hotspot.log overlapping log statements (JITWatch)

[David Holmes]

Hi Chris,

If all the trace/logging output is directed to the default output stream 
(or the same file) then they will be intermixed. Fixing this would be 
non-trivial due to the need for explicit locking around compound 
trace/logging statements; and locking in tracing/log output can itself 
be problematic.

Using different log files where possible would assist, but then you have 
no temporal relationship between the different entries.

David

On 21/02/2014 7:46 AM, Chris Newland wrote:
> 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
>
>
>
>