RFR: 8239138: StyleManager should use a BufferedInputStream

[Kevin Rushforth]

On Tue, 25 May 2021 09:04:07 GMT, Ambarish Rapte <arapte at openjdk.org> wrote:

> `StyleManager.calculateCheckSum()` uses a raw InputStream as the input to a `DigestInputStream` and reads one byte at a time. This is slower in performance and should be changed, either to use `BufferedInputStream` or read byte buffer of 4096 from the stream or use both.
> 
> I have tried three approaches and tested with modena.css which is ~134 KB in size.
> Following are the approaches and time in milliseconds taken by the method StyleManager.calculateCheckSum(), collected from 25 readings,
> 
> 1. Use BufferedInputStream and read one byte at a time [commit#1](https://github.com/openjdk/jfx/commit/6cd7d44d0ce1084c6cdb06a698c7aca127a615ef) : 
> - Maximum: 53 ms,  Minimum: 27 ms, Average: 39 ms
> 2. Use BufferedInputStream and read buffer of 4096 at a time [commit#1+2](https://github.com/openjdk/jfx/pull/518/files/6e0c621ea62691d5402b2bca5951d1012a5b1b91)
> - Maximum: 17 ms,  Minimum: 14 ms, Average: 15.58 ms
> 3. Use raw InputStream(current implementation) and read buffer of 4096 at a time [commit#1+2+3](https://github.com/openjdk/jfx/pull/518/files/215e1a183cfb902247f0d48685f7a901cb5fb003), which also similar to `NativeLibLoader.calculateCheckSum()` and looks faster than previous two.
> - Maximum: 16 ms,  Minimum: 13 ms, Average: 14.25 ms
> 
> 
> The time taken by `StyleManager.calculateCheckSum()` with current implementation is,
> - Maximum: 61 ms,  Minimum: 38 ms, Average: 50.58 ms
> 
> 
> Both approaches 2 & 3 show good improvement. I would prefer approach#3 as it is similar to `NativeLibLoader.calculateCheckSum()`.
> However we can choose approach#2 also.
> If we choose approach#3 then bug summary should be changed accordingly.

I also prefer approach 3, since the body of the try/finally loop is then identical to that of `NativeLibLoader::calculateCheckSum`.

Can you add a unit test to validate the checksum method? It should be sufficient to do this by taking a file that is > 4096 bytes, but not a multiple of 4096, manually running `md5sum` on it to get its checksum that you can then use to compare with the computed one.

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PR: https://git.openjdk.java.net/jfx/pull/518