Class Nexus
This nexus is a global dispatcher for initializing classes with
LoadedTypeInitializer
s. To do so, this class is to be loaded
by the system class loader in an explicit manner. Any instrumented class is then injected a code
block into its static type initializer that makes a call to this very same nexus which had the
loaded type initializer registered before hand.
Note: Availability of the Nexus
class and its injection into the system class loader
can be disabled entirely by setting the PROPERTY
system property to false
.
Important: The nexus must never be accessed directly but only by the NexusAccessor
which makes sure that the nexus is loaded by the system class loader. Otherwise, a class might not
be able to initialize itself if it is loaded by different class loader that does not have the
system class loader in its hierarchy.
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Field Summary
FieldsModifier and TypeFieldDescriptionprivate final int
The class loader's hash code upon registration.private final int
A random value that uniquely identifies a Nexus entry in order to avoid conflicts when applying the self-initialization strategy in multiple transformations.private final String
The name of a type for which a loaded type initializer is registered.private static final ReferenceQueue
<ClassLoader> An type-safe constant for a non-operational reference queue.static final String
A system property that allows to disable the use of theNexus
class which is normally injected into the system class loader.private static final ConcurrentMap
<Nexus, Object> A map of keys identifying a loaded type by its name and class loader mapping their potentialLoadedTypeInitializer
where the class loader of these initializers is however irrelevant. -
Constructor Summary
ConstructorsModifierConstructorDescriptionprivate
Creates a key for identifying a loaded type initializer.private
Nexus
(String name, ClassLoader classLoader, ReferenceQueue<? super ClassLoader> referenceQueue, int identification) Creates a key for identifying a loaded type initializer. -
Method Summary
Modifier and TypeMethodDescriptionstatic void
clean
(Reference<? super ClassLoader> reference) Cleans any stale entries from this nexus.boolean
int
hashCode()
static void
initialize
(Class<?> type, int identification) Initializes a loaded type.private static String
nonAnonymous
(String typeName) Normalizes a type name if it is loaded by an anonymous class loader.static void
register
(String name, ClassLoader classLoader, ReferenceQueue<? super ClassLoader> referenceQueue, int identification, Object typeInitializer) Registers a new loaded type initializer.toString()
Methods inherited from class java.lang.ref.Reference
clear, clone, enqueue, get, isEnqueued, reachabilityFence, refersTo
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Field Details
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PROPERTY
A system property that allows to disable the use of theNexus
class which is normally injected into the system class loader.- See Also:
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NO_QUEUE
An type-safe constant for a non-operational reference queue. -
TYPE_INITIALIZERS
A map of keys identifying a loaded type by its name and class loader mapping their potentialLoadedTypeInitializer
where the class loader of these initializers is however irrelevant. -
name
The name of a type for which a loaded type initializer is registered. -
classLoaderHashCode
private final int classLoaderHashCodeThe class loader's hash code upon registration. -
identification
private final int identificationA random value that uniquely identifies a Nexus entry in order to avoid conflicts when applying the self-initialization strategy in multiple transformations.
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Constructor Details
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Nexus
Creates a key for identifying a loaded type initializer.- Parameters:
type
- The loaded type for which a key is to be created.identification
- An identification for the initializer to run.
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Nexus
private Nexus(String name, @MaybeNull ClassLoader classLoader, @MaybeNull ReferenceQueue<? super ClassLoader> referenceQueue, int identification) Creates a key for identifying a loaded type initializer.- Parameters:
name
- The name of a type for which a loaded type initializer is registered.classLoader
- The class loader for which a loaded type initializer is registered.referenceQueue
- The reference queue to notify upon the class loader's collection ornull
if no queue should be notified.identification
- An identification for the initializer to run.
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Method Details
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nonAnonymous
Normalizes a type name if it is loaded by an anonymous class loader.- Parameters:
typeName
- The name as returned byClass.getName()
.- Returns:
- The non-anonymous name of the given class.
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initialize
Initializes a loaded type. This method must only be invoked via the system class loader.
Important: This method must never be called directly but only by using a
NexusAccessor.InitializationAppender
which enforces to access this class for the system class loader to assure a VM global singleton. This avoids a duplication of the class if this nexus is loaded by different class loaders. For this reason, the last parameter must not use a Byte Buddy specific type as those types can be loaded by different class loaders, too. Any access of the instance is done using Java reflection instead.- Parameters:
type
- The loaded type to initialize.identification
- An identification for the initializer to run.- Throws:
Exception
- If an exception occurs.
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register
public static void register(String name, @MaybeNull ClassLoader classLoader, @MaybeNull ReferenceQueue<? super ClassLoader> referenceQueue, int identification, Object typeInitializer) Registers a new loaded type initializer.
Important: This method must never be called directly but only by using a
NexusAccessor
which enforces to access this class for the system class loader to assure a VM global singleton. This avoids a duplication of the class if this nexus is loaded by different class loaders. For this reason, the last parameter must not use a Byte Buddy specific type as those types can be loaded by different class loaders, too. Any access of the instance is done using Java reflection instead.- Parameters:
name
- The name of the type for the loaded type initializer.classLoader
- The class loader of the type for the loaded type initializer.referenceQueue
- The reference queue to notify upon the class loader's collection which will be enqueued a reference which can be handed toclean(Reference)
ornull
if no reference queue should be notified.identification
- An identification for the initializer to run.typeInitializer
- The type initializer to register. The initializer must be an instance ofLoadedTypeInitializer
where it does however not matter which class loader loaded this latter type.
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clean
Cleans any stale entries from this nexus. Entries are considered stale if their class loader was collected before a class was initialized.
Important: This method must never be called directly but only by using a
NexusAccessor
which enforces to access this class for the system class loader to assure a VM global singleton. This avoids a duplication of the class if this nexus is loaded by different class loaders. For this reason, the last parameter must not use a Byte Buddy specific type as those types can be loaded by different class loaders, too. Any access of the instance is done using Java reflection instead.- Parameters:
reference
- The stale reference to clean.
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hashCode
public int hashCode() -
equals
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toString
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