C#中的双按位NOT(~~) [英] Double bitwise NOT (~~) in C#

问题描述

我一直在阅读ThreadLocal<T>的实现，并且在将int id存储在私有int字段(m_idComplement)中然后将其几乎转换成几乎每个表达式之前都不太了解反转int id的原理.用于.除了适用于JavaScript的这种情况找到任何有关为什么在C#中双重否定会有用的信息吗?

I've been reading through ThreadLocal<T> implementation and don't quite understand the rationale behind inverting an int id before storing it in a private int filed (m_idComplement) and then inverting it back again in almost every expression it's used in. Except for this case applicable to JavaScript, I can't find any information on why would double negation be useful in C#?

在第240行，它确实分配了0，而没有取反，但是它本可以分配为-1，然后丢弃所有其他不必要的值，不是吗?

On line 240 it does assign 0 without negation, but it could've just assigned a -1 and just drop all the other unnecessary ones, no?

https://dl.dropboxusercontent.com/u/65419748/ThreadLocal.cs

https://i.imgur.com/3z3F64V.png

推荐答案

ThreadLocal.cs的参考源对此字段包含以下注释:

The reference source for ThreadLocal.cs contains the following comment against this field:

此ThreadLocal<>实例的插槽ID.我们存储ID的按位补码(即〜ID)，这使我们能够区分ID为0的情况和未完全初始化的对象，这是由于构造函数中的线程中止，也可能是由于内存模型引起的用户代码中出现问题.

Slot ID of this ThreadLocal<> instance. We store a bitwise complement of the ID (that is ~ID), which allows us to distinguish between the case when ID is 0 and an incompletely initialized object, either due to a thread abort in the constructor, or possibly due to a memory model issue in user code.

本质上，他们将ID的默认未初始化值从0(如果直接作为int字段直接存储，则应为0)切换为-1.

They're essentially switching the default, uninitialized value of the ID from 0, which it would be if stored directly as an int field, to -1.

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