Proposal for a small language change

[Mark Thornton]

Angelo Borsotti wrote:
> Author: Angelo Borsotti, former Senior Director Software Technology,
> Alcatel-Lucent Optics
>
> Overview
>   Feature Summary: fast and accurate measurement of execution time
>   Major Advantage: optimization of algorithms by measuring execution
>       times of small snippets of code executed many times
>   Major Benefit: greatly increases observability of programs
>   Major Disadvantage: very little cost
>   Alternatives: there are no alternatives
>
> Examples:
>
>   Simple example:
>        long c0 = System.cycles();
>        i++;
>        long c = System.cycles() - c0;
>   Advanced example:
>        long cycles = 0;
>        for (int i = 0; i < bound; i++){
>           ...
>           long c0 = System.cycles();
>           some statements
>           cycles += System.cycles()- c0;
>        }
>
>   
As Joe has said the proposal period is over and this proposal doesn't 
need a language change.

The existing System.nanoTime() method could be implemented using CPU 
cycle counters. However there are significant problems on multi-core or 
multi-processor systems and where power management is in use. Some 
systems don't keep the cycle counters synchronized across CPUs, so if a 
thread is migrated from one CPU to another the computed elapsed cycle 
time is not reliable.

Some interesting information on timing can be found here:

http://blogs.sun.com/dholmes/entry/inside_the_hotspot_vm_clocks

Mark Thornton