User-Level Scheduling

In Section 3.4, we have seen an example of user-level scheduling that is achieved by explicitly sending messages in application programs. Here, we show a similar scheduling mechanism that is achieved by implicitly communicating with the scheduler object. An evaluator class sched-eval and two methods are defined: (do-method-call) Instead of invoking a method, a message data is sent to the scheduler object. (eval-entry) At the end of each method execution, it notifies the scheduler to yield its thread of control. We assume that the scheduler object is bound to variable *scheduler* and has methods request and run-next.

;;; an evaluator class for user-customized scheduling
(defclass sched-eval ())

;;; send a request to the scheduler for method invocation
(defmethod sched-eval do-method-call
(type target method args meta-args env)
(let ((m (make-message
target method args meta-args)))
(request *scheduler*
(cons m (get-priority env)))))

;;; yield the control to the scheduler
(defmethod sched-eval eval-entry (exp env)
(eval-entry super exp env)
(run-next *scheduler*)) ; notify end of execution

;;; an evaluator class for user-customized scheduling (defclass sched-eval ()) ;;; send a request to the scheduler for method invocation (defmethod sched-eval do-method-call (type target method args meta-args env) (let ((m (make-message target method args meta-args))) (request *scheduler* (cons m (get-priority env))))) ;;; yield the control to the scheduler (defmethod sched-eval eval-entry (exp env) (eval-entry super exp env) (run-next *scheduler*)) ; notify end of execution