On 13/01/2015 3:10 PM, David Holmes wrote:
> Hi Dmitry,
>
> Short version: okay but I'm going to file a bug to have sun.misc.Perf
> fixed properly.
>
> Long version ... read below :)
>
> Thanks,
> David
>
> On 12/01/2015 11:49 PM, Dmitry Samersoff wrote:
>> Hi Everybody,
>>
>> Please review the fix.
>>
>> http://cr.openjdk.java.net/~dsamersoff/JDK-7076820/webrev.01/
>>
>> The fix explicitly checks for UsePerfData and if it's false make
>> Perf:detach a NOP.
>
> That sidesteps the assertion failure but there is a bigger semantic
> issue here I think - which is why the bug has remained open for so long.
> UsePerfData can disable a part of the backend of the "perf"
> functionality used via sun.misc.Perf, but sun.misc.Perf is completely
> oblivious to that. It isn't even really clear what UsePerfData pertains
> to. It impacts PerfMemory turning a number of methods into no-ops - but
> it doesn't turn PerfMemory::attach nor PerfMemory::detach into no-ops.
> What is a no-op is the initialization of PerfMemory (perfMemory_init)
> during VM startup, and also the teardown (perfMemory_exit) during VM
> shutdown (via at_exit handler). So the VM responds to the -UsePerfData
> flag (in part) by not initializing the PerfMemory subsystem, but the
> PerfMemory public apis are still enabled and invoked from the JDK code.
> That doesn't make sense to me - we should fail to attach and in doing so
> not put in place the Cleaner code that will attempt the detach. But
> sun.misc.Perf doesn't understand that anything can fail. :(