[lttng-dev] babeltrace2 python api related question

[蛋丁]

It works, thank you for helping out!!!







At 2022-08-16 04:29:51, "Philippe Proulx" <eeppeliteloop at gmail.com> wrote:

>On Sun, Aug 14, 2022 at 4:48 AM zenan <dantefu9001 at 163.com> wrote:
>>
>> In command line, I use “babeltrace2 net://somehost/some-session” to read live lttng session trace, and I want to use python bindings to do the same, is it possible?
>>
>> here is my code:
>
>Almost there.
>
>Some `src.ctf.lttng-live` component and message iterator methods may
>return a "try again" status code (I don't remember exactly under which
>circumstances). This propagates to bt_graph_run() [1] (in C) eventually
>which itself returns `BT_GRAPH_RUN_STATUS_AGAIN`. The Python
>bt2.Graph.run() method translates this status code to throwing
>`bt2.TryAgain`.
>
>Just catch those `bt2.TryAgain`, wait a bit, and call `graph.run()`
>again:
>
>    # Run the trace processing graph.
>    while True:
>        try:
>            graph.run()
>        except bt2.TryAgain:
>            time.sleep(.1)
>
>Works for me.
>
>If you ever need to access the messages themselves instead of forwarding
>them to a `sink.text.pretty` component, then use a
>`bt2.TraceCollectionMessageIterator` instance [2].
>
>Hope it helps,
>
>Phil
>
>[1]: https://babeltrace.org/docs/v2.0/libbabeltrace2/group__api-graph.html#gad2e1c1ab20d1400af1b552e70b3d567c
>[2]: https://babeltrace.org/docs/v2.0/python/bt2/examples.html#iterate-trace-events
>
>>
>> import bt2
>> import sys
>>
>> # Create an empty graph.
>> graph = bt2.Graph()
>>
>> # Add a `source.text.dmesg` component.
>> #
>> # graph.add_component() returns the created and added component.
>> #
>> # Such a component reads Linux kernel ring buffer messages (see
>> # `dmesg(1)`) from the standard input and creates corresponding event
>> # messages. See `babeltrace2-source.text.dmesg(7)`.
>> #
>> # `my source` is the unique name of this component within `graph`.
>>
>> # the original source code here in the example is:
>> # comp_cls = bt2.find_plugin('text').source_component_classes['dmesg']
>> # src_comp = graph.add_component(comp_cls,'my source')
>> comp_cls = bt2.find_plugin('ctf').source_component_classes['lttng-live']
>> src_comp = graph.add_component(comp_cls, 'my source', params = {
>> 'inputs': [sys.argv[1]],
>> })
>>
>> # Add a `sink.text.pretty` component.
>> #
>> # Such a component pretty-prints event messages on the standard output
>> # (one message per line). See `babeltrace2-sink.text.pretty(7)`.
>> #
>> # The `babeltrace2 convert` CLI command uses a `sink.text.pretty`
>> # sink component by default.
>> comp_cls = bt2.find_plugin('text').sink_component_classes['pretty']
>> sink_comp = graph.add_component(comp_cls, 'my sink')
>>
>> # Connect the `out` output port of the `source.text.dmesg` component
>> # to the `in` input port of the `sink.text.pretty` component.
>> graph.connect_ports(src_comp.output_ports['out'], sink_comp.input_ports['in'])
>>
>> # Run the trace processing graph.
>> graph.run()
>>
>>
>>
>>
>>
>> 发件人: Philippe Proulx
>> 发送时间: 2022年8月10日 22:08
>> 收件人: zenan
>> 抄送: lttng-dev at lists.lttng.org
>> 主题: Re: [lttng-dev] babeltrace2 python api related question
>>
>>
>>
>> On Wed, Aug 10, 2022 at 9:54 AM zenan via lttng-dev
>>
>> <lttng-dev at lists.lttng.org> wrote:
>>
>> >
>>
>> >
>>
>> >
>>
>> > Hi there,
>>
>> >
>>
>> > I’m trying to use babeltrace2 python bindings to track live lttng trace, as shown in some examples in the documents, I tried to use ctf.lttng-live( ctf.fs in the documents) plugin as source, and use text.pretty as sink, but it didn’t work out as I expected.  So does the api support tracking live lttng trace and print them out yet?
>>
>> >
>>
>> >
>>
>>
>>
>> What did you try exactly?
>>
>>
>>
>> I need command lines and/or some code (keep it minimal) to help you.
>>
>>
>>
>> Philippe
>>
>>
>>
>> >
>>
>> >
>>
>> >
>>
>> > Yours sincerely
>>
>> >
>>
>> > _______________________________________________
>>
>> > lttng-dev mailing list
>>
>> > lttng-dev at lists.lttng.org
>>
>> > https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
>>
>>
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