为什么锁是需要实现一个只读整型属性？ [英] Why lock is needed to implement a readonly int property?

问题描述

我是新来的线程和我在的博客。我粘贴的code只是必要的部分：

I'm new to threading and I came accross a custom thread pool implementation example in a blog. I'm pasting just the necessary parts of the code:

Public Class ThreadPool

    Private CountLock As New Object
    Private _Count As Integer

    Public ReadOnly Property ThreadCount() As Integer
      Get
         SyncLock CountLock
           Return _Count
         End SyncLock
      End Get
    End Property

    Public Sub Open()
      Interlocked.Increment(_Count)
    End Sub

    Public Sub Close()
      Interlocked.Decrement(_Count)
      ....
    End Sub

EndClass

我的问题是，为什么我们需要一个锁来实现只读经纬物业？

My question is, why do we need a lock to implement the readonly ThreadCount property?

推荐答案

锁将迫使内存屏障，使从CPU缓存中陈旧的值，如果写的最后的值是由不同的CPU不被读取。同样可以用 Thread.VolatileRead（）进行无锁定。

The lock will force a memory barrier, so that a stale value from the CPU cache isn't read if the last value written was written by a different CPU. The same could be done with Thread.VolatileRead() without locking.

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