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+// © 2016 and later: Unicode, Inc. and others.
+// License & terms of use: http://www.unicode.org/copyright.html
+/*
+******************************************************************************
+* Copyright (C) 2015, International Business Machines Corporation and
+* others. All Rights Reserved.
+******************************************************************************
+*
+* File UNIFIEDCACHE.H - The ICU Unified cache.
+******************************************************************************
+*/
+
+#ifndef __UNIFIED_CACHE_H__
+#define __UNIFIED_CACHE_H__
+
+#include "utypeinfo.h"  // for 'typeid' to work
+
+#include "unicode/uobject.h"
+#include "unicode/locid.h"
+#include "sharedobject.h"
+#include "unicode/unistr.h"
+#include "cstring.h"
+#include "ustr_imp.h"
+
+struct UHashtable;
+struct UHashElement;
+
+U_NAMESPACE_BEGIN
+
+class UnifiedCache;
+
+/**
+ * A base class for all cache keys.
+ */
+class U_COMMON_API CacheKeyBase : public UObject {
+ public:
+   CacheKeyBase() : fCreationStatus(U_ZERO_ERROR), fIsPrimary(false) {}
+
+   /**
+    * Copy constructor. Needed to support cloning.
+    */
+   CacheKeyBase(const CacheKeyBase &other) 
+           : UObject(other), fCreationStatus(other.fCreationStatus), fIsPrimary(false) { }
+   virtual ~CacheKeyBase();
+
+   /**
+    * Returns the hash code for this object.
+    */
+   virtual int32_t hashCode() const = 0;
+
+   /**
+    * Clones this object polymorphically. Caller owns returned value.
+    */
+   virtual CacheKeyBase *clone() const = 0;
+
+   /**
+    * Create a new object for this key. Called by cache on cache miss.
+    * createObject must add a reference to the object it returns. Note
+    * that getting an object from the cache and returning it without calling
+    * removeRef on it satisfies this requirement. It can also return nullptr
+    * and set status to an error.
+    *
+    * @param creationContext the context in which the object is being
+    *                        created. May be nullptr.
+    * @param status          Implementations can return a failure here.
+    *                        In addition, implementations may return a
+    *                        non nullptr object and set a warning status.
+    */
+   virtual const SharedObject *createObject(
+           const void *creationContext, UErrorCode &status) const = 0;
+
+   /**
+    * Writes a description of this key to buffer and returns buffer. Written
+    * description is nullptr terminated.
+    */
+   virtual char *writeDescription(char *buffer, int32_t bufSize) const = 0;
+
+   friend inline bool operator==(const CacheKeyBase& lhs,
+                                 const CacheKeyBase& rhs) {
+       return lhs.equals(rhs);
+   }
+
+   friend inline bool operator!=(const CacheKeyBase& lhs,
+                                 const CacheKeyBase& rhs) {
+       return !lhs.equals(rhs);
+   }
+
+ protected:
+   virtual bool equals(const CacheKeyBase& other) const = 0;
+
+ private:
+   mutable UErrorCode fCreationStatus;
+   mutable UBool fIsPrimary;
+   friend class UnifiedCache;
+};
+
+
+
+/**
+ * Templated version of CacheKeyBase. 
+ * A key of type LocaleCacheKey<T> maps to a value of type T.
+ */
+template<typename T>
+class CacheKey : public CacheKeyBase {
+ public:
+   virtual ~CacheKey() { }
+   /**
+    * The template parameter, T, determines the hash code returned.
+    */
+   virtual int32_t hashCode() const override {
+       const char *s = typeid(T).name();
+       return ustr_hashCharsN(s, static_cast<int32_t>(uprv_strlen(s)));
+   }
+
+   /**
+    * Use the value type, T,  as the description.
+    */
+   virtual char *writeDescription(char *buffer, int32_t bufLen) const override {
+       const char *s = typeid(T).name();
+       uprv_strncpy(buffer, s, bufLen);
+       buffer[bufLen - 1] = 0;
+       return buffer;
+   }
+
+ protected:
+   /**
+    * Two objects are equal if they are of the same type.
