RFR: 8254078: DataOutputStream is very slow post-disabling of Biased Locking [v6]

[Andrew Haley]

> DataOutputStream is very slow post-disabling of Biased Locking. This
> was discovered when benchmarking a transaction library, which showed
> significant performance loss when moving to JDK 15. WIth some small
> changes to DataOutputStream we can get the performance back. There's a
> JMH benchmark at
> http://cr.openjdk.java.net/~aph/JDK-8254078/jmh-tests.tar
> 
> Some Stream classes use very fine-grained locking.
> 
> In particular, writeInt is defined like this:
> 
>         out.write((v >>> 24) & 0xFF);
>         out.write((v >>> 16) & 0xFF);
>         out.write((v >>> 8) & 0xFF);
>         out.write((v >>> 0) & 0xFF);
>         incCount(4);
> 
> Unfortunately, ByteArrayOutputStream.write(byte) is defined like this:
> 
>     public synchronized void write(int b) {
>         ensureCapacity(count + 1);
>         buf[count] = (byte) b;
>         count += 1;
>     }
> 
> so we acquire and release a lock for every byte that is output.
> 
>  For example, writing 4kb of ints goes from 17.3 us/op to 53.9 us/op when biased locking is disabled:
> 
> 
> +UseBiasedLocking DataOutputStreamTest.dataOutputStreamOverByteArray avgt 6 53.895 ± 5.126 us/op
> -UseBiasedLocking DataOutputStreamTest.dataOutputStreamOverByteArray avgt 6 17.291 ± 4.430 us/op
> 
> There are refactorings of DataOutputStream we can do to mitigate this.

Andrew Haley has updated the pull request incrementally with one additional commit since the last revision:

  8254078: DataOutputStream is very slow post-disabling of Biased Locking

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/542/files
  - new: https://git.openjdk.java.net/jdk/pull/542/files/43be1998..cd1d5a0a

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=542&range=05
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=542&range=04-05

  Stats: 18 lines in 2 files changed: 0 ins; 6 del; 12 mod
  Patch: https://git.openjdk.java.net/jdk/pull/542.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/542/head:pull/542

PR: https://git.openjdk.java.net/jdk/pull/542