JAVA-361: add methods to fsync, lock, unlock the db

Author: agirbal

src/main/com/mongodb/Mongo.java

@@ -556,6 +556,55 @@ protected PoolOutputBuffer createNew(){
 
     };
 
+    /**
+     * Forces the master server to fsync the RAM data to disk
+     * This is done automatically by the server at intervals, but can be forced for better reliability. 
+     * @param async if true, the fsync will be done asynchronously on the server.
+     * @return 
+     */
+    public CommandResult fsync(boolean async) {
+        DBObject cmd = new BasicDBObject("fsync", 1);
+        if (async) {
+            cmd.put("async", 1);
+        }
+        return getDB("admin").command(cmd);
+    }
+
+    /**
+     * Forces the master server to fsync the RAM data to disk, then lock all writes.
+     * The database will be read-only after this command returns.
+     * @return 
+     */
+    public CommandResult fsyncAndLock() {
+        DBObject cmd = new BasicDBObject("fsync", 1);
+        cmd.put("lock", 1);
+        return getDB("admin").command(cmd);
+    }
+
+    /**
+     * Unlocks the database, allowing the write operations to go through.
+     * This command may be asynchronous on the server, which means there may be a small delay before the database becomes writable.
+     * @return 
+     */
+    public DBObject unlock() {
+        DB db = getDB("admin");
+        DBCollection col = db.getCollection("$cmd.sys.unlock");
+        return col.findOne();
+    }
+
+    /**
+     * Returns true if the database is locked (read-only), false otherwise.
+     * @return 
+     */
+    public boolean isLocked() {
+        DB db = getDB("admin");
+        DBCollection col = db.getCollection("$cmd.sys.inprog");
+        BasicDBObject res = (BasicDBObject) col.findOne();
+        if (res.containsField("fsyncLock")) {
+            return res.getInt("fsyncLock") == 1;
+        }
+        return false;
+    }
 
     // -------