Reduce allocation in sun.net.www.protocol.jar.Handler.parseURL

[Eirik Bjørsnøs]

Hello,

sun.net.www.protocol.jar.Handler.parseURL unconditionally calls
String.substring twice on the spec string, even when
ParseUtil.canonizeString later determines that no canonization was required.

By letting canonizeString do the substring calls, but only when it
determines that it is needed, we can remove some unnecessary String and
byte[] allocations.

Patch:

https://github.com/eirbjo/jdk/commit/87da9032d7fb622f5d466f43faded4de672ebdda

JMH micro:

@Benchmark
public void initURL(Blackhole blackhole) throws MalformedURLException {
    blackhole.consume(new URL(new URL("jar:file:/spring-aop.jar!/"),
"org/springframework/aop/framework/AbstractSingletonProxyFactoryBean.class"));
}

It shows a performance win for the patch in terms of throughput and bytes /
operation:

Baseline:

Benchmark                                               Mode  Cnt
 Score       Error   Units
ZipBenchmark.initURL                                   thrpt   25
 1673457.129 ± 22857.945   ops/s
ZipBenchmark.initURL:·gc.alloc.rate                    thrpt   25
1410.227 ±    19.283  MB/sec
ZipBenchmark.initURL:·gc.alloc.rate.norm               thrpt   25
 928.080 ±     0.005    B/op
ZipBenchmark.initURL:·gc.churn.G1_Eden_Space           thrpt   25
1412.557 ±    22.575  MB/sec
ZipBenchmark.initURL:·gc.churn.G1_Eden_Space.norm      thrpt   25
 929.589 ±     5.756    B/op
ZipBenchmark.initURL:·gc.churn.G1_Survivor_Space       thrpt   25
 0.006 ±     0.002  MB/sec
ZipBenchmark.initURL:·gc.churn.G1_Survivor_Space.norm  thrpt   25
 0.004 ±     0.001    B/op
ZipBenchmark.initURL:·gc.count                         thrpt   25
1441.000              counts
ZipBenchmark.initURL:·gc.time                          thrpt   25
 961.000                  ms

After:

Benchmark                                               Mode  Cnt
 Score       Error   Units
ZipBenchmark.initURL                                   thrpt   25
 1831971.983 ± 35705.091   ops/s
ZipBenchmark.initURL:·gc.alloc.rate                    thrpt   25
1011.389 ±    19.689  MB/sec
ZipBenchmark.initURL:·gc.alloc.rate.norm               thrpt   25
 608.061 ±     0.001    B/op
ZipBenchmark.initURL:·gc.churn.G1_Eden_Space           thrpt   25
1011.746 ±    20.583  MB/sec
ZipBenchmark.initURL:·gc.churn.G1_Eden_Space.norm      thrpt   25
 608.275 ±     3.609    B/op
ZipBenchmark.initURL:·gc.churn.G1_Survivor_Space       thrpt   25
 0.007 ±     0.001  MB/sec
ZipBenchmark.initURL:·gc.churn.G1_Survivor_Space.norm  thrpt   25
 0.004 ±     0.001    B/op
ZipBenchmark.initURL:·gc.count                         thrpt   25
1197.000              counts
ZipBenchmark.initURL:·gc.time                          thrpt   25
 760.000                  ms

Thanks,
Eirik.