Write locks now check majority when needed.

Since the table loader also sets (table) write locks, a special
lock type, 'load', was needed. Unfortunately, this affects mnesia
activity callbacks that redefine the lock operation.

6 files changed, 52 insertions, 12 deletions

diff --git a/lib/mnesia/src/mnesia.erl b/lib/mnesia/src/mnesia.erl
index 025b32f506..43953f9ad4 100644
--- a/lib/mnesia/src/mnesia.erl
+++ b/lib/mnesia/src/mnesia.erl
@@ -39,6 +39,7 @@
 
 	 %% Access within an activity - Lock acquisition
 	 lock/2, lock/4,
+	 lock_table/2,
 	 read_lock_table/1, 
 	 write_lock_table/1,
 
@@ -415,6 +416,9 @@ lock(LockItem, LockKind) ->
 	    abort(no_transaction)
     end.
 
+lock_table(Tab, LockKind) ->
+    lock({table, Tab}, LockKind).
+
 lock(Tid, Ts, LockItem, LockKind) ->
     case element(1, Tid) of
 	tid ->
@@ -467,6 +471,8 @@ lock_table(Tid, Ts, Tab, LockKind) when is_atom(Tab) ->
 	    mnesia_locker:rlock_table(Tid, Store, Tab);
 	write ->
 	    mnesia_locker:wlock_table(Tid, Store, Tab);
+	load ->
+	    mnesia_locker:load_lock_table(Tid, Store, Tab);
 	sticky_write ->
 	    mnesia_locker:sticky_wlock_table(Tid, Store, Tab);
 	none ->
diff --git a/lib/mnesia/src/mnesia_lib.erl b/lib/mnesia/src/mnesia_lib.erl
index 36bcfe8de9..7e926a6258 100644
--- a/lib/mnesia/src/mnesia_lib.erl
+++ b/lib/mnesia/src/mnesia_lib.erl
@@ -96,6 +96,8 @@
 	 exists/1,
 	 fatal/2,
 	 get_node_number/0,
+	 have_majority/2,
+	 have_majority/3,
 	 fix_error/1,
 	 important/2,
 	 incr_counter/1,
@@ -660,6 +662,14 @@ proc_info(_) -> false.
 get_node_number() ->
     {node(), self()}.
 
+have_majority(Tab, HaveNodes) ->
+    have_majority(Tab, val({Tab, all_nodes}), HaveNodes).
+
+have_majority(_Tab, AllNodes, HaveNodes) ->
+    Missing = AllNodes -- HaveNodes,
+    Present = AllNodes -- Missing,
+    length(Present) > length(Missing).
+
 read_log_files() ->
     [{F, catch file:read_file(F)} || F <- mnesia_log:log_files()].
 
diff --git a/lib/mnesia/src/mnesia_loader.erl b/lib/mnesia/src/mnesia_loader.erl
index 3de329503e..e785b795d1 100644
--- a/lib/mnesia/src/mnesia_loader.erl
+++ b/lib/mnesia/src/mnesia_loader.erl
@@ -702,7 +702,7 @@ send_table(Pid, Tab, RemoteS) ->
 prepare_copy(Pid, Tab, Storage) ->
     Trans =
 	fun() ->
-		mnesia:write_lock_table(Tab),
+		mnesia:lock_table(Tab, load),
 		mnesia_subscr:subscribe(Pid, {table, Tab}),
 		update_where_to_write(Tab, node(Pid)),
 		mnesia_lib:db_fixtable(Storage, Tab, true),
diff --git a/lib/mnesia/src/mnesia_locker.erl b/lib/mnesia/src/mnesia_locker.erl
index ca0cc79c45..9822dfd116 100644
--- a/lib/mnesia/src/mnesia_locker.erl
+++ b/lib/mnesia/src/mnesia_locker.erl
@@ -40,7 +40,8 @@
 	 sticky_wlock_table/3,
 	 wlock/3,
 	 wlock_no_exist/4,
-	 wlock_table/3
+	 wlock_table/3,
+	 load_lock_table/3
 	]).
 
 %% sys callback functions
@@ -657,6 +658,7 @@ rwlock(Tid, Store, Oid) ->
 	    case need_lock(Store, Tab, Key, Lock)  of
 		yes ->
 		    Ns = w_nodes(Tab),
+		    check_majority(Tab, Ns),
 		    Res = get_rwlocks_on_nodes(Ns, rwlock, Node, Store, Tid, Oid),
 		    ?ets_insert(Store, {{locks, Tab, Key}, Lock}),
 		    Res;
@@ -683,6 +685,28 @@ w_nodes(Tab) ->
 	_ ->  mnesia:abort({no_exists, Tab})
     end.
 
