On 02/22/2015 10:16 PM, Xueming Shen wrote:
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);
...
Here's my attempt to resolve this:
webrev: http://cr.openjdk.java.net/~redestad/jdk9/8073497/webrev.2/
incremental:
http://cr.openjdk.java.net/~redestad/jdk9/8073497/webrev.1_to_2/
Calculating exact upper and lower bounds would only make sense for the
current timezone
and would have to be recalculated, while approximate bounds should
suffice for the practical
purpose of avoiding the FileTime creation in the typical case for
performance reasons.
I rather arbitrarily chose an upper bound around 2098. Lower bound check
could test for
some value near 1980, but since there's already code to check if
Date.getYear() is less
than 1980 I figured that might suffice...
... that's when I stumbled on a few subtle bugs in the
dosToJava/javaToDos conversion methods,
first and foremost that a Date representing times before the era
(typically year 1), getYear
returns positive years. While a pretty artificial scenario, this is a
bug in the javaToDosTime
conversion which breaks some tests. A simple check that millisecond long
is larger than 0
is sufficient to resolve this negative-year-overflow for the current
implementation.
We also don't check for year overflow for instants after 2107 in the
local time: these will start
over at 1980. The old behavior is to simply accept the overflow. I've
kept the behavior for the
dostime conversion, while the upper bound check ensure that the mtime
will be calculated in
these cases, which seems reasonable.
This code does come with loss of some precision when setting time via
setTime(long) in the
valid DOS time range (it will be rounded to 2-second precision), but
with setLastModifiedTime
available to get the better precision this might be an acceptable
behavioral regression of
setTime (while slightly weird, it doesn't seem to violate the
specification).
/Claes
-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
