From 411f6240932aab3721ff842c674d9610216cfd88 Mon Sep 17 00:00:00 2001
From: Micael Karlberg <bmk@erlang.org>
Date: Tue, 10 Jan 2012 14:52:00 +0100
Subject: [snmp/agent] Synchronization feature added

OTP-9851
---
 lib/snmp/src/agent/snmpa_vacm.erl | 77 +++++++++++++++++++++++----------------
 1 file changed, 46 insertions(+), 31 deletions(-)

(limited to 'lib/snmp/src/agent/snmpa_vacm.erl')

diff --git a/lib/snmp/src/agent/snmpa_vacm.erl b/lib/snmp/src/agent/snmpa_vacm.erl
index c31b8e61a3..efe6378105 100644
--- a/lib/snmp/src/agent/snmpa_vacm.erl
+++ b/lib/snmp/src/agent/snmpa_vacm.erl
@@ -276,45 +276,60 @@ dump_table(_) ->
 %% If there is already a running dumper process, instead increment
 %% the dump_request counter.
 %% When the dumper process exits, the master agent checks the 
-%% the dump_request counter, and if that is greated than zero,
+%% the dump_request counter, and if that is greater than zero,
 %% create another dumper process and resets the counter.
-%% In this way the dumping is serializede, but the master-agent
-%% process is not burdened by the dumping.
+%% In this way the dumping is serialized, but the master-agent
+%% process is not burdend by the dumping.
 %% </SUGGESTION>
 dump_table() ->
-    [{_, FName}] = ets:lookup(snmp_agent_table, snmpa_vacm_file),
-    TmpName = unique(FName), 
-    case ets:tab2file(snmpa_vacm, TmpName) of
-	ok ->
-	    case file:rename(TmpName, FName) of
-		ok ->
-		    ok;
-		Else -> % What is this? Undocumented return code...
-		    user_err("Warning: could not move VACM db ~p"
-			     " (~p)", [FName, Else])
-	    end;
-	{error, Reason} ->
-	    user_err("Warning: could not save vacm db ~p (~p)",
-		     [FName, Reason])
-    end.
+    %% The dumper fun is executed in a specially started process, 
+    %% that does that one thing and then exits.
+    %% Also, to prevent the system to run "wild" (keep calling 
+    %% dump function before they are done), the agents serialize 
+    %% function return when that dump is done!
+    Dumper = 
+	fun() ->
+		[{_, FName}] = ets:lookup(snmp_agent_table, snmpa_vacm_file),
+		%% TmpName = FName ++ ".tmp",
+		TmpName = unique_name(FName), 
+		case ets:tab2file(snmpa_vacm, TmpName) of
+		    ok ->
+			case file:rename(TmpName, FName) of
+			    ok ->
+				ok;
+			    Else -> % What is this? Undocumented return code...
+				user_err("Warning: could not move VACM db ~p"
+					 " (~p)", [FName, Else])
+			end;
+		    {error, Reason} ->
+			user_err("Warning: could not save vacm db ~p (~p)",
+				 [FName, Reason])
+		end
+	end,
+    snmpa_agent:serialize(snmpa_vacm_dump_request, Dumper).
+
 
 %% This little thing is an attempt to create a "unique" filename
 %% in order to minimize the risk of two processes at the same 
 %% time dumping the table.
-unique(Pre) ->
-    {A, B, C} = os:timestamp(),
-    {D, _}    = erlang:statistics(reductions),
-    {E, _}    = erlang:statistics(runtime),
-    {F, _}    = erlang:statistics(wall_clock),
-    {G, H, _} = erlang:statistics(garbage_collection),
-    Data = [A, B, C, D, E, F, G, H],
-    unique(Pre, Data, 0).
-
-unique(Pre, [], Unique) ->
+%% The serialization handled by the agent does this much better,
+%% but this also gives us a "timestamp" which could be usefull for 
+%% debugging reasons.
+unique_name(Pre) ->
+    unique_name(Pre, os:timestamp()).
+
+unique_name(Pre, {_A, _B, C} = Timestamp) ->
+    {Date, Time}     = calendar:now_to_datetime(Timestamp),
+    {YYYY, MM, DD}   = Date,
+    {Hour, Min, Sec} = Time,
+    FormatDate =
+        io_lib:format("~.4w~.2.0w~.2.0w_~.2.0w~.2.0w~.2.0w_~w",
+                      [YYYY, MM, DD, Hour, Min, Sec, round(C/1000)]), 
+    unique_name2(Pre, FormatDate).
+
+unique_name2(Pre, FormatedDate) ->
     PidPart = unique_pid(), 
-    lists:flatten(io_lib:format("~s.~s~w.tmp", [Pre, PidPart, Unique]));
-unique(Pre, [H|T], Unique) ->
-    unique(Pre, T, Unique bxor H).
+    lists:flatten(io_lib:format("~s.~s~s.tmp", [Pre, PidPart, FormatedDate])).
 
 unique_pid() ->
     case string:tokens(pid_to_list(self()), [$<,$.,$>]) of
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