[Bug classpath/44411] New: System.nanoTime() is not independent of wall-clock time

[adamb at videx dot com]

On Linux, Classpath appears to implement the System.nanoTime() function using
the gettimeofday function (see java_lang_VMSystem.c).  Since gettimeofday
returns a wall-clock time this makes it unreliable for measuring elapsed time,
(because the system clock could be changed by another process at any moment.

According to the Sun javadocs:

    ... This method can only be used to measure elapsed time and is not
    related to any other notion of system or wall-clock time. The
    value returned represents nanoseconds since some fixed but
    arbitrary time ...

In short, gettimeofday is not appropriate for measuring elapsed time.  Perhaps
the clock_gettime function would work
(http://www.tin.org/bin/man.cgi?section=3&topic=clock_gettime) or the getrusage
function.


-- 
           Summary: System.nanoTime() is not independent of wall-clock time
           Product: classpath
           Version: 0.98
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: classpath
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: adamb at videx dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44411