Package com.ibm.icu.impl.coll
Class SharedObject
java.lang.Object
com.ibm.icu.impl.coll.SharedObject
- All Implemented Interfaces:
Cloneable
- Direct Known Subclasses:
CollationSettings
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.
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Nested Class Summary
Nested ClassesModifier and TypeClassDescriptionstatic final class
SharedObject.Reference<T extends SharedObject>
Similar to a smart pointer, basically a port of the static methods of C++ SharedObject. -
Field Summary
Fields -
Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionfinal void
addRef()
Increments the number of references to this object.clone()
Initializes refCount to 0.final void
final int
Returns the reference counter.final void
Decrements the number of references to this object, and auto-deletes "this" if the number becomes 0.
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Field Details
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refCount
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Constructor Details
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SharedObject
public SharedObject()Initializes refCount to 0.
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Method Details
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clone
Initializes refCount to 0. -
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()
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