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Article contents:[[tags: egg]] [[toc:]] == object-evict === Introduction This extension allows to copy arbitrary Scheme data into unmanaged memory, not subject to garbage collection (called /eviction/). This may be useful for "pinning" down data to be used by foreign code. Note that the evicted data needs to be released manually. === Requirements [[srfi-69]] === Usage {{(import object-evict)}} === Programming interface ==== object-evict <procedure>(object-evict X [ALLOCATOR])</procedure> Copies the object {{X}} recursively into the memory pointed to by the foreign pointer object returned by {{ALLOCATOR}}. The freshly copied object is returned. {{ALLOCATOR}} should be a procedure of a single argument (the number of bytes to allocate), and defaults to {{allocate}}. This facility allows moving arbitrary objects into static memory, but care should be taken when mutating evicted data: setting slots in evicted vector-like objects to non-evicted data is not allowed. It '''is''' possible to set characters/bytes in evicted strings or byte-vectors, though. It is advisable '''not''' to evict ports, because they might be mutated by certain file-operations. {{object-evict}} is able to handle circular and shared structures. Evicted symbols are no longer unique: a fresh copy of the symbol is created, so <enscript highlight=scheme> (define x 'foo) (define y (object-evict 'foo)) y ==> foo (eq? x y) ==> #f (define z (object-evict '(bar bar))) (eq? (car z) (cadr z)) ==> #t </enscript> This loss of uniqueness also implies that an evicted structure -- such as one created with {{define-record}} -- cannot be operated on with the existing predicate or accessors, as internally a symbol is used to denote the type: <enscript highlight=scheme> (define-record point x y) (point? (make-point x y)) ; => #t (point? (object-evict (make-point x y))) ; => #f </enscript> ==== object-evict-to-location <procedure>(object-evict-to-location X POINTER* [LIMIT])</procedure> As {{object-evict}} but moves the object at the address pointed to by the pointer-like object {{POINTER*}}. If the number of copied bytes exceeds the optional {{LIMIT}} then an error is signalled (specifically a composite condition of types {{exn}} and {{evict}}. The latter provides a {{limit}} property which holds the exceeded limit. Two values are returned: the evicted object and a new pointer pointing to the first free address after the evicted object. Use of anything other than a pointer object as the {{POINTER*}} argument is questionable. ==== object-evicted? <procedure>(object-evicted? X)</procedure> Returns {{#t}} if {{X}} is a non-immediate evicted data object, or {{#f}} otherwise. ==== object-release <procedure>(object-release X [RELEASER])</procedure> Frees memory occupied by the evicted object {{X}} recursively. {{RELEASER}} should be a procedure of a single argument (a foreign pointer object to the static memory to be freed) and defaults to {{free}}. ==== object-unevict <procedure>(object-unevict X [FULL])</procedure> Copies the object {{X}} and nested objects back into the normal Scheme heap. Symbols are re-interned into the symbol table. Strings and byte-vectors are '''not''' copied, unless {{FULL}} is given and not {{#f}}. ==== object-size <procedure>(object-size X)</procedure> Returns the number of bytes that would be needed to evict the data object {{X}}. If {{X}} is an immediate object, zero is returned. === Author The CHICKEN Team === Repository This egg is hosted on the CHICKEN Subversion repository: [[https://anonymous@code.call-cc.org/svn/chicken-eggs/release/5/object-evict|https://anonymous@code.call-cc.org/svn/chicken-eggs/release/5/object-evict]] If you want to check out the source code repository of this egg and you are not familiar with Subversion, see [[/egg-svn-checkout|this page]]. === License Copyright (c) 2014, The CHICKEN Team All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. 3. The name of the authors may not be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. === Version History ; 1.0.1 : Fix segfault when calling object-evict-to-location with non-fixnum as {{limit}} argument (fixes #1631) ; 1.0 : Extracted from {{lolevel}} core library unit and released as an egg. Description of your changes:

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