299 lines
10 KiB
Racket
299 lines
10 KiB
Racket
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#lang racket/base
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;; Virtualized operating system, this time with presence.
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(require racket/match)
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;;---------------------------------------------------------------------------
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;; Data definitions
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;; A PID is an (arbitrary) VM-unique process identifier.
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;; A SID is an (arbitrary) process-unique subscription identifier.
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;; A QuasiQueue<X> is a list of Xs in *reversed* order.
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(struct vm (processes ;; PID -> Process
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topics ;; Topic -> Set<Flow>
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flows ;; Flow -> Set<Route>
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next-process-id ;; PID
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pending-actions ;; QuasiQueue<(cons PID Action)>
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) #:transparent)
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;; (route PID SID Handlers)
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(struct route (process-id sid handlers) #:transparent)
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(struct process (id ;; PID
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state
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interests ;; SID -> List<Handlers>
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meta-interests ;; SID -> List<Handlers>
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) #:transparent)
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(struct topic (role pattern virtual?) #:prefab)
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;; A Flow is a Topic that comes from the intersection of two dual
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;; topics.
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;; PresenceHandler = Topic -> State -> Transition
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;; AbsenceHandler = Topic * Reason -> State -> Transition
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;; MessageHandler = Topic * Message -> State -> Transition
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(struct handlers (topic presence absence message) #:transparent)
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;; actions is a plain old List<Action>, not a QuasiQueue.
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(struct transition (state actions) #:transparent)
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;; Preactions
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(struct add-role (sid handlers) #:prefab)
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(struct delete-roles (sid) #:prefab)
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(struct send-message (topic body) #:prefab)
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(struct spawn (thunk) #:prefab)
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;; An Action is either a Preaction or an (at-meta-level Preaction).
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(struct at-meta-level (preaction) #:prefab)
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;;---------------------------------------------------------------------------
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;; Topics and roles
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(define (topic-publisher pattern #:virtual? [virtual? #f])
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(topic 'publisher pattern virtual?))
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(define (topic-subscriber pattern #:virtual? [virtual? #f])
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(topic 'subscriber pattern virtual?))
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(define (co-roles r)
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(case r
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[(publisher) '(subscriber)]
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[(subscriber) '(publisher)]
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[else #f]))
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(define (co-topics t)
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(for/list ([role (co-roles (topic-role t))])
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(struct-copy topic t [topic-role role])))
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;;---------------------------------------------------------------------------
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;; QuasiQueue<X>
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(define empty-quasi-queue '())
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;; X QuasiQueue<X> -> QuasiQueue<X>
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(define (quasi-enqueue-one thing existing-quasi-queue)
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(cons thing existing-quasi-queue))
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;; List<X> QuasiQueue<X> -> QuasiQueue<X>
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(define (quasi-enqueue-many many-things-in-order existing-quasi-queue)
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(append (reverse many-things-in-order) existing-quasi-queue))
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;; QuasiQueue<X> -> List<X>
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(define (quasi-queue->list quasi-queue)
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(reverse quasi-queue))
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;; List<X> -> QuasiQueue<X>
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(define (list->quasi-queue xs)
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(reverse xs))
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;;---------------------------------------------------------------------------
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(define (make-vm boot)
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(vm (hash)
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(hash)
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(hash)
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0
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(list->quasi-queue (list (spawn boot)))))
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(define (run-vm state)
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(let loop ((remaining-actions (quasi-queue->list (vm-pending-actions state)))
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(state (struct-copy vm state [pending-actions empty-quasi-queue]))
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(outbound-actions empty-quasi-queue))
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(match remaining-actions
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['() (transition state (quasi-queue->list outbound-actions))]
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[(cons (cons pid action) rest)
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(if (at-meta-level? action)
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(let-values (((state new-actions)
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(perform-meta-action pid (at-meta-level-preaction action) state)))
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(loop rest state (quasi-enqueue-many new-actions outbound-actions)))
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(loop rest (perform-action pid action state) outbound-actions))])))
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(define (run-user-code v)
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;; TODO: use this hook to find all the bits of code that will need
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;; with-handlers and crash compensation.
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v)
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(define (perform-action pid action state)
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(match action
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[(add-role sid handlers) ...]
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[(delete-roles sid) ...]
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[(send-message topic body) ...]
