<i18n dev> RFR: 8223490: Optimize search algorithm for determining default time zone

[naoto.sato at oracle.com]

Hi Seán,

I like your approach to provide the fast path to determine the system 
time zone. One general question is, is UTC/GMT the right set of fast 
path candidates? Should we add some more common ones?

Other comments to the code:

TimeZone_md.c

- Should fast path search come after "dir" validation, i.e., line 146-148?
- Line 126: "statbuf" can be removed.
- Line 134: 'i' is not size_of_something, so 'int' type should suffice 
(and its initialization is done in the for-loop).
- Line 138: the fast path search should "continue" with the next name, 
instead of "break".
- Line 142, 182: I'd wrap this line with parens for the if statement.
- Line 232-242: "pathname" is an argument to this function, so freeing 
it inside the function seems odd. Also, no need to reset dbuf/fd since 
they are no longer reused in the loop.

Naoto

On 9/11/19 3:50 AM, Seán Coffey wrote:
> The current algorithm for determining the default timezone on (non-AIX) 
> unix systems goes something like :
> 
> 1. If TZ environment variable is defined, use it
> 2. else if /etc/timezone exists, use the value contained within it
> 3. else if /etc/localtime exists and is a symbolic link, use the name 
> pointed to
> 4. else if /etc/localtime is a binary, find the first identical time 
> zone binary file in /usr/share/zoneinfo/
> 
> Step 4 is a bit crude in that the zoneinfo directory can contain over 
> 1,800 files on today's systems. I'd like to change the logic so that 
> common timezones are first checked for buffer matching before a full 
> directory traversal is performed. It should be a performance gain and it 
> should also lead to more consistent results for reasons outlined in the 
> bug report.
> 
> https://bugs.openjdk.java.net/browse/JDK-8223490
> webrev: http://cr.openjdk.java.net/~coffeys/webrev.8223490/webrev/ 
> <http://cr.openjdk.java.net/%7Ecoffeys/webrev.8223490/webrev/>
>