Re: NSProcessInfo globallyUniqueString

[Richard Frith-Macdonald]

On Thursday, August 8, 2002, at 09:12 AM, Roland Schwingel wrote:

> Hi...
>
> (I couldn't find David Ayers patch in my gnustep mailinglist mails so I 
> decided
> to also post my solution - I only had the mail of Richard 
> Frith-Macdonald
> forwarded below)
>
> I faced the very same problems a while ago also. I use
> this method very frequently for temporary filenames etc.
>
> So to be unique again (and to avoid the : problem - which
> awfully breaks on windows) I placed a category to that
> method doing this a long time ago:
>
> {
>         //        static time_t                 startTime = 0;
>         static NSString        *hostName = nil;
>         static long                        counter = 1;
>         static pid_t                 pid = 0;
>        
>         if (!hostName)
>         {
>                 hostName = [[NSProcessInfo processInfo] hostName];
>                
>                 if (![hostName length])
>                         hostName = @"localhost";
>                 else
>                 {
>                         NSArray *components = [hostName 
> componentsSeparatedByString:@"."];
>                        
>                         hostName = [[components objectAtIndex:0] 
> retain];
>                 }
>                        
>                 #ifdef __MINGW__
>                 pid = GetCurrentProcessId();
>                 #else
>                 pid = getpid();
>                 #endif
>                
>                 // startTime = time(NULL);
>         }
>        
>         //        return [NSString 
> stringWithFormat:@"tmp-%@-%x-%x-%x",hostName,pid,time(NULL)-startTime,counter+
> +];
>         return [NSString 
> stringWithFormat:@"tmp-%@-%x-%x",hostName,pid,counter++];
> }
>
> I decided that a timestamp is not really necessary when you have a 
> counter which is incremented on every call, so I
> omitted that (but still available commented out). OS4.2 is also always 
> adding a counter to the string.
>
> This version now runs for over a year for me perfectly on windows and 
> unix...

Thanks ... the counter increment is not thread-safe (though problems 
would be *EXTREMELY* rare),
and using a single component of the host name also renders the string 
non-unique.
However I like the idea of replacing '.' with '_' to make the result a 
legal filename under windoze
and I've updated the version in CVS to do this.

NB. The time stamp is necessary to ensure that the string is globally 
unique since the counter
value is only unique (assuming locking is used to prevent two threads 
accessing it at once)
within a single process.

I guess you are only concerned with uniqueness within a single 
process ... but I think the intent of
the method is to be truly, globally unique (ie across all processes and 
systems).  I think the code now
in cvs ensures this ... except for machines which are not in the public 
DNS system on the internet
and may therefore have non-unique host names.