Low performance of (concatenate 'string ...).

[Deiv Astra]

Hello, I have not an idea why builtin (concatenate 'string ) so slow, I am newbie in CL.
I had test string stream vs concatenate performance and got results below:

"Test string output stream"
189993
Evaluation took:
  0.013 seconds of real time
  0.012293 seconds of total run time (0.008819 user, 0.003474 system)
  92.31% CPU
  39,345,984 processor cycles
  6,588,160 bytes consed

"Test concatenate"
190008
Evaluation took:
  3.480 seconds of real time
  3.464029 seconds of total run time (3.059003 user, 0.405026 system)
  [ Real times consist of 0.280 seconds GC time, and 3.200 seconds non-GC time. ]
  [ Run times consist of 0.289 seconds GC time, and 3.176 seconds non-GC time. ]
  99.54% CPU
  11,123,607,584 processor cycles
  38,009,081,712 bytes consed

=== Test code ===

(defconstant *count* 100000)

(print "Test string output stream")
(defparameter out-stream (make-string-output-stream))
(time
   (progn
      (dotimes (i *count*)
         (write-string (write-to-string (random 100)) out-stream))
      (let (
            (result (get-output-stream-string out-stream)))
         (print (length result))
      )))

(print "Test concatenate")
(defparameter out-string nil)
(time
   (progn
      (dotimes (i *count*)
         (setq out-string
            (concatenate 'string out-string (write-to-string (random 100)))))
      (print (length out-string))
   ))

-----
The result above displays how (make-string-output-stream) is much fastest than (concatenate 'string).
I had write own simple implementation (concatenate-string)

(defun concatenate-string (&rest args)
   (let ((stream (make-string-output-stream)))
      (dolist (arg args)
         (write-string
            (if (stringp arg)
               arg
               (write-to-string arg))
     stream))
 (get-output-stream-string stream)))

This issue published for help to improve performance of SBCL.
Maybe using (make-string-output-stream) inside of (concatenate 'string) will increase performance greatly.
Thanks.

[Douglas Katzman (dougk)]

Your tests are not at all equivalent. In the "Test concatenate" example you are producing as many intermediate strings as there are loop iterations, and each intermediate string is a newly made string containing the entire contents of all prior loop iterations.