I tried writing a biggish string to a string port, and it was very
slow. Eg.
(use-modules (ice-9 time))
(let ((str (make-string 100000 #\x)))
(call-with-output-string (lambda (port)
(time (display str port))))
#f)
gives on my poor 333mhz
clock utime stime cutime cstime gctime
7.63 7.58 0.05 0.00 0.00 4.17
I struck this trying to use regexp-substitute/global on a file slurped
into memory. It was 130k, which is a decent size, but it's well
within the realm of reason.
I think strports.c st_write ends up doing a realloc and copy every 80
bytes of the block it's writing. It knows the size, but it lets
st_flush just grow by 80 bytes at a time.
The change below speeds it up from 7 seconds to 10 ms for me.
But I don't know if the read side bits of this change are right. Is
it supposed to update read_pos, read_end and read_buf_size to be the
end of the string, or something?
(Of course what would be even nicer would be to avoid big reallocing
altogether, like keep a list of chunks and only join them when a
get-string call wants the entire block. But that can wait.)
--- strports.c.~1.105.~ 2005-01-28 08:25:34.000000000 +1100
+++ strports.c 2005-02-14 11:20:05.000000000 +1100
@@ -142,18 +142,14 @@
scm_t_port *pt = SCM_PTAB_ENTRY (port);
const char *input = (char *) data;
- while (size > 0)
- {
- int space = pt->write_end - pt->write_pos;
- int write_len = (size > space) ? space : size;
-
- memcpy ((char *) pt->write_pos, input, write_len);
- pt->write_pos += write_len;
- size -= write_len;
- input += write_len;
- if (write_len == space)
- st_flush (port);
- }
+ /* if not enough room for "size" then make that amount and an additional
+ SCM_WRITE_BLOCK */
+ if (size > pt->write_end - pt->write_pos)
+ st_resize_port (pt, pt->write_pos - pt->write_buf
+ + size + SCM_WRITE_BLOCK);
+
+ memcpy ((char *) pt->write_pos, input, size);
+ pt->write_pos += size;
}
static void
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