Actually, I'd place the problem in Process>>#priority: method - it should
make sure that if the active process downgrades it's priority below an
existing runnable process, the active process will automatically be
preempted - something like this (works for your examples):

Process>>priority: anInteger 
	"Set the receiver's priority to anInteger."
	(anInteger >= Processor lowestPriority and:[anInteger <= Processor
highestPriority])
		ifTrue: [
			priority := anInteger.
			(self isActiveProcess and: [anInteger < Processor nextReadyProcess
priority])
				ifTrue: [ [self resume] fork. self suspend ]
			]
		ifFalse: [self error: 'Invalid priority: ', anInteger printString]		

And then the #yield primitive can remain as it is :)

J



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