4.x: Improve AsyncSubject by using lock-free methods #510
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This PR changes
AsyncSubjectto be a lock-free implementation by using atomics.Since the observable protocol forbids calling the
OnXXXmethods concurrently, there was no real need for the locked regions and it didn't protect against most races anyway.Some complication is due to the disposability feature thus that explicit state has to be checked and the relevant exceptions thrown.
The observer management has been also replaced by a straight atomic copy-on-write logic so concurrent subscriptions and subscription-termination races are handled without blocking. Note that the original implementation used
ImmutableList.Addwhich is by itself also copy-on-write thus this change should not worsen the overhead of tracking a lot of observers while the subject is active.