RFR(S): 8073497: Lazy conversion of ZipEntry time

[Xueming Shen]

On 2/21/15 6:11 PM, Claes Redestad wrote:
> Hi Sherman,
>
> On 2015-02-21 19:49, Xueming Shen wrote:
>> Hi Claes,
>>
>> This change basically undo the "fix" for 4759491 [1], for better 
>> performance ...
>>
>
> my intent was never to break current behavior, but that mistake can be 
> rectified
> without missing out on the startup benefit of laziness:
>
> http://cr.openjdk.java.net/~redestad/jdk9/8073497/webrev.1/
>
> The time/mtime getters now use the mtime field if it exists, while the 
> setters will
> update both fields. Since getLastModified already fell back to 
> converting the
> time field rather than null if mtime wasn't set, setting mtime to a 
> FileTime when
> calling setTime seems consistent and a cheap way to preserve the time 
> precision.
>
> I guess a range check to skip the FileTime creation in setTime if the 
> time is within
> the DOS time bounds would be a valid optimization, since that will 
> typically
> always be the case.


It's a reasonable solution. I would assume we probably need that "range 
check" optimization
to avoid setting the "mtime" field in normal use scenario. ZOS now 
outputs the more accurate
"mtime" to the zip file using "extend timestamp" if it's not null (the 
entry gets bigger). The
assumption now is that we only output the extended timestamp if the time 
stamps set
via the setXYZTime() explicitly.

ZOS.java

...

  432         int elenEXTT = 0;               // info-zip extended timestamp
  433         int flagEXTT = 0;
  434         if (e.mtime != null) {
  435             elenEXTT += 4;
  436             flagEXTT |= EXTT_FLAG_LMT;
  437         }
  438         if (e.atime != null) {
  439             elenEXTT += 4;
  440             flagEXTT |= EXTT_FLAG_LAT;
  441         }
  442         if (e.ctime != null) {
  443             elenEXTT += 4;
  444             flagEXTT |= EXTT_FLAT_CT;
  445         }
  446         if (flagEXTT != 0)
  447             elen += (elenEXTT + 5);    // headid(2) + size(2) + flag(1) + data
  448         writeShort(elen);

...

-Sherman


>> If we go with this change, I think we should also update the field 
>> comment back to the
>> original one to clearly indicates the "time" is "in DOS time".
>>
>> -    long time = -1;     // modification time (in DOS time)
>> +    long mtime = -1;    // last modification time
>>
>
> Done.
>
>>
>> The set/getLastModifiedTime() pair also need update to set/get the 
>> "time" field
>> correctly to/from the dos time.
>
> Done.
>
> Thanks!
>
> /Claes
>
>>
>> -Sherman
>>
>> [1] http://hg.openjdk.java.net/jdk8/jdk8/jdk/rev/90df6756406f
>>
>> On 2/21/15 6:34 AM, Claes Redestad wrote:
>>> Hi all,
>>>
>>> please review this patch to re-introduce laziness in the java-to-dos 
>>> time
>>> conversions for the ZipEntry.time field.
>>>
>>> Webrev: http://cr.openjdk.java.net/~redestad/jdk9/8073497/webrev.0/
>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8073497
>>>
>>> See bug for more details.
>>>
>>> This behavior was actually the case before 8-b94, when the time field
>>> was removed in favor of a set of FileTime fields, but when it was later
>>> re-introduced to address some compatibility issues the conversion was
>>> implemented in an eager fashion. This inadvertently affects VM startup
>>> ever so little, since for every entry read via a ZipFile or 
>>> ZipInputStream
>>> we'll do a relatively expensive call creating a Date and doing timezone
>>> conversion.
>>>
>>> Some gains from loading fewer classes during VM startup, as well.
>>>
>>> Thanks!
>>>
>>> /Claes
>>
>