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      1 /*
      2  * Copyright (C) 2012 Google, Inc. All Rights Reserved.
      3  *
      4  * Redistribution and use in source and binary forms, with or without
      5  * modification, are permitted provided that the following conditions
      6  * are met:
      7  * 1. Redistributions of source code must retain the above copyright
      8  *    notice, this list of conditions and the following disclaimer.
      9  * 2. Redistributions in binary form must reproduce the above copyright
     10  *    notice, this list of conditions and the following disclaimer in the
     11  *    documentation and/or other materials provided with the distribution.
     12  *
     13  * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
     14  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     15  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     16  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
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     23  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     24  */
     25 
     26 #ifndef Supplementable_h
     27 #define Supplementable_h
     28 
     29 #include "platform/heap/Handle.h"
     30 #include "wtf/Assertions.h"
     31 #include "wtf/HashMap.h"
     32 #include "wtf/OwnPtr.h"
     33 #include "wtf/PassOwnPtr.h"
     34 
     35 #if ENABLE(ASSERT)
     36 #include "wtf/Threading.h"
     37 #endif
     38 
     39 namespace blink {
     40 
     41 // What you should know about Supplementable and Supplement
     42 // ========================================================
     43 // Supplementable and Supplement instances are meant to be thread local. They
     44 // should only be accessed from within the thread that created them. The
     45 // 2 classes are not designed for safe access from another thread. Violating
     46 // this design assumption can result in memory corruption and unpredictable
     47 // behavior.
     48 //
     49 // What you should know about the Supplement keys
     50 // ==============================================
     51 // The Supplement is expected to use the same const char* string instance
     52 // as its key. The Supplementable's SupplementMap will use the address of the
     53 // string as the key and not the characters themselves. Hence, 2 strings with
     54 // the same characters will be treated as 2 different keys.
     55 //
     56 // In practice, it is recommended that Supplements implements a static method
     57 // for returning its key to use. For example:
     58 //
     59 //     class MyClass : public Supplement<MySupplementable> {
     60 //         ...
     61 //         static const char* supplementName();
     62 //     }
     63 //
     64 //     const char* MyClass::supplementName()
     65 //     {
     66 //         return "MyClass";
     67 //     }
     68 //
     69 // An example of the using the key:
     70 //
     71 //     MyClass* MyClass::from(MySupplementable* host)
     72 //     {
     73 //         return reinterpret_cast<MyClass*>(Supplement<MySupplementable>::from(host, supplementName()));
     74 //     }
     75 //
     76 // What you should know about thread checks
     77 // ========================================
     78 // When assertion is enabled this class performs thread-safety check so that
     79 // provideTo and from happen on the same thread. If you want to provide
     80 // some value for Workers this thread check may not work very well though,
     81 // since in most case you'd provide the value while worker preparation is
     82 // being done on the main thread, even before the worker thread is started.
     83 // If that's the case you can explicitly call reattachThread() when the
     84 // Supplementable object is passed to the final destination thread (i.e.
     85 // worker thread). Please be extremely careful to use the method though,
     86 // as randomly calling the method could easily cause racy condition.
     87 //
     88 // Note that reattachThread() does nothing if assertion is not enabled.
     89 //
     90 
     91 template<typename T, bool isGarbageCollected>
     92 class SupplementBase;
     93 
     94 template<typename T, bool isGarbageCollected>
     95 class SupplementableBase;
     96 
     97 template<typename T, bool isGarbageCollected>
     98 struct SupplementableTraits;
     99 
    100 template<typename T>
    101 struct SupplementableTraits<T, true> {
    102     typedef RawPtr<SupplementBase<T, true> > SupplementArgumentType;
    103 };
    104 
    105 template<typename T>
    106 struct SupplementableTraits<T, false> {
    107     typedef PassOwnPtr<SupplementBase<T, false> > SupplementArgumentType;
    108 };
    109 
    110 template<bool>
    111 class SupplementTracing;
    112 
    113 template<>
    114 class SupplementTracing<true> : public GarbageCollectedMixin { };
    115 
    116 template<>
    117 class SupplementTracing<false> {
    118 public:
    119     virtual ~SupplementTracing() { }
    120     // FIXME: Oilpan: this trace() method is only provided to minimize
    121     // the use of ENABLE(OILPAN) for Supplements deriving from the
    122     // transition type WillBeHeapSupplement<>.
