RFR: 8274276: Cache normalizedBase URL in URLClassPath.FileLoader

[Сергей Цыпанов]

Currently on each invocation of `URLClassPath.FileLoader.getResource()` `normalizedBase` URL is recalculated using same final `baseURL` from parent class. This can be avoided giving significant improvement in memory consumption. Consider the benchmark:

@State(Scope.Benchmark)
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
@Fork(jvmArgsAppend = {"-Xms2g", "-Xmx2g"})
public class URLClassPathBenchmark {
    private final ClassLoader classLoader = getClass().getClassLoader();

    @Benchmark
    public URL getResource() {
        return classLoader.getResource("file:./config/application.properties");
    }
}

it demonstrates improvement brought in by this patch:

before
Benchmark                                                           Mode  Cnt     Score     Error   Units
URLClassPathBenchmark.getResource                                   avgt   50  2840,746 ±  22,206   ns/op
URLClassPathBenchmark.getResource:·gc.alloc.rate                    avgt   50   645,313 ±   8,072  MB/sec
URLClassPathBenchmark.getResource:·gc.alloc.rate.norm               avgt   50  2403,258 ±  17,639    B/op
URLClassPathBenchmark.getResource:·gc.churn.G1_Eden_Space           avgt   50   656,624 ± 116,090  MB/sec
URLClassPathBenchmark.getResource:·gc.churn.G1_Eden_Space.norm      avgt   50  2450,175 ± 440,011    B/op
URLClassPathBenchmark.getResource:·gc.churn.G1_Survivor_Space       avgt   50     0,123 ±   0,149  MB/sec
URLClassPathBenchmark.getResource:·gc.churn.G1_Survivor_Space.norm  avgt   50     0,459 ±   0,556    B/op
URLClassPathBenchmark.getResource:·gc.count                         avgt   50    67,000            counts
URLClassPathBenchmark.getResource:·gc.time                          avgt   50   117,000                ms

after
Benchmark                                                           Mode  Cnt     Score    Error   Units
URLClassPathBenchmark.getResource                                   avgt  100  2596,719 ±  9,786   ns/op
URLClassPathBenchmark.getResource:·gc.alloc.rate                    avgt  100   448,780 ±  1,684  MB/sec
URLClassPathBenchmark.getResource:·gc.alloc.rate.norm               avgt  100  1528,040 ±  0,005    B/op
URLClassPathBenchmark.getResource:·gc.churn.G1_Eden_Space           avgt  100   479,905 ± 23,369  MB/sec
URLClassPathBenchmark.getResource:·gc.churn.G1_Eden_Space.norm      avgt  100  1634,314 ± 79,821    B/op
URLClassPathBenchmark.getResource:·gc.churn.G1_Survivor_Space       avgt  100     0,101 ±  0,097  MB/sec
URLClassPathBenchmark.getResource:·gc.churn.G1_Survivor_Space.norm  avgt  100     0,345 ±  0,329    B/op
URLClassPathBenchmark.getResource:·gc.count                         avgt  100    98,000           counts
URLClassPathBenchmark.getResource:·gc.time                          avgt  100   218,000               ms

-------------

Commit messages:
 - 8274276: Cache normalizedBase URL in URLClassPath.FileLoader

Changes: https://git.openjdk.java.net/jdk/pull/5677/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5677&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8274276
  Stats: 4 lines in 1 file changed: 2 ins; 1 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5677.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5677/head:pull/5677

PR: https://git.openjdk.java.net/jdk/pull/5677