I think Yoshito's suggestion make sense, since the getZoneIndex is an
internal method, if there is no manual setting to change the timezone,
The timezone ID won't be changed for one instance of SimpleDateFormt.
I updated the patch webrev[1] for this suggestion and test the
GetZoneIndexTest.java, the performance is almost the same with webrev.00.
Please review the updated patch[1].
Thanks a lot!
[1] http://cr.openjdk.java.net/~littlee/OJDK-548/webrev.01
<http://cr.openjdk.java.net/%7Elittlee/OJDK-548/webrev.01>
On 04/11/2012 04:00 AM, Yoshito Umaoka wrote:
I'm wondering if caching index matched last time (per
DateFormatSymbols instance) is sufficient, instead of keeping multiple
results in a hash map.
I guess majority of use cases repeatedly refer the index of the zone
used by SimpleDateFormat.
-Yoshito
On 4/9/2012 10:46 AM, Masayoshi Okutsu wrote:
Hi Deven,
Here are my comments on the proposed changes.
- zoneIndexCache should be an instance field because WeakHashMap
isn't thread-safe and the order of IDs in zoneStrings differs in each
DateFormatSymbols.
- equals shouldn't be replaced with equalsIgnoreCase because time
zone IDs are (supposed to be) case-sensitive.
- Utilize auto-boxing/unboxing.
Thanks,
Masayoshi
On 4/9/2012 12:10 PM, Deven You wrote:
Hi i18n-devs,
The getZoneIndex() method is expensive and it's performance depends
on which timezone you're in. This is because the code steps through
a list of timezones until it finds the current one. This is
happening over and over again. An idea would be to either cache it
or rewrite the way we store time zone ids, such as a hashmap instead
of an array.
This patch[1] is for the cache option.
Applications which format/parse dates using SimpleDateFormat
repeatedly may obtain benefits from this patch, especially when run
in a timezone far down the zoneStrings array the improvements will
be even bigger.
I have written a test case[2] which shows when a timezone which is
in lower end of the zone strings array, the performance improvement
this patch can get.
test results:
no patch:
The total time is 742 ms!
with this patch[1] :
The total time is 508 ms!
If increase the loop times to 1000000, the results are:
no patch:
The total time is 4743 ms!
with this patch[1] :
The total time is 2126 ms!
The java version is:
/home/deven/hgrps/jdk8/build/linux-i586/j2sdk-image/bin/java -version
openjdk version "1.8.0-internal"
OpenJDK Runtime Environment (build
1.8.0-internal-deven_2012_03_14_16_14-b00)
OpenJDK Server VM (build 24.0-b02, mixed mode)
[1]
http://cr.openjdk.java.net/~youdwei/DateFormatSymbol_perf/webrev.00/
<http://cr.openjdk.java.net/%7Eyoudwei/DateFormatSymbol_perf/webrev.00/>
[2] GetZoneIndexTest.java
--
Best Regards,
Deven
