You're welcome Ruoxiang!
On 2023-08-10 22:50, LI Ruoxiang wrote:
HiErica,
Thank you for your kind help.
It works for my case.
Best,
Ruoxiang
*From: *Erica Bugden <ebug...@efficios.com>
*Date: *Wednesday, August 9, 2023 at 05:29
*To: *LI Ruoxiang <ruoxiang...@my.cityu.edu.hk>,
lttng-dev@lists.lttng.org <lttng-dev@lists.lttng.org>
*Subject: *[Ext] Re: How to use lttng-live plugin with babeltrace2
python api for live LTTng trace reading?
*CAUTION: External email. Do not reply, click on links or open
attachments unless you recognize the sender and know the content is safe. *
Hello Ruoxiang!
Thank you for your question. It's true that there are no Python bindings
examples specific to lttng live (we've provided a brief example below).
Unfortunately, the python bindings documentation is currently
incomplete, but information about using lttng live can be pieced
together using the various documentation links below (see Useful Links
section).
Some adjustments typically needed when using lttng live and the Python
bindings are:
- When referring to a trace source, use a URL (e.g.
net://localhost/host/luna/my-session) rather than a file path (e.g.
/path/to/trace)
- When querying, use the source.ctf.lttng-live component class (rather
than the file system class: source.ctf.fs) - source.ctf.lttng-live docs
https://babeltrace.org/docs/v2.0/man7/babeltrace2-source.ctf.lttng-live.7/ <https://babeltrace.org/docs/v2.0/man7/babeltrace2-source.ctf.lttng-live.7/>
Hope this helps!
Best,
Erica
----
Useful links
- Python bindings docs (Installation, Examples) -
https://babeltrace.org/docs/v2.0/python/bt2/index.html
<https://babeltrace.org/docs/v2.0/python/bt2/index.html>
- LTTng live, General information -
https://lttng.org/docs/v2.13/#doc-lttng-live
<https://lttng.org/docs/v2.13/#doc-lttng-live> (e.g. How to express a
live trace source: net://localhost/host/HOSTNAME/my-session)
- source.ctf.lttng-live component -
https://babeltrace.org/docs/v2.0/man7/babeltrace2-source.ctf.lttng-live.7/ <https://babeltrace.org/docs/v2.0/man7/babeltrace2-source.ctf.lttng-live.7/> (C API doc not Python, but can be used to adapt the source.ctf.fs examples by comparing)
----
Quick Example: Trace reading with python bindings and lttng live
Note: This is a local example where the tracing and reading with
babeltrace are happening on the same machine (luna).
1. REQUIREMENTS
Make sure babeltrace is installed with the python plugins and python
bindings: https://babeltrace.org/docs/v2.0/python/bt2/installation.html
<https://babeltrace.org/docs/v2.0/python/bt2/installation.html>
2. PROCEDURE
- Start root session daemon: $sudo lttng-sessiond --daemonize
- Create live session: $lttng create my-session --live
- Enable events: $lttng enable-event --kernel
sched_switch,sched_process_fork
- Start tracing: $lttng start
- Run python script: (see below) $python3 lttng-live.py
3. PYTHON SCRIPT
File name: lttng-live.py
File contents:
import bt2
import time
msg_iter =
bt2.TraceCollectionMessageIterator('net://localhost/host/luna/my-session') # The hostname (i.e. machine name) is 'luna'
while True:
try:
for msg in msg_iter:
if type(msg) is bt2._EventMessageConst:
print(msg.event.name)
except bt2.TryAgain:
print('Try again. The iterator has no events to provide
right now.')
time.sleep(0.5)
Reading trace data using the bt2.TraceCollectionMessageIterator and
lttng-live: When using the message iterator with live, the iterator
never ends by default and can be polled for trace data infinitely (hence
the while loop in the example). When there is available data, the
iterator will return it. However, there will not always be data
available to consume. When this is the case, the iterator returns a "Try
again" exception which must be caught in order to continue polling.
4. OUTPUT SNIPPET (Example)
erica@luna:~$ python3 lttng-live-example.py
Try again. The iterator has no events to provide right now.
Try again. The iterator has no events to provide right now.
Try again. The iterator has no events to provide right now.
Try again. The iterator has no events to provide right now.
Try again. The iterator has no events to provide right now.
sched_switch
sched_switch
sched_switch
sched_switch
sched_process_fork
sched_switch
sched_switch
sched_switch
sched_switch
sched_switch
sched_switch
sched_switch
sched_switch
sched_switch
sched_switch
sched_switch
sched_switch
sched_switch
[...]
------------------------------------------------------------------------
*From:*lttng-dev <lttng-dev-boun...@lists.lttng.org> on behalf of LI
Ruoxiang via lttng-dev <lttng-dev@lists.lttng.org>
*Sent:* August 3, 2023 12:44 PM
*To:* lttng-dev@lists.lttng.org <lttng-dev@lists.lttng.org>
*Subject:* [lttng-dev] How to use lttng-live plugin with babeltrace2
python api for live LTTng trace reading?
Hi there,
I am currently involved in a project on designing a Python program for
LTTng trace data analysis online. The following figure illustrates the
program with a live trace data reader using babeltrace2 Python bindings
(the yellow box) connected to the LTTng relay daemon. The program will
read (such as periodically)the trace data from the relay daemon and then
process them while the LLTng keeps tracing. The above “read” and
“process” phases repeat in a loop.
After reading the babeltrace2 documents, examples, and some source code,
I found the lttng-live plugin may be an option for reading trace data
from LTTng relay daemon. However, I didn't find any examples for using
lttng-live plugin with babeltrace2 Python bindings. And I wonder if the
Python bindings support the mentioned live LTTng trace reading for my
case. Is it possible to receive any examples about the usage of
babeltrace2’s live reading, if any?
Thank you.
Best,
Ruoxiang Li
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