PythonModuleManager.cc

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// SPDX-FileCopyrightText: Deutsches Elektronen-Synchrotron DESY, MSK, ChimeraTK Project <chimeratk-support@desy.de>
// SPDX-License-Identifier: LGPL-3.0-or-later
 
#include <pybind11/embed.h>
// pybind11.h must be included first
 
#include "Application.h"
#include "ConfigReader.h"
#include "PyModuleGroup.h"
#include "PythonModuleManager.h"
#include "VersionInfo.h"
 
namespace py = pybind11;
using namespace py::literals;
 
namespace ChimeraTK {
 
  /********************************************************************************************************************/
 
  namespace detail {
    struct __attribute__((visibility("hidden"))) PythonModuleManagerStatics {
      py::scoped_interpreter pyint{false}; // "false" = do not register signal handlers
      py::exception<boost::thread_interrupted> exceptionObject;
      std::function<void(const std::unique_ptr<PyModuleGroup>&)> onMainGroupChangeCallback;
      PythonModuleManagerStatics();
    };
 
    /******************************************************************************************************************/
 
    struct __attribute__((visibility("hidden"))) PythonModuleManagerImpl {
      static std::unique_ptr<PythonModuleManagerStatics> statics;
      std::unique_ptr<PyModuleGroup> mainGroup; // this ModuleGroup is presented to Python as "app"
      std::list<py::object> modules; // Python modules loaded (the language construct, *not* ChimeraTK::Module)
      std::unique_ptr<py::gil_scoped_release> release;
    };
 
    std::unique_ptr<detail::PythonModuleManagerStatics> PythonModuleManagerImpl::statics;
 
    /******************************************************************************************************************/
 
    __attribute__((visibility("hidden"))) PythonModuleManagerStatics::PythonModuleManagerStatics() {
      py::gil_scoped_acquire gil;
 
      auto locals = py::dict("so_version"_a = ChimeraTK::VersionInfo::soVersion);
      py::exec(R"(
        import sys
        import os
 
        new_paths = []
        for p in sys.path:
          new_paths.append(os.path.join(p, 'ChimeraTK', 'ApplicationCore'+so_version))
 
        sys.path = new_paths + sys.path # prepend so old system libraries are not found first
      )",
          py::globals(), locals);
    }
  } // namespace detail
 
  /********************************************************************************************************************/
 
  void PythonModuleManager::init() {
    if(_impl) {
      return;
    }
 
    _impl = std::make_unique<detail::PythonModuleManagerImpl>();
    if(!_impl->statics) {
      // Create impl, with scoped_interpreter etc.
 
      // The impl object outlives the PythonModuleManager, since we need to keep the interpreter instance alive until
      // the end of the process, even across multiple Application instances (e.g. in tests). Otherwise certain Python
      // modules like numpy and datetime lead to crashes when loaded multiple times.
      _impl->statics = std::make_unique<detail::PythonModuleManagerStatics>();
 
      // boost::thread_interrupted does not have a what() function, so we cannot use py::register_exception() directly
      // on it. Also py::set_error() seems to be unavailable for our version of pybind11, also there is this bug:
      // https://github.com/pybind/pybind11/issues/4967
      // As a work around, we roughly replicated what register_exception_impl() is doing in pybind11 2.11
 
      // Create the exception object and store it in a static py::object, so the (state-less) lambda passed to
      // register_exception_translator() below can access it. As long as there is only one PythonModuleManager at a time
      // this is perfectly fine.
      _impl->statics->exceptionObject = {py::module::import("__main__"), "ThreadInterrupted"};
 
      py::register_exception_translator([](std::exception_ptr p) {
        try {
          if(p) std::rethrow_exception(p);
        }
        catch(const boost::thread_interrupted& e) {
          detail::PythonModuleManagerImpl::statics->exceptionObject("Thread Interrupted");
        }
      });
 
      // Make sure all Python modules are imported that we need
      py::exec("import threading, traceback, sys, gc");
    }
 
    // create main group object functioning as "app" object on the Python side
    _impl->mainGroup = std::make_unique<PyModuleGroup>(&Application::getInstance(), ".", "Root for Python Modules");
 
    // If the bindings have been created already set/replace the "app" object with the newly created main group. This
    // happens when a previous instance of the PythonModuleManager in the same process has already loaded Python
    // modules using the ApplicationCore Python bindings. Otherwise the Python bindings are not yet loaded at this
    // point, so this assignment is done later in PythonModuleManager::setBindings().
    if(_impl->statics->onMainGroupChangeCallback) {
      _impl->statics->onMainGroupChangeCallback(_impl->mainGroup);
    }
 
    // The scoped_interpreter keeps the GIL by default, so we have to release it here and do the locking explicitly.
    // In the destructor of the PythonModuleManager (hence when the Application is being destroyed) we have to
    // acquire the lock again to make sure static objects created internally by pybind11 can be destroyed while
    // having the GIL (would otherwise lead to an error).
    _impl->release = std::make_unique<py::gil_scoped_release>();
  }
 
  /********************************************************************************************************************/
 
  PythonModuleManager::PythonModuleManager() = default;
 
  /********************************************************************************************************************/
 
  void PythonModuleManager::deinit() {
    if(!_impl) {
      return;
    }
 
    // terminate all Python ApplicationModule threads
    for(auto* mod : _impl->mainGroup->getSubmoduleListRecursive()) {
      mod->terminate();
    }
 
    // destroy the gil_scoped_release object, see comment in constructor when creating it
    _impl->release.reset();
 
    // de-assign the app object (which points to the root module we are about to destroy)
    if(_impl->statics->onMainGroupChangeCallback) {
      _impl->statics->onMainGroupChangeCallback(std::unique_ptr<PyModuleGroup>{nullptr});
    }
 
    // unload all Python modules, which will destroy all PythonApplicationModules etc. that have been constructed in
    // Python code.
    for(auto& mod : _impl->modules) {
      auto modname = py::cast<std::string>(mod.attr("__name__"));
      py::exec("sys.modules.pop('" + modname + "')");
    }
    _impl->modules.clear();
    py::exec("gc.collect()");
  }
 
  /********************************************************************************************************************/
 
  PythonModuleManager::~PythonModuleManager() {
    if(_impl) {
      deinit();
    }
  }
 
  /********************************************************************************************************************/
 
  void PythonModuleManager::createModules(Application& app) {
    auto& config = app.getConfigReader();
    for(auto& module : config.getModules("PythonModules")) {
      init();
 
      auto name = config.get<std::string>("PythonModules/" + module + "/path");
      py::gil_scoped_acquire gil;
 
      std::cout << "PythonModuleManager: Loading module " << name << std::endl;
 
      try {
        py::object themod = py::module::import(name.c_str());
        _impl->modules.emplace_back(std::move(themod));
      }
      catch(py::error_already_set& err) {
        throw ChimeraTK::logic_error("Error loading Python module from " + name + ": " + err.what());
      }
    }
  }
 
  /********************************************************************************************************************/
 
  void PythonModuleManager::setOnMainGroupChange(std::function<void(const std::unique_ptr<PyModuleGroup>&)> callback) {
    _impl->statics->onMainGroupChangeCallback = std::move(callback);
    _impl->statics->onMainGroupChangeCallback(_impl->mainGroup);
  }
 
  /********************************************************************************************************************/
 
} // namespace ChimeraTK