RFR(S): 8191049: Add alternate version of pns() that is callable from within hotspot source

[Chris Plummer]

Thanks Jerry!

On 11/14/17 12:57 PM, Gerald Thornbrugh wrote:
> Hi Chris,
>
> Your changes look good to me.
>
> Jerry
>
>> On Nov 14, 2017, at 1:44 PM, Chris Plummer <chris.plummer at oracle.com> wrote:
>>
>> [Resending. Didn't seem to get posted first time.]
>>
>> Hi Thomas,
>>
>> Thanks for the review.
>>
>> Can I get one more reviewer please?
>>
>> thanks,
>>
>> Chris
>>
>> On 11/10/17 11:35 PM, Thomas Stüfe wrote:
>>> Oh, you are right, I should have seen this. Knowing this, forget my worries about stability. Sorry for the noise :)
>>>
>>> ..Thomas
>>>
>>> On Fri, Nov 10, 2017 at 11:47 PM, Chris Plummer <chris.plummer at oracle.com <mailto:chris.plummer at oracle.com>> wrote:
>>>
>>>     It's already restricted to non-product builds, but I'll add a
>>>     comment also.
>>>
>>>     thanks,
>>>
>>>     Chris
>>>
>>>
>>>     On 11/10/17 1:27 PM, Thomas Stüfe wrote:
>>>>     Hi Chris,
>>>>
>>>>     Thank you. Yes, a comment may make sense, and/or restricting this
>>>>     function to not product. Otherwise the change is fine and useful,
>>>>     I’ll use it probably before long.
>>>>
>>>>     Thanks, Thomas
>>>>
>>>>     On Fri 10. Nov 2017 at 21:55, Chris Plummer
>>>>     <chris.plummer at oracle.com <mailto:chris.plummer at oracle.com>> wrote:
>>>>
>>>>         Hi Thomas,
>>>>
>>>>         There's certainly no intent to leave in place any calls
>>>>         someone might add to pns2(). It's meant as a temporary
>>>>         debugging aide only. So if it were to fail for any reason,
>>>>         IMO that's no different than adding any other sort of
>>>>         temporary debugging code that could possibly crash. You fix
>>>>         your mistake and resume your debugging. If you want I can add
>>>>         comments that include such a warning.
>>>>
>>>>         thanks,
>>>>
>>>>         Chris
>>>>
>>>>
>>>>
>>>>         On 11/10/17 12:11 AM, Thomas Stüfe wrote:
>>>>>         Hi Chris,
>>>>>
>>>>>         looks fine as a debugging aid.
>>>>>
>>>>>         But it occurred to me that it may be a bit dangerous to call
>>>>>         this from non-errorhandler settings. I recall seeing quite a
>>>>>         few secondary crashes in VMError::print_native_stack() in
>>>>>         hs-err files over time. Especially for native non-java
>>>>>         threads. Usually this did not matter that much because these
>>>>>         crashes are handled by secondary error handling when
>>>>>         printing the hs-err file. But if we call it outside of error
>>>>>         handling, we are on our own.
>>>>>
>>>>>         So. IMHO, to use this functions as a debugging aid is fine,
>>>>>         if one can accept a slight risk of crashing the VM. If this
>>>>>         is not acceptable, may we need some more tests for this
>>>>>         function?
>>>>>
>>>>>         Kind Regards, Thomas
>>>>>
>>>>>
>>>>>
>>>>>         On Thu, Nov 9, 2017 at 9:29 PM, Chris Plummer
>>>>>         <chris.plummer at oracle.com <mailto:chris.plummer at oracle.com>>
>>>>>         wrote:
>>>>>
>>>>>             Hi,
>>>>>
>>>>>             Please review the following:
>>>>>
>>>>>             https://bugs.openjdk.java.net/browse/JDK-8191049
>>>>>             <https://bugs.openjdk.java.net/browse/JDK-8191049>
>>>>>
>>>>>             diff --git a/src/hotspot/share/utilities/debug.cpp
>>>>>             b/src/hotspot/share/utilities/debug.cpp
>>>>>             --- a/src/hotspot/share/utilities/debug.cpp
>>>>>             +++ b/src/hotspot/share/utilities/debug.cpp
>>>>>             @@ -631,6 +631,24 @@
>>>>>                VMError::print_native_stack(tty, fr, t, buf,
>>>>>             sizeof(buf));
>>>>>              }
>>>>>
>>>>>             +//
>>>>>             +// This version of pns() will not work when called from
>>>>>             the debugger, but is
>>>>>             +// useful when called from within hotspot code. The
>>>>>             advantages over pns()
>>>>>             +// are not having to pass in any arguments, and it will
>>>>>             work on Windows/x64.
>>>>>             +//
>>>>>             +extern "C" void pns2() { // print native stack
>>>>>             +  Command c("pns2");
>>>>>             +  static char buf[O_BUFLEN];
>>>>>             +  if (os::platform_print_native_stack(tty, NULL, buf,
>>>>>             sizeof(buf))) {
>>>>>             +    // We have printed the native stack in
>>>>>             platform-specific code,
>>>>>             +    // so nothing else to do in this case.
>>>>>             +  } else {
>>>>>             +    Thread* t = Thread::current_or_null();
>>>>>             +    frame fr = os::current_frame();
>>>>>             + VMError::print_native_stack(tty, fr, t, buf, sizeof(buf));
>>>>>             +  }
>>>>>             +}
>>>>>             +
>>>>>              #endif // !PRODUCT
>>>>>
>>>>>             There is also a pre-existing thread with some discussion:
>>>>>
>>>>>             http://mail.openjdk.java.net/pipermail/hotspot-runtime-dev/2017-November/025134.html
>>>>>             <http://mail.openjdk.java.net/pipermail/hotspot-runtime-dev/2017-November/025134.html>
>>>>>
>>>>>             thanks,
>>>>>
>>>>>             Chris
>>>>>
>>>>>
>>>
>>