    123     //
    124     // When that transition type is removed (or its use is substantially
    125     // reduced), remove this dummy trace method also.
    126     virtual void trace(Visitor*) { }
    127 };
    128 
    129 template<typename T, bool isGarbageCollected = false>
    130 class SupplementBase : public SupplementTracing<isGarbageCollected> {
    131 public:
    132 #if ENABLE(SECURITY_ASSERT)
    133     virtual bool isRefCountedWrapper() const { return false; }
    134 #endif
    135 
    136     static void provideTo(SupplementableBase<T, isGarbageCollected>& host, const char* key, typename SupplementableTraits<T, isGarbageCollected>::SupplementArgumentType supplement)
    137     {
    138         host.provideSupplement(key, supplement);
    139     }
    140 
    141     static SupplementBase<T, isGarbageCollected>* from(SupplementableBase<T, isGarbageCollected>& host, const char* key)
    142     {
    143         return host.requireSupplement(key);
    144     }
    145 
    146     static SupplementBase<T, isGarbageCollected>* from(SupplementableBase<T, isGarbageCollected>* host, const char* key)
    147     {
    148         return host ? host->requireSupplement(key) : 0;
    149     }
    150 };
    151 
    152 template<typename T, bool isGarbageCollected>
    153 class SupplementableTracing;
    154 
    155 template<typename T>
    156 class SupplementableTracing<T, true> : public GarbageCollectedMixin {
    157 public:
    158     virtual void trace(Visitor* visitor)
    159     {
    160         visitor->trace(m_supplements);
    161     }
    162 
    163 protected:
    164     typedef HeapHashMap<const char*, Member<SupplementBase<T, true> >, PtrHash<const char*> > SupplementMap;
    165     SupplementMap m_supplements;
    166 };
    167 
    168 template<typename T>
    169 class SupplementableTracing<T, false> {
    170 protected:
    171     typedef HashMap<const char*, OwnPtr<SupplementBase<T, false> >, PtrHash<const char*> > SupplementMap;
    172     SupplementMap m_supplements;
    173 };
    174 
    175 // Helper class for implementing Supplementable and HeapSupplementable.
    176 template<typename T, bool isGarbageCollected = false>
    177 class SupplementableBase : public SupplementableTracing<T, isGarbageCollected> {
    178 public:
    179     void provideSupplement(const char* key, typename SupplementableTraits<T, isGarbageCollected>::SupplementArgumentType supplement)
    180     {
    181         ASSERT(m_threadId == currentThread());
    182         ASSERT(!this->m_supplements.get(key));
    183         this->m_supplements.set(key, supplement);
    184     }
    185 
    186     void removeSupplement(const char* key)
    187     {
    188         ASSERT(m_threadId == currentThread());
    189         this->m_supplements.remove(key);
    190     }
    191 
    192     SupplementBase<T, isGarbageCollected>* requireSupplement(const char* key)
    193     {
    194         ASSERT(m_threadId == currentThread());
    195         return this->m_supplements.get(key);
    196     }
    197 
    198     void reattachThread()
    199     {
    200 #if ENABLE(ASSERT)
    201         m_threadId = currentThread();
    202 #endif
    203     }
    204 
    205 #if ENABLE(ASSERT)
    206 protected:
    207     SupplementableBase() : m_threadId(currentThread()) { }
    208 
    209 private:
    210     ThreadIdentifier m_threadId;
    211 #endif
    212 };
    213 
    214 template<typename T>
    215 class HeapSupplement : public SupplementBase<T, true> { };
    216 
    217 template<typename T>
    218 class HeapSupplementable : public SupplementableBase<T, true> { };
    219 
    220 template<typename T>
    221 class Supplement : public SupplementBase<T, false> { };
    222 
    223 template<typename T>
    224 class Supplementable : public SupplementableBase<T, false> { };
    225 
    226 template<typename T>
    227 struct ThreadingTrait<SupplementBase<T, true> > {
    228     static const ThreadAffinity Affinity = ThreadingTrait<T>::Affinity;
    229 };
    230 
    231 template<typename T>
    232 struct ThreadingTrait<SupplementableBase<T, true> > {
    233     static const ThreadAffinity Affinity = ThreadingTrait<T>::Affinity;
    234 };
    235 
    236 } // namespace blink
    237 
    238 #endif // Supplementable_h
    239