Avoid a race condition for monitored compaction.

It was technically possible for compaction to finish before a monitor
was requested. This fixes that by giving couch_index:compact a third
options parameter that accepts the atom 'monitor' which will then return
{ok, MonRef} instead of a bare ok.



git-svn-id: https://svn.apache.org/repos/asf/couchdb/trunk@1172378 13f79535-47bb-0310-9956-ffa450edef68

src/couch_index/src/couch_index.erl

@@ -16,7 +16,7 @@
 
 %% API
 -export([start_link/1, stop/1, get_state/2, get_info/1]).
--export([compact/1, get_compactor_pid/1]).
+-export([compact/1, compact/2]).
 -export([config_change/3]).
 
 %% gen_server callbacks
@@ -55,11 +55,15 @@ get_info(Pid) ->
 
 
 compact(Pid) ->
-    gen_server:call(Pid, compact).
+    compact(Pid, []).
 
 
-get_compactor_pid(Pid) ->
-    gen_server:call(Pid, get_compactor_pid).
+compact(Pid, Options) ->
+    {ok, CPid} = gen_server:call(Pid, compact),
+    case lists:member(monitor, Options) of
+        true -> {ok, erlang:monitor(process, CPid)};
+        false -> ok
+    end.
 
 
 config_change("query_server_config", "commit_freq", NewValue) ->
@@ -155,8 +159,8 @@ handle_call(reset, _From, State) ->
     {ok, NewIdxState} = Mod:reset(IdxState),
     {reply, {ok, NewIdxState}, State#st{idx_state=NewIdxState}};
 handle_call(compact, _From, State) ->
-    couch_index_compactor:run(State#st.compactor, State#st.idx_state),
-    {reply, ok, State};
+    Resp = couch_index_compactor:run(State#st.compactor, State#st.idx_state),
+    {reply, Resp, State};
 handle_call(get_compactor_pid, _From, State) ->
     {reply, {ok, State#st.compactor}, State};
 handle_call({compacted, NewIdxState}, _From, State) ->

src/couch_index/src/couch_index_compactor.erl

@@ -15,7 +15,7 @@
 
 
 %% API
--export([start_link/2, run/2, monitor/1, cancel/1, is_running/1]).
+-export([start_link/2, run/2, cancel/1, is_running/1]).
 
 %% gen_server callbacks
 -export([init/1, terminate/2, code_change/3]).
@@ -40,13 +40,6 @@ run(Pid, IdxState) ->
     gen_server:call(Pid, {compact, IdxState}).
 
 
-monitor(Pid) ->
-    case gen_server:call(Pid, get_pid) of
-        {ok, undefined} -> {error, compaction_not_running};
-        {ok, CPid} -> {ok, erlang:monitor(process, CPid)}
-    end.
-
-
 cancel(Pid) ->
     gen_server:call(Pid, cancel).
 
@@ -66,12 +59,10 @@ terminate(_Reason, State) ->
 
 
 handle_call({compact, _}, _From, #st{pid=Pid}=State) when is_pid(Pid) ->
-    {reply, ok, State};
+    {reply, {ok, Pid}, State};
 handle_call({compact, IdxState}, _From, #st{idx=Idx}=State) ->
     Pid = spawn_link(fun() -> compact(Idx, State#st.mod, IdxState) end),
-    {reply, ok, State#st{pid=Pid}};
-handle_call(get_pid, _From, State) ->
-    {reply, {ok, State#st.pid}, State};
+    {reply, {ok, Pid}, State#st{pid=Pid}};
 handle_call(cancel, _From, #st{pid=undefined}=State) ->
     {reply, ok, State};
 handle_call(cancel, _From, #st{pid=Pid}=State) ->

src/couch_mrview/src/couch_mrview.erl

@@ -15,7 +15,7 @@
 -export([query_all_docs/2, query_all_docs/4]).
 -export([query_view/3, query_view/4, query_view/6]).
 -export([get_info/2]).
--export([compact/2, monitor_compaction/2, cancel_compaction/2]).
+-export([compact/2, compact/3, cancel_compaction/2]).
 -export([cleanup/1]).
 
 -include("couch_db.hrl").
@@ -93,14 +93,12 @@ get_info(Db, DDoc) ->
 
 
 compact(Db, DDoc) ->
-    {ok, Pid} = couch_index_server:get_index(couch_mrview_index, Db, DDoc),
-    couch_index:compact(Pid).
+    compact(Db, DDoc, []).
 
 
-monitor_compaction(Db, DDoc) ->
-    {ok, IPid} = couch_index_server:get_index(couch_mrview_index, Db, DDoc),
-    {ok, CPid} = couch_index:get_compactor_pid(IPid),
-    couch_index_compactor:monitor(CPid).
+compact(Db, DDoc, Opts) ->
+    {ok, Pid} = couch_index_server:get_index(couch_mrview_index, Db, DDoc),
+    couch_index:compact(Pid, Opts).
 
 
 cancel_compaction(Db, DDoc) ->

src/couchdb/couch_compaction_daemon.erl

@@ -228,8 +228,7 @@ maybe_compact_view(DbName, GroupId, Config) ->
     {ok, GroupInfo} ->
         case can_view_compact(Config, DbName, GroupId, GroupInfo) of
         true ->
-            ok = couch_mrview:compact(DbName, DDocId),
-            {ok, MonRef} = couch_mrview:monitor_compaction(DbName, DDocId),
+            {ok, MonRef} = couch_mrview:compact(DbName, DDocId, [monitor]),
             TimeLeft = compact_time_left(Config),
             receive
             {'DOWN', MonRef, process, _, normal} ->