RFR: 8267840: Improve URLStreamHandler.parseURL() [v2]

[Daniel Fuchs]

On Wed, 30 Jun 2021 11:47:42 GMT, Сергей Цыпанов <github.com+10835776+stsypanov at openjdk.org> wrote:

>> There is an optimization opportunity for the widespread use-case when a resource is read from classpath using `getClass().getClassLoader().getResource()` or `getClass().getClassLoader().getResourceAsStream()`.
>> 
>> Pay attention to lines starting from 261. In case I run something like
>> 
>> var props = getClass().getClassLoader().getResource("/application.properties");
>> 
>> I get into the if-else block starting from 251 and here 'separator' variable is an empty String. In this case we can skip 'separator' from concatenation chain and use `String.concat()` as there are only two items concatenated.
>> 
>> In the opposite case `separator` variable is `"/"` and at the same time `ind` variable is `-1`. This means that expression `path.substring(0, ind + 1)` always returns an empty String and again can be excluded from concatenation chain allowing usage of `String.concat()` which allows to dodge utilization of `StringBuilder` (here `StringConcatFactory` is not available, see https://github.com/openjdk/jdk/pull/3627)
>> 
>> In the next else-block, starting from 274, again, `String.concat()` is applicable.
>> 
>> In another if-else block, starting from 277, when id is 0 again path.substring(0, ind) returns empty String making concatenation pointless and avoidable.
>> 
>> There are also some other minor clean-ups possible regarding constant conditions (lines 252 and 161).
>> 
>> The change allows to reduce significantly resource look-up costs for a very wide-spread case:
>> 
>> @State(Scope.Benchmark)
>> @BenchmarkMode(Mode.AverageTime)
>> @OutputTimeUnit(TimeUnit.NANOSECONDS)
>> @Fork(jvmArgsAppend = {"-Xms2g", "-Xmx2g"})
>> public class ClassGetResourceBenchmark {
>>     private final Class<?> clazz = getClass();
>> 
>>     @Benchmark
>>     public URL getResource() {
>>         return clazz.getResource("/application.properties");
>>     }
>> }
>> 
>> The change allows to reduce memory consumption significantly:
>> 
>> before
>> 
>> Benchmark                                                               Mode  Cnt     Score     Error   Units
>> ClassGetResourceBenchmark.getResource                                   avgt  100  1649,367 ±   5,904   ns/op
>> ClassGetResourceBenchmark.getResource:·gc.alloc.rate                    avgt  100   619,204 ±   2,413  MB/sec
>> ClassGetResourceBenchmark.getResource:·gc.alloc.rate.norm               avgt  100  1339,232 ±   4,909    B/op
>> ClassGetResourceBenchmark.getResource:·gc.churn.G1_Eden_Space           avgt  100   627,192 ±  74,972  MB/sec
>> ClassGetResourceBenchmark.getResource:·gc.churn.G1_Eden_Space.norm      avgt  100  1356,681 ± 162,354    B/op
>> ClassGetResourceBenchmark.getResource:·gc.churn.G1_Survivor_Space       avgt  100     0,119 ±   0,100  MB/sec
>> ClassGetResourceBenchmark.getResource:·gc.churn.G1_Survivor_Space.norm  avgt  100     0,257 ±   0,217    B/op
>> ClassGetResourceBenchmark.getResource:·gc.count                         avgt  100   128,000            counts
>> ClassGetResourceBenchmark.getResource:·gc.time                          avgt  100   227,000                ms
>> 
>> after
>> 
>> Benchmark                                                               Mode  Cnt     Score     Error   Units
>> ClassGetResourceBenchmark.getResource                                   avgt  100  1599,948 ±   4,115   ns/op
>> ClassGetResourceBenchmark.getResource:·gc.alloc.rate                    avgt  100   358,434 ±   0,922  MB/sec
>> ClassGetResourceBenchmark.getResource:·gc.alloc.rate.norm               avgt  100   752,016 ±   0,004    B/op
>> ClassGetResourceBenchmark.getResource:·gc.churn.G1_Eden_Space           avgt  100   342,778 ±  76,490  MB/sec
>> ClassGetResourceBenchmark.getResource:·gc.churn.G1_Eden_Space.norm      avgt  100   719,264 ± 160,513    B/op
>> ClassGetResourceBenchmark.getResource:·gc.churn.G1_Survivor_Space       avgt  100     0,008 ±   0,005  MB/sec
>> ClassGetResourceBenchmark.getResource:·gc.churn.G1_Survivor_Space.norm  avgt  100     0,017 ±   0,010    B/op
>> ClassGetResourceBenchmark.getResource:·gc.count                         avgt  100    70,000            counts
>> ClassGetResourceBenchmark.getResource:·gc.time                          avgt  100   151,000                ms
>
> Сергей Цыпанов has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:
> 
>  - Merge branch 'master' into 8267840
>  - Merge branch 'master' into 8267840
>  - 8267840: Improve URLStreamHandler.parseURL()

src/java.base/share/classes/java/net/URLStreamHandler.java line 275:

> 273:                 path = "/";
> 274:             } else {
> 275:                 path = path.substring(0, ind).concat("/");

would that be equivalent to 

path = path.substring(0, ind + 1);

given that ind = path.lastIndexOf('/') ?

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

PR: https://git.openjdk.java.net/jdk/pull/4526