CheckedGILRelease: A scope class to release the GIL if the current thread holds it.

Some application may have code being run with or without holding the GIL beyond our control,
so we need a class to release the GIL in case the current thread is holding it.

This is useful in the context of Caribou like applications.

Author: lucienfostier

include/IECorePython/CheckedGILRelease.h

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+//////////////////////////////////////////////////////////////////////////
+//
+//  Copyright (c) 2023, Image Engine Design Inc. All rights reserved.
+//
+//  Redistribution and use in source and binary forms, with or without
+//  modification, are permitted provided that the following conditions are
+//  met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//
+//     * Redistributions in binary form must reproduce the above copyright
+//       notice, this list of conditions and the following disclaimer in the
+//       documentation and/or other materials provided with the distribution.
+//
+//     * Neither the name of Image Engine Design nor the names of any
+//       other contributors to this software may be used to endorse or
+//       promote products derived from this software without specific prior
+//       written permission.
+//
+//  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
+//  IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+//  THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+//  PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+//  CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+//  EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+//  PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+//  PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+//  LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+//  NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+//  SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+//
+//////////////////////////////////////////////////////////////////////////
+
+#ifndef IECOREPYTHON_CHECKEDGILRELEASE_H
+#define IECOREPYTHON_CHECKEDGILRELEASE_H
+
+#include "boost/python.hpp"
+
+#include "IECorePython/Export.h"
+
+namespace IECorePython
+{
+
+/// This class checks if we hold the GIL and if we do releases the GIL upon construction and reacquires it
+/// upon destruction, otherwise it's a no op. It should be used in bindings to C++ functions
+/// which may take a while to return - for instance heavy computations
+/// or IO.
+class IECOREPYTHON_API CheckedGILRelease : boost::noncopyable
+{
+
+	public :
+
+		CheckedGILRelease();
+		~CheckedGILRelease();
+
+	private :
+
+		bool m_gilThreadsInitialised;
+		PyThreadState *m_state;
+
+};
+
+} // namespace IECorePython
+
+#endif // IECOREPYTHON_CHECKEDGILRELEASE_H

src/IECorePython/CheckedGILRelease.cpp

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+//////////////////////////////////////////////////////////////////////////
+//
+//  Copyright (c) 2023, Image Engine Design Inc. All rights reserved.
+//
+//  Redistribution and use in source and binary forms, with or without
+//  modification, are permitted provided that the following conditions are
+//  met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//
+//     * Redistributions in binary form must reproduce the above copyright
+//       notice, this list of conditions and the following disclaimer in the
+//       documentation and/or other materials provided with the distribution.
+//
+//     * Neither the name of Image Engine Design nor the names of any
+//       other contributors to this software may be used to endorse or
+//       promote products derived from this software without specific prior
+//       written permission.
+//
+//  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
+//  IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+//  THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+//  PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+//  CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+//  EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+//  PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+//  PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+//  LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+//  NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+//  SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+//
+//////////////////////////////////////////////////////////////////////////
+
+#include "IECorePython/CheckedGILRelease.h"
+
+using namespace IECorePython;
+
+CheckedGILRelease::CheckedGILRelease()
+#if PY_VERSION_HEX >= 0x03090000
+	:	m_gilThreadsInitialised( Py_IsInitialized() && PyGILState_Check() )
+#else
+	:	m_gilThreadsInitialised( Py_IsInitialized() && PyEval_ThreadsInitialized() && PyGILState_Check() )
+#endif
+{
+	if( m_gilThreadsInitialised )
+	{
+		m_state = PyEval_SaveThread();
+	}
+}
+
+CheckedGILRelease::~CheckedGILRelease()
+{
+	if( m_gilThreadsInitialised )
+	{
+		PyEval_RestoreThread( m_state );
+	}
+}
+