RFR: 8215412: Optimize PrintStream.println methods

[Roger Riggs]

Hi Claes,

611: Can't the loop break after finding the first \n?

916: I'd probably call writeln(String.valueOf(x)) and skip the extra 
method call.

Is there any benefit of doing the String conversions before the 
synchronized block?
As is in the old code for println(Object x).
There isn't much contention I expect so it's probably a benefit, 
(compared to easy to read code).

Thanks, Roger


On 12/14/2018 12:12 PM, Claes Redestad wrote:
> Hi,
>
>  the various PrintStream.println methods are inefficient: nested
> synchronization, multiple flushes and a scan of the input string for
> newlines that in the end is pointless in this context since newLine will
> always flush anyway (if autoflush is enabled).
>
>  While performance of printing to console/file is likely to be
> dominated by the I/O overheads, there are plenty of simple text
> processing applications using stdout to pipe output to another process
> for which performance of println could definitely matter.
>
> Webrev: http://cr.openjdk.java.net/~redestad/8215412/jdk.00/
> Bug: https://bugs.openjdk.java.net/browse/JDK-8215412
>
> Using a simple test program like this:
>
> public class Test {
>   public static void main (String ... args) {
>     for (int i = 0; i < Integer.parseInt(args[0]); i++)
>       System.out.println(args[1]);
>   }
> }
>
> ... and stating the cost of running:
>
> $ java Test 100000 tttttttttttttttttttttttttttttttttttttttttttttt | wc -l
>
> ... I get a 15-30% reduction in cycles and wall clock time (larger
> reduction the more output is produced).
>
> Thanks!
>
> /Claes