ICU-64243.0.1.tar.gz

[apple/icu.git] / icuSources / common / sharedobject.h

diff --git a/icuSources/common/sharedobject.h b/icuSources/common/sharedobject.h
index 671bab137f69df49f967100825c607444b2e7b2d..c0a5aba4782821bb0bd24a0f068850e9b7af08e5 100644 (file)
--- a/icuSources/common/sharedobject.h
+++ b/icuSources/common/sharedobject.h
@@ -1,6 +1,8 @@
+// © 2016 and later: Unicode, Inc. and others.
+// License & terms of use: http://www.unicode.org/copyright.html
 /*
 ******************************************************************************
-* Copyright (C) 2014, International Business Machines
+* Copyright (C) 2015-2016, International Business Machines
 * Corporation and others.  All Rights Reserved.
 ******************************************************************************
 * sharedobject.h
@@ -15,6 +17,31 @@
 
 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 &);
+    UnifiedCacheBase &operator=(const UnifiedCacheBase &);
+};
+
 /**
  * Base class for shared, reference-counted, auto-deleted objects.
  * Subclasses can be immutable.
@@ -26,31 +53,62 @@ U_NAMESPACE_BEGIN
  */
 class U_COMMON_API SharedObject : public UObject {
 public:
-    /** Initializes refCount to 0. */
-    SharedObject() : refCount(0) {}
+    /** Initializes totalRefCount, softRefCount to 0. */
+    SharedObject() :
+            softRefCount(0),
+            hardRefCount(0),
+            cachePtr(NULL) {}
+
+    /** Initializes totalRefCount, softRefCount to 0. */
+    SharedObject(const SharedObject &other) :
+            UObject(other),
+            softRefCount(0),
+            hardRefCount(0),
+            cachePtr(NULL) {}
 
-    /** Initializes refCount to 0. */
-    SharedObject(const SharedObject &/*other*/) : refCount(0) {}
     virtual ~SharedObject();
 
     /**
-     * Increments the number of references to this object. Thread-safe.
+     * 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 references to this object,
-     * and auto-deletes "this" if the number becomes 0. Thread-safe.
+     * 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 reference counter. Uses a memory barrier.
+     * 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
@@ -78,7 +136,7 @@ public:
      * 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 NULL or
-     * own its object. 
+     * be included in the reference count of the object it points to. 
      *
      * T must be a subclass of SharedObject.
      */
@@ -92,7 +150,7 @@ public:
     }
 
     /**
-     * Equivalent to copy(NULL, dest).
+     * Equivalent to copyPtr(NULL, dest).
      */
     template<typename T>
     static void clearPtr(const T *&ptr) {
@@ -103,7 +161,22 @@ public:
     }
 
 private:
-    mutable u_atomic_int32_t refCount;
+    /**
+     * 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