RFR: 8224878: Use JVMFlag parameters instead of name strings

[Stefan Karlsson]

And here's the webrev:
  http://cr.openjdk.java.net/~stefank/8224878/webrev.01/

Thanks,
StefanK

On 2019-05-28 13:35, Stefan Karlsson wrote:
> Hi all,
> 
> Please review this patch to use JVMFlag parameters instead of name 
> strings in the JVM flag handling code.
> 
> https://bugs.openjdk.java.net/browse/JDK-8224878
> 
> The intention is to reduce the places where the API uses "const char* 
> name" parameters to describe a JVM flag, and instead use a JVMFlag* when 
> performing various flag handling code. The places where we translate 
> from "const char* name" to JVMFlag* has been pushed to the outer layers 
> of the code, which explicitly uses the JVMFlag::find_flag functions.
> 
> This allows us to replace strcmp with simple JVMFlag pointer equality 
> checks in jvmFlagRangeList.cpp and jvmFlagConstraintList.cpp.
> 
> This gets rid of the need to store a typed pointer to the flag in 
> jvmFlagRangeList.cpp and jvmFlagConstraintList.cpp.
> 
> This gets rid of the the need to propagate the 'allow_locked' and 
> 'return_flag' parameters down the call chain. For example, see the 
> changes to JVMFlag::<type>At and JVMFlag::<type>AtPut:
> -  static JVMFlag::Error intAt(const char* name, int* value, bool 
> allow_locked = false, bool return_flag = false)      { return 
> intAt(name, strlen(name), value, allow_locked, return_flag); }
> +  static JVMFlag::Error intAt(const JVMFlag* flag, int* value);
>    static JVMFlag::Error intAtPut(JVMFlag* flag, int* value, 
> JVMFlag::Flags origin);
> -  static JVMFlag::Error intAtPut(const char* name, size_t len, int* 
> value, JVMFlag::Flags origin);
> -  static JVMFlag::Error intAtPut(const char* name, int* value, 
> JVMFlag::Flags origin)   { return intAtPut(name, strlen(name), value, 
> origin); }
> 
>   It changes the JVMFlag::find_flag API. The way it uses default values 
> have a surprising effect for users of those functions. find_flag(name) 
> searches among all flags (even locked and constants), while 
> find_flag(name, strlen(name)) doesn't return locked or constants flags. 
> To make it less likely to accidentally call the wrong version, this has 
> been changed to the following:
> * JVMFlag::find_flag(name) - Fetches the flag if it is available 
> (unlocked and not constant).
> * JVMFlag::find_flag_unrestricted(name) - Fetches the flag even if it is 
> locked or a constant.
> 
> Removed the unused JVMFlag::wasSetOnCmdline.
> 
> Small cleanups
> - Renamed address_of_flag to flag_from_enum
> - Renamed local JVMFlag* variable from results to flag
> - Use initializer lists
> - Removed superfluous semicolons
> 
> I don't mind splitting patch up into more than one RFE, if that seems 
> more appropriate.
> 
> Tested with:
> - test/hotspot/jtreg/runtime/CommandLine
> - tier1 (tier2-3 80% done)
> 
> Suggestions on other testing is appreciated.
> 
> Thanks,
> StefanK