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135 lines
4.2 KiB
Scheme
135 lines
4.2 KiB
Scheme
;;; engine.ss
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;;; Copyright 1984-2017 Cisco Systems, Inc.
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;;;
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;;; Licensed under the Apache License, Version 2.0 (the "License");
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;;; you may not use this file except in compliance with the License.
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;;; You may obtain a copy of the License at
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;;;
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;;; http://www.apache.org/licenses/LICENSE-2.0
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;;;
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;;; Unless required by applicable law or agreed to in writing, software
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;;; distributed under the License is distributed on an "AS IS" BASIS,
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;;; WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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;;; See the License for the specific language governing permissions and
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;;; limitations under the License.
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;;; Notes:
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;;; The engine code defines three functions: make-engine,
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;;; engine-block, and engine-return.
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;;; Keyboard interrupts are caught while an engine is running
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;;; and the engine disabled while the handler is running.
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;;; All of the engine code is defined within local state
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;;; containing the following variables:
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;;; *active* true iff an engine is running
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;;; *exit* the continuation to the engine invoker
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;;; *keybd* the saved keyboard interrupt handler
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;;; *timer* the saved timer interrupt handler
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(let ()
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(define-threaded *exit*)
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(define-threaded *keybd*)
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(define-threaded *timer*)
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(define-threaded *active* #f)
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(define cleanup
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(lambda (who)
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(unless *active* ($oops who "no engine active"))
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(set! *active* #f)
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(keyboard-interrupt-handler *keybd*)
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(timer-interrupt-handler *timer*)
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(set! *keybd* (void))
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(set! *exit* (void))
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(set! *timer* (void))))
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(define setup
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(lambda (exit)
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(set! *active* #t)
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(set! *keybd* (keyboard-interrupt-handler))
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(keyboard-interrupt-handler (exception *keybd*))
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(set! *timer* (timer-interrupt-handler))
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(timer-interrupt-handler block)
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(set! *exit* exit)))
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(define block
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; disable engine and return the continuation
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(lambda ()
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(let ([exit *exit*])
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(cleanup 'engine-block)
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(set-timer (call/cc (lambda (k) (exit (lambda () k))))))))
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(define return
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; disable engine and return list (ticks value ...)
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(lambda (args)
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(let ([n (set-timer 0)])
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(let ([exit *exit*])
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(cleanup 'engine-return)
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(exit (lambda () (cons n args)))))))
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(define exception
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; disable engine while calling the handler
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(lambda (handler)
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(lambda args
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(let ([ticks (set-timer 0)])
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(let ([exit *exit*])
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(cleanup 'engine-exception)
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(apply handler args)
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(setup exit)
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(if (= ticks 0) (block) (set-timer ticks)))))))
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(define run-engine
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; run a continuation as an engine
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(lambda (k ticks)
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((call/cc
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(lambda (exit)
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(set-timer 0)
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(when *active* ($oops 'engine "cannot nest engines"))
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(setup exit)
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(k ticks))))))
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(define eng
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; create an engine from a procedure or continuation
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(lambda (k)
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(lambda (ticks complete expire)
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(unless (and (fixnum? ticks) (not (negative? ticks)))
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($oops 'engine "invalid ticks ~s" ticks))
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(unless (procedure? complete)
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($oops 'engine "~s is not a procedure" complete))
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(unless (procedure? expire)
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($oops 'engine "~s is not a procedure" expire))
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(if (= ticks 0)
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(expire (eng k))
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(let ([x (run-engine k ticks)])
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(if (procedure? x)
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(expire (eng x))
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(apply complete x)))))))
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(set! engine-return (lambda args (return args)))
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(set! engine-block (lambda () (set-timer 0) (block)))
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(set! make-engine
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(lambda (x)
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(unless (procedure? x) ($oops 'make-engine "~s is not a procedure" x))
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(eng (lambda (ticks)
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(with-exception-handler
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(lambda (c)
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(let ([ticks (set-timer 0)])
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(let ([exit *exit*])
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(cleanup 'raise)
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(call/cc
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(lambda (k)
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(exit
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(lambda ()
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(let-values ([vals (raise-continuable c)])
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(setup exit)
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(if (= ticks 0) (block) (set-timer ticks))
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(apply k vals)))))))))
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(lambda ()
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(set-timer ticks)
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(call-with-values x (lambda args (return args)))))))))
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)
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