[lttng-dev] Questions about JUL (was: Re: lttng-dev Digest, Vol 67, Issue 48)

[Daniel.Thibault@drdc-rddc.gc.ca (Thibault, Daniel)]

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Date: Tue, 4 Feb 2014 12:17:36 -0500
From: David Goulet <dgoulet@efficios.com>
To: Jim Dumont <jim.dumont at ericsson.com>
Cc: "lttng-dev at lists.lttng.org" <lttng-dev at lists.lttng.org>

>> 3) add-context: does --jul have the same possible context types as --userspace (i.e. ip, pthread_id, procname, vpid, vtid)?
>
> Nope.

   What are the possible context types then?  Or is it just that you can't apply a filter to a jul event?

>> 4) enable-channel:
>> 4.1) Are the --jul --subbuf-size, --num-subbuf and --read-timer defaults the same as with --userspace?
>
> Nope. JUL uses it's internal channel so basically enable channel does NOT support the jul domain thus not having -j in the help/man.

   So you turn jul events on and off using enable/disable-event --all instead?  This is getting a tad confusing: jul events force you to use only enable/disable-event but kernel syscalls force you to use only enable/disable-channel...

>> 4.4) If yes, won't they all degenerate to the virtual machine's user and process IDs?
>
> Not sure I understand this one?

   A Java application is interpreted and runs in a Java virtual machine (JVM).  The userID and processID of any jul events are thus likely to be those of the JVM process.  I would expect Java apps launched by separate users to launch separate JVM instances, but I would also expect two separate Java apps launched by the same user to share a single JVM (the user's) and, therefore, their process IDs.  This could get fun with multi-threaded Java apps.

> Now after answering all this, I feel like either creating a lttng-jul man page or adding a special section in "lttng.1" for the JUL domain explaining all this. Thoughts?

   We definitely need an additional section in "lttng.1".

Daniel U. Thibault
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