The following came from the not uncommon Question/Answer pair
Q: I Want Threads A: You Have An [Event] Loop
mailto:[email protected] (Uwe Klein) wrote in the comp.lang.tcl newsgroup:
Your answer says only that tcl has an event loop, but gives no explamation as to the differences / advantages.
1st Try:
POLLED
see if any in a list of jobs have to be done and process them. loop till dead.
THREAD
In a threaded program one will do each "primitive" loop of action in its own thread.
thread1 { block in read ; read file ; process read ;
signal whats been done }
thread2 { block on user input ; process user input ;
signal for crt update }
thread3 { ...Where threads interact they have to be synced somehow.
EVENT
In event-oriented programming one will set up an event handler for anything that should / will happen.
event1 { fileevent readable datafile { do what must be done
i.e. put data into dataarray } }
event2 { writing to dataarray { compute depending values } }
event2a { writing to dataarray { update crt } }
event3 { button EXIT { clean up and exit }
event4 { ...Generated events are queued and then processed by the event loop.
If all dependencies are described correctly through "trace variable" , "fileevent", "widget -command" , .. any internal/external stimulus will cascade down its described dependecies. Think of an event-looped program as something equivalent to a Makefile for your functional requirements.
Caveat: if your code contains "computing monoblocs" your program becomes unresponsive.