initial commit, 4.5 stable

thirdparty/icu4c/common/sharedobject.h

@@ -0,0 +1,184 @@
+// © 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