Set process label #7720

dgud · 2023-10-06T08:32:34Z

Add (and use) proc_lib:set(and get)_label/1

Make it possible for the user to set a process_description which
can be used in tools and crash reports to identity processes
but it doesn't have to be unique, as an registered name needs to be.

The process description can any term, for example {worker, 1..N},
{pool_process, 1..N} or something entirely different to identify
process that use general code.

While at it optimize fetching process info, so we don't have to
(rpc:) call the process_info(..) several times.

github-actions · 2023-10-06T08:33:34Z

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// Erlang/OTP Github Action Bot

lib/stdlib/doc/src/proc_lib.xml

u3s

Some comments dropped inline.

I didn't comment on commented out code. I assumed you are still developing and it is needed for reference. If not really needed, should be removed before merging I guess.

lib/stdlib/src/c.erl

lib/stdlib/src/proc_lib.erl

garazdawi

LGTM. I've added some minor comments.

As with all great features this leaves me wanting more :D

Some of the things I would like are:

Ancestors shown with their process description (both for self() and neighbors) in crash reports
Links shown with their process description (both for self() and neighbors) in crash reports
A convenience SpawnOpt to all gen behaviours to set the process description. This both makes it easier to set and exposes the functionality to users so that they know it exists without digging in the proc_lib docs.

PS. Are there really no tests for appmon_info, observer_backend and c:i? :( DS.

lib/observer/doc/src/observer_ug.xml

lib/stdlib/src/proc_lib.erl

lib/stdlib/test/proc_lib_SUITE.erl

lib/stdlib/doc/src/proc_lib.xml

u3s

Great PR! Thanks.

u3s · 2023-10-18T08:49:09Z

lib/stdlib/src/c.erl

+fetch_name([], Info) ->
+    case fetch({dictionary, '$process_label'}, Info) of
+        undefined -> "";
+        Id -> format_name(Id)
+    end;
+fetch_name(Reg, _) ->
+    Reg.
+
+format_name(Id) when is_list(Id); is_binary(Id) ->
+    case unicode:characters_to_binary(Id) of
+        {error, _, _} ->
+            io_lib:format("~0.tp", [Id]);
+        BinString ->
+            BinString
+    end;
+format_name(TermId) ->
+    io_lib:format("~0.tp", [TermId]).


this part is about fetching and formatting label. at a glance, name might suggest registered name.

IngelaAndin · 2023-10-24T07:28:02Z

lib/observer/src/observer_pro_wx.erl

+sort_name(#etop_proc_info{name={_,_,_}}, _) ->
+    false.
+
+%% sort_name(#etop_proc_info{name=Reg}, #etop_proc_info{name={M,_F,_A}})


Why are we keeping this code as a comment?

rlipscombe · 2023-11-07T12:07:14Z

If I use proc_lib:set_label(?MODULE), then -- in observer -- it's hard to tell the difference from register(?MODULE, self()).

Do we need a way to denote that these are labels, rather than registered names?

dgud · 2023-11-07T12:15:58Z

Does it matter? It identifies the process(s).
If it is needed we can change that later.

rlipscombe · 2023-11-07T13:04:58Z

Possibly not.

rlipscombe · 2023-11-07T13:05:19Z

A bug, though -- probably in observer, rather than this: If two children have the same label, observer merges the nodes together.

dgud · 2023-11-07T15:18:10Z

A bug, though -- probably in observer, rather than this: If two children have the same label, observer merges the nodes together.

Where? In which tab?

rlipscombe · 2023-11-07T15:26:43Z

Where? In which tab?

In the "Applications" tab. When I click on my application, all of my poolboy workers are represented by the same object (I assume because they've all got the same label). If I remove the label, they go back to separate objects.

rlipscombe · 2023-11-07T15:48:05Z

See https://github.com/rlipscombe/observer_example for a repro. Specifically https://github.com/rlipscombe/observer_example/blob/main/src/observer_example_worker.erl#L23

rlipscombe · 2023-11-07T15:49:33Z

Oh, and on the earlier observation, note that I was also talking about the applications tab (it's my favourite!), in case that makes a difference about whether it matters.

dgud · 2023-11-10T08:43:13Z

@rlipscombe I have pushed a version it kind of solves both your issues, the test app was useful thanks.

Make it possible for the user to set a process label which can be used in tools and crash reports to identity processes but it doesn't have to be unique, as an registered name needs to be. The process label can any term, for example {worker, 1..N}, {pool_process, 1..N} or something entirely different to identify process that use general code. While at it optimize fetching process info, so we don't have to (rpc:) call the process_info(..) several times.

tomas-abrahamsson · 2023-12-04T08:10:06Z

lib/stdlib/doc/src/proc_lib.xml

@@ -159,6 +159,17 @@
      </desc>
    </func>

+    <func>
+      <name name="get_label" arity="1" since="OTP 26.2"/>


I'm interested to learn if this will get included in the upcoming 26.2? It seems this branch was merged to master instead of maint, but the docs say since 26.2 here and for set_label/1.

No master only, we changed our mind and forgot to update the docs, thanks.

dgud requested a review from rickard-green October 6, 2023 08:32

dgud self-assigned this Oct 6, 2023

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dgud requested a review from u3s October 9, 2023 12:32

dgud mentioned this pull request Oct 9, 2023

Display value of '$process_label' in observer #5039

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dgud merged commit 106765e into erlang:master Nov 17, 2023

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tomas-abrahamsson mentioned this pull request Jan 5, 2024

stdlib: Include process label in gen_statem, gen_server, gent_event, gen_fsm crash messages #8003

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This was referenced Mar 5, 2024

Logger handles :process_label from OTP27 elixir-lang/elixir#13392

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Logger logs :process_label if present elixir-lang/elixir#13396

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Set process label #7720

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Set process label #7720

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