RFR: 8175891, 8192892: JrtPath improvements

[Jim Laskey (Oracle)]

+1


> On Dec 1, 2017, at 9:34 AM, Claes Redestad <claes.redestad at oracle.com> wrote:
> 
> Hi,
> 
> please review this patch that resolves two small but sometimes significant inefficiencies in jdk.internal.jrtfs.JrtPath:
> 
> Improve JrtPath::getResolved fast-path test:
> https://bugs.openjdk.java.net/browse/JDK-8192892
> 
> Testing for '.' is insufficient as it's likely all paths have a dot in them, while resolving is rare. Patch uses a test that is logically equivalent to that in ZipPath::getResolved to better filter out paths that don't need to take the slow path.
> 
> JrtPath::resolve off-by-one pre-sizing cause for memory pressure:
> https://bugs.openjdk.java.net/browse/JDK-8175891
> 
> As path is normalized to never end with a / this code can be simplified.
> 
> Webrev: http://cr.openjdk.java.net/~redestad/8192892/open.0/
> 
> In a JMH micro[1] that naively walks all entries in the JDK lib/modules and counts classes, these fixes work together to remove overhead both in repeated and single-shot settings (the latter is relevant since jrtfs usage may influence startup times in certain applications and tools):
> 
> Benchmark           Mode  Cnt  Score   Error  Units
> JRTWalk.walkJImage  avgt   25  0.049 ± 0.003   s/op
> JRTWalk.walkJImage  avgt   25  0.027 ± 0.001   s/op  # 1.8x
> 
> Benchmark           Mode  Cnt  Score   Error  Units
> JRTWalk.walkJImage    ss   20  0.436 ± 0.018   s/op  (best: 0.389 s/op)
> JRTWalk.walkJImage    ss   20  0.388 ± 0.017   s/op  (best: 0.363 s/op)
> 
> Thanks!
> 
> /Claes
> 
> [1] http://cr.openjdk.java.net/~redestad/8192892/JRTWalk.java