如何使用postThreadMessage传递一个struct [英] how to use postThreadMessage to pass a struct

问题描述

我希望使用Windows的消息队列设施，以一个struct发送到另一个线程。
但我发现，在postthreadmessage功能只提供两个整数参数，wParam和lParam我通过arguments.So我决定把该结构的地址lparam中。这是正确的方式使用的窗口传递结构？

I want to use windows's message queue facilities to send a struct to another thread. But I find out that the postthreadmessage function only provide two integer parameters, lparam and wparam for me to pass arguments.So I decide to put the address of the struct in lparam. Is this the correct way windows use to pass struct?

和我打算使用boost :: shared_ptr的持有结构的地址，同时在接收线程和发送者线程。我怀疑，当两个shared_ptrs超出范围，将在结构被释放两次？我不能想出一个办法，以确保堆上分配将被100％释放的结构，任何想法？

And I intend to use boost::shared_ptr to hold the address of struct in both the receiver thread and sender thread. I doubt that when the two shared_ptrs goes out of scope, will the struct be freed twice? I can not figure out a way to ensure the struct allocated on heap will be 100% freed, Any ideas?

推荐答案

要第一个问题，是的，LPARAM是打算用来为一个整数或一个指针。这是明确的自定义：

To the first question, yes, LPARAM is intended to be used as an integer or a pointer. That is clear from the definition:

typedef LONG_PTR LPARAM;

这是足够长，以容纳一个指针的整数。

That is an integer long enough to hold a pointer.

关于shared_ptr的事情，你是对的，如果传递的原始指针，并将其包装成另一个shared_ptr的，你会释放它两次：

About the shared_ptr thing, you are right, if you pass the raw pointer and wrap it into another shared_ptr you will free it twice:

shared_ptr<Thing> a;
PostThreadMessage(x, 0, (LPARAM)a.get());
...
LRESULT OnMessage(int msg, WPARAM wp, LPARAM lp)
{
    shared_ptr<Thing> p((Thing*)lp); //Bad!!!
}

不过你可以试试这个解决方法，而不是：

But you can try this workaround instead:

shared_ptr<Thing> a;
PostThreadMessage(x, 0, new shared_ptr<Thing>(a)); //pointer to smart-pointer
...
LRESULT OnMessage(int msg, WPARAM wp, LPARAM lp)
{
    shared_ptr<Thing> *pp = (shared_ptr<Thing>*)lp;
    shared_ptr<Thing> p(*pp);
    delete pp; //no leak
}

事后：注意PostThreadMessage可能会失败......你不想泄露一个shared_ptr

AFTERTHOUGHT: Note that PostThreadMessage may fail... and you don't want to leak a shared_ptr.

在我的经验，一般最好使用一个std ::双端队列来保存数据，并使用PostThreadMessage来通知有数据存在。这样你永远不会失去的对象！因人而异

In my experience it is generally better to use a std::deque to hold the data and use the PostThreadMessage to notify that there is data there. In this way you'll never lose an object! YMMV

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