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// © 2016 and later: Unicode, Inc. and others.
// License & terms of use: http://www.unicode.org/copyright.html
/*
******************************************************************************
* Copyright (C) 2015-2016, International Business Machines
* Corporation and others. All Rights Reserved.
******************************************************************************
* sharedobject.h
*/
#ifndef __SHAREDOBJECT_H__
#define __SHAREDOBJECT_H__
#include "unicode/uobject.h"
#include "umutex.h"
U_NAMESPACE_BEGIN
class SharedObject;
/**
* Base class for unified cache exposing enough methods to SharedObject
* instances to allow their addRef() and removeRef() methods to
* update cache metrics. No other part of ICU, except for SharedObject,
* should directly call the methods of this base class.
*/
class U_COMMON_API UnifiedCacheBase : public UObject {
public:
UnifiedCacheBase() { }
/**
* Notify the cache implementation that an object was seen transitioning to
* zero hard references. The cache may use this to keep track the number of
* unreferenced SharedObjects, and to trigger evictions.
*/
virtual void handleUnreferencedObject() const = 0;
virtual ~UnifiedCacheBase();
private:
UnifiedCacheBase(const UnifiedCacheBase &) = delete;
UnifiedCacheBase &operator=(const UnifiedCacheBase &) = delete;
};
/**
* Base class for shared, reference-counted, auto-deleted objects.
* Subclasses can be immutable.
* If they are mutable, then they must implement their copy constructor
* so that copyOnWrite() works.
*
* Either stack-allocate, use LocalPointer, or use addRef()/removeRef().
* Sharing requires reference-counting.
*/
class U_COMMON_API SharedObject : public UObject {
public:
/** Initializes totalRefCount, softRefCount to 0. */
SharedObject() :
softRefCount(0),
hardRefCount(0),
cachePtr(nullptr) {}
/** Initializes totalRefCount, softRefCount to 0. */
SharedObject(const SharedObject &other) :
UObject(other),
softRefCount(0),
hardRefCount(0),
cachePtr(nullptr) {}
virtual ~SharedObject();
/**
* Increments the number of hard references to this object. Thread-safe.
* Not for use from within the Unified Cache implementation.
*/
void addRef() const;
/**
* Decrements the number of hard references to this object, and
* arrange for possible cache-eviction and/or deletion if ref
* count goes to zero. Thread-safe.
*
* Not for use from within the UnifiedCache implementation.
*/
void removeRef() const;
/**
* Returns the number of hard references for this object.
* Uses a memory barrier.
*/
int32_t getRefCount() const;
/**
* If noHardReferences() == true then this object has no hard references.
* Must be called only from within the internals of UnifiedCache.
*/
inline UBool noHardReferences() const { return getRefCount() == 0; }
/**
* If hasHardReferences() == true then this object has hard references.
* Must be called only from within the internals of UnifiedCache.
*/
inline UBool hasHardReferences() const { return getRefCount() != 0; }
/**
* Deletes this object if it has no references.
* Available for non-cached SharedObjects only. Ownership of cached objects
* is with the UnifiedCache, which is solely responsible for eviction and deletion.
*/
void deleteIfZeroRefCount() const;
/**
* Returns a writable version of ptr.
* If there is exactly one owner, then ptr itself is returned as a
* non-const pointer.
* If there are multiple owners, then ptr is replaced with a
* copy-constructed clone,
* and that is returned.
* Returns nullptr if cloning failed.
*
* T must be a subclass of SharedObject.
*/
template<typename T>
static T *copyOnWrite(const T *&ptr) {
const T *p = ptr;
if(p->getRefCount() <= 1) { return const_cast<T *>(p); }
T *p2 = new T(*p);
if(p2 == nullptr) { return nullptr; }
p->removeRef();
ptr = p2;
p2->addRef();
return p2;
}
/**
* Makes dest an owner of the object pointed to by src while adjusting
* reference counts and deleting the previous object dest pointed to
* if necessary. Before this call is made, dest must either be nullptr or
* be included in the reference count of the object it points to.
*
* T must be a subclass of SharedObject.
*/
template<typename T>
static void copyPtr(const T *src, const T *&dest) {
if(src != dest) {
if(dest != nullptr) { dest->removeRef(); }
dest = src;
if(src != nullptr) { src->addRef(); }
}
}
/**
* Equivalent to copyPtr(nullptr, dest).
*/
template<typename T>
static void clearPtr(const T *&ptr) {
if (ptr != nullptr) {
ptr->removeRef();
ptr = nullptr;
}
}
private:
/**
* The number of references from the UnifiedCache, which is
* the number of times that the sharedObject is stored as a hash table value.
* For use by UnifiedCache implementation code only.
* All access is synchronized by UnifiedCache's gCacheMutex
*/
mutable int32_t softRefCount;
friend class UnifiedCache;
/**
* Reference count, excluding references from within the UnifiedCache implementation.
*/
mutable u_atomic_int32_t hardRefCount;
mutable const UnifiedCacheBase *cachePtr;
};
U_NAMESPACE_END
#endif
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