I think Object.hashCode() will be better distributed than a static increment
- wouldn't that have better performance in Hash* objects?
On Mon, Jul 14, 2008 at 11:44 AM, Aleksey Shipilev <
[EMAIL PROTECTED]> wrote:
> Nevertheless, Object.hashCode() performance is unclear and as such it
> should be specifically avoided if not required explicitly. Will static
> increment suit better?
>
> Thanks,
> Aleksey.
>
> On Mon, Jul 14, 2008 at 10:38 PM, Andrew Cornwall
> <[EMAIL PROTECTED]> wrote:
> > Sorry - I didn't explain fully. I intended that my code would cache the
> > Object.hashCode() rather than recomputing the hashCode each time.
> >
> > On Mon, Jul 14, 2008 at 11:25 AM, Aleksey Shipilev <
> > [EMAIL PROTECTED]> wrote:
> >
> >> I think that's bad for performance. Using Object.hashCode() leads to
> >> System.identityHashCode(), which is handled by VM. The exact mechanism
> >> is VM-dependent, but at least on Harmony it's pretty slow. If you want
> >> to mark each instance as not-identical to another (warning here, you
> >> may break something), then I suggest to use static increment, e.g.:
> >>
> >> private static int hashcodeBase = 1;
> >> private int cachedHashCode = hashcodeBase++;
> >>
> >> This may end up with cache collisions if objects are created from
> >> different threads, but that's not the case for now.
> >>
> >> Anyway, Andrew, your code lacks caching again ;)
> >>
> >> Thanks,
> >> Aleksey.
> >>
> >> On Mon, Jul 14, 2008 at 9:51 PM, Andrew Cornwall
> >> <[EMAIL PROTECTED]> wrote:
> >> > And in fact, I just tried the following (which makes even more sense):
> >> >
> >> > - add objectHashCode() to ClassFileEntry:
> >> > protected int objectHashCode() {
> >> > return super.hashCode();
> >> > }
> >> >
> >> > - change generateHashCode in ByteCode to return objectHashCode()
> >> > private int generateHashCode() {
> >> > hashcodeComputed = true;
> >> > return objectHashCode();
> >> > }
> >> >
> >> > Since ByteCodes are equal if and only if they are identical, this
> seems
> >> to
> >> > be the right thing to do. What do you think?
> >> >
> >> >
> >> > On Mon, Jul 14, 2008 at 10:44 AM, Andrew Cornwall <
> >> [EMAIL PROTECTED]>
> >> > wrote:
> >> >
> >> >> I applied Aleksey's changes, and they look pretty good. I disagree
> with
> >> >> Sian to some degree about ByteCode. On my VM (which isn't Harmony), a
> >> new
> >> >> empty array's hashCode() is dependent on the array's location in
> memory,
> >> and
> >> >> not the array's contents. In other words:
> >> >>
> >> >> int[] x = new int[3];
> >> >> System.out.println(x.hashCode());
> >> >> x[1] = 5;
> >> >> System.out.println(x.hashCode());
> >> >>
> >> >> prints the same value for in both cases. rewrite.hashCode() is a
> handy
> >> (if
> >> >> lazy) way to distinguish among different instances.
> >> >>
> >> >> If we take rewrite out of hashCode(), HashMap and HashSet get really
> >> slow -
> >> >> essentially a linear search among all the ByteCodes of the same form.
> >> This
> >> >> brings my test case from 39 seconds up to 1:02.
> >> >>
> >> >> Perhaps the right thing to do is to give each unique instance of
> >> ByteCode
> >> >> an integer ID which is used in creating the hashCode rather than
> relying
> >> on
> >> >> rewrite to give us uniqueness?
> >> >>
> >> >>
> >> >> On Mon, Jul 14, 2008 at 7:19 AM, Sian January <
> >> [EMAIL PROTECTED]>
> >> >> wrote:
> >> >>
> >> >>> Ok - we'll wait and see what Andrew says. The only one that I'm not
> >> happy
> >> >>> with is Bytecode.hashCode, because rewrite always seems to be an
> empty
> >> >>> array
> >> >>> at the point when generateHashCode is called so it's a bit
> misleading
> >> >>> using
> >> >>> it. I think it should be ok to just remove that line, and still
> cache
> >> the
> >> >>> hashCode.