+    */
+   virtual bool equals(const CacheKeyBase &other) const override {
+       return this == &other || typeid(*this) == typeid(other);
+   }
+};
+
+/**
+ * Cache key based on locale.
+ * A key of type LocaleCacheKey<T> maps to a value of type T.
+ */
+template<typename T>
+class LocaleCacheKey : public CacheKey<T> {
+ protected:
+   Locale   fLoc;
+   virtual bool equals(const CacheKeyBase &other) const override {
+       if (!CacheKey<T>::equals(other)) {
+           return false;
+       }
+       // We know this and other are of same class because equals() on
+       // CacheKey returned true.
+       return operator==(static_cast<const LocaleCacheKey<T> &>(other));
+   }
+ public:
+   LocaleCacheKey(const Locale &loc) : fLoc(loc) {}
+   LocaleCacheKey(const LocaleCacheKey<T> &other)
+           : CacheKey<T>(other), fLoc(other.fLoc) { }
+   virtual ~LocaleCacheKey() { }
+   virtual int32_t hashCode() const override {
+       return (int32_t)(37u * (uint32_t)CacheKey<T>::hashCode() + (uint32_t)fLoc.hashCode());
+   }
+   inline bool operator == (const LocaleCacheKey<T> &other) const {
+       return fLoc == other.fLoc;
+   }
+   virtual CacheKeyBase *clone() const override {
+       return new LocaleCacheKey<T>(*this);
+   }
+   virtual const T *createObject(
+           const void *creationContext, UErrorCode &status) const override;
+   /**
+    * Use the locale id as the description.
+    */
+   virtual char *writeDescription(char *buffer, int32_t bufLen) const override {
+       const char *s = fLoc.getName();
+       uprv_strncpy(buffer, s, bufLen);
+       buffer[bufLen - 1] = 0;
+       return buffer;
+   }
+
+};
+
+/**
+ * The unified cache. A singleton type.
+ * Design doc here:
+ * https://docs.google.com/document/d/1RwGQJs4N4tawNbf809iYDRCvXoMKqDJihxzYt1ysmd8/edit?usp=sharing
+ */
+class U_COMMON_API UnifiedCache : public UnifiedCacheBase {
+ public:
+   /**
+    * @internal
+    * Do not call directly. Instead use UnifiedCache::getInstance() as
+    * there should be only one UnifiedCache in an application.
+    */
+   UnifiedCache(UErrorCode &status);
+
+   /**
+    * Return a pointer to the global cache instance.
+    */
+   static UnifiedCache *getInstance(UErrorCode &status);
+
+   /**
+    * Fetches a value from the cache by key. Equivalent to
+    * get(key, nullptr, ptr, status);
+    */
+   template<typename T>
+   void get(
+           const CacheKey<T>& key,
+           const T *&ptr,
+           UErrorCode &status) const {
+       get(key, nullptr, ptr, status);
+   }
+
+   /**
+    * Fetches value from the cache by key.
+    *
+    * @param key             the cache key.
+    * @param creationContext passed verbatim to createObject method of key
+    * @param ptr             On entry, ptr must be nullptr or be included if
+    *                        the reference count of the object it points
+    *                        to. On exit, ptr points to the fetched object
+    *                        from the cache or is left unchanged on
+    *                        failure. Caller must call removeRef on ptr
+    *                        if set to a non nullptr value.
+    * @param status          Any error returned here. May be set to a
+    *                        warning value even if ptr is set.
+    */
+   template<typename T>
+   void get(
+           const CacheKey<T>& key,
+           const void *creationContext,
+           const T *&ptr,
+           UErrorCode &status) const {
+       if (U_FAILURE(status)) {
+           return;
+       }
+       UErrorCode creationStatus = U_ZERO_ERROR;
+       const SharedObject *value = nullptr;
+       _get(key, value, creationContext, creationStatus);
+       const T *tvalue = (const T *) value;
+       if (U_SUCCESS(creationStatus)) {
+           SharedObject::copyPtr(tvalue, ptr);
+       }
+       SharedObject::clearPtr(tvalue);
+       // Take care not to overwrite a warning status passed in with
+       // another warning or U_ZERO_ERROR.
