in PyEval_AcquireThread
                below. Note we don't save this state with internals.tstate, since we don't
                create it we would fail to clear it (its reference count should be > 0). */
             tstate = PyGILState_GetThisThreadState();
         }
 
         if (!tstate) {
             tstate = PyThreadState_New(internals.istate);
 #    if defined(PYBIND11_DETAILED_ERROR_MESSAGES)
             if (!tstate) {
                 pybind11_fail("scoped_acquire: could not create thread state!");
             }
 #    endif
             tstate->gilstate_counter = 0;
             PYBIND11_TLS_REPLACE_VALUE(internals.tstate, tstate);
         } else {
             release = detail::get_thread_state_unchecked() != tstate;
         }
 
         if (release) {
             PyEval_AcquireThread(tstate);
         }
 
         inc_ref();
     }
 
     gil_scoped_acquire(const gil_scoped_acquire &) = delete;
     gil_scoped_acquire &operator=(const gil_scoped_acquire &) = delete;
 
     void inc_ref() { ++tstate->gilstate_counter; }
 
     PYBIND11_NOINLINE void dec_ref() {
         --tstate->gilstate_counter;
 #    if defined(PYBIND11_DETAILED_ERROR_MESSAGES)
         if (detail::get_thread_state_unchecked() != tstate) {
             pybind11_fail("scoped_acquire::dec_ref(): thread state must be current!");
         }
         if (tstate->gilstate_counter < 0) {
             pybind11_fail("scoped_acquire::dec_ref(): reference count underflow!");
         }
 #    endif
         if (tstate->gilstate_counter == 0) {
 #    if defined(PYBIND11_DETAILED_ERROR_MESSAGES)
             if (!release) {
                 pybind11_fail("scoped_acquire::dec_ref(): internal error!");
             }
 #    endif
             PyThreadState_Clear(tstate);
             if (active) {
                 PyThreadState_DeleteCurrent();
             }
             PYBIND11_TLS_DELETE_VALUE(detail::get_internals().tstate);
             release = false;
         }
     }
 
     /// This method will disable the PyThreadState_DeleteCurrent call and the
     /// GIL won't be acquired. This method should be used if the interpreter
     /// could be shutting down when this is called, as thread deletion is not
     /// allowed during shutdown. Check _Py_IsFinalizing() on Python 3.7+, and
     /// protect subsequent code.
     PYBIND11_NOINLINE void disarm() { active = false; }
 
     PYBIND11_NOINLINE ~gil_scoped_acquire() {
         dec_ref();
         if (release) {
             PyEval_SaveThread();
         }
     }
 
 private:
     PyThreadState *tstate = nullptr;
     bool release = true;
     bool active = true;
 };
 
 class gil_scoped_release {
 public:
     // PRECONDITION: The GIL must be held when this constructor is called.
     explicit gil_scoped_release(bool disassoc = false) : disassoc(disassoc) {
         assert(PyGILState_Check());
         // `get_internals()` must be called here unconditionally in order to initialize
         // `internals.tstate` for subsequent `gil_scoped_acquire` calls. Otherwise, an
         // initialization race could occur as multiple threads try `gil_scoped_acquire`.
         auto &internals = detail::get_internals();
         // NOLINTNEXTLINE(cppcoreguidelines-prefer-member-initializer)
         tstate = PyEval_SaveThread();
         if (disassoc) {
             // Python >= 3.7 can remove this, it's an int before 3.7
             // NOLINTNEXTLINE(readability-qualified-auto)
             auto key = internals.tstate;
             PYBIND11_TLS_DELETE_VALUE(key);
         }
     }
 
     gil_scoped_release(const gil_scoped_release &) = delete;
     gil_scoped_release &operator=(const gil_scoped_release &) = delete;
 
     /// This method will disable the PyThreadState_DeleteCurrent call and the
     /// GIL won't be acquired. This method should be used if the interpreter
     /// could be shutting down when this is called, as thread deletion is not
     /// allowed during shutdown. Check _Py_IsFinalizing() on Python 3.7+, and
     /// protect subsequent code.
     PYBIND11_NOINLINE void disarm() { active = false; }
 
     ~gil_scoped_release() {
         if (!tstate) {
             return;
         }
         // `PyEval_RestoreThread()` should not be called if runtime is finalizing
         if (active) {
             PyEval_RestoreThread(tstate);
         }
         if (disassoc) {
             // Python >= 3.7 can remove this, it's an int before 3.7
             // NOLINTNEXTLINE(readability-qualified-auto)
             auto key = detail::get_internals().tstate;
             PYBIND11_TLS_REPLACE_VALUE(key, tstate);
         }
     }
 
 private:
     PyThreadState *tstate;
     bool disassoc;
     bool active = true;
 };
 
 #else // PYBIND11_SIMPLE_GIL_MANAGEMENT
 
 class gil_scoped_acquire {
     PyGILState_STATE state;
 
 public:
     gil_scoped_acquire() : state{PyGILState_Ensure()} {}
     gil_scoped_acquire(const gil_scoped_acquire &) = delete;
     gil_scoped_acquire &operator=(const gil_scoped_acquire &) = delete;
     ~gil_scoped_acquire() { PyGILState_Release(state); }
     void disarm() {}
 };
 
 class gil_scoped_release {
     PyThreadState *state;
 
 public:
     // PRECONDITION: The GIL must be held when this constructor is called.
     gil_scoped_release() {
         assert(PyGILState_Check());
         state = PyEval_SaveThread();
     }
     gil_scoped_release(const gil_scoped_release &) = delete;
     gil_scoped_release &operator=(const gil_scoped_release &) = delete;
     ~gil_scoped_release() { PyEval_RestoreThread(state); }
     void disarm() {}
 };
 
 #endif // PYBIND11_SIMPLE_GIL_MANAGEMENT
 
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)

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