35 lines
1.1 KiB
Scheme
35 lines
1.1 KiB
Scheme
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; Copyright (c) 1993, 1994 Richard Kelsey and Jonathan Rees. See file COPYING.
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; Mailboxes (to be used with the threads package)
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(define (make-mailbox)
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(vector (make-lock) (make-queue) (make-queue)))
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(define (mailbox-lock mbx) (vector-ref mbx 0))
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(define (mailbox-messages mbx) (vector-ref mbx 1))
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(define (mailbox-readers mbx) (vector-ref mbx 2))
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(define (mailbox-empty? mbx)
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(queue-empty? (mailbox-readers mbx)))
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(define (mailbox-write mbx message)
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(with-lock (mailbox-lock mbx)
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(lambda ()
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(if (queue-empty? (mailbox-readers mbx))
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(enqueue (mailbox-messages mbx) message)
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(condvar-set! (dequeue (mailbox-readers mbx)) message)))))
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(define (mailbox-read mbx)
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((with-lock (mailbox-lock mbx)
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(lambda ()
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(if (queue-empty? (mailbox-messages mbx))
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(let ((cv (make-condvar)))
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(enqueue (mailbox-readers mbx) cv)
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;; The condvar-ref *must* happen after lock is released,
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;; otherwise deadlock will result.
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(lambda () (condvar-ref cv)))
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(let ((message (dequeue (mailbox-messages mbx))))
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(lambda () message)))))))
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