db: Import db/commmitlog/*

Signed-off-by: Calle Wilund <calle@cloudius-systems.com>

db/commitlog/PeriodicCommitLogService.java

@@ -0,0 +1,59 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.cassandra.db.commitlog;
+
+import org.apache.cassandra.config.DatabaseDescriptor;
+import org.apache.cassandra.utils.concurrent.WaitQueue;
+
+class PeriodicCommitLogService extends AbstractCommitLogService
+{
+
+    private static final int blockWhenSyncLagsMillis = (int) (DatabaseDescriptor.getCommitLogSyncPeriod() * 1.5);
+
+    public PeriodicCommitLogService(final CommitLog commitLog)
+    {
+        super(commitLog, "PERIODIC-COMMIT-LOG-SYNCER", DatabaseDescriptor.getCommitLogSyncPeriod());
+    }
+
+    protected void maybeWaitForSync(CommitLogSegment.Allocation alloc)
+    {
+        if (waitForSyncToCatchUp(Long.MAX_VALUE))
+        {
+            // wait until periodic sync() catches up with its schedule
+            long started = System.currentTimeMillis();
+            pending.incrementAndGet();
+            while (waitForSyncToCatchUp(started))
+            {
+                WaitQueue.Signal signal = syncComplete.register(CommitLog.instance.metrics.waitingOnCommit.time());
+                if (waitForSyncToCatchUp(started))
+                    signal.awaitUninterruptibly();
+                else
+                    signal.cancel();
+            }
+            pending.decrementAndGet();
+        }
+    }
+
+    /**
+     * @return true if sync is currently lagging behind inserts
+     */
+    private boolean waitForSyncToCatchUp(long started)
+    {
+        return started > lastSyncedAt + blockWhenSyncLagsMillis;
+    }
+}