Add compile option to select GIL implementation (Ref T11804)

See pybind#1276 for the rationale.

Author: fjourdes

CMakeLists.txt

@@ -27,6 +27,7 @@ endif()
 
 option(PYBIND11_INSTALL "Install pybind11 header files?" ${PYBIND11_MASTER_PROJECT})
 option(PYBIND11_TEST    "Build pybind11 test suite?"     ${PYBIND11_MASTER_PROJECT})
+option(PYBIND11_USE_PYGILSTATE_API "Use PyGILState API for gil management?" OFF)
 
 list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_LIST_DIR}/tools")
 
@@ -101,7 +102,9 @@ if(NOT (CMAKE_VERSION VERSION_LESS 3.0))  # CMake >= 3.0
                                                 $<BUILD_INTERFACE:${PYTHON_INCLUDE_DIRS}>
                                                 $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>)
   target_compile_options(pybind11 INTERFACE $<BUILD_INTERFACE:${PYBIND11_CPP_STANDARD}>)
-
+  if( PYBIND11_USE_PYGILSTATE_API )
+    target_compile_definitions(pybind11 INTERFACE PYBIND11_USE_PYGILSTATE_API)
+  endif()
   add_library(module INTERFACE)
   add_library(pybind11::module ALIAS module)
   if(NOT MSVC)

include/pybind11/pybind11.h

@@ -1866,8 +1866,22 @@ void print(Args &&...args) {
     detail::print(c.args(), c.kwargs());
 }
 
-#if defined(WITH_THREAD) && !defined(PYPY_VERSION)
+#if defined(PYPY_VERSION)
+class gil_scoped_acquire {
+    PyGILState_STATE state;
+public:
+    gil_scoped_acquire() { state = PyGILState_Ensure(); }
+    ~gil_scoped_acquire() { PyGILState_Release(state); }
+};
 
+class gil_scoped_release {
+    PyThreadState *state;
+public:
+    gil_scoped_release() { state = PyEval_SaveThread(); }
+    ~gil_scoped_release() { PyEval_RestoreThread(state); }
+};
+#else
+#if defined(WITH_THREAD) && !defined(PYBIND11_USE_PYGILSTATE_API)
 /* The functions below essentially reproduce the PyGILState_* API using a RAII
  * pattern, but there are a few important differences:
  *
@@ -1992,7 +2006,7 @@ class gil_scoped_release {
     PyThreadState *tstate;
     bool disassoc;
 };
-#elif defined(PYPY_VERSION)
+#elif defined(PYBIND11_USE_PYGILSTATE_API)
 class gil_scoped_acquire {
     PyGILState_STATE state;
 public:
@@ -2011,6 +2025,8 @@ class gil_scoped_acquire { };
 class gil_scoped_release { };
 #endif
 
+#endif
+
 error_already_set::~error_already_set() {
     if (m_type) {
         gil_scoped_acquire gil;