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Provides an abstraction for a managed object, known as a resource, with a fixed lifetime. This might be used to create a file port that will automatically close if unused for some amount of time.
make-timed-resource[procedure] (make-timed-resource OPENER CLOSER TIMEOUT [NAME]) => timed-resource
Returns a new timed-resource object that covers a resource with a lifetime of TIMEOUT seconds. The resource is acquired by the OPENER and released by the CLOSER. An acquired resource will be released automatically at the end of its' life.
The OPENER is a (procedure () *) returning the resource object.
The CLOSER is a (procedure (*)) taking a resource object returned by the OPENER.
The NAME is used as a prefix for the generated unique identifier of the created timed-resource and is usually a string or symbol. There is no semantic content.
No attempt is made to serialize access to a resource, this is up to the caller; just don't share the thing.
Exceptions occurring during resource acquisition or release abort the operation. Exceptions during resource release at shutdown are just displayed but no further action is taken.
with-timed-resource[procedure] (with-timed-resource TIMED-RESOURCE ACTION) => *
Returns the result of invoking ACTION with the resource covered by the TIMED-RESOURCE. The acquired resource will not be released during the extent of the with-timed-resource invocation.
ACTION is a (procedure (timed-resource) *).
timed-resource?[procedure] (timed-resource? OBJECT) => boolean
Is the OBJECT a timed-resource?
timed-resource-name[procedure] (timed-resource-name TIMED-RESOURCE) => *
Returns unique id for TIMED-RESOURCE.
timed-resource-timeout[procedure] (timed-resource-timeout) => (or #f number)
[procedure] (timed-resource-timeout SECONDS) =>
Gets & sets the number of seconds to wait for a thread to quit.
Default is #f.
Currently only used at shutdown.
(use timed-resource srfi-4) ;; Returns a blob of random bits. ;; ;; (random-blob [BITS]) ;; BITS - the number of random bits, default is 128 (define random-blob (let ((tr-random-dev (make-timed-resource ;Use the random device (*nix only) (lambda () (open-input-file "/dev/random" #:binary)) (lambda (port) (close-output-port port)) ;Only keep open for 10 seconds 10.0))) (lambda (#!optional (bits 128)) (let ((bytes (inexact->exact (floor (/ (+ bits 7) 8))))) (with-timed-resource tr-random-dev (lambda (port) (u8vector->blob (read-u8vector bytes))))) ) ) )
- Fix for reporting an expected condition, timed-resource-closed, during shutdown.
- Moved from srfi-27 into own extension.
Copyright (C) 2010 Kon Lovett. All rights reserved.
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