et_selector(3erl)

🎀 NAME 🎀

et_selector — Define event transforms and trace patterns

This is the et_selector(3erl) page, bestie — the Erlang manual for picking what trace events are interesting, transforming trace data into event records, and changing trace patterns. It’s giving small module, big main-character energy. 💅

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🦋 DESCRIPTION 🦋

Okay so the original DESCRIPTION section is literally empty here. No prose, no extra tea, just a heading and then straight into EXPORTS. We’re not inventing facts — the real details are all below. ✨

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🔥 EXPORTS 🔥

Three functions, all iconic, no filler. Let’s go. 🫶

💖 make_pattern/1 💖

make_pattern(RawPattern) -> TracePattern

Types

RawPattern = detail_level()
TracePattern = erlang_trace_pattern_match_spec()
detail_level() = min | max | integer(X) when X >= 0, X =< 100

This one makes a trace pattern that is suitable to feed into change_pattern/1. It’s basically the pre-game snack before the actual pattern change. 🍓

• min detail level deactivates tracing of calls to et:trace_me/4,5. bye tracing 👋
• max detail level activates tracing of all calls to et:trace_me/4,5. all of them. periodt.
• integer(X) detail level activates tracing of calls to et:trace_me/4,5 whose detail level argument is lesser than X. (And yeah, X stays in the 0 to 100 range from the type.)
• Also: see erlang:trace_pattern/2 for more info about its match_spec(). iykyk.

💜 change_pattern/1 💜

change_pattern(Pattern) -> ok

Types

Pattern = detail_level() | empty_match_spec() | erlang_trace_pattern_match_spec()
detail_level() = min | max | integer(X) when X >= 0, X =< 100
empty_match_spec() = []

This activates/deactivates tracing by changing the current trace pattern. It’s the vibe check for your trace pattern. 🔥

• min detail level deactivates tracing of calls to et:trace_me/4,5.
• max detail level activates tracing of all calls to et:trace_me/4,5.
• integer(X) detail level activates tracing of all calls to et:trace_me/4,5 whose detail level argument is lesser than X.
• An empty match spec deactivates tracing of calls to et:trace_me/4,5. That’s [], bestie — empty and powerful. 💀
• Other match specs activate tracing of calls to et:trace_me/4,5 accordingly with erlang:trace_pattern/2.

🦋 parse_event/2 🦋

parse_event(Mod, ValidTraceData) -> false | true | {true, Event}

Types

Mod = module_name() | undefined
module_name() = atom()
ValidTraceData = erlang_trace_data() | record(event)
erlang_trace_data() = {trace, Pid, Label, Info} | {trace, Pid, Label, Info, Extra} | {trace_ts, Pid, Label, Info, ReportedTS} | {trace_ts, Pid, Label, Info, Extra, ReportedTS} | {seq_trace, Label, Info} | {seq_trace, Label, Info, ReportedTS} | {drop, NumberOfDroppedItems}

This transforms trace data and makes an event record out of it. It’s literally the glow-up from raw trace tuple to #event{} record. ✨

See erlang:trace/3 for more info about the semantics of the trace data.

An event record consists of the following fields:

• detail_level: Noise has a high level as opposed to essentials.
• trace_ts: Time when the trace was generated. Same as event_ts if omitted in trace data.
• event_ts: Time when the event record was created.
• from: From actor, such as sender of a message.
• to: To actor, such as receiver of message.
• label: Label intended to provide a brief event summary.
• contents: All nitty gritty details of the event.

See et:trace_me/4 and et:trace_me/5 for details.

Returns:

• {true, Event}: where Event is an #event{} record representing the trace data.
• true: means that the trace data already is an event record and that it is valid as it is. No transformation is needed.
• false: means that the trace data is uninteresting and should be dropped.

bestie, that false is not a sad ending — it just means the trace data didn’t pass the vibe check and gets dropped. 🫶

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💖 that’s the whole page, bestie. Cute little sign-off: source is Ericsson AB, version is et 1.6.5. The footer didn’t give a date, so I’m not inventing one — no cap. 🎀✨