RFR 8170348: Appendable.appendN(char, int) method to append multiple copies of char

[Jason Mehrens]

Ivan,

Will java.util.StringJoiner be modified too?  I assume a nCopies char sequence object doesn't pan out performance wise?

Thanks,

Jason

________________________________________
From: core-libs-dev <core-libs-dev-bounces at openjdk.java.net> on behalf of Ivan Gerasimov <ivan.gerasimov at oracle.com>
Sent: Sunday, December 4, 2016 6:07 AM
To: core-libs-dev at openjdk.java.net
Subject: RFR 8170348: Appendable.appendN(char, int) method to append multiple   copies of char

Hello!

There are several places in JDK where the same character is appended to
a StringBuilder object multiple times (usually padding).
With each append there are a few routine checks performed.
They could have been done only once, if we had a method for appending
multiple copies at a time.
A simple benchmark shows that such method may save us a few machine
cycles (see the results below).

In the benchmark, three approaches were compared:
0) Using the new appendN(char, int) method to append several chars at once,
1) Calling append(char) in a loop,
2) Appending a prepared-in-advance string

On my machine, the new method demonstrates better or comparable
performance for all sizes up to 20.

In the webrev, there are two changesets included:
- the new default Appendable.appendN(char, int) method, its overrides in
StringBuilder/Buffer and a basic test,
- several applications of the new method across JDK.

Would you please help review?
Comments, suggestions are welcome.

BUGURL: https://bugs.openjdk.java.net/browse/JDK-8170348
WEBREV: http://cr.openjdk.java.net/~igerasim/8170348/00/webrev/
Benchmark: http://cr.openjdk.java.net/~igerasim/8170348/00/MyBenchmark.java


Benchmark                 (size)   Mode  Cnt Score          Error  Units
MyBenchmark.test_0_New         0  thrpt   70  331922128.215 ±
16399254.452  ops/s
MyBenchmark.test_0_New         1  thrpt   70  209207932.893 ±
14955800.231  ops/s
MyBenchmark.test_0_New         5  thrpt   70   72926671.621 ±
4841791.555  ops/s
MyBenchmark.test_0_New        10  thrpt   70   67779575.053 ±
3234366.239  ops/s
MyBenchmark.test_0_New        20  thrpt   70   59731629.661 ±
2769497.288  ops/s
MyBenchmark.test_1_Old         0  thrpt   70  333467628.860 ±
15981678.430  ops/s
MyBenchmark.test_1_Old         1  thrpt   70  156126381.967 ±
9619653.294  ops/s
MyBenchmark.test_1_Old         5  thrpt   70   46550204.382 ±
2009987.637  ops/s
MyBenchmark.test_1_Old        10  thrpt   70   23309297.849 ±
1268874.282  ops/s
MyBenchmark.test_1_Old        20  thrpt   70   13143637.821 ±
662265.103  ops/s
MyBenchmark.test_2_Solid       0  thrpt   70  138548108.540 ±
6408775.462  ops/s
MyBenchmark.test_2_Solid       1  thrpt   70   63890936.132 ±
3918274.970  ops/s
MyBenchmark.test_2_Solid       5  thrpt   70   65838879.075 ±
2701493.698  ops/s
MyBenchmark.test_2_Solid      10  thrpt   70   65387238.993 ±
3131562.548  ops/s
MyBenchmark.test_2_Solid      20  thrpt   70   57528150.828 ±
3171453.716  ops/s


With kind regards,
Ivan