JDK-8048093 : Explicitly setting := vs = in the -XX:+PrintFlagsFinal output
  • Type: Bug
  • Component: hotspot
  • Sub-Component: gc
  • Affected Version: 8
  • Priority: P3
  • Status: Resolved
  • Resolution: Fixed
  • Submitted: 2014-06-25
  • Updated: 2016-08-11
  • Resolved: 2016-07-12
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JDK 9
9 b131Fixed
Related Reports
Blocks :  
JDK-8024137 - Flags should be set using the proper macro
Blocks :  
JDK-8037283 - Flags should remember their cmd line state also if modified by ergonomics
Blocks :  
JDK-8012591 - Flags shown by jmap are not updated after argument processing and ergonomics handling
Description
The following convention seems to be broken:

If you explicitly specify a command line flag, you get ":=" instead of "=" in the -XX:+PrintFlagsFinal output: 

For example, 
    uintx MarkStackSize                            := 4194304       {product} 

The ":=" is also set if the value has been ergonomically decided. From PrintFlagsFinal there is no way to find out whether the flag has been set on command line or via ergonomics. 

Some GC argument processing code may not adhere to this, i.e. may set option values without influencing the output. There are a few bugs already filed for that: 

JDK-8024137
JDK-8012591
JDK-8037283