bytecode/Watchpoint.h

   1 /*
   2  * Copyright (C) 2012 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 Watchpoint_h
  27 #define Watchpoint_h
  28
  29 #include <wtf/RefCounted.h>
  30 #include <wtf/SentinelLinkedList.h>
  31
  32 namespace JSC {
  33
  34 class Watchpoint : public BasicRawSentinelNode<Watchpoint> {
  35 public:
  36     Watchpoint()
  37     {
  38     }
  39
  40     virtual ~Watchpoint();
  41
  42     void fire() { fireInternal(); }
  43
  44 protected:
  45     virtual void fireInternal() = 0;
  46 };
  47
  48 enum InitialWatchpointSetMode { InitializedWatching, InitializedBlind };
  49
  50 class InlineWatchpointSet;
  51
  52 class WatchpointSet : public RefCounted<WatchpointSet> {
  53 public:
  54     WatchpointSet(InitialWatchpointSetMode);
  55     ~WatchpointSet();
  56
  57     bool isStillValid() const { return !m_isInvalidated; }
  58     bool hasBeenInvalidated() const { return m_isInvalidated; }
  59
  60     // As a convenience, this will ignore 0. That's because code paths in the DFG
  61     // that create speculation watchpoints may choose to bail out if speculation
  62     // had already been terminated.
  63     void add(Watchpoint*);
  64
  65     // Force the watchpoint set to behave as if it was being watched even if no
  66     // watchpoints have been installed. This will result in invalidation if the
  67     // watchpoint would have fired. That's a pretty good indication that you
  68     // probably don't want to set watchpoints, since we typically don't want to
  69     // set watchpoints that we believe will actually be fired.
  70     void startWatching() { m_isWatched = true; }
  71
  72     void notifyWrite()
  73     {
  74         if (!m_isWatched)
  75             return;
  76         notifyWriteSlow();
  77     }
  78
  79     bool* addressOfIsWatched() { return &m_isWatched; }
  80
  81     JS_EXPORT_PRIVATE void notifyWriteSlow(); // Call only if you've checked isWatched.
  82
  83 private:
  84     void fireAllWatchpoints();
  85
  86     friend class InlineWatchpointSet;
  87
  88     SentinelLinkedList<Watchpoint, BasicRawSentinelNode<Watchpoint> > m_set;
  89     bool m_isWatched;
  90     bool m_isInvalidated;
  91 };
  92
  93 // InlineWatchpointSet is a low-overhead, non-copyable watchpoint set in which
  94 // it is not possible to quickly query whether it is being watched in a single
  95 // branch. There is a fairly simple tradeoff between WatchpointSet and
  96 // InlineWatchpointSet:
  97 //
  98 // Do you have to emit JIT code that rapidly tests whether the watchpoint set
  99 // is being watched?  If so, use WatchpointSet.
 100 //
 101 // Do you need multiple parties to have pointers to the same WatchpointSet?
 102 // If so, use WatchpointSet.
 103 //
 104 // Do you have to allocate a lot of watchpoint sets?  If so, use
 105 // InlineWatchpointSet unless you answered "yes" to the previous questions.
 106 //
 107 // InlineWatchpointSet will use just one pointer-width word of memory unless
 108 // you actually add watchpoints to it, in which case it internally inflates
 109 // to a pointer to a WatchpointSet, and transfers its state to the
 110 // WatchpointSet.
 111
 112 class InlineWatchpointSet {
 113     WTF_MAKE_NONCOPYABLE(InlineWatchpointSet);
 114 public:
 115     InlineWatchpointSet(InitialWatchpointSetMode mode)
 116         : m_data((mode == InitializedWatching ? IsWatchedFlag : 0) | IsThinFlag)
 117     {
 118     }
 119
 120     ~InlineWatchpointSet()
 121     {
 122         if (isThin())
 123             return;
 124         freeFat();
 125     }
 126
 127     bool hasBeenInvalidated() const
 128     {
 129         if (isFat())
 130             return fat()->hasBeenInvalidated();
 131         return m_data & IsInvalidatedFlag;
 132     }
 133
 134     bool isStillValid() const
 135     {
 136         return !hasBeenInvalidated();
 137     }
 138
 139     void add(Watchpoint*);
 140
 141     void startWatching()
 142     {
 143         if (isFat()) {
 144             fat()->startWatching();
 145             return;
 146         }
 147         m_data |= IsWatchedFlag;
 148     }
 149
 150     void notifyWrite()
 151     {
 152         if (isFat()) {
 153             fat()->notifyWrite();
 154             return;
 155         }
 156         if (!(m_data & IsWatchedFlag))
 157             return;
 158         m_data |= IsInvalidatedFlag;
 159     }
 160
 161 private:
 162     static const uintptr_t IsThinFlag        = 1;
 163     static const uintptr_t IsInvalidatedFlag = 2;
 164     static const uintptr_t IsWatchedFlag     = 4;
 165
 166     bool isThin() const { return m_data & IsThinFlag; }
 167     bool isFat() const { return !isThin(); };
 168
 169     WatchpointSet* fat()
 170     {
 171         ASSERT(isFat());
 172         return bitwise_cast<WatchpointSet*>(m_data);
 173     }
 174
 175     const WatchpointSet* fat() const
 176     {
 177         ASSERT(isFat());
 178         return bitwise_cast<WatchpointSet*>(m_data);
 179     }
 180
 181     WatchpointSet* inflate()
 182     {
 183         if (LIKELY(isFat()))
 184             return fat();
 185         return inflateSlow();
 186     }
 187
 188     JS_EXPORT_PRIVATE WatchpointSet* inflateSlow();
 189     JS_EXPORT_PRIVATE void freeFat();
 190
 191     uintptr_t m_data;
 192 };
 193
 194 } // namespace JSC
 195
 196 #endif // Watchpoint_h
 197