sodonnel commented on code in PR #6613:
URL: https://github.com/apache/ozone/pull/6613#discussion_r2457505281
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hadoop-hdds/client/src/main/java/org/apache/hadoop/hdds/scm/XceiverClientGrpc.java:
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@@ -504,6 +516,65 @@ private XceiverClientReply sendCommandWithRetry(
}
}
+ /**
+ * Starts a streaming read operation, intended to read entire blocks from
the datanodes. This method expects a
+ * {@link StreamObserver} to be passed in, which will be used to receive the
streamed data from the datanode.
+ * Upon successfully starting the streaming read, a {@link
StreamingReadResponse} is returned, which contains
+ * information about the datanode used for the read, and the request
observer that can be used to manage the stream
+ * (e.g., to cancel it if needed). A semaphore is acquired to limit the
number of concurrent streaming reads so upon
+ * successful return of this method, the caller must ensure to call {@link
#completeStreamRead(StreamingReadResponse)}
+ * to release the semaphore once the streaming read is complete.
+ * @param request The container command request to initiate the streaming
read.
+ * @param streamObserver The observer that will handle the streamed
responses.
+ * @return A {@link StreamingReadResponse} containing details of the
streaming read operation.
+ * @throws IOException
+ * @throws InterruptedException
+ */
+ @Override
+ public StreamingReadResponse streamRead(ContainerCommandRequestProto request,
+ StreamObserver<ContainerCommandResponseProto> streamObserver) throws
IOException, InterruptedException {
+ List<DatanodeDetails> datanodeList = sortDatanodes(request);
+ IOException lastException = null;
+ for (DatanodeDetails dn : datanodeList) {
+ try {
+ checkOpen(dn);
+ semaphore.acquire();
+ XceiverClientProtocolServiceStub stub = asyncStubs.get(dn.getID());
+ if (stub == null) {
+ throw new IOException("Failed to get gRPC stub for DataNode: " + dn);
+ }
+ if (LOG.isDebugEnabled()) {
+ LOG.debug("Executing command {} on datanode {}",
processForDebug(request), dn);
+ }
+ StreamObserver<ContainerCommandRequestProto> requestObserver = stub
+ .withDeadlineAfter(timeout, TimeUnit.SECONDS)
+ .send(streamObserver);
+ requestObserver.onNext(request);
+ requestObserver.onCompleted();
+ return new StreamingReadResponse(dn,
(ClientCallStreamObserver<ContainerCommandRequestProto>) requestObserver);
Review Comment:
From
https://github.com/grpc/grpc-java/blob/ea7444607565f9d3ba8e6fe6e9d70a828f7645de/examples/src/main/java/io/grpc/examples/cancellation/CancellationClient.java#L97
It is valid to call `cancel` after `onComplete`, but it is not valid to call
`onError` after `onComplete`.
From what I read, `cancel` effectively calls `onError`, but the different is
the meaning of what you are trying to do but not really any difference in
functionality. The signal we sent to the server doesn't actually do anything
except (hopefully) terminate the flow of streaming reads.
But the error flow isn't working correctly. The combination of failed /
completed in the code isn't working as expected when both error and complete
have been set to true. I need to look at it a bit more.
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