Class SharedObject

java.lang.Object

com.ibm.icu.impl.coll.SharedObject

All Implemented Interfaces:

Cloneable

Direct Known Subclasses:

CollationSettings

public class SharedObject
extends Object
implements Cloneable

Base class for shared, reference-counted, auto-deleted objects. Java subclasses are mutable and must implement clone().

In C++, the SharedObject base class is used for both memory and ownership management. In Java, memory management (deletion after last reference is gone) is up to the garbage collector, but the reference counter is still used to see whether the referent is the sole owner.

Usage:

class S extends SharedObject {
    public clone() { ... }
}

// Use the nest class Reference (which costs an extra allocation),
class U {
    // For read-only access, use s.readOnly().
    // For writable access, use S ownedS = s.copyOnWrite();
    private SharedObject.Reference<S> s;
    public U(Reference<U> ref) {
        ...
    }
    // Returns a writable version of s.
    // If there is exactly one owner, then s itself is returned.
    // If there are multiple owners, then s is replaced with a clone,
    // and that is returned.
    private S getOwnedS() {
        return s.copyOnWrite();
    }
}

Either use only Java memory management, or use addRef()/removeRef(). Sharing requires reference-counting.

TODO: Consider making this more widely available inside ICU, or else adopting a different model.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static final class	SharedObject.Reference<T extends SharedObject>
private static final class	SharedObject.SharedObjectHolder<T extends SharedObject>	A class wrapping SharedObject.

Field Summary

Fields

Modifier and Type	Field	Description
private AtomicInteger	refCount

Constructor Summary

Constructors

Constructor	Description
SharedObject()	Initializes refCount to 0.

Method Summary

Modifier and Type	Method	Description
final void	addRef()	Increments the number of references to this object.
SharedObject	clone()	Initializes refCount to 0.
final void	deleteIfZeroRefCount()
final int	getRefCount()	Returns the reference counter.
final void	removeRef()	Decrements the number of references to this object, and auto-deletes "this" if the number becomes 0.

Methods inherited from class Object

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

Field Details

refCount

private AtomicInteger refCount

Constructor Details

SharedObject

public SharedObject()

Initializes refCount to 0.

Method Details

clone

public SharedObject clone()

Initializes refCount to 0.

Overrides:

clone in class Object

addRef

public final void addRef()

Increments the number of references to this object. Thread-safe.

removeRef

public final void removeRef()

Decrements the number of references to this object, and auto-deletes "this" if the number becomes 0. Thread-safe.

getRefCount

public final int getRefCount()

Returns the reference counter. Uses a memory barrier.

deleteIfZeroRefCount

public final void deleteIfZeroRefCount()