From ac1a648ff518e0aa92cb14773b617829081a75d0 Mon Sep 17 00:00:00 2001
From: Siri Hansen <siri@erlang.org>
Date: Wed, 14 Sep 2016 18:19:16 +0200
Subject: [ttb] Add option <c>queue_size</c> to tracer/2

This sets the maximum queue size for the IP trace driver which is used
when tracing to shell and/or <c>{local,File}</c>.

Also, change the default queue size set by dbg:trace_port/2 to 200.
---
 lib/observer/doc/src/ttb.xml | 16 +++++++++++++++-
 lib/observer/src/ttb.erl     |  9 ++++++++-
 2 files changed, 23 insertions(+), 2 deletions(-)

(limited to 'lib/observer')

diff --git a/lib/observer/doc/src/ttb.xml b/lib/observer/doc/src/ttb.xml
index 42b0fa1d8a..7cd15e15d3 100644
--- a/lib/observer/doc/src/ttb.xml
+++ b/lib/observer/doc/src/ttb.xml
@@ -114,7 +114,8 @@ ttb:p(all, call).</input></pre>
         <v>Opt = {file,Client} | {handler, FormatHandler} | {process_info,PI} |
           shell | {shell, ShellSpec} | {timer, TimerSpec} |
 	  {overload_check, {MSec, Module, Function}} |
-	{flush, MSec} | resume | {resume, FetchTimeout}</v>
+	{flush, MSec} | resume | {resume, FetchTimeout} |
+	{queue_size, QueueSize}</v>
         <v>TimerSpec = MSec | {MSec, StopOpts}</v>
         <v>MSec = FetchTimeout = integer()</v>
         <v>Module = Function = atom() </v>
@@ -126,6 +127,7 @@ ttb:p(all, call).</input></pre>
         <v>FormatHandler = See format/2</v>
         <v>PI = true | false </v>
         <v>ShellSpec = true | false | only</v>
+	<v>QueueSize = non_neg_integer()</v>
       </type>
       <desc>
         <p>Starts a file trace port on all specified nodes
@@ -147,6 +149,18 @@ ttb:p(all, call).</input></pre>
           <c>Client</c> must be <c>{local, File}</c>. All
           trace information is then sent to the trace control node where
           it is written to file.</p></item>
+       <tag><c>queue_size</c></tag>
+       <item><p>When tracing to shell or <c>{local,File}</c>, an ip
+	  trace driver is used internally. The ip trace driver has a
+	  queue of maximum <c>QueueSize</c> messages waiting to be
+	  delivered. If the driver cannot deliver messages as fast as
+	  they are produced, the queue size might be exceeded and
+	  messages are dropped. This parameter is optional, and is
+	  only useful if many <c>{drop,N}</c> trace messages are
+	  received by the trace handler. It has no meaning if shell
+	  or <c>{local,File}</c> is not used. See
+	  <seealso marker="runtime_tools:dbg#trace_port/2">dbg:trace_port/2</seealso>
+	  for more information about the ip trace driver.</p></item>
        <tag><c>process_info</c></tag>
        <item><p>Indicates if process
           information is to be collected. If <c>PI = true</c> (which is
diff --git a/lib/observer/src/ttb.erl b/lib/observer/src/ttb.erl
index ac6c4572eb..87a50e046b 100644
--- a/lib/observer/src/ttb.erl
+++ b/lib/observer/src/ttb.erl
@@ -78,6 +78,11 @@ do_tracer(Nodes0,PI,Client,Traci) ->
 
 do_tracer(Clients,PI,Traci) ->
     Shell = proplists:get_value(shell, Traci, false),
+    IpPortSpec =
+	case proplists:get_value(queue_size, Traci) of
+	    undefined -> 0;
+	    QS -> {0,QS}
+	end,
     DefShell = fun(Trace) -> dbg:dhandler(Trace, standard_io) end,
     {ClientSucc,Succ} =
 	lists:foldl(
@@ -98,7 +103,7 @@ do_tracer(Clients,PI,Traci) ->
 				 [_,H] = string:tokens(atom_to_list(N),"@"),
 				 H
 			 end,
-		  case catch dbg:tracer(N,port,dbg:trace_port(ip,0)) of
+		  case catch dbg:tracer(N,port,dbg:trace_port(ip,IpPortSpec)) of
 		      {ok,N} ->
 			  {ok,Port} = dbg:trace_port_control(N,get_listen_port),
 			  {ok,T} = dbg:get_tracer(N),
@@ -160,6 +165,8 @@ opt([{resume,MSec}|O],{PI,Client,Traci}) ->
     opt(O,{PI,Client,[{resume, {true, MSec}}|Traci]});
 opt([{flush,MSec}|O],{PI,Client,Traci}) ->
     opt(O,{PI,Client,[{flush, MSec}|Traci]});
+opt([{queue_size,QueueSize}|O],{PI,Client,Traci}) ->
+    opt(O,{PI,Client,[{queue_size,QueueSize}|Traci]});
 opt([],Opt) ->
     ensure_opt(Opt).
 
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