@startuml

hide footbox

participant "E20 main thread" as main
participant "tdm thread" as sub

sub <-- : a synchronous event
activate sub
--> main: a synchronous event
activate main
sub -> sub: calling thread callbacks in tdm-thread
activate sub
deactivate sub
sub --> main: sending a synchronous event
sub -> sub: pthread_cond_wait
activate sub
main -> main: calling thread callbacks in main-thread
activate main
deactivate main
main --> sub: sending a synchronous event
main -> main: pthread_cond_wait
activate main
deactivate sub
deactivate main
deactivate main
deactivate sub

... <color #red>(DEADLOCK)</color> ...
note over main, sub
	* 만약 main-thread, tdm-thread에서 동시에 synchronous event가 발생되게 되면 deadlock발생됨
		- 양쪽에서 모두 pthread_cond_wait에서 대기
	* sync event는 한쪽 thread에서만 발생되도록 보장되어야 함.
		- tdm-thread -> main-thread방향으로만 sync event전달만 허용
	* sync event의 종류
		- backend에서 스스로 발생되는 event들만 가능
		- output status변경중에 connection/disconnection, virtual output creation/destruction
end note

@enduml