Re: [patch] 21.3 executable.find - Use cache in `executable-find'

[jari.aalto@poboxes.com (Jari Aalto+mail.linux)]

* 2004-03-25 Eli Zaretskii <eliz <AT> elta.co.il> mail.default.spool
| > From: jari.aalto <AT> poboxes.com (Jari Aalto+mail.linux)
| > Date: Thu, 25 Mar 2004 00:24:10 +0200
| > 
| > | Any measurements to show that this indeed yields significant savings
| > | in Emacs?
| > 
| > No, but just common sense.
| 
| My common sense says ``profile before you optimize''.

But the results in this time are obvious. Cached path value is always
faster than doing directory searches. Disk I/O is always slower than
memory based search. Depending on how busy disk is, things are even
worse.

| > I have 50 directories in path and depending
| > just where the /bin might be it could take ages to find same programs
| > all again.
| 
| I'd like to know how long is ``ages''.  With today's caching OSes,
| you'd be surprised how fast that could be.
| 
| I could be wrong, of course, but only measurements will prove or
| disprove that.

See results above. I used slightly different Emacs version, because
Cygwin is the "non patched" and Native NT Emacs is "patched" and
I don't have an easy way to make NTEmacs "unpatched". 

It suprised, that NTEmacs were even slower - I though it would have
been the other way round.

Every time program is called the "search time" is added. Now if the
program is called in a loop, that will even more make it slower (those
cases are rare I believe).

But anyway, it does improve things.
Jari

Emacs 21.3 / Win32 native, caching active

time: 90000 microseconds                << First search, without cache
time: 0 microseconds                    << now cached.
time: 0 microseconds
time: 0 microseconds
time: 0 microseconds
time: 0 microseconds
time: 0 microseconds
time: 0 microseconds
time: 0 microseconds
time: 0 microseconds

Emacs 21.3 / Win32 Cygwin version, no caching
 
time: 13000 microseconds
time: 14000 microseconds
time: 13000 microseconds
time: 14000 microseconds
time: 13000 microseconds
time: 36000 microseconds
time: 14000 microseconds
time: 14000 microseconds
time: 14000 microseconds
time: 15000 microseconds


Test case:

(let ((exec-path exec-path)
      a
      b 
      list)
  (dotimes (x 40)
    (push "/this/dummy" list))
  (append list exec-path)
  (dotimes (x 10)
    (setq a (current-time))
    (executable-find "ls")
    (setq b (current-time))
    (sit-for 0.3)
    (insert
     (format "\ntime: %s microseconds"
             (- (caddr b) (caddr a))))))


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