this is minor optimization following JDK-8254078.
based on my tests with jmh, it has better performance when apply following
patch:
diff --git a/src/java.base/share/classes/java/io/DataOutputStream.java
b/src/java.base/share/classes/java/io/DataOutputStream.java
index 9a9a687403c..4ea497fc7c0 100644
--- a/src/java.base/share/classes/java/io/DataOutputStream.java
+++ b/src/java.base/share/classes/java/io/DataOutputStream.java
@@ -300,8 +300,9 @@ public class DataOutputStream extends FilterOutputStream
implements DataOutput {
int len = s.length();
for (int i = 0 ; i < len ; i++) {
int v = s.charAt(i);
- out.write((v >>> 8) & 0xFF);
- out.write((v >>> 0) & 0xFF);
+ writeBuffer[0] = (byte)(v >>> 8);
+ writeBuffer[1] = (byte)(v >>> 0);
+ out.write(writeBuffer, 0, 2);
}
incCount(len * 2);
}
Basically, it has better performance when apply above patch:
// without writeChars optimization patch, (-XX:-UseBiasedLocking)
Benchmark (basicType) (size) Mode Cnt Score Error Units
DataOutputStreamTest.dataOutputStreamOverBufferedFileStream STRING 4096 avgt 6
115.208 ± 0.327 us/op
DataOutputStreamTest.dataOutputStreamOverByteArray STRING 4096 avgt 6 276.795 ±
0.449 us/op
DataOutputStreamTest.dataOutputStreamOverRawFileStream STRING 4096 avgt 6
12356.969 ± 22.427 us/op
// with writeChars optimization patch, (-XX:-UseBiasedLocking)
Benchmark (basicType) (size) Mode Cnt Score Error Units
DataOutputStreamTest.dataOutputStreamOverBufferedFileStream STRING 4096 avgt 6
133.706 ± 0.274 us/op
DataOutputStreamTest.dataOutputStreamOverByteArray STRING 4096 avgt 6 130.979 ±
0.155 us/op
DataOutputStreamTest.dataOutputStreamOverRawFileStream STRING 4096 avgt 6
6814.272 ± 52.770 us/op
// without writeChars optimization patch, (-XX:+UseBiasedLocking)
Benchmark (basicType) (size) Mode Cnt Score Error Units
DataOutputStreamTest.dataOutputStreamOverBufferedFileStream STRING 4096 avgt 6
130.367 ± 8.759 us/op
DataOutputStreamTest.dataOutputStreamOverByteArray STRING 4096 avgt 6 37.559 ±
0.059 us/op
DataOutputStreamTest.dataOutputStreamOverRawFileStream STRING 4096 avgt 6
12385.030 ± 376.560 us/op
// with writeChars optimization patch, (-XX:+UseBiasedLocking)
Benchmark (basicType) (size) Mode Cnt Score Error Units
DataOutputStreamTest.dataOutputStreamOverBufferedFileStream STRING 4096 avgt 6
45.494 ± 7.018 us/op
DataOutputStreamTest.dataOutputStreamOverByteArray STRING 4096 avgt 6 33.015 ±
0.349 us/op
DataOutputStreamTest.dataOutputStreamOverRawFileStream STRING 4096 avgt 6
6845.549 ± 38.712 us/op
-------------
Commit messages:
- JDK-8260273: DataOutputStream writeChars optimization
Changes: https://git.openjdk.java.net/jdk/pull/2190/files
Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2190&range=00
Issue: https://bugs.openjdk.java.net/browse/JDK-8260273
Stats: 4 lines in 2 files changed: 1 ins; 0 del; 3 mod
Patch: https://git.openjdk.java.net/jdk/pull/2190.diff
Fetch: git fetch https://git.openjdk.java.net/jdk pull/2190/head:pull/2190
PR: https://git.openjdk.java.net/jdk/pull/2190
