Sergio Bossa created CASSANDRA-15666:
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Summary: Race condition when completing stream sessions
Key: CASSANDRA-15666
URL: https://issues.apache.org/jira/browse/CASSANDRA-15666
Project: Cassandra
Issue Type: Bug
Components: Legacy/Streaming and Messaging
Reporter: Sergio Bossa
{{StreamSession#prepareAsync()}} executes, as the name implies, asynchronously
from the IO thread: this opens up for race conditions between the sending of
the {{PrepareSynAckMessage}} and the call to
{{StreamSession#maybeCompleted()}}. I.e., the following could happen:
1) Node A sends {{PrepareSynAckMessage}} from the {{prepareAsync()}} thread.
2) Node B receives it and starts streaming.
3) Node A receives the streamed file and sends {{ReceivedMessage}}.
4) At this point, if this was the only file to stream, both nodes are ready to
close the session via {{maybeCompleted()}}, but:
a) Node A will call it twice from both the IO thread and the thread at #1,
closing the session and its channels.
b) Node B will attempt to send a {{CompleteMessage}}, but will fail because the
session has been closed in the meantime.
There are other subtle variations of the pattern above, depending on the order
of concurrently sent/received messages.
I believe the best fix would be to modify the message exchange so that:
1) Only the "follower" is allowed to send the {{CompleteMessage}}.
2) Only the "initiator" is allowed to close the session and its channels after
receiving the {{CompleteMessage}}.
By doing so, the message exchange logic would be easier to reason about, which
is overall a win anyway.
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