Hello, Am Tue, 11 Oct 2016 20:55:54 +0000 schrieb Jun Zhuang <jun.zhu...@hobsons.com>:
> * A Finalizer instance is created for every finalizeable > object Yes, the java.lang.ref.Finalizer.Finalizer(Object) constructor will put the referent in the referent` field of Finalizer (declared in parent class Referent) and then link this instance with add() method at the head of the list. The head is kept alive by Finalizer#unfinalized (which is static). This constructor is called (via Finalizer#register(Object)) by the JVM when it creates a new finalizeable object. > * All the Finalizer instances are linked together using a > double linked list Yes, they dont use a LikedList class but implement the next/prev fields themself (so this needs no additional instances). > * All the Finalizer instances are tracked by the > java.lang.ref.Finalizer class. Or is it only the first one by the > unfinalized field? The head of the linked list is referenced by `unfinalized field. It points to a Finalizer instance, which points which the next field to the next Finalized and so on (and each of them has a referee). > What I am still not clear are: > > 1. Is there a finalization queue at all? If so, what does it do? There is a ReferenceQueue in the static field queue. This queue is given to all Finalize instances (the field "queue" in Reference holds thatuntil needed). The objets are enqueued to this queue by the GC. The Finalizer thread reads them from this queue and knows "this one is now not reachable anymore" and does its work (and removes it from the queue and also remove the Finalize wrapper from its linked list). > 2. What goes into the ReferenceQueue? The finalizeable objects? References go to the ReferenceQueue, the wrapper Finalizer instance is also a (Final)Reference. In case of FinalReference the queue can look at the Finalize#get() to get the referent and call finalize() on this. Same mechanism asdone for allother Reference types (with the exception of phantom references which do not allow this get). The Finalize class is a real beast: - instances are a Reference wrapping the finalizeable objects - instances form a double linked list of all Finalize instances - the class itself holds the head of the list and the queue alive in statics - the FinalizerThread (which removes Finalizer instances from the ReferenceQueue and invokes the finalizer method on it (once) is a inner class: Finalizer$FinalizerThread - the static initializer of Finalizer actually starts the FinalizerThread (as a daemon with MAX-2 prio). - the static field lock in Finalizer is used to synchronize the daemon thread with secondary finalizer threads (from runAllFinalizers() on shutdown or Runtime.runFinalizazion()) Lots of the finalization logic is done in Java, only the register() and Reference discovery is done by the runtime/gc. You can see that here, note especially the "Invoked by" comments (and parents): http://hg.openjdk.java.net/jdk9/jdk9/jdk/file/2bf254421854/src/java.base/share/classes/java/lang/ref/Finalizer.java Bernd _______________________________________________ hotspot-gc-use mailing list hotspot-gc-use@openjdk.java.net http://mail.openjdk.java.net/mailman/listinfo/hotspot-gc-use
