Hello
sorry for such a delay. Here what I've got with my experiments. Please
refer to classloadertest2.java attached to JIRA.
Talking about the Pavel's case: CL1 <- CL2 <- CL3, loading via CL3
then loading via CL2.
SUN JDK 6:
mycl1.parent = [EMAIL PROTECTED]
mycl2.parent = [MyClassLoader [dir:my]]
mycl3.parent = [MyClassLoader [dir:X2]]
[MyClassLoader [dir:X3]].loadClass(hi) enter...
[MyClassLoader [dir:my]].findClass(hi) enter...
[MyClassLoader [dir:my]].loadClassData(hi) enter...
[MyClassLoader [dir:my]].loadClassData(hi) exit. out = [EMAIL PROTECTED]
[MyClassLoader [dir:my]].findClass(hi) exit. out = [EMAIL PROTECTED]
[MyClassLoader [dir:my]].loadClass(java.lang.Object) enter...
[MyClassLoader [dir:my]].loadClass(java.lang.Object) exit. out = class
java.lang.Object
[MyClassLoader [dir:X3]].loadClass(hi) exit. out = class hi
Class.forName("hi", true, mycl3) = [class hi]
[MyClassLoader [dir:X2]].loadClass(hi) enter...
[MyClassLoader [dir:X2]].loadClass(hi) exit. out = class hi
Class.forName("hi", true, mycl2) = [class hi]
mycl1.findLoadedClass(hi) = [class hi]
mycl2.findLoadedClass(hi) = [class hi]
mycl3.findLoadedClass(hi) = [class hi]
HARMONY:
mycl1.parent = [EMAIL PROTECTED]
mycl2.parent = [MyClassLoader [dir:my]]
mycl3.parent = [MyClassLoader [dir:X2]]
[MyClassLoader [dir:X3]].loadClass(hi) enter...
[MyClassLoader [dir:X2]].loadClass(hi) enter...
[MyClassLoader [dir:my]].loadClass(hi) enter...
[MyClassLoader [dir:my]].findClass(hi) enter...
[MyClassLoader [dir:my]].loadClassData(hi) enter...
[MyClassLoader [dir:my]].loadClassData(hi) exit. out = [EMAIL PROTECTED]
[MyClassLoader [dir:my]].findClass(hi) exit. out = [EMAIL PROTECTED]
[MyClassLoader [dir:my]].loadClass(java.lang.Object) enter...
[MyClassLoader [dir:my]].loadClass(java.lang.Object) exit. out = class
java.lang.Object
[MyClassLoader [dir:my]].loadClass(hi) exit. out = class hi
[MyClassLoader [dir:X2]].loadClass(hi) exit. out = class hi
[MyClassLoader [dir:X3]].loadClass(hi) exit. out = class hi
Class.forName("hi", true, mycl3) = [class hi]
[MyClassLoader [dir:X2]].loadClass(hi) enter...
[MyClassLoader [dir:my]].loadClass(hi) enter...
[MyClassLoader [dir:my]].loadClass(hi) exit. out = class hi
[MyClassLoader [dir:X2]].loadClass(hi) exit. out = class hi
Class.forName("hi", true, mycl2) = [class hi]
mycl1.findLoadedClass(hi) = [class hi]
mycl2.findLoadedClass(hi) = [null]
mycl3.findLoadedClass(hi) = [null]
First thing that one can catch: in case of SUN we don't touch the CL2
at all during the loading via CL3. Interesting.
And during the loading via CL2 SUN does not touch the CL1.
Thanks
Sergey
On 10/23/07, Evgueni Brevnov <[EMAIL PROTECTED]> wrote:
> Pavel,
>
> I don't know exact answer to you question :-(, sorry, I hope Dmitry
> will provide such information soon :-)
>
> I have two notes:
>
> 1) I believe the spec requires to return the same class each time
> since a pair <ClassLoader, ClassName> must uniquely identify java
> class. So in you example from the first letter CL2 should always
> return the same class.
