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	tshareable-vectors.txt (1537B)
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	1
	2 # Shareable Byte Vectors
	3
	4 Function: make-shareable-byte-vector size
	5
	6 Create a vector of element type (UNSIGNED-BYTE 8) suitable for passing
	7 to WITH-POINTER-TO-VECTOR-DATA.
	8
	9 ;; Minimal implementation:
	10 (defun make-shareable-byte-vector (size)
	11 (make-array size :element-type '(unsigned-byte 8)))
	12
	13
	14 Macro: with-pointer-to-vector-data (ptr-var vector) &body body
	15
	16 Bind PTR-VAR to a pointer to the data contained in a shareable byte
	17 vector.
	18
	19 VECTOR must be a shareable vector created by MAKE-SHAREABLE-BYTE-VECTOR.
	20
	21 PTR-VAR may point directly into the Lisp vector data, or it may point
	22 to a temporary block of foreign memory which will be copied to and
	23 from VECTOR.
	24
	25 Both the pointer object in PTR-VAR and the memory it points to have
	26 dynamic extent. The results are undefined if foreign code attempts to
	27 access this memory outside this dynamic contour.
	28
	29 The implementation must guarantee the memory pointed to by PTR-VAR
	30 will not be moved during the dynamic contour of this operator, either
	31 by creating the vector in a static area or temporarily disabling the
	32 garbage collector.
	33
	34 ;; Minimal (copying) implementation:
	35 (defmacro with-pointer-to-vector-data ((ptr-var vector) &body body)
	36 (let ((vector-var (gensym))
	37 (size-var (gensym)))
	38 `(let* ((,vector-var ,vector)
	39 (,size-var (length ,vector-var)))
	40 (with-foreign-ptr (,ptr-var ,size-var)
	41 (mem-write-vector ,vector-var ,ptr :uint8)
	42 (prog1
	43 (progn ,@body)
	44 (mem-read-vector ,vector-var ,ptr-var :uint8 ,size-var))))))