Unexpected behaviour may occur when AsyncDisruptorAppender#producerType is set to `SINGLE` with multiple appending threads

[brenuart]

Unexpected behaviour may happen when AsyncDisruptorAppender#producerType is set to SINGLE while multiple threads are appending to the appender.

Setting the producer type to SINGLE is an optimisation of the LMX disruptor for cases where only one thread is ever appending to the ring buffer. However, behaviour is unpredictable if the single thread condition is not verified. There is unfortunately no easy way to verify this condition when the appender is first initialised and therefore no way to protect ourselves from a "bad" configuration.

I was wondering if the performance improvement is worth it... I mean, most people won't even notice the difference and worst, are likely to loose events without even noticing it if they set the parameter to an inappropriate value. And if they loose some, they are unlikely to find the cause by themselves :-(

Hence the question: should we keep this configuration option at all ?

[brenuart]

@philsttr What do you think?

[philsttr]

Can be deprecated, for removal in 8.0

[brenuart]

@philsttr I mentioned the deprecation in the release note.

Don't you think we should also remove the section about the producer type from the README?
(my bad, nothing is said about this setting in the documentation)