icuSources/common/unifiedcache.h

   1 // © 2016 and later: Unicode, Inc. and others.
   2 // License & terms of use: http://www.unicode.org/copyright.html
   3 /*
   4 ******************************************************************************
   5 * Copyright (C) 2015, International Business Machines Corporation and
   6 * others. All Rights Reserved.
   7 ******************************************************************************
   8 *
   9 * File UNIFIEDCACHE.H - The ICU Unified cache.
  10 ******************************************************************************
  11 */
  12
  13 #ifndef __UNIFIED_CACHE_H__
  14 #define __UNIFIED_CACHE_H__
  15
  16 #include "utypeinfo.h"  // for 'typeid' to work
  17
  18 #include "unicode/uobject.h"
  19 #include "unicode/locid.h"
  20 #include "sharedobject.h"
  21 #include "unicode/unistr.h"
  22 #include "cstring.h"
  23 #include "ustr_imp.h"
  24
  25 struct UHashtable;
  26 struct UHashElement;
  27
  28 U_NAMESPACE_BEGIN
  29
  30 class UnifiedCache;
  31
  32 /**
  33  * A base class for all cache keys.
  34  */
  35 class U_COMMON_API CacheKeyBase : public UObject {
  36  public:
  37    CacheKeyBase() : fCreationStatus(U_ZERO_ERROR), fIsMaster(FALSE) {}
  38
  39    /**
  40     * Copy constructor. Needed to support cloning.
  41     */
  42    CacheKeyBase(const CacheKeyBase &other)
  43            : UObject(other), fCreationStatus(other.fCreationStatus), fIsMaster(FALSE) { }
  44    virtual ~CacheKeyBase();
  45
  46    /**
  47     * Returns the hash code for this object.
  48     */
  49    virtual int32_t hashCode() const = 0;
  50
  51    /**
  52     * Clones this object polymorphically. Caller owns returned value.
  53     */
  54    virtual CacheKeyBase *clone() const = 0;
  55
  56    /**
  57     * Equality operator.
  58     */
  59    virtual UBool operator == (const CacheKeyBase &other) const = 0;
  60
  61    /**
  62     * Create a new object for this key. Called by cache on cache miss.
  63     * createObject must add a reference to the object it returns. Note
  64     * that getting an object from the cache and returning it without calling
  65     * removeRef on it satisfies this requirement. It can also return NULL
  66     * and set status to an error.
  67     *
  68     * @param creationContext the context in which the object is being
  69     *                        created. May be NULL.
  70     * @param status          Implementations can return a failure here.
  71     *                        In addition, implementations may return a
  72     *                        non NULL object and set a warning status.
  73     */
  74    virtual const SharedObject *createObject(
  75            const void *creationContext, UErrorCode &status) const = 0;
  76
  77    /**
  78     * Writes a description of this key to buffer and returns buffer. Written
  79     * description is NULL terminated.
  80     */
  81    virtual char *writeDescription(char *buffer, int32_t bufSize) const = 0;
  82
  83    /**
  84     * Inequality operator.
  85     */
  86    UBool operator != (const CacheKeyBase &other) const {
  87        return !(*this == other);
  88    }
  89  private:
  90    mutable UErrorCode fCreationStatus;
  91    mutable UBool fIsMaster;
  92    friend class UnifiedCache;
  93 };
  94
  95
  96
  97 /**
  98  * Templated version of CacheKeyBase.
  99  * A key of type LocaleCacheKey<T> maps to a value of type T.
 100  */
 101 template<typename T>
 102 class CacheKey : public CacheKeyBase {
 103  public:
 104    virtual ~CacheKey() { }
 105    /**
 106     * The template parameter, T, determines the hash code returned.
 107     */
 108    virtual int32_t hashCode() const {
 109        const char *s = typeid(T).name();
 110        return ustr_hashCharsN(s, uprv_strlen(s));
 111    }
 112
 113    /**
 114     * Use the value type, T,  as the description.
 115     */
 116    virtual char *writeDescription(char *buffer, int32_t bufLen) const {
 117        const char *s = typeid(T).name();
 118        uprv_strncpy(buffer, s, bufLen);
 119        buffer[bufLen - 1] = 0;
 120        return buffer;
 121    }
 122
 123    /**
 124     * Two objects are equal if they are of the same type.
 125     */
 126    virtual UBool operator == (const CacheKeyBase &other) const {
 127        return typeid(*this) == typeid(other);
 128    }
 129 };
 130
 131 /**
 132  * Cache key based on locale.
 133  * A key of type LocaleCacheKey<T> maps to a value of type T.
