1.x: observeOn + immediate scheduler to be a request rebatcher #3964
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This PR removes the
immediate()
scheduler "optimization" fromobserveOn
and treats it as a common scheduler. SinceobserveOn
has a stable request pattern, this turns it into a rebatching operator. No matter what the downstream requests, the upstream will requests of the specified size (with 25% as low water mark; i.e., replenishment after 75%). Sinceimmediate
is synchronous, this will run the drain loop, non-reentrant, on the caller thread.I found this mode of operation very handy in my Reactive-RPC prototype and a simple streaming echo RPC call; it prevents going unbounded and bloating the message sender threads: