refactor: pull out to file

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

Author: henryiii

CMakeLists.txt

@@ -205,6 +205,7 @@ set(PYBIND11_HEADERS
     include/pybind11/conduit/pybind11_conduit_v1.h
     include/pybind11/conduit/pybind11_platform_abi_id.h
     include/pybind11/conduit/wrap_include_python_h.h
+    include/pybind11/critical_section.h
     include/pybind11/options.h
     include/pybind11/eigen.h
     include/pybind11/eigen/common.h

docs/advanced/misc.rst

@@ -301,7 +301,9 @@ using a Python critical section. This will do nothing if not in free-threaded
 Python. You can have it lock one or two Python objects. You cannot nest it.
 
 .. code-block:: cpp
-    :emphasize-lines: 1,5,10
+    :emphasize-lines: 4,8
+    #include <pybind11/critical_section.h>
+    // ...
 
     PYBIND11_MODULE(example, m, py::multiple_interpreters::per_interpreter_gil(), py::mod_gil_not_used()) {
         m.def("calc_next", []() {

include/pybind11/critical_section.h

@@ -0,0 +1,50 @@
+// Copyright (c) 2016-2025 The Pybind Development Team.
+// 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 "pytypes.h"
+
+PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
+
+/// This does not do anything if there's a GIL. On free-threaded Python,
+/// it locks an object. This uses the CPython API, which has limits
+class scoped_critical_section {
+public:
+#ifdef Py_GIL_DISABLED
+    explicit scoped_critical_section(handle obj) : has2(false) {
+        PyCriticalSection_Begin(&section, obj.ptr());
+    }
+
+    scoped_critical_section(handle obj1, handle obj2) : has2(true) {
+        PyCriticalSection2_Begin(&section2, obj1.ptr(), obj2.ptr());
+    }
+
+    ~scoped_critical_section() {
+        if(has2) {
+            PyCriticalSection2_End(&section2);
+        } else {
+            PyCriticalSection_End(&section);
+        }
+    }
+#else
+    explicit scoped_critical_section(handle _obj) = default;
+    scoped_critical_section(handle _obj1, handle _obj2) = default;
+    ~scoped_critical_section() = default;
+#endif
+
+    scoped_critical_section(const scoped_critical_section &) = delete;
+    scoped_critical_section &operator=(const scoped_critical_section &) = delete;
+
+private:
+#ifdef Py_GIL_DISABLED
+    bool has2;
+    union {
+        PyCriticalSection section;
+        PyCriticalSection2 section2;
+    };
+#endif
+};
+
+PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)

include/pybind11/gil.h

@@ -199,43 +199,3 @@ class gil_scoped_release {
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
 
 #endif // !PYBIND11_SIMPLE_GIL_MANAGEMENT
-
-PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
-
-class scoped_critical_section {
-public:
-    /// This does not do anything if there's a GIL. On free-threaded Python,
-    /// it locks an object. This uses the CPython API, which has limits
-    scoped_critical_section(handle obj) : single(true) {
-#ifdef Py_GIL_DISABLED
-        PyCriticalSection_Begin(&section, obj.ptr());
-#endif
-    }
-
-    scoped_critical_section(handle obj1, handle obj2) : single(true) {
-#ifdef Py_GIL_DISABLED
-        PyCriticalSection2_Begin(&section2, obj1.ptr(), obj2.ptr());
-#endif
-    }
-
-    ~scoped_critical_section() {
-#ifdef Py_GIL_DISABLED
-        if(single) {
-            PyCriticalSection_End(&section);
-        } else {
-            PyCriticalSection2_End(&section2);
-        }
-#endif
-    }
-
-private:
-    bool single;
-#ifdef Py_GIL_DISABLED
-    union {
-        PyCriticalSection section;
-        PyCriticalSection2 section2;
-    };
-#endif
-};
-
-PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)

tests/extra_python_package/test_files.py

@@ -44,6 +44,7 @@
     "include/pybind11/chrono.h",
     "include/pybind11/common.h",
     "include/pybind11/complex.h",
+    "include/pybind11/critical_section.h",
     "include/pybind11/eigen.h",
     "include/pybind11/embed.h",
     "include/pybind11/eval.h",

tests/test_embed/test_interpreter.cpp

@@ -1,4 +1,5 @@
 #include <pybind11/embed.h>
+#include <pybind11/critical_section.h>
 
 // Silence MSVC C++17 deprecation warning from Catch regarding std::uncaught_exceptions (up to
 // catch 2.0.1; this should be fixed in the next catch release after 2.0.1).