Hi Kevin, So when you say pushing and popping, you are painting the picture that there is some basal loader, and every time a new class is compiled, a new dynamic classloader is created and used to load the new class, then the class is stored by some context reference, instances of that class can be created. Then, we want to load a new class, and we do the same thing, create a new classloader, set the context reference to this new classloader, create new class instances. So now we lost the reference to the old classloader, but objects of the old class still exist, and will continue until they stop getting pointed to.
So two main points to confirm with you: -A new Dynamic Classloader is created during each deftyp call -the old classloader is lost This would imply that the new classloader, would have to re-"find" the classes the old classloader found from before. How does the pushing/ popping mechanism work so that it only applies to the deftypes? Best, Brent On Sep 22, 2:56 pm, Kevin Downey <redc...@gmail.com> wrote: > most likely the compiler is creating a new DynamicClassLoader, it uses > a var clojure.lang.Compiler/LOADER and pushes and pops class loaders > from there. > > > > > > > > > > On Thu, Sep 22, 2011 at 1:52 PM, Brent Millare <brent.mill...@gmail.com> > wrote: > > Hi, > > > An update to this question. While Chouser gave a good explanation > > about the details behind proxy, reify, and gen-class, I feel that the > > explanation behind deftype is incomplete. It's not clear how clojure > > is able to reload deftype defined classes. Calling deftype eventually > > leads to a call to clojure.lang.DynamicClassLoader/defineClass. > > Calling deftype again leads to another call to defineClass, but doing > > this manually results in a Linkage Error. What is happening underneath > > here that allows clojure to do this with deftypes? > > > -Brent > > > On Sep 19, 9:07 am, Brent Millare <brent.mill...@gmail.com> wrote: > >> (Note: I've copied my question from stackoverflow to get more looks in > >> case there are people in here that are not on > >> stack.http://stackoverflow.com/questions/7471316/how-does-clojure-class-rel... > >> I will sync the good answers) > > >> I've been reading code and documentation to try to understand how > >> class reloading works in clojure. According to many websites, such > >> ashttp://tutorials.jenkov.com/java-reflection/dynamic-class-loading-rel... > >> , whenever you load a class essentially you obtain the bytecode (via > >> any data mechanism), convert the bytecode into an instance of class > >> Class (via defineClass), and then resolve (link) the class via > >> resolveClass. (Does defineClass implicitly call resolveClass?). Any > >> given classloader is only allowed to link a class once. If it attempts > >> to link an existing class, it does nothing. This creates a problem > >> since you cannot link a newly instantiated class, therefore you have > >> to create a new instance of a classloader everytime you reload a > >> class. > > >> Going back to clojure, I tried examining the paths to load classes. > > >> In clojure, you can define new classes in multiple ways depending on > >> what you want: > > >> Anonymous Class: reify proxy > > >> Named Class: deftype defrecord (which uses deftype under the hood) gen- > >> class > > >> Ultimately, those codes point to clojure/src/jvm/clojure/lang/ > >> DynamicClassLoader.java > > >> where DynamicClassLoader/defineClass creates an instance with super's > >> defineClass and then caches the instance. When you want to retrieve > >> the class, clojure load with a call to forName which calls the > >> classloader and DynamicClassLoader/findClass, which first looks in the > >> cache before delegating to the super class (which is contrary to the > >> way most normal classloaders work, where they delegate first, than try > >> it themselves.) *********The important point of confusion is the > >> following: forName is documented to link the class before it returns > >> but this would imply you can not reload a class from the existing > >> DynamicClassLoader and instead need to create a new > >> DynamicClassLoader, however I don't see this in the code.******** I > >> understand that proxy and reify define anonymous classes, so their > >> names are different thus can be treated as if its a different class. > >> However, for the named classes, this breaks down. In real clojure > >> code, you can have references to the old version of the classes and > >> references to the new version of the classes simultaneously, but > >> attempts to create new class instances will be of the new version. > > >> Please explain how clojure is able to reload classes without creating > >> new instances of DynamicClassLoader, if I can understand the mechanism > >> to reload classes, I would like to extend this reloading functionality > >> to java's .class files I may create using javac. > > >> Notes: This question refers to class RELOADING, not simply dynamic > >> loading. Reloading means that I have already interned a class but want > >> to intern a new updated version of that instance. > > > -- > > You received this message because you are subscribed to the Google > > Groups "Clojure" group. > > To post to this group, send email to clojure@googlegroups.com > > Note that posts from new members are moderated - please be patient with > > your first post. > > To unsubscribe from this group, send email to > > clojure+unsubscr...@googlegroups.com > > For more options, visit this group at > >http://groups.google.com/group/clojure?hl=en > > -- > And what is good, Phaedrus, > And what is not good— > Need we ask anyone to tell us these things? -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. 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