RFR: 8264777: Overload optimized FileInputStream::readAllBytes [v4]

[Daniel Fuchs]

On Wed, 5 May 2021 17:10:13 GMT, Brian Burkhalter <bpb at openjdk.org> wrote:

>> Please consider this request to override the `java.io.InputStream` methods `readAllBytes()` and `readNBytes(int)` in `FileInputStream` with more performant implementations. The method overrides attempt to read all requested bytes into a single array of the required size rather than composing the result from a sequence of smaller arrays. An example of the performance improvements is as follows.
>> 
>> **readAllBytes**
>> Before
>> 
>> Benchmark                                    (length)   Mode  Cnt      Score     Error  Units
>> ReadAllBytes.readAllBytesFileInputStream      1000000  thrpt   20   2412.031 ±   7.309  ops/s
>> ReadAllBytes.readAllBytesFileInputStream     10000000  thrpt   20    212.181 ±   0.369  ops/s
>> ReadAllBytes.readAllBytesFileInputStream    100000000  thrpt   20     19.860 ±   0.048  ops/s
>> ReadAllBytes.readAllBytesFileInputStream   1000000000  thrpt   20      1.298 ±   0.183  ops/s
>> 
>> After
>> 
>> Benchmark                                    (length)   Mode  Cnt      Score     Error  Units
>> ReadAllBytes.readAllBytesFileInputStream      1000000  thrpt   20   8218.473 ±  43.425  ops/s
>> ReadAllBytes.readAllBytesFileInputStream     10000000  thrpt   20    302.781 ±   1.273  ops/s
>> ReadAllBytes.readAllBytesFileInputStream    100000000  thrpt   20     22.461 ±   0.084  ops/s
>> ReadAllBytes.readAllBytesFileInputStream   1000000000  thrpt   20      1.502 ±   0.003  ops/s
>> 
>> 
>> **readNBytes**
>> 
>> `N = file_size / 2`
>> 
>> Before
>> 
>> Benchmark                                    (length)   Mode  Cnt      Score     Error  Units
>> ReadAllBytes.readHalfBytesFileInputStream     1000000  thrpt   20   5585.500 ± 153.353  ops/s
>> ReadAllBytes.readHalfBytesFileInputStream    10000000  thrpt   20    436.164 ±   1.104  ops/s
>> ReadAllBytes.readHalfBytesFileInputStream   100000000  thrpt   20     40.167 ±   0.141  ops/s
>> ReadAllBytes.readHalfBytesFileInputStream  1000000000  thrpt   20      3.291 ±   0.211  ops/s
>> 
>> 
>> After
>> 
>> Benchmark                                    (length)   Mode  Cnt      Score     Error  Units
>> ReadAllBytes.readHalfBytesFileInputStream     1000000  thrpt   20  15463.210 ±  66.045  ops/s
>> ReadAllBytes.readHalfBytesFileInputStream    10000000  thrpt   20    561.752 ±   0.951  ops/s
>> ReadAllBytes.readHalfBytesFileInputStream   100000000  thrpt   20     45.043 ±   0.102  ops/s
>> ReadAllBytes.readHalfBytesFileInputStream  1000000000  thrpt   20      4.629 ±   0.035  ops/s
>
> Brian Burkhalter has updated the pull request incrementally with one additional commit since the last revision:
> 
>   8264777: Fix typo in error message

src/java.base/share/classes/java/io/FileInputStream.java line 289:

> 287:         }
> 288:         if (size <= 0L)
> 289:             return new byte[0];

Maybe the case where size <= 0L should also default to `return super.readAllBytes()`?

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

PR: https://git.openjdk.java.net/jdk/pull/3845