Flux#sampleFirst(Duration) marble diagram does not match implementation semantics

[oliviercoma]

Documentation Issue

The marble diagram for Flux#sampleFirst(Duration) do not match the actual behavior implemented in FluxSampleFirst.

Observed behavior (from FluxSampleFirst source):

• The delay window starts only after the first element is emitted (not on subscribe() and not on request()).
• When the gate is open, the element is emitted immediately, not delayed until the end of the sampling period.
• Any element emitted while the gate is closed is discarded.
• No element is emitted when the delay expires (ie there is no “last seen” / trailing emission).

This behavior matches the semantics of sampleFirst(Publisher<?> sampler), whose marble diagram is correct.

However, the marble diagram for sampleFirst(Duration) currently suggests:

• a timer starting on request()
• a trailing emission at timer expiration,
  neither of which are implemented.

Improvement Suggestion

Marble diagram should be updated to match implemented semantic