RFR: 8048093 - Explicitly setting := vs = in the -XX:+PrintFlagsFinal output

[Daniel D. Daugherty]

Would it be useful to distinguish which "bucket" the VM option came from?
We have the "-XX:Flags=<path>" option , the JAVA_TOOL_OPTIONS env var, the
_JAVA_OPTIONS env var, the JNI invocation cmd line (from the launcher),
and the new "-XX:VMOptionsFile=<path>" option. With this dizzying array
of sources for VM options, it might be useful to have a way to report
which bucket provided the "last one wins" value...

Sorry if this would muddy the waters too much...

Dan



On 6/21/16 1:09 PM, Jesper Wilhelmsson wrote:
> Hi,
>
> Please review this change to make -XX:+PrintFlagsFinal distinguish 
> between flags changed on the command line and flags changed by the 
> ergonomics.
>
> To enable us to remember if a flag was set on the command line or not 
> after having been changed by the ergonomics I use another bit in the 
> Flag struct.
>
> The actual symbols printed by PrintFlagsFinal are chosen somewhat 
> arbitrary and I'm open to suggestions (bike sheding) about how to 
> visualize this the best.
>
> The old decorations are:
>
> ' =' - Default value (no decoration)
> ':=' - Value was changed, either by command line or ergonomics or other
>
> The new decorations are:
>
> ' =' - Default value (no decoration)
> ':=' - Set on the command line
> '?=' - Changed by the ergonomics
> '!=' - Set on the command line AND changed by the ergonomics
> '-=' - Any other origin, like changed by management API or taken from 
> a config file
>
> My reasoning behind selecting these characters are that ':=' looks 
> like a solid assignment and will therefore represent the command line. 
> You never know what you get from the ergonomics, so '?=' seems 
> appropriate. '!=' because you'd want to know that the ergonomics 
> changed a value you had set on the command line.
>
> Another option could be to use a colon ':=' for the command line, and 
> a comma ',=' for the ergonomics. That would naturally give us the 
> semi-colon ';=' for something set on the command line and changed by 
> the ergonomics. I didn't go with this because the colon and semi-colon 
> can be hard to distinguish from each other.
>
> As mentioned above there are other origins, the enum contains eight 
> values. There is no mention of the other types in the bug and there 
> are no is_...() for the other types in globals.cpp, so they didn't 
> seem as important. If the general opinion is that these other origins 
> are as important, or we might as well..., I'd suggest that we use 
> letters as decorations. Let me know if you have an opinion.
>
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8048093
> Webrev: http://cr.openjdk.java.net/~jwilhelm/8048093/webrev.00/
>
> Thanks,
> /Jesper