Chuck Rolke created DISPATCH-863:
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Summary: Excessive locking between message receive and send
Key: DISPATCH-863
URL: https://issues.apache.org/jira/browse/DISPATCH-863
Project: Qpid Dispatch
Issue Type: Bug
Components: Router Node
Affects Versions: 1.0.0
Reporter: Chuck Rolke
Priority: Major
Support for streaming messages (commit c9262728) introduced locking between
message receive and message send.
Before streaming:
* message_receive creates the message buffer list with no locks
* message_send sends messages with no locks
* When all copies of the message are sent then the last sender deletes the
message content including all buffers
With streaming:
* message_receive takes the content lock (per buffer) as each buffer is added
* message_send takes the content lock (per buffer) as each buffer is consumed.
This happens once for each message copy.
* message_send possibly frees the buffer if all message copies have sent that
buffer.
* When all copies of the message are sent then the last sender deletes the
message content. All buffers are already freed.
There may be a problem with all those locks:
* *Lock ownership* If the message is being streamed to N destinations then the
buffer lock will have contention from N I/O threads and the mutex ownership
will surely bounce from thread to thread.
* *Lock per buffer add/remove* If a 1 Mbyte message is streamed to N
destinations then the buffer lock will be taken 2000 times by message_receive
and (N * 2000) times by message_send.
With some careful design lock usage could be greatly reduced or even eliminated.
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