 134  */
 135 template<typename T>
 136 class LocaleCacheKey : public CacheKey<T> {
 137  protected:
 138    Locale   fLoc;
 139  public:
 140    LocaleCacheKey(const Locale &loc) : fLoc(loc) {};
 141    LocaleCacheKey(const LocaleCacheKey<T> &other)
 142            : CacheKey<T>(other), fLoc(other.fLoc) { }
 143    virtual ~LocaleCacheKey() { }
 144    virtual int32_t hashCode() const {
 145        return (int32_t)(37u * (uint32_t)CacheKey<T>::hashCode() + (uint32_t)fLoc.hashCode());
 146    }
 147    virtual UBool operator == (const CacheKeyBase &other) const {
 148        // reflexive
 149        if (this == &other) {
 150            return TRUE;
 151        }
 152        if (!CacheKey<T>::operator == (other)) {
 153            return FALSE;
 154        }
 155        // We know this and other are of same class because operator== on
 156        // CacheKey returned true.
 157        const LocaleCacheKey<T> *fOther =
 158                static_cast<const LocaleCacheKey<T> *>(&other);
 159        return fLoc == fOther->fLoc;
 160    }
 161    virtual CacheKeyBase *clone() const {
 162        return new LocaleCacheKey<T>(*this);
 163    }
 164    virtual const T *createObject(
 165            const void *creationContext, UErrorCode &status) const;
 166    /**
 167     * Use the locale id as the description.
 168     */
 169    virtual char *writeDescription(char *buffer, int32_t bufLen) const {
 170        const char *s = fLoc.getName();
 171        uprv_strncpy(buffer, s, bufLen);
 172        buffer[bufLen - 1] = 0;
 173        return buffer;
 174    }
 175
 176 };
 177
 178 /**
 179  * The unified cache. A singleton type.
 180  * Design doc here:
 181  * https://docs.google.com/document/d/1RwGQJs4N4tawNbf809iYDRCvXoMKqDJihxzYt1ysmd8/edit?usp=sharing
 182  */
 183 class U_COMMON_API UnifiedCache : public UnifiedCacheBase {
 184  public:
 185    /**
 186     * @internal
 187     * Do not call directly. Instead use UnifiedCache::getInstance() as
 188     * there should be only one UnifiedCache in an application.
 189     */
 190    UnifiedCache(UErrorCode &status);
 191
 192    /**
 193     * Returns the cache instance.
 194     */
 195    static UnifiedCache *getInstance(UErrorCode &status);
 196
 197    /**
 198     * Fetches a value from the cache by key. Equivalent to
 199     * get(key, NULL, ptr, status);
 200     */
 201    template<typename T>
 202    void get(
 203            const CacheKey<T>& key,
 204            const T *&ptr,
 205            UErrorCode &status) const {
 206        get(key, NULL, ptr, status);
 207    }
 208
 209    /**
 210     * Fetches value from the cache by key.
 211     *
 212     * @param key             the cache key.
 213     * @param creationContext passed verbatim to createObject method of key
 214     * @param ptr             On entry, ptr must be NULL or be included if
 215     *                        the reference count of the object it points
 216     *                        to. On exit, ptr points to the fetched object
 217     *                        from the cache or is left unchanged on
 218     *                        failure. Caller must call removeRef on ptr
 219     *                        if set to a non NULL value.
 220     * @param status          Any error returned here. May be set to a
 221     *                        warning value even if ptr is set.
 222     */
 223    template<typename T>
 224    void get(
 225            const CacheKey<T>& key,
 226            const void *creationContext,
 227            const T *&ptr,
 228            UErrorCode &status) const {
 229        if (U_FAILURE(status)) {
 230            return;
 231        }
 232        UErrorCode creationStatus = U_ZERO_ERROR;
 233        const SharedObject *value = NULL;
 234        _get(key, value, creationContext, creationStatus);
 235        const T *tvalue = (const T *) value;
 236        if (U_SUCCESS(creationStatus)) {
 237            SharedObject::copyPtr(tvalue, ptr);
 238        }
 239        SharedObject::clearPtr(tvalue);
 240        // Take care not to overwrite a warning status passed in with
 241        // another warning or U_ZERO_ERROR.
 242        if (status == U_ZERO_ERROR || U_FAILURE(creationStatus)) {
 243            status = creationStatus;
 244        }
 245    }
 246
 247 #ifdef UNIFIED_CACHE_DEBUG
 248    /**
 249     * Dumps the contents of this cache to standard error. Used for testing of
 250     * cache only.
 251     */
 252    void dumpContents() const;
 253 #endif
 254
 255    /**
 256     * Convenience method to get a value of type T from cache for a
 257     * particular locale with creationContext == NULL.
 258     * @param loc    the locale
 259     * @param ptr    On entry, must be NULL or included in the ref count
 260     *               of the object to which it points.
 261     *               On exit, fetched value stored here or is left
 262     *               unchanged on failure. Caller must call removeRef on
 263     *               ptr if set to a non NULL value.
 264     * @param status Any error returned here. May be set to a
 265     *               warning value even if ptr is set.
 266     */
 267    template<typename T>
 268    static void getByLocale(
 269            const Locale &loc, const T *&ptr, UErrorCode &status) {
 270        const UnifiedCache *cache = getInstance(status);
 271        if (U_FAILURE(status)) {
 272            return;
 273        }
 274        cache->get(LocaleCacheKey<T>(loc), ptr, status);
 275    }
 276
 277 #ifdef UNIFIED_CACHE_DEBUG
 278    /**
 279     * Dumps the cache contents to stderr. For testing only.
