@startuml
scale max 900*520
skinparam backgroundColor transparent
skinparam shadowing false
skinparam defaultFontName "DejaVu Sans Mono"
skinparam defaultFontSize 13
skinparam stateBorderColor #2b6f8e
skinparam stateBackgroundColor #edf6fa
skinparam ArrowColor #8295a0
left to right direction
title A6 STATE — queue occupancy controls task readiness

state "01 EMPTY\nreceiver can block" as Empty
state "02 FULL(M2)\nsender can block" as Full
state "03 HANDOFF\nhigher receiver Ready" as Handoff
state "04 EMPTY\nspace wakes sender" as Space
state "05 FULL(M3)" as Full3
state "06 DONE\nFIFO 1,2,3" as Done

[*] --> Empty
Empty --> Handoff : send M1
Handoff --> Empty : receive M1
Empty --> Full : send M2
Full --> Space : receive M2
Space --> Full3 : blocked send completes
Full3 --> Done : receive M3
Done --> [*]
@enduml