[GitHub] [rocketmq] BurningCN commented on issue #4505: Questions about the legal judgment of indexCount

[GitBox <gi...@apache.org>]

BurningCN commented on issue #4505:
URL: https://github.com/apache/rocketmq/issues/4505#issuecomment-1165106301

   多谢，从你的描述我想了下从1计数的原因是这样的。
   当`putKey`方法触发，某个`slot`被第一次命中的时候，该`slot`本身的值就是`0`。如果`indexCount`从`0`计数的话，当`this.mappedByteBuffer.getInt(absSlotPos)`返回`0`的时候，无法确认返回的`0`是表示【从来没有过`key`落在该`slot`上】，还是表示【之前已经有一个`indexCount=0`的`indexEntry`落到了该`slot`上】。
   
   Thanks a lot. From your description, I think the reason for counting from 1 is like this.
   When the putKey method is triggered and a slot is hit for the first time, the value of the slot itself is 0. If indexCount counts from 0, when this `this.mappedByteBuffer.getInt(absSlotPos)` returns 0, it is not possible to confirm whether the returned 0 means that [no key has ever landed on the slot] or that [an indexEntry with indexCount=0 has previously landed on the slot].


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