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

[Chris Plummer]

[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
>>>
>>>
>>
>
>