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

[Coleen Phillimore]

I agree with Vladimir.  There's no way I'm going to remember that a 
colon mean that the value was changed.
Coleen


On 6/21/16 4:15 PM, Vladimir Kozlov wrote:
> Nobody will remember the meaning of such marking. You should use 
> normal words.
> The output already have flag's type as, for example, "{C2 product}". 
> You can add an other word there to indicate type of initialization: 
> default|command|ergo.
>
> Thanks,
> Vladimir
>
> On 6/21/16 12:09 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