> >> >>>
> >> >>>
> >> >>> On 14/07/2008, Aleksey Shipilev <[EMAIL PROTECTED]> wrote:
> >> >>> >
> >> >>> > Sian,
> >> >>> >
> >> >>> > Actually I had tried to extend Andrew's approach to these classes
> >> >>> > first, but somehow I caught the degradation, that leaved me no
> choice
> >> >>> > except the lazy initialization. My concern is, the
> >> >>> > constructor-initialized hashcode is really depend on usage pattern
> >> for
> >> >>> > each specific class, while lazy initialization has more guarantees
> to
> >> >>> > be performance-stable. Moreover, I suspect the lazy initialization
> >> can
> >> >>> > degrade performance much less because the only overhead it causes
> is
> >> >>> > checking the value of boolean field. On the other hand, the
> >> >>> > constructor initialization may degrade performance a lot since the
> >> >>> > generation of hashCode is expensive.
> >> >>> >
> >> >>> > I can recheck which classes favor lazy initialization and which
> are
> >> >>> > not, but I think it's not valuable in terms of efficiency. I mean
> >> here
> >> >>> > that the boost connected with changing lazy initialization to
> >> >>> > constructor one is much lower than boost from caching hashcode
> >> anyway.
> >> >>> >
> >> >>> > Can we accept the patch in this form and revisit this difference
> >> later?
> >> >>> > It would be better to focus on more profitable areas for
> improvements
> >> >>> for
> >> >>> > now.
> >> >>> >
> >> >>> > P.S. I had asked Andrew to recheck whether my patch works as fast
> as
> >> >>> > his, also to check lazy initialization approach. On my tests the
> >> boost
> >> >>> > is stable and good.
> >> >>> >
> >> >>> > Thanks,
> >> >>> > Aleksey.
> >> >>> >
> >> >>> > On Mon, Jul 14, 2008 at 5:25 PM, Sian January
> >> >>> > <[EMAIL PROTECTED]> wrote:
> >> >>> > > Hi Aleksey,
> >> >>> > >
> >> >>> > > It's a really good idea to extend this patch to cover some more
> >> >>> classes,
> >> >>> > but
> >> >>> > > I think Andrew's method is faster (a final cachedHashCode field
> >> that
> >> >>> is
> >> >>> > > initialized in the constructor). The only reason I see to do it
> >> later
> >> >>> > would
> >> >>> > > be if we thought some of these objects never had hashCode called
> on
> >> >>> them,
> >> >>> > > but I don't think that's the case. Would you be able to try
> that
> >> >>> method
> >> >>> > > instead in your patch and see if I'm right about it being
> faster?
> >> >>> > >
> >> >>> > > Thanks,
> >> >>> > >
> >> >>> > > Sian
> >> >>> > >
> >> >>> > >
> >> >>> > >
> >> >>> > > On 12/07/2008, Aleksey Shipilev <[EMAIL PROTECTED]>
> >> wrote:
> >> >>> > >>
> >> >>> > >> Andrew,
> >> >>> > >>
> >> >>> > >> I had attached the patch to HARMONY-5907, covering several
> first
> >> >>> > >> methods. Can you confirm this patch helps for your scenario?
> >> >>> > >>
> >> >>> > >> Thanks,
> >> >>> > >> Aleksey.
> >> >>> > >>
> >> >>> > >> On Sat, Jul 12, 2008 at 1:58 PM, Aleksey Shipilev
> >> >>> > >> <[EMAIL PROTECTED]> wrote:
> >> >>> > >> > And the sorted list:
> >> >>> > >> >
> >> >>> > >> > 95462388 bc.cputf8
> >> >>> > >> > 18646908 bc.bytecode
> >> >>> > >> > 15118425 bc.cpclass
> >> >>> > >> > 14928914 bc.cpnametype
> >> >>> > >> > 12103799 bc.cpmethref
> >> >>> > >> > 5159994 bc.cpfieldref
> >> >>> > >> > 3420605 bc.methref
> >> >>> > >> > 1840965 bc.cpstring
> >> >>> > >> > 839916 bc.codeattr
> >> >>> > >> > 839916 bc.locvarattr
> >> >>> > >> > 839916 bc.linenumattr
> >> >>> > >> > 430234 bc.cpmethod
> >> >>> > >> > 277144 bc.cpfield
> >> >>> > >> > 263753 bc.attr
> >> >>> > >> > 153811 bc.cpinteger
> >> >>> > >> > 121856 bc.newattr
> >> >>> > >> > 93471 bc.cvalattr
> >> >>> > >> > 72492 bc.excpattr
> >> >>> > >> > 57428 bc.srcfileattr
> >> >>> > >> > 57428 bc.srcfileattr
