Hi Peter,
On 2015-02-22 21:21, Peter Levart wrote:
Hi,
I noticed internal JDK class java.util.zip.ZipUtils uses deprecated
java.util.Date API for implementing two methods for converting DOS to
Java time and back. I thought I'd try translating them to use new
java.time API. Translation was straightforward, but I noticed that new
implementations are not on par with speed to old java.util.Date
versions. Here's a JMH benchmark implementing those two conversion
methods with java.util.Date and java.time.ZonedDateTime APIs:
http://cr.openjdk.java.net/~plevart/jdk9-dev/ZoneId.systemDefault/ZipUtilsTest.java
https://bugs.openjdk.java.net/browse/JDK-8066644 was filed to fix the
deprecation warnings of practically identical code in
jdk/nio/zipfs/ZipUtils.java, maybe this could be fixed at the same time?
I did a similar experiment recently and think I saw better throughput
going from LocalDateTime to the sufficient second precision via
toEpochSecond:
- @SuppressWarnings("deprecation")
public static long dosToJavaTime(long dtime) {
- Date d = new Date((int)(((dtime >> 25) & 0x7f) + 80),
- (int)(((dtime >> 21) & 0x0f) - 1),
- (int)((dtime >> 16) & 0x1f),
- (int)((dtime >> 11) & 0x1f),
- (int)((dtime >> 5) & 0x3f),
- (int)((dtime << 1) & 0x3e));
- return d.getTime();
+ LocalDateTime time = LocalDateTime.of((int) (((dtime >> 25) &
0x7f) + 1980),
+ (int) ((dtime >> 21) & 0x0f),
+ (int) ((dtime >> 16) & 0x1f),
+ (int) ((dtime >> 11) & 0x1f),
+ (int) ((dtime >> 5) & 0x3f),
+ (int) ((dtime << 1) & 0x3e));
+ return
time.toEpochSecond(ZoneId.systemDefault().getRules().getOffset(time)) *
1000L;
}
This avoids a few allocations.
Similarly for the javaToDos case going from an Instant to LocalDateTime
with a ZoneOffset seemed to win out:
+ Instant instant = Instant.ofEpochMilli(time);
+ LocalDateTime d = LocalDateTime.ofInstant(instant,
+ ZoneOffset.systemDefault().getRules().getOffset(instant));
The results show the following:
Benchmark Mode Samples Score Score
error Units
j.t.ZipUtilsTest.dosToJavaTime_Date avgt 5 101.890
17.570 ns/op
j.t.ZipUtilsTest.dosToJavaTime_ZDT avgt 5 137.587
13.533 ns/op
j.t.ZipUtilsTest.javaToDosTime_Date avgt 5 67.114 10.382
ns/op
j.t.ZipUtilsTest.javaToDosTime_ZDT avgt 5 143.739
15.243 ns/op
Quick sampling with jvisualvm shows that a substantial time is spent
repeatedly obtaining ZoneId.systemDefault() instance. I checked the
implementation and came up with the following optimization:
http://cr.openjdk.java.net/~plevart/jdk9-dev/ZoneId.systemDefault/webrev.01/
TimeZone is a mutable object and has to be defensively cloned when
TimeZone.getDefault() is invoked. So there's no point in caching a
ZoneId instance inside TimeZone instance if we cache it on a clone
that is thrown away each time ZoneId.systemDefault() is invoked. I use
SharedSecrets to access the uncloned TimeZone.defaultTimeZone instance
where caching of ZoneId pays of.
I think that it was never meant to change TimeZone's ID
(TimeZone.setID()) after such instance was put into operation (for
example installed as default time zone with TimeZone.setDefault()).
Such use is unintended and buggy. So I also changed the implementation
of TimeZone.setDefault() to save a defensive copy of TimeZone object
as default time zone instead of a reference to it.
With this patch, the DOS/Java time conversion benchmark shows an
improvement:
Benchmark Mode Samples Score Score
error Units
j.t.ZipUtilsTest.dosToJavaTime_Date avgt 5 97.986 18.379
ns/op
j.t.ZipUtilsTest.dosToJavaTime_ZDT avgt 5 85.010 10.863
ns/op
j.t.ZipUtilsTest.javaToDosTime_Date avgt 5 71.073 25.408
ns/op
j.t.ZipUtilsTest.javaToDosTime_ZDT avgt 5 95.298 17.620
ns/op
Is this patch correct or did I miss something from the internals of
java.time API that does not permit such caching?
Seems OK to me - perhaps an alternative would be to add a public static
ZoneId getDefaultZoneId() on TimeZone rather than adding backdoors to
the getDefaultRef? The caching seems sound, and I guess we don't have to
worry about making it volatile.
The defensive copy in TimeZone.setDefault() seems like maybe it should
be a separate bug.
Thanks!
/Claes
Regards, Peter
