SERVER-1713 a WriteBackManager and exposing its queuesEmpty() method

1 files changed, 75 insertions, 0 deletions

diff --git a/s/d_writeback.h b/s/d_writeback.h
new file mode 100644
index 00000000000..365a3e6aadc
--- /dev/null
+++ b/s/d_writeback.h
@@ -0,0 +1,75 @@
+// @file d_writeback.h
+
+/**
+*    Copyright (C) 2010 10gen Inc.
+*
+*    This program is free software: you can redistribute it and/or  modify
+*    it under the terms of the GNU Affero General Public License, version 3,
+*    as published by the Free Software Foundation.
+*
+*    This program is distributed in the hope that it will be useful,
+*    but WITHOUT ANY WARRANTY; without even the implied warranty of
+*    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+*    GNU Affero General Public License for more details.
+*
+*    You should have received a copy of the GNU Affero General Public License
+*    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#pragma once
+
+#include "../pch.h"
+
+#include "../util/queue.h"
+
+namespace mongo {
+
+    /*
+     * The WriteBackManager keeps one queue of pending operations per mongos. The operations get here
+     * if they were directed to a chunk that is no longer in this mongod server. The operations are
+     * "written back" to the mongos server per its request (command 'writebacklisten').
+     *
+     * The class is thread safe.
+     */
+    class WriteBackManager{
+    public:
+        WriteBackManager();
+        ~WriteBackManager();
+
+        /*
+         * @param remote server ID this operation came from
+         * @param op the operation itself
+         *
+         * Enqueues opeartion 'op' in server 'remote's queue. The operation will be written back to
+         * remote at a later stager.
+         */
+        void queueWriteBack( const string& remote , const BSONObj& op );
+
+        /*
+         * @param remote server ID
+         * @return the queue for operations that came from 'remote'
+         *
+         * Gets access to server 'remote's queue, which is synchronized.
+         */
+        BlockingQueue<BSONObj>* getWritebackQueue( const string& remote );
+
+        /*
+         * @return true if there is no operation queued for write back
+         */
+        bool queuesEmpty() const;
+
+    private:
+        // a map from mongos's serverIDs to queues of "rejected" operations
+        // an operation is rejected if it targets data that does not live on this shard anymore
+        typedef map< string , BlockingQueue<BSONObj>* > WriteBackQueuesMap;
+
+        // '_writebackQueueLock' protects only the map itself, since each queue is syncrhonized.
+        mutable mongo::mutex _writebackQueueLock;
+        WriteBackQueuesMap _writebackQueues;
+
+    };
+
+    // TODO collect global state in a central place and init during startup
+    extern WriteBackManager writeBackManager;
+
+} // namespace mongo