+       if (status == U_ZERO_ERROR || U_FAILURE(creationStatus)) {
+           status = creationStatus;
+       }
+   }
+
+#ifdef UNIFIED_CACHE_DEBUG
+   /**
+    * Dumps the contents of this cache to standard error. Used for testing of
+    * cache only.
+    */
+   void dumpContents() const;
+#endif
+
+   /**
+    * Convenience method to get a value of type T from cache for a
+    * particular locale with creationContext == nullptr.
+    * @param loc    the locale
+    * @param ptr    On entry, must be nullptr or included in the ref count
+    *               of the object to which it points.
+    *               On exit, fetched value stored here or is left
+    *               unchanged on failure. Caller must call removeRef on
+    *               ptr if set to a non nullptr value.
+    * @param status Any error returned here. May be set to a
+    *               warning value even if ptr is set.
+    */
+   template<typename T>
+   static void getByLocale(
+           const Locale &loc, const T *&ptr, UErrorCode &status) {
+       const UnifiedCache *cache = getInstance(status);
+       if (U_FAILURE(status)) {
+           return;
+       }
+       cache->get(LocaleCacheKey<T>(loc), ptr, status);
+   }
+
+#ifdef UNIFIED_CACHE_DEBUG
+   /**
+    * Dumps the cache contents to stderr. For testing only.
+    */
+   static void dump();
+#endif
+
+   /**
+    * Returns the number of keys in this cache. For testing only.
+    */
+   int32_t keyCount() const;
+
+   /**
+    * Removes any values from cache that are not referenced outside
+    * the cache.
+    */
+   void flush() const;
+
+   /**
+    * Configures at what point eviction of unused entries will begin.
+    * Eviction is triggered whenever the number of evictable keys exceeds
+    * BOTH count AND (number of in-use items) * (percentageOfInUseItems / 100).
+    * Once the number of unused entries drops below one of these,
+    * eviction ceases. Because eviction happens incrementally,
+    * the actual unused entry count may exceed both these numbers
+    * from time to time.
+    *
+    * A cache entry is defined as unused if it is not essential to guarantee
+    * that for a given key X, the cache returns the same reference to the
+    * same value as long as the client already holds a reference to that
+    * value.
+    *
+    * If this method is never called, the default settings are 1000 and 100%.
+    *
+    * Although this method is thread-safe, it is designed to be called at
+    * application startup. If it is called in the middle of execution, it
+    * will have no immediate effect on the cache. However over time, the
+    * cache will perform eviction slices in an attempt to honor the new
+    * settings.
+    *
+    * If a client already holds references to many different unique values
+    * in the cache such that the number of those unique values far exceeds
+    * "count" then the cache may not be able to maintain this maximum.
+    * However, if this happens, the cache still guarantees that the number of
+    * unused entries will remain only a small percentage of the total cache
+    * size.
+    *
+    * If the parameters passed are negative, setEvctionPolicy sets status to
+    * U_ILLEGAL_ARGUMENT_ERROR.
+    */
+   void setEvictionPolicy(
+           int32_t count, int32_t percentageOfInUseItems, UErrorCode &status);
+
+
+   /**
+    * Returns how many entries have been auto evicted during the lifetime
+    * of this cache. This only includes auto evicted entries, not
+    * entries evicted because of a call to flush().
+    */
+   int64_t autoEvictedCount() const;
+
+   /**
+    * Returns the unused entry count in this cache. For testing only,
+    * Regular clients will not need this.
