org.apache.cassandra.utils.concurrent

Class Ref<T>

java.lang.Object

org.apache.cassandra.utils.concurrent.Ref<T>

All Implemented Interfaces:

java.lang.AutoCloseable, RefCounted<T>

public final class Ref<T>
extends java.lang.Object
implements RefCounted<T>, java.lang.AutoCloseable

An object that needs ref counting does the two following: - defines a Tidy object that will cleanup once it's gone, (this must retain no references to the object we're tracking (only its resources and how to clean up)) Then, one of two options: 1) Construct a Ref directly pointing to it, and always use this Ref; or 2) - implements RefCounted - encapsulates a Ref, we'll call selfRef, to which it proxies all calls to RefCounted behaviours - users must ensure no references to the selfRef leak, or are retained outside of a method scope. (to ensure the selfRef is collected with the object, so that leaks may be detected and corrected) This class' functionality is achieved by what may look at first glance like a complex web of references, but boils down to: Target --> selfRef --> [Ref.State] <--> Ref.GlobalState --> Tidy ^ | Ref ---------------------------------------- | Global ------------------------------------- So that, if Target is collected, Impl is collected and, hence, so is selfRef. Once ref or selfRef are collected, the paired Ref.State's release method is called, which if it had not already been called will update Ref.GlobalState and log an error. Once the Ref.GlobalState has been completely released, the Tidy method is called and it removes the global reference to itself so it may also be collected.

Nested Class Summary

Nested classes/interfaces inherited from interface org.apache.cassandra.utils.concurrent.RefCounted

RefCounted.Tidy

Field Summary

Fields

Modifier and Type	Field and Description
static boolean	DEBUG_ENABLED

Constructor Summary

Constructors

Constructor and Description
Ref(T referent, RefCounted.Tidy tidy)

Method Summary

Modifier and Type	Method and Description
void	close()
void	ensureReleased()
T	get()
int	globalCount() A convenience method for reporting:
java.lang.String	printDebugInfo()
Ref<T>	ref()
void	release() Must be called exactly once, when the logical operation for which this Ref was created has terminated.
Ref<T>	tryRef()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

DEBUG_ENABLED

public static final boolean DEBUG_ENABLED

Constructor Detail

Ref

public Ref(T referent,
           RefCounted.Tidy tidy)

Method Detail

release

public void release()

Must be called exactly once, when the logical operation for which this Ref was created has terminated. Failure to abide by this contract will result in an error (eventually) being reported, assuming a hard reference to the resource it managed is not leaked.

ensureReleased

public void ensureReleased()

close

public void close()

Specified by:

close in interface java.lang.AutoCloseable

get

public T get()

tryRef

public Ref<T> tryRef()

Specified by:

tryRef in interface RefCounted<T>

Returns:

the a new Ref() to the managed object, incrementing its refcount, or null if it is already released

ref

public Ref<T> ref()

Specified by:

ref in interface RefCounted<T>

printDebugInfo

public java.lang.String printDebugInfo()

globalCount

public int globalCount()

A convenience method for reporting:

Returns:

the number of currently extant references globally, including the shared reference