Obtaining methods executed at least once?

[Krystal Mok]

Hi Andreas,

There are a couple of ways off the top of my head. Their viability depends
on the original purpose of getting the list of executed methods.

HotSpot keeps the invocation count (at least in the interpreter) for all
Java methods. It may not be precise, because it'll decay periodically, or
it may be set to certain values for triggering standard compilation, etc.
But if you only care about zero and non-zero, this counter would be
sufficient.

The problem is: how to get the list of invoked methods?
There's no flag within the VM that I'm aware of that would print the list
of invoked methods, unfortunately.

You could try the Serviceability Agent. See this example that I just made:
https://gist.github.com/2710667#file_print_invoked_methods.java

It can attach to your target Java process, and extract all invoked methods.

Caveat:

1. If you're on JDK6, you may need to include these two VM flags in your
target Java application:
-XX:-UseFastEmptyMethods -XX:-UseFastAccessorMethods
Otherwise empty methods and accessor methods will not show up in the list,
because the "fast" version doesn't increment the invocation counter for
these methods.
In JDK7 these two flags default to false, so you don't have to bother
setting them to false explicitly.

2. If any of your classes are unloaded when you use this tool, then their
methods won't show up in the output.

3. If you'd like the list to be printed before process exit, then an easy
way to do this is to set up a shutdown hook with a Java agent, and make
this hook run the tool above (in a new process). You may miss some methods
that are only run in the shutdown hook, but I guess that's an acceptable
tradeoff.

- Kris

On Wed, May 16, 2012 at 6:11 PM, David Holmes <david.holmes at oracle.com>wrote:

> Andreas,
>
> I've cc'd this to hotspot-dev which is the right place to ask.
>
> Please drop the discuss list from further replies.
>
> David
>
> On 16/05/2012 6:56 PM, Andreas Sewe wrote:
>
>> Hi all,
>>
>> I hope this is the right mailing list to ask such questions (if not,
>> please point me to the right one), as I couldn't find an obvious
>> analogue to lists like jikesrvm-researchers.
>>
>> Is the a way (preferably using "diagnostic" rather than "develop"
>> options) to obtain a list of all methods executed at least once?
>> Currently I am considering "-XX:-UseInterpreter -XX:+LogCompilation",
>> but this seems to be an awfully indirect way to achieve my goal -- and
>> it may not even give correct results if the only call of m() is inlined
>> during compilation.
>>
>> Any help is greatly appreciated.
>>
>> Best wishes,
>>
>> Andreas
>>
>
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