资源获取即初始化(RAII)是什么意思? [英] What is meant by Resource Acquisition is Initialization (RAII)?

问题描述

资源获取即初始化 (RAII) 是什么意思?

What is meant by Resource Acquisition is Initialization (RAII)?

推荐答案

对于一个非常强大的概念来说，这是一个非常糟糕的名字，也许是 C++ 开发人员在切换到其他语言时错过的第一件事.有一些运动试图将这个概念重新命名为范围绑定资源管理，尽管它似乎还没有流行起来.

It's a really terrible name for an incredibly powerful concept, and perhaps one of the number 1 things that C++ developers miss when they switch to other languages. There has been a bit of a movement to try to rename this concept as Scope-Bound Resource Management, though it doesn't seem to have caught on just yet.

当我们说资源"时，我们不仅仅指内存——它可以是文件句柄、网络套接字、数据库句柄、GDI 对象……简而言之，我们供应有限的东西，因此我们需要能够控制它们的使用.范围绑定"方面意味着对象的生命周期绑定到变量的范围，因此当变量超出范围时，析构函数将释放资源.一个非常有用的特性是它提供了更大的异常安全性.例如，比较这个:

When we say 'Resource' we don't just mean memory - it could be file handles, network sockets, database handles, GDI objects... In short, things that we have a finite supply of and so we need to be able to control their usage. The 'Scope-bound' aspect means that the lifetime of the object is bound to the scope of a variable, so when the variable goes out of scope then the destructor will release the resource. A very useful property of this is that it makes for greater exception-safety. For instance, compare this:

RawResourceHandle* handle=createNewResource();
handle->performInvalidOperation();  // Oops, throws exception
...
deleteResource(handle); // oh dear, never gets called so the resource leaks

与 RAII 一起

class ManagedResourceHandle {
public:
   ManagedResourceHandle(RawResourceHandle* rawHandle_) : rawHandle(rawHandle_) {};
   ~ManagedResourceHandle() {delete rawHandle; }
   ... // omitted operator*, etc
private:
   RawResourceHandle* rawHandle;
};

ManagedResourceHandle handle(createNewResource());
handle->performInvalidOperation();

在后一种情况下，当抛出异常并解开堆栈时，局部变量会被销毁，以确保我们的资源被清理并且不会泄漏.

In this latter case, when the exception is thrown and the stack is unwound, the local variables are destroyed which ensures that our resource is cleaned up and doesn't leak.

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