>
> 2) Regarding "initiating" class loader notion. My understanding is
> that each class loader in the hierarhy chain up to defining one should
> be marked as initiating class loader. At least this is written in [1]
>
> [1] "Inside the Jva2 Virtual Machine" by Bill Venners.
>
> Thanks
> Evgueni
> On 10/23/07, Pavel Pervov <[EMAIL PROTECTED]> wrote:
> > Evgueni,
> >
> > 1) Our own URLClassLoader overrides ClassLoader.loadClass method, so the
> > idea of adding such registry to base class will not work from the start.
> >
> > 2) The question in my previous letter is not answered. If the answer is
> > positive, then adding the registry of "initiated" classes to URLClassLoader
> > (which AFAIU will cover the issue described by Sergey) still requires solid
> > algorithm to distinguish the class loader which was initially asked to load
> > a class from the one, which resides in the middle of delegation chain.
> >
> > I'm not against caching, I just see problems I do not know how to solve.
> >
> > WBR,
> > Pavel.
> >
> > P.S. BTW, we have the registry of "initiated" classes but it is only
> > appended on class resolutions.
> > On 10/23/07, Evgueni Brevnov <[EMAIL PROTECTED]> wrote:
> > >
> > > Pavel,
> > >
> > > As you pointed out to change delegation model user must override
> > > ClassLoader.loadClass() method. By doing so user can specify any
> > > search order he only want and doesn't depend on caching capabilities
> > > provided by java.lang.ClassLoader. If user uses default implementation
> > > of ClassLoader.loadClass() method then it should be safe to use cache.
> > > What do you think?
> > >
> > > Thanks
> > > Evgueni
> > >
> > > On 10/23/07, Pavel Pervov <[EMAIL PROTECTED]> wrote:
> > > > Evgueni,
> > > >
> > > > ClassLoader.loadClass is not final. One can overload this and build any
> > > > delegation model his or her application requires. So, -1 here.
> > > >
> > > > It would be good to answer the following case before considering class
> > > > caching.
> > > >
> > > > Assume, we have delegation of three class loaders: CL1<-CL2<-CL3.
> > > > Assume, class Foo is only available from CL1.
> > > >
> > > > We call to CL3.loadClass("Foo"). The call chain will look like
> > > > CL3.loadClass->CL2.loadClass->CL1.loadClass. As far as we know, the
> > > second
> > > > and subsequent calls to CL3.loadClass("Foo") will not call to
> > > > CL2.loadClass("Foo")
> > > > but return "cached" copy from CL3 on RI (as described by Sergey).
> > > >
> > > > But it would be really interesting to know if the call to
> > > > CL2.loadClasswill
> > > > result in call chain CL2.loadClass->CL1.loadClass.
> > > >
> > > > If this is true, my initial idea that it is only allowed to register the
> > > > class in "initiating" and "defining" loaders is also true. And I have no
> > > > solid solution to determining "initiating" class loader.
> > > >
> > > > Otherwise, it is ok to create the cache in URLClassLoader as Sergey
> > > > initially suggested.
> > > >
> > > > Pavel.
> > > >
> > > > On 10/23/07, Evgueni Brevnov <[EMAIL PROTECTED]> wrote:
> > > > >
> > > > > Pavel,
> > > > >
> > > > > I think its not common situation when parent class loader is changed
> > > > > at runtime. To be honest I don't know how it's possible since parent
> > > > > class loader is kept in private field. Anyway, can we somehow detect
> > > > > such situation and switch to normal scheme or discard cached classes
> > > > > upon switching parent class loader.
> > > > >
> > > > > Thanks
> > > > > Evgueni
> > > > >
> > > > > On 10/22/07, Pavel Pervov <[EMAIL PROTECTED]> wrote:
> > > > > > Looking at the Java Virtual Machine Specification there are two
> > > terms:
> > > > > > initiating loader and defining loader.
