Yoshito,
It is good to me for your suggestion. So Masayoshi, what is your
opinion, is cache the last zone index better than cache recent zone ID
and zone indexes, do you have any concern about using last zone index?
[1] The updated version of this patch
http://cr.openjdk.java.net/~youdwei/DateFormatSymbol_perf/webrev.02/
<http://cr.openjdk.java.net/%7Eyoudwei/DateFormatSymbol_perf/webrev.02/>
Thanks a lot!
On 04/11/2012 10:35 PM, Yoshito Umaoka wrote:
Deven,
If last time zone ID is cached along with the previously resolved
index, and getZoneIndex does not check the contents of array, it might
not work when zone strings are updated (setZoneStrings). So, to make
this change work properly, you have to reset lastZoneID/zoneIndex in
setZoneStrings(String[][]).
In my opinion, we just need to keep last zone index. And it should be
'transient'.
For every getZoneIndex(String) call, input ID is compared to
zoneStrings[lastZoneIndex][0] - and if they matches, simply return
lastIndex. Otherwise, do the linear search and update lastZoneIndex-
like below.
private transient int lastZoneIndex = 0; // with initial value to be
0, you do not need to check lastZoneIndex >= 0 every time
final int getZoneIndex(String ID) {
// fast path
// note: if you want to get rid of lastZoneIndex < zoneStrings.length,
// setZoneStrings(String[][]) should reset lastZoneIndex to 0 or any
valid index.
if (lastZoneIndex < zoneStrings.length &&
ID.equals(zoneStrings[lastZoneIndex ][0]) {
return lastIndex;
}
// slow path
for (int index = 0; index < zoneStrings.length; index++) {
if (ID.equals(zoneStrings[index][0]) {
lastZoneIndex = index;
return index;
}
}
}
-Yoshito
On 4/11/2012 3:02 AM, Deven You wrote:
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
--
Best Regards,
Deven
