121 lines
3.7 KiB
Scheme
121 lines
3.7 KiB
Scheme
;;; Scsh
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;;; Posix advisory record-locking for file descriptors.
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;;; These procs may only be applied to integer file descriptors;
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;;; they may not be applied to ports.
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;;; Copyright (c) 1995 by David Albertz and Olin Shivers.
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;;; C syscall interface
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;;;;;;;;;;;;;;;;;;;;;;;
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(define-stubless-foreign %set-lock/eintr (fd cmd type whence start len)
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"set_lock")
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(define-retrying-syscall %set-lock %set-lock/eintr)
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(define-stubless-foreign %get-lock/eintr (fd cmd type whence start len)
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"get_lock")
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(define-retrying-syscall %get-lock %get-lock/eintr)
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;;; The LOCK record type
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;;;;;;;;;;;;;;;;;;;;;;;;
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(define-record %lock-region
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exclusive?
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start ; integer
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len ; Positive integer or #f
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whence ; seek/set, seek/delta, or seek/end.
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proc ; Process holding lock
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)
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(define lock-region? %lock-region?)
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(define lock-region:exclusive? %lock-region:exclusive?)
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(define lock-region:whence %lock-region:whence)
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(define lock-region:start %lock-region:start)
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(define lock-region:len %lock-region:len)
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(define lock-region:proc %lock-region:proc)
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(define set-lock-region:exclusive? set-%lock-region:exclusive?)
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(define set-lock-region:whence set-%lock-region:whence)
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(define set-lock-region:start set-%lock-region:start)
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(define set-lock-region:len set-%lock-region:len)
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(define set-lock-region:proc set-%lock-region:proc)
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;;; Backwards compatibility for one or two releases.
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(define lock-region:pid
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(deprecated-proc (lambda (lr)
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(cond ((lock-region:proc lr) => proc:pid)
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(else #f)))
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'lock-region:pid
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"Use lock-region:proc instead."))
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(define (make-lock-region exclusive? start len . maybe-whence)
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(let ((whence (:optional maybe-whence seek/set)))
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(make-%lock-region exclusive? start len whence #f)))
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;;; Internal middleman routine
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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(define (call-lock-region proc cmd fdes lock)
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(check-arg lock-region? lock proc)
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(let ((lock-type (if (lock-region:exclusive? lock) lock/write lock/read)))
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(proc fdes cmd lock-type
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(lock-region:whence lock)
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(lock-region:start lock)
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(lock-region:len lock))))
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;;; The main routines
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;;;;;;;;;;;;;;;;;;;;;
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(define (lock-region fdes lock)
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(if (not (lock-region/no-block fdes lock))
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(begin
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(relinquish-timeslice)
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(lock-region fdes lock))))
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;;; Return true/false indicating success/failure.
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(define (lock-region/no-block fdes lock)
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(with-errno-handler
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((errno data)
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((errno/again errno/acces) #f))
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(call-lock-region %set-lock fcntl/set-record-lock-no-block fdes lock)
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#t))
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;;; Return first lock that conflicts w/LOCK; if none, return #f.
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(define (get-lock-region fdes lock)
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(apply (lambda (type whence start len pid)
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(and (not (= type lock/release))
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(make-%lock-region (= type lock/write) start len whence
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(pid->proc pid 'create))))
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(call-lock-region %get-lock fcntl/get-record-lock fdes lock)))
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(define (unlock-region fdes lock)
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(%set-lock fdes fcntl/set-record-lock lock/release
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(lock-region:whence lock)
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(lock-region:start lock)
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(lock-region:len lock)))
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;;; Locks with dynamic extent -- with and without sugar
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;;; Throwing out frees the lock. Don't throw back in.
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(define (with-region-lock* fd lock thunk)
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(let ((returned? #f))
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(dynamic-wind (lambda ()
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(if returned?
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(error "Can't throw back into a with-region-lock" lock)
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(lock-region fd lock)))
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thunk
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(lambda ()
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(unlock-region fd lock)
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(set! returned? #t)))))
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(define-syntax with-region-lock
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(syntax-rules ()
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((with-region-lock fd lock body ...)
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(with-region-lock* fd lock (lambda () body ...)))))
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