com.ibm.icu.impl.coll

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() { ... }
 }

 // Either use the nest class Reference (which costs an extra allocation),
 // or duplicate its code in the class that uses S
 // (which duplicates code and is more error-prone).
 class U {
     // For read-only access, use s.readOnly().
     // For writable access, use S ownedS = s.copyOnWrite();
     private SharedObject.Reference<S> s;
     // 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();
     }
     public U clone() {
         ...
         c.s = s.clone();
         ...
     }
 }

 class V {
     // For read-only access, use s directly.
     // For writable access, use S ownedS = getOwnedS();
     private S s;
     // 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() {
         if(s.getRefCount() > 1) {
             S ownedS = s.clone();
             s.removeRef();
             s = ownedS;
             ownedS.addRef();
         }
         return s;
     }
     public U clone() {
         ...
         s.addRef();
         ...
     }
     protected void finalize() {
         ...
         if(s != null) {
             s.removeRef();
             s = null;
         }
         ...
     }
 }
 

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 and Description
static class	SharedObject.Reference<T extends SharedObject> Similar to a smart pointer, basically a port of the static methods of C++ SharedObject.

Constructor Summary

Constructors

Constructor and Description
SharedObject() Initializes refCount to 0.

Method Summary

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

Methods inherited from class java.lang.Object

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

Constructor Detail

SharedObject

public SharedObject()

Initializes refCount to 0.

Method Detail

clone

public SharedObject clone()

Initializes refCount to 0.

Overrides:

clone in class Object

Returns:

a copy of this 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()