JDK-8074023: Clock.system(ZoneId) could be optimized to always return the same clock for a given zone

[Daniel Fuchs]

On 4/23/15 11:28 PM, Roger Riggs wrote:
> Hi Peter,
>
> Setting the user.timezone property doesn't reset the value returned 
> from getDefaultRef().
> You can see the new value through java.util.TimeZone but not through 
> java.time.ZoneId.
>
> Its a bad idea to allow the default timezone change and in java.time 
> it was purposefully
> handled as an initialize once value.
Hi Nadeesh, Roger,

I wonder whether this piece of code:

  203         } else if (zone.equals(ZoneId.systemDefault())) {
  204             return SystemClock.DEFAULT_ZONE_CLOCK;
  205         }

should be instead

           } else if (zone.equals(SystemClock.DEFAULT_ZONE_CLOCK.zone) {
               return SystemClock.DEFAULT_ZONE_CLOCK;
          }

Note: What would be the recommended way to set the default time zone?

I have some tests [1] in logging that set the default time zone to UTC:

     TimeZone.setDefault(TimeZone.getTimeZone(ZoneId.of("UTC")));

they do that to ensure that the log record formatted date will always be
the same - wherever the machine the test runs on is located.
If the default time zone is not UTC then the test will become unstable...

best regards,

-- daniel
[1] 
http://cr.openjdk.java.net/~dfuchs/webrev_8072645/webrev.03/test/java/util/logging/HigherResolutionTimeStamps/SerializeLogRecord.java.html
>
> Roger
>
>
> On 4/23/2015 5:20 PM, Peter Levart wrote:
>>
>>
>> On 04/23/2015 10:33 PM, Roger Riggs wrote:
>>> Hi Peter,
>>>
>>> The defaultTimeZone is cached in java.util.TimeZone the first time 
>>> it is referenced
>>> and is not updated after that.  See java.util.TimeZone.getDefaultRef().
>>>
>>> Regards, Roger
>>>
>>
>> But any code (with enough privilege) can update it:
>>
>> abstract public class TimeZone .... {
>>
>>     public static void setDefault(TimeZone zone)
>>     {
>>         SecurityManager sm = System.getSecurityManager();
>>         if (sm != null) {
>>             sm.checkPermission(new PropertyPermission
>>                                ("user.timezone", "write"));
>>         }
>>         defaultTimeZone = zone;
>>     }
>>
>>
>>
>> Peter
>>
>>>
>>> On 4/23/2015 4:11 PM, Peter Levart wrote:
>>>>
>>>>
>>>> On 04/23/2015 09:53 PM, nadeesh tv wrote:
>>>>> Hi all,
>>>>>
>>>>> Please review this minor change which  optimized 
>>>>> Clock.systemDefaultZone() and Clock.system(ZoneId)  to avoid 
>>>>> creating new instance of Clock.SystemClock every time they are 
>>>>> called.
>>>>>
>>>>> Bug ID : https://bugs.openjdk.java.net/browse/JDK-8074023
>>>>>
>>>>> Webrev : http://cr.openjdk.java.net/~rriggs/nadeesh-tv-8074023/
>>>>>
>>>>
>>>> Hi Nadeesh,
>>>>
>>>> What happens if ZondeId.systemDefault() changes 
>>>> (TimeZone.setDefault()) *after* Clock class has already been 
>>>> initialized?
>>>>
>>>> Regards, Peter
>>>>
>>>
>>
>