RFR: 7264: Improve the performance of the JFR parser

[Jean-Philippe Bempel]

On Mon, 14 Jun 2021 08:10:46 GMT, Jean-Philippe Bempel <jpbempel at openjdk.org> wrote:

> When parsing a JFR file, StackFrames are the objects that are the most
> deserialized using Readers.
> By default, JMC core parser used a generic ReflectiveReaders
> which use reflection to parser the structure. However, we have known
> objects like stack frames where we could directly map to the typed
> object instead on relying on reflection, which speed up significantly
> the parsing.
> 
> Here the results for c5.2xlarge instance single threaded parsing with 24MB jfr recording with 100 iterations:
> 
> | runs | baseline | specific readers optim | improvement |
> | --- | --- | --- | --- |
> | run 1 | 54,317ms | 39,623ms | -27% |
> | run 2 | 54,988ms | 39,520ms | -28% |
> | run 3 | 54,209ms | 39,904ms | -26% |

Agreed that this code is fragile.
I can precompute the index and make sure readers are meant for the field at construction time.
I will try that.

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PR: https://git.openjdk.java.net/jmc/pull/266