# a round robin scheduler for pf 

# FIXME: DEPRECATED: consider using coroutines/generators instead of
# this, or proper tasks.



provide >taskq

# define words to run round robin tasks.
# a task is a structure containing a datastack and a return stack
# tasks suspend by calling yield.


variable tasks
variable backup-tasks
: clear-tasks tasks @> backup-tasks ! () tasks ! ;
clear-tasks


# task queue access
: >taskq  tasks push ;
: >>taskq tasks queue ;
: taskq>  tasks pop ;

: task-trampoline execute ;			# startup stub
: make-task-rs () ['] task-trampoline xt>body + ;	# entry address = stub body

: make-task + make-task-rs swap 2 pack ;   	# ( datastack xt -- task )
: start-task make-task >taskq ;
: drop-task taskq> drop ;			# kill last task
: swap-task taskq> taskq> swap >taskq >taskq ; 	# swap tasks
: dup-task taskq> dup >taskq >taskq ;

# control flow
: yield taskq> swaptask >>taskq ;		# transfers control to the next task
: exit-task taskq> swaptask drop ;		# exit current task



# NOTE: tasks & exceptions
# each task needs its own error handler, which should call
# exit-task.. needs to be done in the task boot code.

:noname clear-tasks ; is idle


# like make-task, but in addition the words defined by the loader word 
# are captured on the return stack. arguments are passed to 'start'


: boot-task
	# next words are temporary. links (code & data) will be stored on task's RS.
	# setup code is symbolic for ease of connecting things.
	mark

	# execute loader
	execute

	# get boot data
	` start find mark>		 	# ( ds xt.start links )

	# prepare task
	>r + r>					# ( mod.ds links )
	make-task-rs swap +			# ( mod.ds rs )
	swap 2 pack				# ( task )

; "( datastack xt.loader -- task )\tLoad and boot a task and convert to task structure. This avoids child dicts, and stores links in task struct (RS)." ,


: load-task boot-task >taskq 
; "( datastack xt.loader -- )\tLoad, boot and schedule a task." ,