[couchdb] 01/01: fix race condition (#3150)

[jiangphcn]

This is an automated email from the ASF dual-hosted git repository.

jiangphcn pushed a commit to branch 3.x-fix-compaction-race-condition
in repository https://gitbox.apache.org/repos/asf/couchdb.git

commit db872d0a2be7f5915c0dfba43db2914fdc501811
Author: Tony Sun <tony.sun...@gmail.com>
AuthorDate: Mon Sep 14 11:12:47 2020 -0700

    fix race condition (#3150)
    
    This fixes a94e693f32672e4613bce0d80d0b9660f85275ea because a race
    condition exisited where the 'DOWN' message could be received
    before the compactor pid is spawned. Adding a synchronous call to
    get the compactor pid guarantees that the couch_db_updater process
    handling of finish_compaction has occurred.
---
 src/couch/src/couch_db.erl        | 9 +++++++++
 src/smoosh/src/smoosh_channel.erl | 2 +-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/src/couch/src/couch_db.erl b/src/couch/src/couch_db.erl
index e1d726d..390a198 100644
--- a/src/couch/src/couch_db.erl
+++ b/src/couch/src/couch_db.erl
@@ -37,6 +37,7 @@
     get_committed_update_seq/1,
     get_compacted_seq/1,
     get_compactor_pid/1,
+    get_compactor_pid_sync/1,
     get_db_info/1,
     get_partition_info/2,
     get_del_doc_count/1,
@@ -572,6 +573,14 @@ get_compacted_seq(#db{}=Db) ->
 get_compactor_pid(#db{compactor_pid = Pid}) ->
     Pid.
 
+get_compactor_pid_sync(#db{main_pid=Pid}=Db) ->
+    case gen_server:call(Pid, compactor_pid, infinity) of
+        CPid when is_pid(CPid) ->
+            CPid;
+        _ ->
+            nil
+    end.
+
 get_db_info(Db) ->
     #db{
         name = Name,
diff --git a/src/smoosh/src/smoosh_channel.erl 
b/src/smoosh/src/smoosh_channel.erl
index d8a8d14..058f551 100644
--- a/src/smoosh/src/smoosh_channel.erl
+++ b/src/smoosh/src/smoosh_channel.erl
@@ -276,7 +276,7 @@ start_compact(State, Db) ->
     false ->
         DbPid = couch_db:get_pid(Db),
         Key = couch_db:name(Db),
-        case couch_db:get_compactor_pid(Db) of
+        case couch_db:get_compactor_pid_sync(Db) of
             nil ->
                 Ref = erlang:monitor(process, DbPid),
                 DbPid ! {'$gen_call', {self(), Ref}, start_compact},