zhijiangW commented on a change in pull request #11515: [FLINK-16744][task] 
implement channel state persistence for unaligned checkpoints
URL: https://github.com/apache/flink/pull/11515#discussion_r401526771
 
 

 ##########
 File path: 
flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/tasks/SubtaskCheckpointCoordinatorImpl.java
 ##########
 @@ -175,6 +203,77 @@ public void checkpointState(
                }
        }
 
+       private OperatorSnapshotFutures buildOperatorSnapshotFutures(
+                       CheckpointMetaData checkpointMetaData,
+                       CheckpointOptions checkpointOptions,
+                       OperatorChain<?, ?> operatorChain,
+                       StreamOperator<?> op,
+                       Supplier<Boolean> isCanceled,
+                       ChannelStateWriteResult channelStateWriteResult) throws 
Exception {
+               CheckpointStreamFactory storage = 
checkpointStorage.resolveCheckpointStorageLocation(
+                       checkpointMetaData.getCheckpointId(),
+                       checkpointOptions.getTargetLocation());
+               OperatorSnapshotFutures snapshotInProgress = 
checkpointStreamOperator(
+                       op,
+                       checkpointMetaData,
+                       checkpointOptions,
+                       storage,
+                       isCanceled);
+               if (op == operatorChain.getHeadOperator()) {
+                       
snapshotInProgress.setInputChannelStateFuture(channelStateWriteResult
+                                                                               
                                        .getInputChannelStateHandles()
+                                                                               
                                        .thenApply(StateObjectCollection::new)
+                                                                               
                                        .thenApply(SnapshotResult::of)
+                       );
+               }
+               if (op == operatorChain.getTailOperator()) {
+                       
snapshotInProgress.setResultSubpartitionStateFuture(channelStateWriteResult
+                                                                               
                                                        
.getResultSubpartitionStateHandles()
+                                                                               
                                                        
.thenApply(StateObjectCollection::new)
+                                                                               
                                                        
.thenApply(SnapshotResult::of)
+                       );
+               }
+               return snapshotInProgress;
+       }
+
+       @Override
+       public void close() {
+               channelStateWriter.close();
+       }
+
+       // Caches checkpoint output stream factories to prevent multiple output 
stream per checkpoint.
+       // This could result from requesting output stream by different 
entities (this and channelStateWriter)
+       // We can't just pass a stream to the channelStateWriter because it can 
receive checkpoint call earlier than this class
+       // in some unaligned checkpoints scenarios
+       private static class CachingCheckpointStorageWorkerView implements 
CheckpointStorageWorkerView {
+               private final Map<Long, CheckpointStreamFactory> cache = new 
ConcurrentHashMap<>();
+               private final CheckpointStorageWorkerView delegate;
+
+               private 
CachingCheckpointStorageWorkerView(CheckpointStorageWorkerView delegate) {
+                       this.delegate = delegate;
+               }
+
+               void clearCacheFor(long checkpointId) {
+                       cache.remove(checkpointId);
+               }
+
+               @Override
+               public CheckpointStreamFactory 
resolveCheckpointStorageLocation(long checkpointId, 
CheckpointStorageLocationReference reference) {
+                       return cache.computeIfAbsent(checkpointId, id -> {
+                               try {
+                                       return 
delegate.resolveCheckpointStorageLocation(checkpointId, reference);
+                               } catch (IOException e) {
+                                       throw new WrappingRuntimeException(e);
 
 Review comment:
   `WrappingRuntimeException` is used for wrapping non-runtime exceptions? I 
guess this should belong to runtime exception. If so, how about using 
`ExceptionUtils.rethrow(e)`?

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