#305: Slow writing to binary streams -------------------------+-------------------------------------------------- Reporter: sboukarev | Owner: mevenson Type: enhancement | Status: new Priority: minor | Milestone: Component: streams | Version: Keywords: | -------------------------+-------------------------------------------------- Slow writing to binary streams
{{{ (defun test () (with-open-file (stream "/dev/null" :direction :output :if-exists :overwrite :element-type '(unsigned-byte 8)) (time (loop repeat 10000000 do (write-byte 23 stream))))) }}}
(test)
2.065 seconds real time 30000260 cons cells
The problem boils down to write-byte doing (typep 23 '(unsigned-byte 8)), and typep calls normalize-type, which conses a new type each time: (list 'integer 0 (1- (expt 2 8)))
http://trac.common- lisp.net/armedbear/browser/trunk/abcl/src/org/armedbear/lisp/byte- io.lisp#L34 http://trac.common- lisp.net/armedbear/browser/trunk/abcl/src/org/armedbear/lisp/early- defuns.lisp#L155
Just changing that part to
{{{
(UNSIGNED-BYTE (return-from normalize-type (if (or (null i) (eq (car i) '*)) '(integer 0 *) (case (car i) (8 '(integer 0 255)) (16 '(integer 0 65535)) (32 '(integer 0 4294967295)) (64 '(integer 0 18446744073709551615)) (t (list 'integer 0 (1- (expt 2 (car i))))))))) }}}
gives (test) 1.682 seconds real time 45 cons cells
But even better solution would be to assign efficient writing and reading routines to streams during a stream creation. When I change the body of write-byte to
{{{ (defun write-byte (byte pstream) (declare (type stream stream)) (write-8-bits byte stream)) }}}
I get (test) 0.521 seconds real time 12 cons cells
And by extension this problem also affects TYPEP, (time (typep 23 '(unsigned-byte 8))) => 3 cons cells (time (typep #(a) '(simple-vector 2))) => 5 cons cells