 280     */
 281    static void dump();
 282 #endif
 283
 284    /**
 285     * Returns the number of keys in this cache. For testing only.
 286     */
 287    int32_t keyCount() const;
 288
 289    /**
 290     * Removes any values from cache that are not referenced outside
 291     * the cache.
 292     */
 293    void flush() const;
 294
 295    /**
 296     * Configures at what point evcition of unused entries will begin.
 297     * Eviction is triggered whenever the number of unused entries exeeds
 298     * BOTH count AND (number of in-use items) * (percentageOfInUseItems / 100).
 299     * Once the number of unused entries drops below one of these,
 300     * eviction ceases. Because eviction happens incrementally,
 301     * the actual unused entry count may exceed both these numbers
 302     * from time to time.
 303     *
 304     * A cache entry is defined as unused if it is not essential to guarantee
 305     * that for a given key X, the cache returns the same reference to the
 306     * same value as long as the client already holds a reference to that
 307     * value.
 308     *
 309     * If this method is never called, the default settings are 1000 and 100%.
 310     *
 311     * Although this method is thread-safe, it is designed to be called at
 312     * application startup. If it is called in the middle of execution, it
 313     * will have no immediate effect on the cache. However over time, the
 314     * cache will perform eviction slices in an attempt to honor the new
 315     * settings.
 316     *
 317     * If a client already holds references to many different unique values
 318     * in the cache such that the number of those unique values far exeeds
 319     * "count" then the cache may not be able to maintain this maximum.
 320     * However, if this happens, the cache still guarantees that the number of
 321     * unused entries will remain only a small percentage of the total cache
 322     * size.
 323     *
 324     * If the parameters passed are negative, setEvctionPolicy sets status to
 325     * U_ILLEGAL_ARGUMENT_ERROR.
 326     */
 327    void setEvictionPolicy(
 328            int32_t count, int32_t percentageOfInUseItems, UErrorCode &status);
 329
 330
 331    /**
 332     * Returns how many entries have been auto evicted during the lifetime
 333     * of this cache. This only includes auto evicted entries, not
 334     * entries evicted because of a call to flush().
 335     */
 336    int64_t autoEvictedCount() const;
 337
 338    /**
 339     * Returns the unused entry count in this cache. For testing only,
 340     * Regular clients will not need this.
 341     */
 342    int32_t unusedCount() const;
 343
 344    virtual void incrementItemsInUse() const;
 345    virtual void decrementItemsInUseWithLockingAndEviction() const;
 346    virtual void decrementItemsInUse() const;
 347    virtual ~UnifiedCache();
 348  private:
 349    UHashtable *fHashtable;
 350    mutable int32_t fEvictPos;
 351    mutable int32_t fItemsInUseCount;
 352    int32_t fMaxUnused;
 353    int32_t fMaxPercentageOfInUse;
 354    mutable int64_t fAutoEvictedCount;
 355    UnifiedCache(const UnifiedCache &other);
 356    UnifiedCache &operator=(const UnifiedCache &other);
 357    UBool _flush(UBool all) const;
 358    void _get(
 359            const CacheKeyBase &key,
 360            const SharedObject *&value,
 361            const void *creationContext,
 362            UErrorCode &status) const;
 363    UBool _poll(
 364            const CacheKeyBase &key,
 365            const SharedObject *&value,
 366            UErrorCode &status) const;
 367    void _putNew(
 368            const CacheKeyBase &key,
 369            const SharedObject *value,
 370            const UErrorCode creationStatus,
 371            UErrorCode &status) const;
 372    void _putIfAbsentAndGet(
 373            const CacheKeyBase &key,
 374            const SharedObject *&value,
 375            UErrorCode &status) const;
 376    const UHashElement *_nextElement() const;
 377    int32_t _computeCountOfItemsToEvict() const;
 378    void _runEvictionSlice() const;
 379    void _registerMaster(
 380         const CacheKeyBase *theKey, const SharedObject *value) const;
 381    void _put(
 382            const UHashElement *element,
 383            const SharedObject *value,
 384            const UErrorCode status) const;
 385 #ifdef UNIFIED_CACHE_DEBUG
 386    void _dumpContents() const;
 387 #endif
 388    static void copyPtr(const SharedObject *src, const SharedObject *&dest);
 389    static void clearPtr(const SharedObject *&ptr);
 390    static void _fetch(
 391            const UHashElement *element,
 392            const SharedObject *&value,
 393            UErrorCode &status);
 394    static UBool _inProgress(const UHashElement *element);
 395    static UBool _inProgress(
 396            const SharedObject *theValue, UErrorCode creationStatus);
 397    static UBool _isEvictable(const UHashElement *element);
 398 };
 399
 400 U_NAMESPACE_END
 401
 402 #endif