如何取消升级asio io_service帖子 [英] How to cancel boost asio io_service post

问题描述

如何取消已发布的回调：

  getIoService（） - & MyClass :: myCallback，this））; 
  

并保持其他已发布的回调不变？

问题是，我有一些对象从不同的线程接收事件，我发布他们到ioservice为了处理主线程中的事件。如果在某个时候我想删除我的对象 - ioservice将尝试执行已经发布的回调在被销毁的对象。在这种情况下，我不能在对象中存储任何标志，因为它将被删除。

有一个可能的解决方案使用 enable_shared_from_this 和

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>解决方案

您不能通过 io_service 以这种方式选择性地取消回调。一个选项是将逻辑移动到更高的级别，例如 MyClass 内。示例实现可以是：

  class MyClass：public boost :: enable_shared_from_this< MyClass> 
 {
 public：
 typedef boost :: shared_ptr< MyClas> Ptr; 
 static Ptr create（boost :: asio :: io_service& io_service）{
 const Ptr result（new MyClass） 
 io_service.post（boost :: bind（& MyClass :: myCallback，result））; 
 return result; 
} 
 
 void myCallback（）{
 if（_canceled）return; 
} 
 
 void cancel（）{_canceled = true; } 
 
 private：
 MyClass（）：_canceled（false）{} 
 
 private：
 bool _canceled; 
}; 
  

此类使用 boost :: shared_ptr 以实施共享所有权语义。执行此gurantees对象生命周期将持续存在，只要回调仍然在 io_service 队列中，在分派之前。

How can I cancel already posted callback:

getIoService()->post(boost::bind(&MyClass::myCallback, this));

and keep other posted callbacks untouched?

The problem is that I have some object that receives events from different thread and I post them to ioservice in order to handle events in main thread. What if at some point I want to delete my object - ioservice will try to execute already posted callbacks in destroyed object. And in this case I can't store any flag in object since it will be removed.

There is a possible solution to use enable_shared_from_this and shared_from_this(), but wondering whether another solution or not.

Thanks

解决方案

You cannot selectively cancel callbacks in such a manner through an io_service. One option is to move the logic to a higher level, such as inside of MyClass. A sample implementation may be:

class MyClass : public boost::enable_shared_from_this<MyClass>
{
public:
    typedef boost::shared_ptr<MyClas> Ptr;
    static Ptr create( boost::asio::io_service& io_service ) { 
        const Ptr result( new MyClass );
        io_service.post( boost::bind(&MyClass::myCallback, result) );
        return result;
    }

    void myCallback() { 
        if ( _canceled ) return;
    }

    void cancel() { _canceled = true; }

private:
    MyClass() : _canceled(false) { }

private:
    bool _canceled;
};

This class uses a boost::shared_ptr to enforce shared ownership semantics. Doing this gurantees the object lifetime will persist as long as the callback remains in the io_service queue before being dispatched.

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