+    */
+   int32_t unusedCount() const;
+
+   virtual void handleUnreferencedObject() const override;
+   virtual ~UnifiedCache();
+   
+ private:
+   UHashtable *fHashtable;
+   mutable int32_t fEvictPos;
+   mutable int32_t fNumValuesTotal;
+   mutable int32_t fNumValuesInUse;
+   int32_t fMaxUnused;
+   int32_t fMaxPercentageOfInUse;
+   mutable int64_t fAutoEvictedCount;
+   SharedObject *fNoValue;
+   
+   UnifiedCache(const UnifiedCache &other) = delete;
+   UnifiedCache &operator=(const UnifiedCache &other) = delete;
+   
+   /**
+    * Flushes the contents of the cache. If cache values hold references to other
+    * cache values then _flush should be called in a loop until it returns false.
+    * 
+    * On entry, gCacheMutex must be held.
+    * On exit, those values with are evictable are flushed.
+    * 
+    *  @param all if false flush evictable items only, which are those with no external
+    *                    references, plus those that can be safely recreated.<br>
+    *            if true, flush all elements. Any values (sharedObjects) with remaining
+    *                     hard (external) references are not deleted, but are detached from
+    *                     the cache, so that a subsequent removeRefs can delete them.
+    *                     _flush is not thread safe when all is true.
+    *   @return true if any value in cache was flushed or false otherwise.
+    */
+   UBool _flush(UBool all) const;
+   
+   /**
+    * Gets value out of cache.
+    * On entry. gCacheMutex must not be held. value must be nullptr. status
+    * must be U_ZERO_ERROR.
+    * On exit. value and status set to what is in cache at key or on cache
+    * miss the key's createObject() is called and value and status are set to
+    * the result of that. In this latter case, best effort is made to add the
+    * value and status to the cache. If createObject() fails to create a value,
+    * fNoValue is stored in cache, and value is set to nullptr. Caller must call
+    * removeRef on value if non nullptr.
+    */
+   void _get(
+           const CacheKeyBase &key,
+           const SharedObject *&value,
+           const void *creationContext,
+           UErrorCode &status) const;
+
+    /**
+     * Attempts to fetch value and status for key from cache.
+     * On entry, gCacheMutex must not be held value must be nullptr and status must
+     * be U_ZERO_ERROR.
+     * On exit, either returns false (In this
+     * case caller should try to create the object) or returns true with value
+     * pointing to the fetched value and status set to fetched status. When
+     * false is returned status may be set to failure if an in progress hash
+     * entry could not be made but value will remain unchanged. When true is
+     * returned, caller must call removeRef() on value.
+     */
+    UBool _poll(
+            const CacheKeyBase &key,
+            const SharedObject *&value,
+            UErrorCode &status) const;
+    
+    /**
+     * Places a new value and creationStatus in the cache for the given key.
+     * On entry, gCacheMutex must be held. key must not exist in the cache. 
+     * On exit, value and creation status placed under key. Soft reference added
+     * to value on successful add. On error sets status.
+     */
+    void _putNew(
+        const CacheKeyBase &key,
+        const SharedObject *value,
+        const UErrorCode creationStatus,
+        UErrorCode &status) const;
+           
+    /**
+     * Places value and status at key if there is no value at key or if cache
+     * entry for key is in progress. Otherwise, it leaves the current value and
+     * status there.
+     * 
+     * On entry. gCacheMutex must not be held. Value must be
+     * included in the reference count of the object to which it points.
+     * 
+     * On exit, value and status are changed to what was already in the cache if
+     * something was there and not in progress. Otherwise, value and status are left
+     * unchanged in which case they are placed in the cache on a best-effort basis.
+     * Caller must call removeRef() on value.
+     */
+   void _putIfAbsentAndGet(
+           const CacheKeyBase &key,
+           const SharedObject *&value,
+           UErrorCode &status) const;
+
+    /**
+     * Returns the next element in the cache round robin style.
+     * Returns nullptr if the cache is empty.
+     * On entry, gCacheMutex must be held.
+     */
+    const UHashElement *_nextElement() const;
+   
+   /**
+    * Return the number of cache items that would need to be evicted
+    * to bring usage into conformance with eviction policy.
