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boost.python c多线程

作者:互联网

我正在编写一个包含c模块的python程序(.so,使用boost.python).
我正在启动几个运行c函数的python线程.

这是C代码的样子:

#include <boost/python.hpp>
using namespace boost;
void f(){
    // long calculation

    // call python function

    // long calculation
}

BOOST_PYTHON_MODULE(test)
{
    python::def("f", &f);
}

和python代码:

from test import f
t1 = threading.Thread(target=f)
t1.setDaemon(True)
t1.start()
print "Still running!"

我遇到一个问题:“仍在运行!”消息未显示,我发现c线程正在保存GIL.

在从python代码运行c代码的情况下,处理GIL的最佳方法是什么?

谢谢!
加尔

解决方法:

我经常发现使用RAII-style类来管理Global Interpreter Lock(GIL)提供了一种优雅的异常安全解决方案.

例如,对于以下with_gil类,在创建with_gil对象时,调用线程将获取GIL.当with_gil对象被销毁时,它将恢复GIL状态.

/// @brief Guard that will acquire the GIL upon construction, and
///        restore its state upon destruction.
class with_gil
{
public:
  with_gil()  { state_ = PyGILState_Ensure(); }
  ~with_gil() { PyGILState_Release(state_);   }

  with_gil(const with_gil&)            = delete;
  with_gil& operator=(const with_gil&) = delete;
private:
  PyGILState_STATE state_;
};

互补的no_gil类则相反:

/// @brief Guard that will unlock the GIL upon construction, and
///        restore its staet upon destruction.
class without_gil
{
public:
  without_gil()  { state_ = PyEval_SaveThread(); }
  ~without_gil() { PyEval_RestoreThread(state_); }

  without_gil(const without_gil&)            = delete;
  without_gil& operator=(const without_gil&) = delete;
private:
  PyThreadState* state_;
};

它们在函数中的用法如下:

void f()
{
  without_gil no_gil;       // release gil
  // long calculation
  ...

  {
    with_gil gil;           // acquire gil
    // call python function
    ...
  }                         // restore gil (release)

  // long calculation
  ...
}                           // restore gil (acquire)

也可以使用更高级别的便捷类来提供类似std :: lock_guard的体验. GIL的获取和释放,保存和还原语义与普通互斥锁略有不同.因此,gil_guard接口是不同的:

> gil_guard.acquire()将获取GIL
> gil_guard.release()将释放GIL
> gil_guard_restore()将恢复以前的状态

/// @brief Guard that provides higher-level GIL controls.
class gil_guard
{
public:
  struct no_acquire_t {} // tag type used for gil acquire strategy
  static no_acquire;

  gil_guard()             { acquire(); }
  gil_guard(no_acquire_t) { release(); }
  ~gil_guard()            { while (!stack_.empty()) { restore(); } }

  void acquire()          { stack_.emplace(new with_gil); }
  void release()          { stack_.emplace(new without_gil); }
  void restore()          { stack_.pop(); }

  static bool owns_gil()
  {
    // For Python 3.4+, one can use `PyGILState_Check()`.
    return _PyThreadState_Current == PyGILState_GetThisThreadState();
  }

  gil_guard(const gil_guard&)            = delete;
  gil_guard& operator=(const gil_guard&) = delete;

private:
  // Use std::shared_ptr<void> for type erasure.
  std::stack<std::shared_ptr<void>> stack_;
};

它的用法是:

void f()
{
  gil_guard gil(gil_guard::no_acquire); // release gil
  // long calculation
  ...

  gil.acquire();                        // acquire gil
  // call python function
  ...
  gil.restore();                        // restore gil (release)

  // long calculation
  ...
}                                       // restore gil (acquire)

这是带有这些辅助类的完整示例demonstrating GIL管理:

#include <cassert>
#include <iostream> // std::cout, std::endl
#include <memory>   // std::shared_ptr
#include <thread>   // std::this_thread
#include <stack>    // std::stack
#include <boost/python.hpp>

/// @brief Guard that will acquire the GIL upon construction, and
///        restore its state upon destruction.
class with_gil
{
public:
  with_gil()  { state_ = PyGILState_Ensure(); }
  ~with_gil() { PyGILState_Release(state_);   }

  with_gil(const with_gil&)            = delete;
  with_gil& operator=(const with_gil&) = delete;
private:
  PyGILState_STATE state_;
};

/// @brief Guard that will unlock the GIL upon construction, and
///        restore its staet upon destruction.
class without_gil
{
public:
  without_gil()  { state_ = PyEval_SaveThread(); }
  ~without_gil() { PyEval_RestoreThread(state_); }

  without_gil(const without_gil&)            = delete;
  without_gil& operator=(const without_gil&) = delete;
private:
  PyThreadState* state_;
};

/// @brief Guard that provides higher-level GIL controls.
class gil_guard
{
public:
  struct no_acquire_t {} // tag type used for gil acquire strategy
  static no_acquire;

  gil_guard()             { acquire(); }
  gil_guard(no_acquire_t) { release(); }
  ~gil_guard()            { while (!stack_.empty()) { restore(); } }

  void acquire()          { stack_.emplace(new with_gil); }
  void release()          { stack_.emplace(new without_gil); }
  void restore()          { stack_.pop(); }

  static bool owns_gil()
  {
    // For Python 3.4+, one can use `PyGILState_Check()`.
    return _PyThreadState_Current == PyGILState_GetThisThreadState();
  }

  gil_guard(const gil_guard&)            = delete;
  gil_guard& operator=(const gil_guard&) = delete;

private:
  // Use std::shared_ptr<void> for type erasure.
  std::stack<std::shared_ptr<void>> stack_;
};

void f()
{
  std::cout << "in f()" << std::endl;

  // long calculation
  gil_guard gil(gil_guard::no_acquire);
  assert(!gil.owns_gil());
  std::this_thread::sleep_for(std::chrono::milliseconds(500));
  std::cout << "calculating without gil..." << std::endl;

  // call python function
  gil.acquire();
  assert(gil.owns_gil());
  namespace python = boost::python;
  python::object print =
  python::import("__main__").attr("__builtins__").attr("print");
    print(python::str("calling a python function"));
  gil.restore();

  // long calculation
  assert(!gil.owns_gil());
  std::cout << "calculating without gil..." << std::endl;
}

BOOST_PYTHON_MODULE(example)
{
  // Force the GIL to be created and initialized.  The current caller will
  // own the GIL.
  PyEval_InitThreads();

  namespace python = boost::python;
  python::def("f", +[] {
    // For exposition, assert caller owns GIL before and after
    // invoking function `f()`.
    assert(gil_guard::owns_gil());
    f();
    assert(gil_guard::owns_gil());
  });
}

互动用法:

>>> import threading
>>> import example
>>> t1 = threading.Thread(target=example.f)
>>> t1.start(); print "Still running"
in f()
Still running
calculating without gil...
calling a python function
calculating without gil...
>>> t1.join()

标签:boost-python,multithreading,gil,python,c-4
来源: https://codeday.me/bug/20191112/2023531.html