RFC 8236988 - Modular Design for JVM Flags

[Ioi Lam]

The code for specifying HotSpot command-line flags used to be simple. At 
the very beginning it was something like

     #define ALL_FLAGS(develop, develop) \
        product(int, SomeFlag, def_value, "some doc") \
        develop(int, MoreFlag, def_value, "more doc") \

but like all good ideas, it has gradually degraded into a mess [1][2]. 
It's now very difficult to add any new functionality (e.g., add 
"manageable" annotations to the flags [3]).

I think it's time for a complete rewrite :-)

My proposal is here. Please comment if it's a good or bad idea.

https://wiki.openjdk.java.net/display/HotSpot/HotSpot+Command-Line+Flags+Overhaul+-+Design+Doc



tldr; ---


OLD:

   product(intx, AliasLevel, 3,                                          \
           "0 for no aliasing, 1 for oop/field/static/array split, 
"         \
           "2 for class split, 3 for unique 
instances")                      \
           range(0, 3) 
/*optional*/                                         \
           constraint(AliasLevelConstraintFunc,AfterErgo) /*optional*/   
     \


NEW:

   PRODUCT_FLAG(intx,   AliasLevel, 3, JVMFlag::RANGE | JVMFlag::CONSTRAINT,
                        "0 for no aliasing, 1 for oop/field/static/array 
split, "
                        "2 for class split, 3 for unique instances");
    // optional
    FLAG_RANGE(         AliasLevel, 0, 3);
    // optional
    FLAG_CONSTRAINT(    AliasLevel, (void*)AliasLevelConstraintFunc, 
JVMFlag::AfterErgo);




[1] 
http://hg.openjdk.java.net/jdk/jdk/file/7af6364e1792/src/hotspot/share/runtime/globals.hpp#l115
[2] 
http://hg.openjdk.java.net/jdk/jdk/file/7af6364e1792/src/hotspot/share/runtime/flags/jvmFlag.cpp#l635
[3] https://bugs.openjdk.java.net/browse/JDK-7123237

Thanks
- Ioi