Add otel_monitor #461
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| %%%------------------------------------------------------------------------ | ||
| %% Copyright 2020, OpenTelemetry Authors | ||
| %% Licensed under the Apache License, Version 2.0 (the "License"); | ||
| %% you may not use this file except in compliance with the License. | ||
| %% You may obtain a copy of the License at | ||
| %% | ||
| %% http://www.apache.org/licenses/LICENSE-2.0 | ||
| %% | ||
| %% Unless required by applicable law or agreed to in writing, software | ||
| %% distributed under the License is distributed on an "AS IS" BASIS, | ||
| %% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| %% See the License for the specific language governing permissions and | ||
| %% limitations under the License. | ||
| %% | ||
| %% @doc | ||
| %% Process that can optionally monitor the process a span is in and end the | ||
| %% span if the process stops for any reason with the span still unfinished. | ||
| %% @end | ||
| %%%------------------------------------------------------------------------- | ||
| -module(otel_monitor). | ||
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| -behaviour(gen_server). | ||
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| -export([start_link/0, | ||
| monitor/1]). | ||
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| -export([init/1, | ||
| handle_call/3, | ||
| handle_cast/2, | ||
| handle_info/2]). | ||
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| -include("otel_tracer.hrl"). | ||
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| -define(SERVER, ?MODULE). | ||
| -define(TABLE, ?MODULE). | ||
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| start_link() -> | ||
| gen_server:start_link({local, ?SERVER}, ?MODULE, nil, [{name, ?SERVER}]). | ||
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| init(nil) -> | ||
| _TableId = ets:new(?TABLE, [set, named_table]), | ||
| {ok, nil}. | ||
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| handle_call({monitor, SpanCtx, Pid}, _From, State) -> | ||
| Ref = erlang:monitor(process, Pid), | ||
| true = ets:insert(?TABLE, {Ref, SpanCtx}), | ||
| {reply, ok, State}. | ||
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| handle_info({'DOWN', Ref, process, _Pid, normal}, State) -> | ||
| case ets:take(?TABLE, Ref) of | ||
| [] -> nil; | ||
| [{_Ref, SpanCtx}] -> otel_span:end_span(SpanCtx) | ||
| end, | ||
| {noreply, State}; | ||
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| handle_info({'DOWN', Ref, process, _Pid, {shutdown, _}}, State) -> | ||
| case ets:take(?TABLE, Ref) of | ||
| [] -> nil; | ||
| [{_Ref, SpanCtx}] -> otel_span:end_span(SpanCtx) | ||
| end, | ||
| {noreply, State}; | ||
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| handle_info({'DOWN', Ref, process, _Pid, Reason}, State) -> | ||
| case ets:take(?TABLE, Ref) of | ||
| [] -> nil; | ||
| [{_Ref, SpanCtx}] -> | ||
| otel_span:add_event(SpanCtx, 'Process died', #{<<"reason">> => iolist_to_binary(io_lib:format("~p", [Reason]))}), | ||
| otel_span:end_span(SpanCtx) | ||
| end, | ||
| {noreply, State}. | ||
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| handle_cast(_Msg, State) -> | ||
| {noreply, State}. | ||
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| monitor(SpanCtx) -> | ||
| ok = gen_server:call(?SERVER, {monitor, SpanCtx, self()}), | ||
|
There was a problem hiding this comment. User probably doesn't want to crash if the monitor fails. I'd say probably just want a There was a problem hiding this comment. I like that idea, returning true / false based for success / failure. |
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| true. | ||
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Could be more than 1 span being monitored in the same process.
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Yes, but each span will get its own ref, no? I guess this is what I will find out when I write tests...
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Ooh, my mistake. I was thinking it was like my implementation which monitors all spans in a process, so it looks up all spans for a pid, not by ref.
Which is a separate question I have, is it really worth doing it per-span, are there spans that a user wouldn't want ended when a process crashes?
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If you are asking why I didn't write a PR that monitors every span's process, it's because bigger changes like that are less likely to be accepted. I am aiming with this PR for the incremental approach: first offer the api optionally, if it turns out that everyone uses it all the time, then contemplate making it mandatory.
But if you are comfortable going directly to monitoring every span's process, then I am happy coding that up.
I'm not sure whether it's cheaper to have a single monitor per pid and juggling spans associated with that pid in an ets table, or just creating a new monitor and ets row per span.
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No, I'm asking why not monitor every span in a single process the user requests.
If the user requests to monitor Span X in process P do they really not want Span Y that is also active in process P to be ended when the process dies? If they do they have to call
monitor(X)andmonitor(Y). The API I had in mind was justmonitor(), and then every span inself()is monitored. I suppose also amonitor(Pid)makes sense to include if we go that route.There was a problem hiding this comment.
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Also, if going the route of just monitoring the Pid and all its spans we can add a
pidto the span itself. In my PR for the monitor I add a pid to span so that the existing table can just be used to look up the spans to end.There was a problem hiding this comment.
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I'm asking in slack. It is hard to know what is best without people's input on how they'd use it, or if they are already using their own solution, like you have been.
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👍 glad we are having this discussion
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I would want to have this applied to every span.