Github user StephanEwen commented on a diff in the pull request:
https://github.com/apache/flink/pull/643#discussion_r29582495
--- Diff:
flink-staging/flink-streaming/flink-streaming-core/src/main/java/org/apache/flink/streaming/api/checkpoint/Checkpointed.java
---
@@ -0,0 +1,53 @@
+/*
+ * 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.flink.streaming.api.checkpoint;
+
+import org.apache.flink.runtime.state.OperatorState;
+
+/**
+ * This method must be implemented by functions that have state that needs
to be
+ * checkpointed. The functions get a call whenever a checkpoint should
take place
+ * and return a snapshot of their state, which will be checkpointed.
+ *
+ * <p>This interface marks a function as <i>synchronously</i>
checkpointed. While the
+ * state is written, the function is not called, so the function needs not
return a
+ * copy of its state, but may return a reference to its state. Functions
that can
+ * continue to work and mutate the state, even while the state snapshot is
being accessed,
+ * can implement the {@link
org.apache.flink.streaming.api.checkpoint.CheckpointedAsynchronously}
+ * interface.</p>
+ */
+public interface Checkpointed {
+
+ /**
+ * Gets the current operator state as a checkpoint. The state must
reflect all operations
+ * from all prior operations if this function.
+ *
+ * @param checkpointId The ID of the checkpoint.
+ * @param checkpointTimestamp The timestamp of the checkpoint, as
derived by
+ * System.currentTimeMillis() on the
JobManager.
+ *
+ * @return A snapshot of the operator state.
+ *
+ * @throws Exception Thrown if the creation of the state object failed.
This causes the
+ * checkpoint to fail. The system may decide to fail
the operation (and trigger
+ * recovery), or to discard this checkpoint attempt
and to continue running
+ * and to try again with the next checkpoint attempt.
+ */
+ OperatorState<?> snapshotState(long checkpointId, long
checkpointTimestamp) throws Exception;
+}
--- End diff --
The checkpoint ID and the timestamp are also different. The ID is random
unique and the timstamp is time
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