Add option to force the use of the PYPY GIL scoped acquire/release lo…

…gic to support nested gil access, see pybind#1276 and pytorch/pytorch#83101

CMakeLists.txt

@@ -91,10 +91,15 @@ endif()
 option(PYBIND11_INSTALL "Install pybind11 header files?" ${PYBIND11_MASTER_PROJECT})
 option(PYBIND11_TEST "Build pybind11 test suite?" ${PYBIND11_MASTER_PROJECT})
 option(PYBIND11_NOPYTHON "Disable search for Python" OFF)
+option(PYBIND11_USE_PYPY_GIL "Force use of PYPY GIL acquire/release logic in gil.h" OFF)
 set(PYBIND11_INTERNALS_VERSION
     ""
     CACHE STRING "Override the ABI version, may be used to enable the unstable ABI.")
 
+if(PYBIND11_USE_PYPY_GIL)
+  add_compile_definitions(USE_PYPY_GIL)
+endif()
+
 cmake_dependent_option(
   USE_PYTHON_INCLUDE_DIR
   "Install pybind11 headers in Python include directory instead of default installation prefix"

include/pybind11/gil.h

@@ -21,7 +21,7 @@ PyThreadState *get_thread_state_unchecked();
 
 PYBIND11_NAMESPACE_END(detail)
 
-#if defined(WITH_THREAD) && !defined(PYPY_VERSION)
+#if defined(WITH_THREAD) && !defined(PYPY_VERSION) && !defined(USE_PYPY_GIL)
 
 /* The functions below essentially reproduce the PyGILState_* API using a RAII
  * pattern, but there are a few important differences:
@@ -178,7 +178,7 @@ class gil_scoped_release {
     bool disassoc;
     bool active = true;
 };
-#elif defined(PYPY_VERSION)
+#elif defined(PYPY_VERSION) || defined(USE_PYPY_GIL)
 class gil_scoped_acquire {
     PyGILState_STATE state;