runtime/CodeCache.h

   1 /*
   2  * Copyright (C) 2012, 2013 Apple 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
  17  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  18  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  19  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  20  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  21  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  22  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  23  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  24  */
  25
  26 #ifndef CodeCache_h
  27 #define CodeCache_h
  28
  29 #include "CodeSpecializationKind.h"
  30 #include "ParserModes.h"
  31 #include "SourceCode.h"
  32 #include "Strong.h"
  33 #include "WeakRandom.h"
  34 #include <wtf/CurrentTime.h>
  35 #include <wtf/Forward.h>
  36 #include <wtf/PassOwnPtr.h>
  37 #include <wtf/RandomNumber.h>
  38 #include <wtf/text/WTFString.h>
  39
  40 namespace JSC {
  41
  42 class EvalExecutable;
  43 class FunctionBodyNode;
  44 class Identifier;
  45 class JSScope;
  46 class ProgramExecutable;
  47 class UnlinkedCodeBlock;
  48 class UnlinkedEvalCodeBlock;
  49 class UnlinkedFunctionCodeBlock;
  50 class UnlinkedFunctionExecutable;
  51 class UnlinkedProgramCodeBlock;
  52 class VM;
  53 struct ParserError;
  54 class SourceCode;
  55 class SourceProvider;
  56
  57 class SourceCodeKey {
  58 public:
  59     enum CodeType { EvalType, ProgramType, FunctionType };
  60
  61     SourceCodeKey()
  62     {
  63     }
  64
  65     SourceCodeKey(const SourceCode& sourceCode, const String& name, CodeType codeType, JSParserStrictness jsParserStrictness)
  66         : m_sourceCode(sourceCode)
  67         , m_name(name)
  68         , m_flags((codeType << 2) | jsParserStrictness)
  69         , m_hash(string().impl()->hash())
  70     {
  71     }
  72
  73     SourceCodeKey(WTF::HashTableDeletedValueType)
  74         : m_sourceCode(WTF::HashTableDeletedValue)
  75     {
  76     }
  77
  78     bool isHashTableDeletedValue() const { return m_sourceCode.isHashTableDeletedValue(); }
  79
  80     unsigned hash() const { return m_hash; }
  81
  82     size_t length() const { return m_sourceCode.length(); }
  83
  84     bool isNull() const { return m_sourceCode.isNull(); }
  85
  86     // To save memory, we compute our string on demand. It's expected that source
  87     // providers cache their strings to make this efficient.
  88     String string() const { return m_sourceCode.toString(); }
  89
  90     bool operator==(const SourceCodeKey& other) const
  91     {
  92         return m_hash == other.m_hash
  93             && length() == other.length()
  94             && m_flags == other.m_flags
  95             && m_name == other.m_name
  96             && string() == other.string();
  97     }
  98
  99 private:
 100     SourceCode m_sourceCode;
 101     String m_name;
 102     unsigned m_flags;
 103     unsigned m_hash;
 104 };
 105
 106 struct SourceCodeKeyHash {
 107     static unsigned hash(const SourceCodeKey& key) { return key.hash(); }
 108     static bool equal(const SourceCodeKey& a, const SourceCodeKey& b) { return a == b; }
 109     static const bool safeToCompareToEmptyOrDeleted = false;
 110 };
 111
 112 struct SourceCodeKeyHashTraits : SimpleClassHashTraits<SourceCodeKey> {
 113     static const bool hasIsEmptyValueFunction = true;
 114     static bool isEmptyValue(const SourceCodeKey& sourceCodeKey) { return sourceCodeKey.isNull(); }
 115 };
 116
 117 struct SourceCodeValue {
 118     SourceCodeValue()
 119     {
 120     }
 121
 122     SourceCodeValue(VM& vm, JSCell* cell, int64_t age)
 123         : cell(vm, cell)
 124         , age(age)
 125     {
 126     }
 127
 128     Strong<JSCell> cell;
 129     int64_t age;
 130 };
 131
 132 class CodeCacheMap {
 133 public:
 134     typedef HashMap<SourceCodeKey, SourceCodeValue, SourceCodeKeyHash, SourceCodeKeyHashTraits> MapType;
 135     typedef MapType::iterator iterator;
 136     typedef MapType::AddResult AddResult;
 137
 138     CodeCacheMap()
 139         : m_size(0)
 140         , m_sizeAtLastPrune(0)
 141         , m_timeAtLastPrune(monotonicallyIncreasingTime())
 142         , m_minCapacity(0)
 143         , m_capacity(0)
 144         , m_age(0)
 145     {
 146     }
 147
 148     AddResult add(const SourceCodeKey& key, const SourceCodeValue& value)
 149     {
 150         prune();
 151
 152         AddResult addResult = m_map.add(key, value);
 153         if (addResult.isNewEntry) {
 154             m_size += key.length();
 155             m_age += key.length();
 156             return addResult;
 157         }
 158
 159         int64_t age = m_age - addResult.iterator->value.age;
 160         if (age > m_capacity) {
 161             // A requested object is older than the cache's capacity. We can
 162             // infer that requested objects are subject to high eviction probability,
 163             // so we grow the cache to improve our hit rate.
