RFR(S): 8241638: launcher time metrics alway report 1 on Linux when _JAVA_LAUNCHER_DEBUG set(Internet mail)

[linzang(臧琳)]

Hi David, Henry, Alan,
    Thanks a lot for your review. 
    I have considered use clock_gettime() first, but I seached the code and found there is a marco SUPPORTS_CLOCK_MONOTONIC guard the usage of it. Which makes me think it may not be available under specific situation. So I choosed gettimeofday.  
   Do you think the patch need to be refined to remove HAVE_GETHRTIME as Alan suggested?  Thanks. 

BRs,
Lin

>On 2020/3/31, 8:05 AM, "David Holmes" <david.holmes at oracle.com> wrote:
>
>    On 31/03/2020 4:08 am, Henry Jen wrote:
>    > Based on my understanding to gethrtime(), the main benefit is not to be affected by settimeofday or adjtime. I think it is probably better to use
>    > 
>    > clock_gettime(CLOCK_MONOTONIC_RAW, ts);
>    > 
>    > which I checked seems to be available on both Linux and Mac. Haven’t test it though.
>    
>    Not guaranteed to be available - either clock_gettime function or that 
>    particular clock - at build time or runtime. We use a check in the build 
>    system to determine build-time availability for hotspot, and then use 
>    dl_lookup etc at runtime to determine if actually available. We should 
>    be able to get rid of this one day but we checked fairly recently and 
>    there were still some issues.
    
>    gettimeofday is a lot better than returning 1. Otherwise call into the 
>    VM and use JVM_NanoTime.
>    
>    Cheers,
>    David
>    -----
>    
>    > Cheers,
>    > Henry
>    > 
>    >> On Mar 30, 2020, at 1:37 AM, Alan Bateman <Alan.Bateman at oracle.com> wrote:
>    >>
>    >> On 30/03/2020 03:41, linzang(臧琳) wrote:
>    >>> Dear All,
>    >>>       May I ask your help to reivew this tiny patch? Thanks.
>    >>>
>    >>>
>    >>>
>    >>> BRs,
>    >>> Lin
>    >>>
>    >>> From: "linzang(臧琳)" <linzang at tencent.com>
>    >>> Date: Thursday, March 26, 2020 at 3:13 PM
>    >>> To: "core-libs-dev at openjdk.java.net" <core-libs-dev at openjdk.java.net>
>    >>> Subject: RFR(S): 8241638: launcher time metrics alway report 1 on Linux when _JAVA_LAUNCHER_DEBUG set
>    >>>
>    >>> Dear All,
>    >>> May I ask your help to review this tiny fix?
>    >>>      Bug: https://bugs.openjdk.java.net/browse/JDK-8241638
>    >>>      Webrev: http://cr.openjdk.java.net/~lzang/8241638/webrev01/
>    >>> Thanks!
>    >>>
>    >> Using gettimeofday on non-Solaris platforms seems reasonable here. The comment in the patch suggests Linux but it's other Unix builds too. Also just a minor nit that the code in java.base uses 4-space indent, not 2. Looking at the patch makes me wondering if we should remove HAVE_GETHRTIME as it seems to be only used on Solaris >and the launcher is already using #ifdef __solaris__ in several places. Henry, do you have any comments on this?
 >   >>
 >   >> -Alan
 >   >