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;;; Asynchronous queues
;; Copyright (C) 2012 Free Software Foundation, Inc.
;; This library is free software; you can redistribute it and/or
;; modify it under the terms of the GNU Lesser General Public
;; License as published by the Free Software Foundation; either
;; version 3 of the License, or (at your option) any later version.
;;
;; This library is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
;; Lesser General Public License for more details.
;;
;; You should have received a copy of the GNU Lesser General Public
;; License along with this library; if not, write to the Free Software
;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
;; 02110-1301 USA
;;; Commentary:
;;;
;;; An implementation of thread-safe asynchronous queues, with both
;;; blocking and nonblocking interfaces.
;;;
;;; Code:
(define-module (ice-9 async-queue)
#:use-module (srfi srfi-9)
#:use-module (srfi srfi-9 gnu)
#:use-module (ice-9 format)
#:use-module (ice-9 threads)
#:export (make-async-queue
async-queue?
async-queue-length async-queue-capacity
async-queue-stop-accepting! async-queue-restart!
async-queue-push!
async-queue-pop! async-queue-try-pop!))
;; One thing that we should be careful about is to avoid exposing
;; information about the way this queue is implemented.
;;
;; Currently we use an array, but it's easy to imagine a functional
;; implementation facilitated by compare-and-swap operations, with
;; perhaps the option to disable the blocking interfaces (and thereby
;; remove the need for the mutex and cond var).
;;
(define-record-type <async-queue>
(make-aq mutex condvar buf capacity length read-idx fixed? underflow-thunk)
async-queue?
(mutex aq-mutex)
(condvar aq-condvar)
(buf aq-buf set-aq-buf!)
(capacity aq-capacity set-aq-capacity!)
(length aq-length set-aq-length!)
(read-idx aq-read-idx set-aq-read-idx!)
(fixed? aq-fixed?)
(underflow-thunk aq-underflow-thunk set-aq-underflow-thunk!))
(set-record-type-printer!
<async-queue>
(lambda (aq port)
(format port "<async-queue ~x ~a/~a>" (object-address aq)
(aq-length aq) (aq-capacity aq))))
(define (aq-inc! aq)
(set-aq-length! aq (1+ (aq-length aq)))
(signal-condition-variable (aq-condvar aq)))
(define (aq-dec! aq)
(set-aq-length! aq (1- (aq-length aq)))
(signal-condition-variable (aq-condvar aq)))
(define (aq-idx aq idx)
(modulo idx (aq-capacity aq)))
(define (aq-wait aq time)
(if time
(wait-condition-variable (aq-condvar aq) (aq-mutex aq) time)
(wait-condition-variable (aq-condvar aq) (aq-mutex aq))))
(define* (make-async-queue #:key (capacity 10) (fixed? #t))
(make-aq (make-mutex)
(make-condition-variable)
(make-vector capacity #f)
capacity
0
0
fixed?
#f))
(define (async-queue-length aq)
(with-mutex (aq-mutex aq)
(aq-length aq)))
(define (async-queue-capacity aq)
(with-mutex (aq-mutex aq)
(aq-capacity aq)))
(define* (async-queue-stop-accepting! aq #:optional
(underflow-thunk (lambda () #f)))
(with-mutex (aq-mutex aq)
(set-aq-underflow-thunk! aq underflow-thunk)
(broadcast-condition-variable (aq-condvar aq))))
(define (async-queue-restart! aq)
(with-mutex (aq-mutex aq)
(set-aq-underflow-thunk! aq #f)
(broadcast-condition-variable (aq-condvar aq))))
(define* (async-queue-push! aq item #:optional time)
(with-mutex (aq-mutex aq)
(let lp ()
(cond
((aq-underflow-thunk aq)
;; Not accepting values any more.
#f)
((< (aq-length aq) (aq-capacity aq))
(let ((idx (aq-idx aq (+ (aq-read-idx aq) (aq-length aq)))))
(vector-set! (aq-buf aq) idx item)
(aq-inc! aq)
#t))
((aq-fixed? aq)
(and (aq-wait aq time)
(lp)))
(else
(let* ((capacity (* (aq-capacity 2)))
(buf (make-vector capacity #f)))
(vector-move-left! (aq-buf aq) (aq-read-idx aq) (aq-capacity aq)
buf 0)
(vector-move-left! (aq-buf aq) 0 (aq-read-idx aq)
buf (aq-read-idx aq))
(set-aq-buf! aq buf)
(set-aq-capacity! aq capacity)
(set-aq-read-idx! aq 0)
(lp)))))))
(define* (async-queue-pop! aq #:optional time
#:key (default (lambda () #f)))
((with-mutex (aq-mutex aq)
(let lp ()
(if (zero? (aq-length aq))
(or (aq-underflow-thunk aq)
(if (aq-wait aq time)
(lp)
default))
(let* ((idx (aq-read-idx aq))
(item (vector-ref (aq-buf aq) idx)))
(vector-set! (aq-buf aq) idx #f)
(set-aq-read-idx! aq (aq-idx aq (1+ idx)))
(aq-dec! aq)
(lambda () item)))))))
(define* (async-queue-try-pop! aq
#:key (default (lambda () #f)))
((with-mutex (aq-mutex aq)
(if (zero? (aq-length aq))
default
(let* ((idx (aq-read-idx aq))
(item (vector-ref (aq-buf aq) idx)))
(vector-set! (aq-buf aq) idx #f)
(set-aq-read-idx! aq (aq-idx aq (1+ idx)))
(aq-dec! aq)
(lambda () item))))))
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