From 798f09de48b1a7abe43d54d6fa0377ad15c3f6aa Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Lo=C3=AFc=20Hoguin?= <essen@ninenines.eu>
Date: Fri, 3 Jun 2016 12:13:09 +0200
Subject: Propagate exceptions fully when using proc_lib

This makes proc_lib behaves like a normal process as far
as the propagation of exceptions is concerned.

Before this commit, the following difference could be
observed:

  6> spawn_link(fun() -> ssl:send(a,b) end).
  <0.43.0>
  7> flush().
  Shell got {'EXIT',<0.43.0>,
             {function_clause,
              [{ssl,send,[a,b],[{file,"..."},{line,275}]}]}}
  ok

  8> proc_lib:spawn_link(fun() -> ssl:send(a,b) end).
  <0.46.0>
  9> flush().
  Shell got {'EXIT',<0.46.0>,function_clause}

After this commit, we get the following instead:

  3> flush().
  Shell got {'EXIT',<0.61.0>,
             {function_clause,
              [{ssl,send,[a,b],[{file,"..."},{line,275}]},
               {proc_lib,init_p,3,[{file,"..."},{line,232}]}]}}

The stacktrace will show minor differences of course
but the form is now the same as without proc_lib.

The rationale behind this commit is that:

* We now have a single form regardless of how the process
  was started

* We can use the stacktrace to programmatically alter behavior
  (for example an HTTP server identifying problems in input
  decoding to send back a generic 400, or a 500 otherwise)

* We can access the stacktrace to print it somewhere (for
  example an HTTP server could send it back to the client
  when a debug mode is enabled)
---
 lib/stdlib/src/proc_lib.erl | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

(limited to 'lib/stdlib/src/proc_lib.erl')

diff --git a/lib/stdlib/src/proc_lib.erl b/lib/stdlib/src/proc_lib.erl
index 3dc1848550..363705b0f4 100644
--- a/lib/stdlib/src/proc_lib.erl
+++ b/lib/stdlib/src/proc_lib.erl
@@ -232,7 +232,7 @@ init_p(Parent, Ancestors, Fun) when is_function(Fun) ->
 	Fun()
     catch
 	Class:Reason ->
-	    exit_p(Class, Reason)
+	    exit_p(Class, Reason, erlang:get_stacktrace())
     end.
 
 -spec init_p(pid(), [pid()], atom(), atom(), [term()]) -> term().
@@ -247,7 +247,7 @@ init_p_do_apply(M, F, A) ->
 	apply(M, F, A) 
     catch
 	Class:Reason ->
-	    exit_p(Class, Reason)
+	    exit_p(Class, Reason, erlang:get_stacktrace())
     end.
 
 -spec wake_up(atom(), atom(), [term()]) -> term().
@@ -257,22 +257,29 @@ wake_up(M, F, A) when is_atom(M), is_atom(F), is_list(A) ->
 	apply(M, F, A) 
     catch
 	Class:Reason ->
-	    exit_p(Class, Reason)
+	    exit_p(Class, Reason, erlang:get_stacktrace())
     end.
 
-exit_p(Class, Reason) ->
+exit_p(Class, Reason, Stacktrace) ->
     case get('$initial_call') of
 	{M,F,A} when is_atom(M), is_atom(F), is_integer(A) ->
 	    MFA = {M,F,make_dummy_args(A, [])},
 	    crash_report(Class, Reason, MFA),
-	    exit(Reason);
+	    erlang:raise(exit, exit_reason(Class, Reason, Stacktrace), Stacktrace);
 	_ ->
 	    %% The process dictionary has been cleared or
 	    %% possibly modified.
 	    crash_report(Class, Reason, []),
-	    exit(Reason)
+	    erlang:raise(exit, exit_reason(Class, Reason, Stacktrace), Stacktrace)
     end.
 
+exit_reason(error, Reason, Stacktrace) ->
+    {Reason, Stacktrace};
+exit_reason(exit, Reason, _Stacktrace) ->
+    Reason;
+exit_reason(throw, Reason, Stacktrace) ->
+    {{nocatch, Reason}, Stacktrace}.
+
 -spec start(Module, Function, Args) -> Ret when
       Module :: module(),
       Function :: atom(),
-- 
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