> >> >>> > >> > 48104 bc.cplong
> >> >>> > >> > 40362 bc.innerclass
> >> >>> > >> > 5593 bc.depattr
> >> >>> > >> > 3255 bc.cpfloat
> >> >>> > >> > 1638 bc.cpdouble
> >> >>> > >> > 532 attrlayout
> >> >>> > >> > 0 archive
> >> >>> > >> > 0 attrdef
> >> >>> > >> > 0 newattrband
> >> >>> > >> > 0 bc.anndefarg
> >> >>> > >> > 0 bc.rtannattr
> >> >>> > >> > 0 classbands
> >> >>> > >> > 0 filebands
> >> >>> > >> > 0 metabandgr
> >> >>> > >> > 0 segheader
> >> >>> > >> > 0 bc.remattr
> >> >>> > >> > 0 bc.annattr
> >> >>> > >> > 0 bc.cpconst
> >> >>> > >> > 0 bc.cpmember
> >> >>> > >> > 0 bc.signattr
> >> >>> > >> > 0 bandset
> >> >>> > >> > 0 bcbands
> >> >>> > >> > 0 cpbands
> >> >>> > >> > 0 icbands
> >> >>> > >> > 0 ictuple
> >> >>> > >> > 0 segment
> >> >>> > >> > 0 segopts
> >> >>> > >> > 0 bc.classf
> >> >>> > >> > 0 bc.cpref
> >> >>> > >> > 0 bc.opmgr
> >> >>> > >> > 0 bc.rtattr
> >> >>> > >> > 0 segcp
> >> >>> > >> > 0 bc.ccp
> >> >>> > >> > 0 attrlayoutmap
> >> >>> > >> > 0 bc.encmethattr
> >> >>> > >> > 0 bc.exptableent
> >> >>> > >> > 0 bc.locvartable
> >> >>> > >> > 0 bc.signattr
> >> >>> > >> >
> >> >>> > >> > Thanks,
> >> >>> > >> > Aleksey.
> >> >>> > >> >
> >> >>> > >> > On Sat, Jul 12, 2008 at 1:50 PM, Aleksey Shipilev
> >> >>> > >> > <[EMAIL PROTECTED]> wrote:
> >> >>> > >> >> Hi, Andrew!
> >> >>> > >> >>
> >> >>> > >> >> I had updated the internal profiler to support hashCode()
> >> probes
> >> >>> [1],
> >> >>> > >> >> to extend your effort in hashcode optimization. There are
> bunch
> >> of
> >> >>> > >> >> heavily used hashcodes, most of them are going to
> >> >>> Object.hashCode()
> >> >>> > >> >> and then to System.identityHashCode(). We can
> cache/implement
> >> >>> > hashcode
> >> >>> > >> >> for these classes. Here's the profile:
> >> >>> > >> >>
> >> >>> > >> >> Hashcodes:
> >> >>> > >> >> archive: 0
> >> >>> > >> >> attrdef: 0
> >> >>> > >> >> attrlayout: 532
> >> >>> > >> >> attrlayoutmap: 0
> >> >>> > >> >> bandset: 0
> >> >>> > >> >> bcbands: 0
> >> >>> > >> >> classbands: 0
> >> >>> > >> >> cpbands: 0
> >> >>> > >> >> filebands: 0
> >> >>> > >> >> icbands: 0
> >> >>> > >> >> ictuple: 0
> >> >>> > >> >> metabandgr: 0
> >> >>> > >> >> newattrband: 0
> >> >>> > >> >> segcp: 0
> >> >>> > >> >> segheader: 0
> >> >>> > >> >> segment: 0
> >> >>> > >> >> segopts: 0
> >> >>> > >> >> bc.attr: 263753
> >> >>> > >> >> bc.remattr: 0
> >> >>> > >> >> bc.anndefarg: 0
> >> >>> > >> >> bc.annattr: 0
> >> >>> > >> >> bc.bytecode: 18646908
> >> >>> > >> >> bc.ccp: 0
> >> >>> > >> >> bc.classf: 0
> >> >>> > >> >> bc.codeattr: 839916
> >> >>> > >> >> bc.cvalattr: 93471
> >> >>> > >> >> bc.cpclass: 15118425
> >> >>> > >> >> bc.cpconst: 0
> >> >>> > >> >> bc.cpdouble: 1638
> >> >>> > >> >> bc.cpfield: 277144
> >> >>> > >> >> bc.cpfieldref: 5159994
> >> >>> > >> >> bc.cpfloat: 3255
> >> >>> > >> >> bc.cpinteger: 153811
> >> >>> > >> >> bc.methref: 3420605
> >> >>> > >> >> bc.cplong: 48104
> >> >>> > >> >> bc.cpmember: 0
> >> >>> > >> >> bc.cpmethod: 430234
> >> >>> > >> >> bc.cpmethref: 12103799
> >> >>> > >> >> bc.cpnametype: 14928914
> >> >>> > >> >> bc.cpref: 0
> >> >>> > >> >> bc.cpstring: 1840965
> >> >>> > >> >> bc.cputf8: 95462388
> >> >>> > >> >> bc.depattr: 5593
> >> >>> > >> >> bc.encmethattr: 0
> >> >>> > >> >> bc.excpattr: 72492
> >> >>> > >> >> bc.exptableent: 0
> >> >>> > >> >> bc.innerclass: 40362
> >> >>> > >> >> bc.linenumattr: 839916
> >> >>> > >> >> bc.locvarattr: 839916
> >> >>> > >> >> bc.locvartable: 0
> >> >>> > >> >> bc.newattr: 121856
> >> >>> > >> >> bc.opmgr: 0
> >> >>> > >> >> bc.rtattr: 0
> >> >>> > >> >> bc.rtannattr: 0
> >> >>> > >> >> bc.signattr: 0
> >> >>> > >> >> bc.srcfileattr: 57428
> >> >>> > >> >>
> >> >>> > >> >> Would you like to produce the patch?