+    * 
+    * An item corresponds to an entry in the hash table, a hash table element.
+    * 
+    * On entry, gCacheMutex must be held.
+    */
+   int32_t _computeCountOfItemsToEvict() const;
+   
+   /**
+    * Run an eviction slice.
+    * On entry, gCacheMutex must be held.
+    * _runEvictionSlice runs a slice of the evict pipeline by examining the next
+    * 10 entries in the cache round robin style evicting them if they are eligible.
+    */
+   void _runEvictionSlice() const;
+ 
+   /**
+    * Register a primary cache entry. A primary key is the first key to create
+    * a given  SharedObject value. Subsequent keys whose create function
+    * produce references to an already existing SharedObject are not primary -
+    * they can be evicted and subsequently recreated.
+    * 
+    * On entry, gCacheMutex must be held.
+    * On exit, items in use count incremented, entry is marked as a primary
+    * entry, and value registered with cache so that subsequent calls to
+    * addRef() and removeRef() on it correctly interact with the cache.
+    */
+   void _registerPrimary(const CacheKeyBase *theKey, const SharedObject *value) const;
+        
+   /**
+    * Store a value and creation error status in given hash entry.
+    * On entry, gCacheMutex must be held. Hash entry element must be in progress.
+    * value must be non nullptr.
+    * On Exit, soft reference added to value. value and status stored in hash
+    * entry. Soft reference removed from previous stored value. Waiting
+    * threads notified.
+    */
+   void _put(
+           const UHashElement *element,
+           const SharedObject *value,
+           const UErrorCode status) const;
+    /**
+     * Remove a soft reference, and delete the SharedObject if no references remain.
+     * To be used from within the UnifiedCache implementation only.
+     * gCacheMutex must be held by caller.
+     * @param value the SharedObject to be acted on.
+     */
+   void removeSoftRef(const SharedObject *value) const;
+   
+   /**
+    * Increment the hard reference count of the given SharedObject.
+    * gCacheMutex must be held by the caller.
+    * Update numValuesEvictable on transitions between zero and one reference.
+    * 
+    * @param value The SharedObject to be referenced.
+    * @return the hard reference count after the addition.
+    */
+   int32_t addHardRef(const SharedObject *value) const;
+   
+  /**
+    * Decrement the hard reference count of the given SharedObject.
+    * gCacheMutex must be held by the caller.
+    * Update numValuesEvictable on transitions between one and zero reference.
+    * 
+    * @param value The SharedObject to be referenced.
+    * @return the hard reference count after the removal.
+    */
+   int32_t removeHardRef(const SharedObject *value) const;
+
+   
+#ifdef UNIFIED_CACHE_DEBUG
+   void _dumpContents() const;
+#endif
+   
+   /**
+    *  Fetch value and error code from a particular hash entry.
+    *  On entry, gCacheMutex must be held. value must be either nullptr or must be
+    *  included in the ref count of the object to which it points.
+    *  On exit, value and status set to what is in the hash entry. Caller must
+    *  eventually call removeRef on value.
+    *  If hash entry is in progress, value will be set to gNoValue and status will
+    *  be set to U_ZERO_ERROR.
+    */
+   void _fetch(const UHashElement *element, const SharedObject *&value,
+                       UErrorCode &status) const;
+                       
+    /**
+     * Determine if given hash entry is in progress.
+     * On entry, gCacheMutex must be held.
+     */
+   UBool _inProgress(const UHashElement *element) const;
+   
+   /**
+    * Determine if given hash entry is in progress.
+    * On entry, gCacheMutex must be held.
+    */
+   UBool _inProgress(const SharedObject *theValue, UErrorCode creationStatus) const;
+   
+   /**
+    * Determine if given hash entry is eligible for eviction.
+    * On entry, gCacheMutex must be held.
+    */
+   UBool _isEvictable(const UHashElement *element) const;
+};
+
+U_NAMESPACE_END
+
+#endif