3rdparties/software/cffi_0.21.0/doc/shareable-vectors.txt (1537 bytes)
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))))))