Re: Suggestion : Use unique string type instead of two (short and long)

[云风 <cloudwu@...>]

在 2019年6月17日，23:41，Roberto Ierusalimschy <roberto@inf.puc-rio.br> 写道：

>> Maybe a 32bit id is enough, because we can rearrange the id during the gc process. It’s a little complicated, but I think it’s possible.
> 
> Can you be more specific? It is easy for the GC to set a watermark
> (e.g., to keep the highest/lower id still in use), but that does
> not guarantee anything. We can also renumber all strings, paying
> the price for a little overhead in the first comparisons after each
> GC cycle.

My idea is use a fixed size hash cache. For example , there are 10 slots .

During the mark stage, we put the highest id and lowest id into the slots.

For example

high: 80 81 92 93 74 95 86 97 98 89
low:   00 11 02 03 14 05 16 27 28 09

It means the highest id we used is 89-98, and 01, 04, 06-08 can be reused. We can always find the highest id we still used, and a few unused id .

And then, we can remap 92, 93, 95, 97, 98 to 01 04 06 07 08 during the sweep stage.

So that , we can recycle a few id for each gc cycle.

For the length, we can still store 1 byte for small string length, if the string longer than 255 bytes, store 0xff and an additional size_t.