I'm familiar with how to use mmap() in C for this (reading large text
files), but I'm not sure how to go about it under CMUCL.
I found this example in comp.lang.lisp, but since it just returns the
pointer (the output of the mmap call as an integer), how do I convert
that pointer into some kind of lisp object/structure that I can use to
read the results, either with (read-sequence) or (read-line)?
(defun mmap (file offset length &optional write-p)
(let* ((ofs32 (if (zerop (logand offset #x80000000))
offset
(- offset #x100000000))) ; Fake up a "(signed-byte 32)"
(mode (logior #+linux unix::O_SYNC ; Not on BSD (*sigh*)
(if write-p unix:O_RDWR unix:O_RDONLY)))
(fd (unix:unix-open file mode 0)))
(if (not fd)
(error "Can't open ~s: ~s" file (unix:get-unix-error-msg))
(unwind-protect
(let ((mode (logior unix:PROT_READ
(if write-p unix:PROT_WRITE 0))))
(system:sap-int
(unix:unix-mmap nil length mode unix:MAP_SHARED fd ofs32)))
(unix:unix-close fd)))))
Also, when using CMUCL's mmap call, am I forced to open the file with
(unix:unix-open) or can I use (with-open-file) as well?
When I tried the latter, the call to (unix:unix-mmap) returned a null value:
CL-USER> (with-open-file (file-stream "/path/to/very_large_file.txt" :direction
:input)
(let ((mmap-ptr (unix:unix-mmap nil (file-length
file-stream) unix:PROT_READ unix:MAP_PRIVATE (system:fd-stream-fd
file-stream) 0)))
mmap-ptr))
NIL
