hotspot.log overlapping log statements (JITWatch)

[Chris Newland]

Hi all,

I've written a visualiser/analyser for the hotspot.log JIT compilation log
called JITWatch[1] and I'm encountering problems with log statements from
various parts of the VM/HotSpot overlapping and producing garbled output
in hotspot.log[2].

For example, if I combine the VM switches

-XX:+UnlockDiagnosticVMOptions
-XX:+TraceClassLoading
-XX:+LogCompilation
-XX:+PrintAssembly

then I get overlap between classloading statements, log compilation XML,
and disassembled native code:

Decoding compiled method 0x009dfec8:
Code:
[Entry Point]
[Constants]
  # {method} 'hashCode' '()I' in 'java/lang/String'
  #           [sp+0x20]  (sp of caller)
  0x009dffc0: nop
  0x009dffc1: nop
  0x009dffc2: nop
<writer thread='3340'/>            <-- assembly interrupted by XML
[Loaded java.lang.Enum             <-- assembly interrupted by classloader
<writer thread='2660'/>

  0x009dffc3: nop
  0x009dffc4: nop
  0x009dffc5:
<writer thread='3340'/>
 from shared objects file]
<writer thread='2660'/>
nop
  0x009dffc6: nop

I couldn't find this in the Oracle or OpenJDK bug trackers and was
wondering if this is a known problem and if it is fixable?

It seems to happen fairly infrequently but means that JITWatch can't parse
the compilation information when the garbling occurs.

Thanks for any pointers you can give me.

Kind regards,

Chris
@chriswhocodes

[1] https://github.com/AdoptOpenJDK/jitwatch/wiki
[2] https://github.com/AdoptOpenJDK/jitwatch/issues/3