安全读取元素同时更改的long []内容的最快方法 [英] Fastest way to safely read contents of long[] whose elements are changed concurrently

问题描述

当你有一个

long[] myArray = new long[256];

使用多个线程更改了其项目

whose items are changed by multiple threads using

Interlocked.Increment(ref myArray[x])

肯定不会在某个时间点获得myArray的快照，因为同时发生了非锁定写入，因此我不打算这样做.

it sure won't be possible to get a snapshot of myArray at one point in time, as there are non-locked writes going on concurrently, so I'm not trying to get that.

那么我真的必须对每个这样的元素进行Volatile.Read来获得过去某个时候所有值的副本吗?

So do I really have to Volatile.Read of every single element like this to get a copy of all values at some point in the past?

long[] copy = new long[256];
for (int i = 0; i < 256; i++)
    copy[i] = Volatile.Read(ref myArray[i]);

由于我对某一时刻的快照不感兴趣，所以过时的值不是问题，但是由于64位非易失性读取不是原子的，因此我担心以下内容可能会给我带来预增的作用长度的一半，以及后增量的一半，这可能会提供数组中从未存在的值.

As I'm not interested in a snapshot at one point in time, stale values are not a problem, but as 64-bit non-volatile reads are not atomic, I fear that the following may give me a pre-increment half of a long, and a post-increment half, which may give a value that never existed in the array.

long[] copy = new long[256];
for (int i = 0; i < 256; i++)
    copy[i] = myArray[i];

鉴于我不想使用任何锁定功能，因此Volatile.Read变体是正确的选择吗?

So is the Volatile.Read variant the proper choice, given I don't want to use any locking?

推荐答案

如果过时的值对您而言不是问题，而您所需的只是原子读取(不是有序读取)，则在x64上，您可以使用普通读取而不是Volatile.Read. 在使用DMB实现易失性读写的ARM系统上，这可能是有益的.

If stale values is not an issue for you and all you need is atomic read (not ordered one) then on x64 you can just use plain read instead of Volatile.Read. It can be beneficial on on ARM systems where volatile reads/writes are fairly heavyweight as they are implemented with DMB.

重要 根据此和那，您需要在64位模式下(构建和)运行.Net程序，这样才能正常工作:

Important According to this and that, you need to (build and) run your .Net program in 64-bit mode for this to work:

如果要在64位操作系统上以64位运行C#代码 版本的CLR然后读取和写入64位double和long 整数也保证是原子的

if you are running C# code on a 64 bit operating system in a 64 bit version of the CLR then reads and writes of 64 bit doubles and long integers are also guaranteed to be atomic

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