From 38eef7af0f8bc1d2d152cefb8df1e1303ddcac45 Mon Sep 17 00:00:00 2001
From: Ulf Wiger <ulf.wiger@erlang-solutions.com>
Date: Thu, 9 Dec 2010 18:14:15 +0100
Subject: 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.
---
 lib/mnesia/src/mnesia_locker.erl | 33 ++++++++++++++++++++++++++++++++-
 1 file changed, 32 insertions(+), 1 deletion(-)

(limited to 'lib/mnesia/src/mnesia_locker.erl')

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) ->
-- 
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