> > > > > >
> > > > > > Initiating loader is the class loader which was first asked to load
> > > > > class in
> > > > > > delegation chain (CL2 in your example).
> > > > > >
> > > > > > Defining loader is the class loader which has found bytes for class
> > > > > > definition and called to JNI->DefineClass.
> > > > > >
> > > > > > Lets review the following delegation model.
> > > > > >
> > > > > > CL1<-CL2<-CL3
> > > > > >
> > > > > > CL4<-CL2<-CL5
> > > > > >
> > > > > > There is nothing wrong with CL2: its delegation model simply assumes
> > > > > > switching delegation parent depending on some external property.
> > > > > >
> > > > > > Different versions of class Foo are available from CL1 and CL4. Now,
> > > we
> > > > > do
> > > > > > something like CL3.loadClass("Foo") and CL5.loadClass("Foo").
> > > > > > If CL2 will cache the class Foo, then the call to CL5 will return
> > > wrong
> > > > > > result.
> > > > > >
> > > > > > So the caching is possible, but it is only allowed to register class
> > > in
> > > > > > initiating loader and in defining loader. Otherwise, you may have
> > > wrong
> > > > > > classes returned to your application.
> > > > > >
> > > > > > Determining defining loader is simple. Can you suggest some working
> > > idea
> > > > > on
> > > > > > how to determine initiating loader for a class?
> > > > > >
> > > > > > WBR,
> > > > > > Pavel.
> > > > > >
> > > > > > On 10/22/07, Sergey Dmitriev <[EMAIL PROTECTED]> wrote:
> > > > > > >
> > > > > > > Hello
> > > > > > >
> > > > > > > This letter is actually about HARMONY-4965, I just changed a
> > > little
> > > > > > > bit a subject. :)
> > > > > > >
> > > > > > > During my play with SPECjAppServer2004 on OC4J I've found out that
> > > we
> > > > > > > have a way to optimize the class loader. Or in other words
> > > currently
> > > > > > >
> > > > > > > Lets say we have class loaders CL1 and CL2, and CL2.getParent() ==
> > > > > > > CL1. And lets say we have a class C which is loaded by the CL1
> > > (the
> > > > > > > parent one). And then we try to load class via the class loader
> > > CL2:
> > > > > > > of course CL2 first of all tries to load it via its parent CL1 and
> > > > > > > succeed in it. When we try to load class C via CL2 again we will
> > > have
> > > > > > > the same chain of calls: CL2 -> CL1. But if CL2 have support of
> > > > > > > caching of classes loaded by not itself - the chain can become
> > > much
> > > > > > > shorter - it could end at CL2.findFinishedClass().
> > > > > > >
> > > > > > > For example RI behaves like this. See JIRA's demo.
> > > > > > >
> > > > > > > Back to the SPECjAppServer2004 @ OC4J. In this case we have a
> > > deeper
> > > > > > > chain: we have a concrete class which is been searched so deep
> > > that we
> > > > > > > looking for this class in boot strap class path. And this is what
> > > we
> > > > > > > have in steady state of the benchmark. Don't you think it is
> > > useless?
> > > > > > > :)
> > > > > > >
> > > > > > > Talking about numbers: my measurements show that we can take up to
> > > 20%
> > > > > > > of burst having this bug fixed. Could some competent guy take a
> > > look
> > > > > > > into this?
> > > > > > >
> > > > > > >
> > > > > > > Thanks
> > > > > > > Sergey
> > > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > > --
> > > > > > Pavel Pervov,
> > > > > > Intel Enterprise Solutions Software Division
> > > > > >
> > > > >
> > > >
> > > >
> > > >
> > > > --
> > > > Pavel Pervov,
> > > > Intel Enterprise Solutions Software Division
> > > >
> > >
> >
> >
> >
> > --
> > Pavel Pervov,
> > Intel Enterprise Solutions Software Division
> >
>
