PythonObjectInstantiator.h

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// Mantid Repository : https://github.com/mantidproject/mantid
//
// Copyright © 2011 ISIS Rutherford Appleton Laboratory UKRI,
//   NScD Oak Ridge National Laboratory, European Spallation Source,
//   Institut Laue - Langevin & CSNS, Institute of High Energy Physics, CAS
// SPDX - License - Identifier: GPL - 3.0 +
#pragma once
 
//-----------------------------------------------------------------------------
// Includes
//-----------------------------------------------------------------------------
#include "MantidKernel/Instantiator.h"
#include "MantidPythonInterface/core/GlobalInterpreterLock.h"
 
#include <boost/python/extract.hpp>
#include <boost/python/object.hpp>
// older versions of boost::python seem to require this last, after the object
// include
#include <memory>
 
namespace Mantid {
namespace PythonInterface {
struct GILSharedPtrDeleter {
  GILSharedPtrDeleter(const boost::python::converter::shared_ptr_deleter &deleter)
      : m_deleter(boost::python::converter::shared_ptr_deleter(deleter.owner)) {}
  void operator()(void const *data) {
    GlobalInterpreterLock gil;
    m_deleter(data);
  }
  boost::python::converter::shared_ptr_deleter m_deleter;
};
 
template <typename Base> class PythonObjectInstantiator : public Kernel::AbstractInstantiator<Base> {
public:
  PythonObjectInstantiator(const boost::python::object &classObject) : m_classObject(classObject) {}
 
  std::shared_ptr<Base> createInstance() const override;
 
  Base *createUnwrappedInstance() const override;
 
private:
  boost::python::object m_classObject;
};
 
template <typename Base> std::shared_ptr<Base> PythonObjectInstantiator<Base>::createInstance() const {
  using namespace boost::python;
  GlobalInterpreterLock gil;
 
  object instance = m_classObject();
  // The instantiator assumes that the exported type uses a
  // HeldType=std::shared_ptr<Adapter>,
  // where Adapter inherits from Base,
  // see
  // http://www.boost.org/doc/libs/1_42_0/libs/python/doc/v2/class.html#class_-spec.
  // The advantage is that the memory management is very simple as it is all
  // handled within the
  // boost layer.
 
  // Swap the deleter for one that acquires the GIL before actually deallocating
  // the
  // Python object or we get a segfault when deleting the objects on later
  // versions of Python 2.7
  auto instancePtr = extract<std::shared_ptr<Base>>(instance)();
  auto *deleter = std::get_deleter<converter::shared_ptr_deleter, Base>(instancePtr);
  instancePtr.reset(instancePtr.get(), GILSharedPtrDeleter(*deleter));
  return instancePtr;
}
 
template <typename Base> Base *PythonObjectInstantiator<Base>::createUnwrappedInstance() const {
  throw std::runtime_error("Unable to create unwrapped instance of Python object");
}
} // namespace PythonInterface
} // namespace Mantid