''
'' $Id: SimpleTask.bas,v 1.2 1994/03/16 15:07:24 alex Rel $
''
'' Task creation and co-ordination from BASIC
''
'' Derived from RKM example (c) Copyright 1992 Commodore-Amiga, Inc.
''

DEFINT A-Z

' multi-threaded code runs in several contexts, so the normal checks may
' crash correct programs - lets turn everything off
REM $NOAUTODIM
REM $NOARRAY
REM $NOBREAK
REM $NOOVERFLOW
REM $NOEVENT
REM $NOSTACK

'REM $INCLUDE Exec.bh
'REM $INCLUDE Utility.bc

REM $INCLUDE BLib/ExecSupport.bas
REM $INCLUDE BLib/HookEntryTask.bas

LIBRARY OPEN "exec.library", LIBRARY_MINIMUM&

CONST STACK_SIZE& = 1000

DIM SHARED sharedvar&, junk&

'
' The sub-task, the range of things this can do are pretty limited: it absolutely
' must not-ever call DOS (since you must be a process to do that), this means that
' many BASIC commands are out. It must not do anything which may cause non-reentrant
' BASIC runtimes to be reentered (e.g. string handling, dynamic array usage).
'
' Basically you can call the OS do simple BASIC stuff and little else.
'
SUB simpletask
	SHARED parent&, sigf_quitchild&
	STATIC sigb_quitchild

	sigf_quitchild& = -1	' so the parent knows we had a problem
	sigb_quitchild = AllocSignal&(-1)
	IF sigb_quitchild <> -1 THEN
		sigf_quitchild& = 1& << sigb_quitchild
		Signal parent&, SIGF_SINGLE&	' signal our parent we're initialised
		DO WHILE sharedvar& < &h7fffffff
			INCR sharedvar&
			IF SetSignal&(0, sigf_quitchild&) AND sigf_quitchild& THEN EXIT LOOP
		LOOP
		FreeSignal sigb_quitchild
	END IF
	Forbid		' forcibly run us to completion
	Signal parent&, SIGF_SINGLE&	' signal our parent we're about to quit
END SUB

SUB main
	SHARED parent&, sigf_quitchild&
	STATIC task&
	
	sharedvar& = 0
	
	parent& = FindTask&(NULL&)	' so the child nows who its parent was
	task& = CreateHookEntryTask&(SADD("SimpleTask" + CHR$(0)), 0, _
	  VARPTRS(simpletask), STACK_SIZE&)
	IF task& <> NULL& THEN
		junk& = SetSignal&(0, SIGF_SINGLE&)	' ensure signal is clear
		junk& = xWait&(SIGF_SINGLE&)		' wait until task has started
		IF sigf_quitchild& <> -1 THEN
			PRINT "This program initialised a variable to zero, then started a"
			PRINT "separate task which is incrementing that variable right now,"
			PRINT "while this program waits for an event."
			PRINT "Cause an event now (click in the window!)"
			
			SLEEP
			
			PRINT "The shared variable now equals"; sharedvar&
			
			' Tasks created via CreateHookEntryTask must not be DeleteTask'd or
			' RemTask'd (since not all of the memory is attached to the MemLists)
			' So we first ask the child to terminate by giving it a signal which
			' it allocated, then borrow the SIGF_SINGLE signal to co-ordinate our
			' actions with our child task
			
			Signal task&, sigf_quitchild&		' ask the child to terminate
			
			' Whilst the RKMs say say you can't use any of the systems signal bits
			' SIGF_SINGLE can be legitimately used in this way; you clear the signal,
			' then immediately wait on it
			
			junk& = SetSignal&(0, SIGF_SINGLE&)	' ensure signal is clear
			junk& = xWait&(SIGF_SINGLE&)		' and wait until it does quit
		ELSE
			PRINT "Child couldn't allocate a termination signal"
		END IF
	ELSE
		PRINT "Can't create task"
	END IF
END SUB

main
END