+%% If the table has the 'majority' flag set, we can
+%% only take a write lock if we see a majority of the
+%% nodes.
+
+check_majority(true, Tab, HaveNs) ->
+    check_majority(Tab, HaveNs);
+check_majority(false, _, _) ->
+    ok.
+
+check_majority(Tab, HaveNs) ->
+    case ?catch_val({Tab, majority}) of
+	true ->
+	    case mnesia_lib:have_majority(Tab, HaveNs) of
+		true ->
+		    ok;
+		false ->
+		    mnesia:abort({no_majority, Tab})
+	    end;
+	_ ->
+	    ok
+    end.
+
 %% aquire a sticky wlock, a sticky lock is a lock
 %% which remains at this node after the termination of the
 %% transaction.
@@ -773,10 +797,14 @@ sticky_wlock_table(Tid, Store, Tab) ->
 %% local store when we have aquired the lock.
 %% 
 wlock(Tid, Store, Oid) ->
+    wlock(Tid, Store, Oid, _CheckMajority = true).
+
+wlock(Tid, Store, Oid, CheckMajority) ->
     {Tab, Key} = Oid,
     case need_lock(Store, Tab, Key, write) of
 	yes ->
 	    Ns = w_nodes(Tab),
+	    check_majority(CheckMajority, Tab, Ns),
 	    Op = {self(), {write, Tid, Oid}},
 	    ?ets_insert(Store, {{locks, Tab, Key}, write}),
 	    get_wlocks_on_nodes(Ns, Ns, Store, Op, Oid);
@@ -789,6 +817,9 @@ wlock(Tid, Store, Oid) ->
 wlock_table(Tid, Store, Tab) ->
     wlock(Tid, Store, {Tab, ?ALL}).
 
+load_lock_table(Tid, Store, Tab) ->
+    wlock(Tid, Store, {Tab, ?ALL}, _CheckMajority = false).
+
 %% Write lock even if the table does not exist
 
 wlock_no_exist(Tid, Store, Tab, Ns) ->
diff --git a/lib/mnesia/src/mnesia_schema.erl b/lib/mnesia/src/mnesia_schema.erl
index a6c8ffec01..b3f06322d9 100644
--- a/lib/mnesia/src/mnesia_schema.erl
+++ b/lib/mnesia/src/mnesia_schema.erl
@@ -179,6 +179,7 @@ do_set_schema(Tab, Cs) ->
     set({Tab, load_order}, Cs#cstruct.load_order),
     set({Tab, access_mode}, Cs#cstruct.access_mode),
     set({Tab, majority}, Cs#cstruct.majority),
+    set({Tab, all_nodes}, mnesia_lib:cs_to_nodes(Cs)),
     set({Tab, snmp}, Cs#cstruct.snmp),
     set({Tab, user_properties}, Cs#cstruct.user_properties),
     [set({Tab, user_property, element(1, P)}, P) || P <- Cs#cstruct.user_properties],
diff --git a/lib/mnesia/src/mnesia_tm.erl b/lib/mnesia/src/mnesia_tm.erl
index c7a0c28589..0b87c40add 100644
--- a/lib/mnesia/src/mnesia_tm.erl
+++ b/lib/mnesia/src/mnesia_tm.erl
@@ -1259,23 +1259,15 @@ needs_majority(Tab, #prep{majority = M}) ->
 		false ->
 		    [{Tab, []} | M];
 		true ->
-		    CopyHolders = all_copy_holders(Tab),
+		    CopyHolders = val({Tab, all_nodes}),
 		    [{Tab, CopyHolders} | M]
 	    end
     end.
 
-all_copy_holders(Tab) ->
-    DC = val({Tab, disc_copies}),
-    DO = val({Tab, disc_only_copies}),
-    RC = val({Tab, ram_copies}),
-    DC ++ DO ++ RC.
-
 have_majority([], _) ->
     ok;
 have_majority([{Tab, AllNodes} | Rest], Nodes) ->
-    Missing = AllNodes -- Nodes,
-    Present = AllNodes -- Missing,
-    case length(Present) > length(Missing) of
+    case mnesia_lib:have_majority(Tab, AllNodes, Nodes) of
 	true ->
 	    have_majority(Rest, Nodes);
 	false ->