> >> >>> > >> >> I think it would be funny :)
> >> >>> > >> >>
> >> >>> > >> >> Thanks,
> >> >>> > >> >> Aleksey.
> >> >>> > >> >>
> >> >>> > >> >> [1] https://issues.apache.org/jira/browse/HARMONY-5905
> >> >>> > >> >>
> >> >>> > >> >> On Sat, Jul 12, 2008 at 12:48 AM, Andrew Cornwall (JIRA)
> >> >>> > >> >> <[EMAIL PROTECTED]> wrote:
> >> >>> > >> >>>
> >> >>> > >> >>> [
> >> >>> > >>
> >> >>> >
> >> >>>
> >>
> https://issues.apache.org/jira/browse/HARMONY-5907?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
> >> >>> > ]
> >> >>> > >> >>>
> >> >>> > >> >>> Andrew Cornwall updated HARMONY-5907:
> >> >>> > >> >>> -------------------------------------
> >> >>> > >> >>>
> >> >>> > >> >>> Attachment: main.patch
> >> >>> > >> >>>
> >> >>> > >> >>> main.patch includes change to CPUTF8.java
> >> >>> > >> >>>
> >> >>> > >> >>>
> >> >>> > >> >>>> [classlib][pack200]CPUTF8.hashCode() is slow
> >> >>> > >> >>>> --------------------------------------------
> >> >>> > >> >>>>
> >> >>> > >> >>>> Key: HARMONY-5907
> >> >>> > >> >>>> URL:
> >> >>> > >> https://issues.apache.org/jira/browse/HARMONY-5907
> >> >>> > >> >>>> Project: Harmony
> >> >>> > >> >>>> Issue Type: Improvement
> >> >>> > >> >>>> Affects Versions: 5.0M6
> >> >>> > >> >>>> Environment: Latest pack200
> >> >>> > >> >>>> Reporter: Andrew Cornwall
> >> >>> > >> >>>> Attachments: main.patch
> >> >>> > >> >>>>
> >> >>> > >> >>>>
> >> >>> > >> >>>> The unpack process spends a lot of time doing
> >> CPUTF8.hashCode()
> >> >>> -
> >> >>> > >> which does String.hashCode(). We can save about 1.5 seconds of
> my
> >> 39
> >> >>> > second
> >> >>> > >> test case (about 4%) by caching the hashCode. (I thought we did
> >> this
> >> >>> > before
> >> >>> > >> - or maybe I dreamt it?)
> >> >>> > >> >>>
> >> >>> > >> >>> --
> >> >>> > >> >>> This message is automatically generated by JIRA.
> >> >>> > >> >>> -
> >> >>> > >> >>> You can reply to this email to add a comment to the issue
> >> online.
> >> >>> > >> >>>
> >> >>> > >> >>>
> >> >>> > >> >>
> >> >>> > >> >
> >> >>> > >>
> >> >>> > >
> >> >>> > >
> >> >>> > >
> >> >>> > > --
> >> >>> > > Unless stated otherwise above:
> >> >>> > > IBM United Kingdom Limited - Registered in England and Wales
> with
> >> >>> number
> >> >>> > > 741598.
> >> >>> > > Registered office: PO Box 41, North Harbour, Portsmouth,
> Hampshire
> >> PO6
> >> >>> > 3AU
> >> >>> > >
> >> >>> >
> >> >>>
> >> >>>
> >> >>>
> >> >>> --
> >> >>> Unless stated otherwise above:
> >> >>> IBM United Kingdom Limited - Registered in England and Wales with
> >> number
> >> >>> 741598.
> >> >>> Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire
> PO6
> >> 3AU
> >> >>>
> >> >>
> >> >>
> >> >
> >>
> >
>
