From 2f8d59aa9e8a96d094172db339fd94aae45a90b5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?H=C3=A5kan=20Mattsson?= <hm@tail-f.com>
Date: Wed, 2 Nov 2016 12:56:39 +0100
Subject: erts: Make depth of current_stacktrace configurable

The BIF process_info(Pid, current_stacktrace) truncates the
stacktrace. The old behavior was to truncate long stacktraces to max
8 items. And this was hard coded. Now it is truncated to the value of
system_flag(backtrace_depth) instead. The backtrace_depth defaults to
8, but is configurable.
---
 erts/doc/src/erlang.xml              |  8 ++++++--
 erts/emulator/beam/erl_bif_info.c    |  4 ++--
 erts/emulator/test/process_SUITE.erl | 11 +++++++++++
 3 files changed, 19 insertions(+), 4 deletions(-)

(limited to 'erts')

diff --git a/erts/doc/src/erlang.xml b/erts/doc/src/erlang.xml
index 9646953518..112682d713 100644
--- a/erts/doc/src/erlang.xml
+++ b/erts/doc/src/erlang.xml
@@ -4899,7 +4899,9 @@ RealSystem = system + MissedSystem</code>
             <p>Returns the current call stack back-trace (<em>stacktrace</em>)
               of the process. The stack has the same format as returned by
               <seealso marker="#get_stacktrace/0">
-              <c>erlang:get_stacktrace/0</c></seealso>.</p>
+              <c>erlang:get_stacktrace/0</c></seealso>. The depth of the
+              stacktrace is truncated according to the <c>backtrace_depth</c>
+              system flag setting.</p>
           </item>
           <tag><c>{dictionary, <anno>Dictionary</anno>}</c></tag>
           <item>
@@ -6611,7 +6613,9 @@ ok
       <fsummary>Set system flag <c>backtrace_depth</c>.</fsummary>
       <desc>
         <p>Sets the maximum depth of call stack back-traces in the
-          exit reason element of <c>'EXIT'</c> tuples.</p>
+          exit reason element of <c>'EXIT'</c> tuples. The flag
+          also limits the stacktrace depth returned by <c>process_info</c>
+          item <c>current_stacktrace.</c></p>
         <p>Returns the old value of the flag.</p>
       </desc>
     </func>
diff --git a/erts/emulator/beam/erl_bif_info.c b/erts/emulator/beam/erl_bif_info.c
index 735aabbee3..88a052cad7 100644
--- a/erts/emulator/beam/erl_bif_info.c
+++ b/erts/emulator/beam/erl_bif_info.c
@@ -1672,11 +1672,11 @@ current_stacktrace(Process* p, Process* rp, Eterm** hpp)
     Eterm mfa;
     Eterm res = NIL;
 
-    depth = 8;
+    depth = erts_backtrace_depth;
     sz = offsetof(struct StackTrace, trace) + sizeof(BeamInstr *)*depth;
     s = (struct StackTrace *) erts_alloc(ERTS_ALC_T_TMP, sz);
     s->depth = 0;
-    if (rp->i) {
+    if (depth > 0 && rp->i) {
 	s->trace[s->depth++] = rp->i;
 	depth--;
     }
diff --git a/erts/emulator/test/process_SUITE.erl b/erts/emulator/test/process_SUITE.erl
index 0f999e0efe..2289cbabc7 100644
--- a/erts/emulator/test/process_SUITE.erl
+++ b/erts/emulator/test/process_SUITE.erl
@@ -437,11 +437,22 @@ t_process_info(Config) when is_list(Config) ->
     verify_loc(Line2, Res2),
     pi_stacktrace([{?MODULE,t_process_info,1,?LINE}]),
 
+    verify_stacktrace_depth(),
+
     Gleader = group_leader(),
     {group_leader, Gleader} = process_info(self(), group_leader),
     {'EXIT',{badarg,_Info}} = (catch process_info('not_a_pid')),
     ok.
 
+verify_stacktrace_depth() ->
+    CS = current_stacktrace,
+    OldDepth = erlang:system_flag(backtrace_depth, 0),
+    {CS,[]} = erlang:process_info(self(), CS),
+    _ = erlang:system_flag(backtrace_depth, 8),
+    {CS,[{?MODULE,verify_stacktrace_depth,0,_},_|_]} =
+        erlang:process_info(self(), CS),
+    _ = erlang:system_flag(backtrace_depth, OldDepth).
+
 pi_stacktrace(Expected0) ->
     {Line,Res} = {?LINE,erlang:process_info(self(), current_stacktrace)},
     {current_stacktrace,Stack} = Res,
-- 
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