Re: [MacPerl] Folder recursion and recognition problem

[Matthias Ulrich Neeracher <neeri@iis.ee.ethz.ch>]

hal@dtor.com (Hal Wine) writes:
>At 16:16 96-06-03, Brad Cox wrote:
>>At 1:02 PM -0500 03/06/96, Hal Wine wrote:
>>>This means you should either:
>>>a) do a chdir() to the supplied directory, then always do an opendir()
>>>on the current directory (':' for Mac, '.' for unix/dos).  Or,
>>>b) always prepend the directory to the filename returned by readdir().
>>>
>>>My hunch is (a) runs faster on the Mac (due to internals of the Mac
>>>file system), and no slower on other file systems.
>>
>>No, according to Matthias, a) shouldn't run faster. He said MacPerl fully
>>expands relative pathnames to absolute pathnames before doing anything with
>>them.
>
>Well, I hate to disagree with Matthias, but (a) DOES run faster, and
>works correctly, while (b) has bugs.

Well, I'd hate to disagree with either Hal's facts or my opionions, so
I'll just claim that *all* of us are right :-)

>(See attached script)  Here's the
>timing for 10,000 stats of a directory where the path string is 223
>characters, and 7 levels deep (excluding volume name):
>    Perl 5.0.7r1m:
>      194 seconds for full path stat
>      120 seconds for relative stat
>    MacPerl 4.1.8:
>      200 seconds for full path stat
>      126 seconds for relative stat

Cool! I speeded up Perl by 6E-4 seconds per stat() :-)

>So, we see that using a full path is about 60% slower than relative directorie
s.

I think I can explain: GUSI converts each path name, absolute or relative, into
an FSSpec (that's unavoidable). Then, under some conditions, it converts the
FSSpec back to a path name (that's avoidable). However, this currently only
happens for open(), and only with the MPW tool. So, what I said to Brad Cox
last fall (and I *do* remember that I said it) was not very accurate for
MacPerl4 then, and is somewhat less accurate for MacPerl5 now (path conversion
constantly keeps changing a little).

The performance impact is difficult to quantify in the general case: The path
conversion sometimes calls FSMakeFSSpec and sometimes it calls GetCatInfo
a few times instead. Performance depends on how deeply the path is nested.

>Using a full path is limited to strings of less than 256 characters,

Oops! you shouldn't be.

>and, there are some wierd things that happen at the extremity of that
>limit.  In the attached script, the name of the final directory created
>gets truncated, without any error notice, in both MacPerl 4 & 5.

I'll look at this.

>I'm not sure when the conversion from relative to full path occurs.

This conversion was necessary for routines that call through to the original
MPW counterparts. MPW a few years ago didn't respect current directories, so
I had to convert between GUSI current directories and MPW ones. However,
Perl 5 uses CWGUSI, which is more emancipated from the MPW library, and
usually doesn't even call MPW open() anymore.

Matthias

-----
Matthias Neeracher   <neeri@iis.ee.ethz.ch>   http://www.iis.ee.ethz.ch/~neeri
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