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[(spawn thunk)
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(match-define (transition initial-state initial-actions) (run-user-code (thunk)))
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(define new-pid (vm-next-process-id state))
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(struct-copy vm (enqueue-actions state new-pid initial-actions)
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[processes (hash-set (vm-processes state) new-pid (process new-pid
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initial-state
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(hash)
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(hash)))]
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[next-process-id (+ new-pid 1)])]))
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(define (enqueue-actions state pid actions)
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(struct-copy vm state
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[pending-actions (quasi-enqueue-many (for/list ([a actions]) (cons pid a))
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(vm-pending-actions state))]))
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-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
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(let* ((state (requeue-pollers state))
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(state (run-runnables state))
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(state (dispatch-messages state))
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(meta-messages (reverse (vm-pending-meta-messages state)))
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(meta-handlers (append-map extract-downward-meta-message-handlers (vm-suspensions state)))
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(poller-k (and (should-poll? state) run-vm)) ;; only block if there's nothing left to do
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(state (struct-copy vm state [pending-meta-messages (list)])))
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(kernel-mode-transition (suspension state poller-k meta-handlers '())
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meta-messages
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'()
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'())))
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(define (requeue-pollers state)
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(foldl (lambda (susp state)
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(if (suspension-polling? susp)
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(enqueue-runnable (lambda () ((suspension-k susp) (suspension-state susp))) state)
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(enqueue-suspension susp state)))
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(struct-copy vm state [suspensions '()])
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(vm-suspensions state)))
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(define (run-runnables state)
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(foldl (lambda (r state) (perform-transition (r) state))
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(struct-copy vm state [pending-processes (list)])
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(reverse (vm-pending-processes state))))
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(define (dispatch-messages state)
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(foldl dispatch-message
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(struct-copy vm state [pending-messages (list)])
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(reverse (vm-pending-messages state))))
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(define (extract-downward-meta-message-handlers susp)
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(for/list ([mmh (suspension-meta-message-handlers susp)])
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(message-handler (message-handler-pattern mmh) dispatch-meta-message)))
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(define ((dispatch-meta-message message) state)
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(run-vm
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(foldl (match-suspension message
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(vm-meta-pattern-predicate state)
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suspension-meta-message-handlers)
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(struct-copy vm state [suspensions '()])
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(vm-suspensions state))))
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(define (perform-transition transition state)
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(match transition
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[(kernel-mode-transition new-suspension
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messages
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meta-messages
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new-processes)
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(let* ((state (foldl enqueue-message state messages))
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(state (foldl enqueue-runnable state new-processes))
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(state (enqueue-suspension new-suspension state))
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(state (foldl enqueue-meta-message state meta-messages)))
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state)]
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[other
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(error 'vm "Processes must return a kernel-mode-transition struct; got ~v" other)]))
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(define (enqueue-message message state)
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(struct-copy vm state [pending-messages (cons message (vm-pending-messages state))]))
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(define (enqueue-runnable r state)
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(struct-copy vm state [pending-processes (cons r (vm-pending-processes state))]))
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(define (enqueue-suspension susp state)
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(match susp
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[(suspension _ #f '() '())
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;; dead process because no continuations offered
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state]
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[(suspension _ _ _ _)
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(struct-copy vm state [suspensions (cons susp (vm-suspensions state))])]))
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(define (enqueue-meta-message message state)
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(struct-copy vm state [pending-meta-messages (cons message (vm-pending-meta-messages state))]))
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(define (dispatch-message message state)
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(foldl (match-suspension message
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(vm-pattern-predicate state)
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suspension-message-handlers)
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(struct-copy vm state [suspensions '()])
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(vm-suspensions state)))
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(define ((match-suspension message apply-pattern handlers-getter) susp state)
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(let search-handlers ((message-handlers (handlers-getter susp)))
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(cond
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[(null? message-handlers)
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;; No handler matched this message. Put the suspension
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;; back on the list for some future message.
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(enqueue-suspension susp state)]
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[(apply-pattern (message-handler-pattern (car message-handlers)) message)
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(define trapk (message-handler-k (car message-handlers)))
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(define interruptk (trapk message))
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(perform-transition (interruptk (suspension-state susp)) state)]
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[else
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(search-handlers (cdr message-handlers))])))
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(define (suspension-polling? susp)
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(not (eq? (suspension-k susp) #f)))
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(define (should-poll? state)
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(or (not (null? (vm-pending-processes state)))
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(not (null? (vm-pending-messages state)))
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(ormap suspension-polling? (vm-suspensions state))))
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(define (nested-vm boot
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#:pattern-predicate [pattern-predicate default-pattern-predicate]
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#:meta-pattern-predicate [meta-pattern-predicate default-pattern-predicate])
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(lambda () (run-vm (make-vm boot
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#:pattern-predicate pattern-predicate
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#:meta-pattern-predicate meta-pattern-predicate))))
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(define default-pattern-predicate
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(lambda (p m) (p m)))
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;;---------------------------------------------------------------------------
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(define (nested-vm-inert? susp)
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(match susp
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[(suspension (vm _ '() '() '() _ _) #f '() '())
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;; Inert iff not waiting for any messages or metamessages, and
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;; with no internal work left to do.
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#t]
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[_ #f]))
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(struct ground-event-pattern (tag evt) #:transparent)
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(struct ground-event-value (tag val) #:transparent)
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(define (match-ground-event p m)
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(equal? (ground-event-pattern-tag p) (ground-event-value-tag m)))
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(define (ground-vm boot
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#:pattern-predicate [pattern-predicate default-pattern-predicate])
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(let loop ((transition (run-vm (make-vm boot
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#:pattern-predicate pattern-predicate
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#:meta-pattern-predicate match-ground-event))))
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(for-each (lambda (thunk) (thunk)) (kernel-mode-transition-messages transition))
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(when (not (nested-vm-inert? (kernel-mode-transition-suspension transition)))
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(match transition
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[(kernel-mode-transition (suspension new-state
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polling-k
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message-handlers
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'())
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_
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'()
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'())
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(define inbound-messages
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(map (match-lambda [(message-handler (ground-event-pattern tag evt) k)
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(wrap-evt evt (lambda (v) (cons (ground-event-value tag v) k)))])
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message-handlers))
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(match-define (cons inbound-value inbound-continuation)
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(apply sync
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(wrap-evt (if polling-k always-evt never-evt)
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(lambda (v) (cons (ground-event-value 'idle (void))
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(lambda (dummy) polling-k))))
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inbound-messages))
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(loop ((inbound-continuation inbound-value) new-state))]
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[_
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(error 'ground-vm
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"Outermost VM may not spawn new siblings or send or receive metamessages")]))))
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