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.
- object-evict X #!optional ALLOCATORprocedure
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
(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
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:
(define-record point x y) (point? (make-point x y)) ; => #t (point? (object-evict (make-point x y))) ; => #f
- object-evict-to-location X POINTER* #!optional LIMITprocedure
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? Xprocedure
Returns #t if X is a non-immediate evicted data object, or #f otherwise.
- object-release X #!optional RELEASERprocedure
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 X #!optional FULLprocedure
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 Xprocedure
Returns the number of bytes that would be needed to evict the data object X. If X is an immediate object, zero is returned.
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- Fix segfault when calling object-evict-to-location with non-fixnum as limit argument (fixes #1631)
- Extracted from lolevel core library unit and released as an egg.