 164             m_capacity += recencyBias * oldObjectSamplingMultiplier * key.length();
 165         } else if (age < m_capacity / 2) {
 166             // A requested object is much younger than the cache's capacity. We can
 167             // infer that requested objects are subject to low eviction probability,
 168             // so we shrink the cache to save memory.
 169             m_capacity -= recencyBias * key.length();
 170             if (m_capacity < m_minCapacity)
 171                 m_capacity = m_minCapacity;
 172         }
 173
 174         addResult.iterator->value.age = m_age;
 175         m_age += key.length();
 176         return addResult;
 177     }
 178
 179     void remove(iterator it)
 180     {
 181         m_size -= it->key.length();
 182         m_map.remove(it);
 183     }
 184
 185     void clear()
 186     {
 187         m_size = 0;
 188         m_age = 0;
 189         m_map.clear();
 190     }
 191
 192     int64_t age() { return m_age; }
 193
 194 private:
 195     // This constant factor biases cache capacity toward allowing a minimum
 196     // working set to enter the cache before it starts evicting.
 197     static const double workingSetTime;
 198     static const int64_t workingSetMaxBytes = 16000000;
 199     static const size_t workingSetMaxEntries = 2000;
 200
 201     // This constant factor biases cache capacity toward recent activity. We
 202     // want to adapt to changing workloads.
 203     static const int64_t recencyBias = 4;
 204
 205     // This constant factor treats a sampled event for one old object as if it
 206     // happened for many old objects. Most old objects are evicted before we can
 207     // sample them, so we need to extrapolate from the ones we do sample.
 208     static const int64_t oldObjectSamplingMultiplier = 32;
 209
 210     size_t numberOfEntries() const { return static_cast<size_t>(m_map.size()); }
 211     bool canPruneQuickly() const { return numberOfEntries() < workingSetMaxEntries; }
 212
 213     void pruneSlowCase();
 214     void prune()
 215     {
 216         if (m_size <= m_capacity && canPruneQuickly())
 217             return;
 218
 219         if (monotonicallyIncreasingTime() - m_timeAtLastPrune < workingSetTime
 220             && m_size - m_sizeAtLastPrune < workingSetMaxBytes
 221             && canPruneQuickly())
 222                 return;
 223
 224         pruneSlowCase();
 225     }
 226
 227     MapType m_map;
 228     int64_t m_size;
 229     int64_t m_sizeAtLastPrune;
 230     double m_timeAtLastPrune;
 231     int64_t m_minCapacity;
 232     int64_t m_capacity;
 233     int64_t m_age;
 234 };
 235
 236 // Caches top-level code such as <script>, eval(), new Function, and JSEvaluateScript().
 237 class CodeCache {
 238     WTF_MAKE_FAST_ALLOCATED;
 239 public:
 240     static PassOwnPtr<CodeCache> create() { return adoptPtr(new CodeCache); }
 241
 242     UnlinkedProgramCodeBlock* getProgramCodeBlock(VM&, ProgramExecutable*, const SourceCode&, JSParserStrictness, DebuggerMode, ProfilerMode, ParserError&);
 243     UnlinkedEvalCodeBlock* getEvalCodeBlock(VM&, EvalExecutable*, const SourceCode&, JSParserStrictness, DebuggerMode, ProfilerMode, ParserError&);
 244     UnlinkedFunctionExecutable* getFunctionExecutableFromGlobalCode(VM&, const Identifier&, const SourceCode&, ParserError&);
 245     ~CodeCache();
 246
 247     void clear()
 248     {
 249         m_sourceCode.clear();
 250     }
 251
 252 private:
 253     CodeCache();
 254
 255     template <class UnlinkedCodeBlockType, class ExecutableType>
 256     UnlinkedCodeBlockType* getGlobalCodeBlock(VM&, ExecutableType*, const SourceCode&, JSParserStrictness, DebuggerMode, ProfilerMode, ParserError&);
 257
 258     CodeCacheMap m_sourceCode;
 259 };
 260
 261 }
 262
 263 #endif // CodeCache_h