112 lines
3.0 KiB
C++
112 lines
3.0 KiB
C++
/*
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******************************************************************************
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* Copyright (C) 2014, International Business Machines
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* Corporation and others. All Rights Reserved.
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******************************************************************************
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* sharedobject.h
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*/
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#ifndef __SHAREDOBJECT_H__
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#define __SHAREDOBJECT_H__
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#include "unicode/uobject.h"
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#include "umutex.h"
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U_NAMESPACE_BEGIN
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/**
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* Base class for shared, reference-counted, auto-deleted objects.
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* Subclasses can be immutable.
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* If they are mutable, then they must implement their copy constructor
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* so that copyOnWrite() works.
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*
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* Either stack-allocate, use LocalPointer, or use addRef()/removeRef().
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* Sharing requires reference-counting.
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*/
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class U_COMMON_API SharedObject : public UObject {
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public:
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/** Initializes refCount to 0. */
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SharedObject() : refCount(0) {}
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/** Initializes refCount to 0. */
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SharedObject(const SharedObject &other) : UObject(other), refCount(0) {}
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virtual ~SharedObject();
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/**
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* Increments the number of references to this object. Thread-safe.
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*/
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void addRef() const;
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/**
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* Decrements the number of references to this object,
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* and auto-deletes "this" if the number becomes 0. Thread-safe.
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*/
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void removeRef() const;
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/**
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* Returns the reference counter. Uses a memory barrier.
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*/
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int32_t getRefCount() const;
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void deleteIfZeroRefCount() const;
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/**
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* Returns a writable version of ptr.
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* If there is exactly one owner, then ptr itself is returned as a
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* non-const pointer.
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* If there are multiple owners, then ptr is replaced with a
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* copy-constructed clone,
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* and that is returned.
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* Returns NULL if cloning failed.
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*
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* T must be a subclass of SharedObject.
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*/
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template<typename T>
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static T *copyOnWrite(const T *&ptr) {
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const T *p = ptr;
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if(p->getRefCount() <= 1) { return const_cast<T *>(p); }
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T *p2 = new T(*p);
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if(p2 == NULL) { return NULL; }
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p->removeRef();
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ptr = p2;
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p2->addRef();
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return p2;
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}
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/**
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* Makes dest an owner of the object pointed to by src while adjusting
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* reference counts and deleting the previous object dest pointed to
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* if necessary. Before this call is made, dest must either be NULL or
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* be included in the reference count of the object it points to.
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*
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* T must be a subclass of SharedObject.
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*/
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template<typename T>
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static void copyPtr(const T *src, const T *&dest) {
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if(src != dest) {
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if(dest != NULL) { dest->removeRef(); }
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dest = src;
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if(src != NULL) { src->addRef(); }
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}
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}
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/**
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* Equivalent to copyPtr(NULL, dest).
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*/
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template<typename T>
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static void clearPtr(const T *&ptr) {
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if (ptr != NULL) {
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ptr->removeRef();
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ptr = NULL;
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}
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}
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private:
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mutable u_atomic_int32_t refCount;
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};
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U_NAMESPACE_END
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#endif
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