Marek Laca created QPID-8532:
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Summary: [Broker-J] Inaccurate calculation of selection timeout
Key: QPID-8532
URL: https://issues.apache.org/jira/browse/QPID-8532
Project: Qpid
Issue Type: Improvement
Components: Broker-J
Reporter: Marek Laca
The SelectorThread.SelectTask inner class is responsible for selecting the
incoming data from the connection socket.
The selection timeout in SelectorThread.SelectionTask defines how long will be
the IO-thread blocked in select method waiting for new connection data.
The timeout is calculated based on the nearest connection event of all
registered connection.
SelectionTask is working in the loop:
# IO-thread waits for new connection data, the timeout is utilized.
# The new connection jobs are registered pushed into the scheduler queue.
# The nearest connection event is picked up from all registered connections.
# The next timeout is calculated based on current time.
# IO-thread processes all new connection jobs.
Hence, the calculated timeout is inaccurate and absolute when the 'select'
method is called.
The '_nextTimeout' is neither volatile nor atomic variable despite the fact
that it could be used by multiple IO-threads.
If the SelectionTask kept the time of the nearest connection event instead of
the next timeout then the timeout would be calculated just before calling the
select method based on the current time.
If the timeout is bigger than zero then the select method (blocking selection
operation) will be called. If the time of the nearest connection event has
passed then the selectNow (non-blocking selection operation) method will be
called.
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