runtime/SamplingCounter.h

   1 /*
   2  * Copyright (C) 2011 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
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   8  * 1.  Redistributions of source code must retain the above copyright
   9  *     notice, this list of conditions and the following disclaimer.
  10  * 2.  Redistributions in binary form must reproduce the above copyright
  11  *     notice, this list of conditions and the following disclaimer in the
  12  *     documentation and/or other materials provided with the distribution.
  13  * 3.  Neither the name of Apple Computer, Inc. ("Apple") nor the names of
  14  *     its contributors may be used to endorse or promote products derived
  15  *     from this software without specific prior written permission.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
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  26  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  27  */
  28
  29 #ifndef SamplingCounter_h
  30 #define SamplingCounter_h
  31
  32 #include <stdint.h>
  33 #include <wtf/Assertions.h>
  34
  35 namespace JSC {
  36
  37 // AbstractSamplingCounter:
  38 //
  39 // Implements a named set of counters, printed on exit if ENABLE(SAMPLING_COUNTERS).
  40 // See subclasses below, SamplingCounter, GlobalSamplingCounter and DeletableSamplingCounter.
  41 class AbstractSamplingCounter {
  42     friend class DeletableSamplingCounter;
  43 public:
  44     void count(uint32_t count = 1)
  45     {
  46         m_counter += count;
  47     }
  48
  49     JS_EXPORT_PRIVATE static void dump();
  50
  51     int64_t* addressOfCounter() { return &m_counter; }
  52
  53 protected:
  54     // Effectively the contructor, however called lazily in the case of GlobalSamplingCounter.
  55     void init(const char* name)
  56     {
  57         m_counter = 0;
  58         m_name = name;
  59
  60         // Set m_next to point to the head of the chain, and inform whatever is
  61         // currently at the head that this node will now hold the pointer to it.
  62         m_next = s_abstractSamplingCounterChain;
  63         s_abstractSamplingCounterChain->m_referer = &m_next;
  64         // Add this node to the head of the list.
  65         s_abstractSamplingCounterChain = this;
  66         m_referer = &s_abstractSamplingCounterChain;
  67     }
  68
  69     int64_t m_counter;
  70     const char* m_name;
  71     AbstractSamplingCounter* m_next;
  72     // This is a pointer to the pointer to this node in the chain; used to
  73     // allow fast linked list deletion.
  74     AbstractSamplingCounter** m_referer;
  75     // Null object used to detect end of static chain.
  76     static AbstractSamplingCounter s_abstractSamplingCounterChainEnd;
  77     JS_EXPORTDATA static AbstractSamplingCounter* s_abstractSamplingCounterChain;
  78     static bool s_completed;
  79 };
  80
  81 #if ENABLE(SAMPLING_COUNTERS)
  82 // SamplingCounter:
  83 //
  84 // This class is suitable and (hopefully!) convenient for cases where a counter is
  85 // required within the scope of a single function. It can be instantiated as a
  86 // static variable since it contains a constructor but not a destructor (static
  87 // variables in WebKit cannot have destructors).
  88 //
  89 // For example:
  90 //
  91 // void someFunction()
  92 // {
  93 //     static SamplingCounter countMe("This is my counter. There are many like it, but this one is mine.");
  94 //     countMe.count();
  95 //     // ...
  96 // }
  97 //
  98 class SamplingCounter : public AbstractSamplingCounter {
  99 public:
 100     SamplingCounter(const char* name) { init(name); }
 101 };
 102
 103 // GlobalSamplingCounter:
 104 //
 105 // This class is suitable for use where a counter is to be declared globally,
 106 // since it contains neither a constructor nor destructor. Instead, ensure
 107 // that 'name()' is called to provide the counter with a name (and also to
 108 // allow it to be printed out on exit).
 109 //
 110 // GlobalSamplingCounter globalCounter;
 111 //
 112 // void firstFunction()
 113 // {
 114 //     // Put this within a function that is definitely called!
 115 //     // (Or alternatively alongside all calls to 'count()').
 116 //     globalCounter.name("I Name You Destroyer.");
 117 //     globalCounter.count();
 118 //     // ...
 119 // }
 120 //
 121 // void secondFunction()
 122 // {
 123 //     globalCounter.count();
 124 //     // ...
 125 // }
 126 //
 127 class GlobalSamplingCounter : public AbstractSamplingCounter {
 128 public:
 129     void name(const char* name)
 130     {
 131         // Global objects should be mapped in zero filled memory, so this should
 132         // be a safe (albeit not necessarily threadsafe) check for 'first call'.
 133         if (!m_next)
 134             init(name);
 135     }
 136 };
 137
 138 // DeletableSamplingCounter:
 139 //
 140 // The above classes (SamplingCounter, GlobalSamplingCounter), are intended for
 141 // use within a global or static scope, and as such cannot have a destructor.
 142 // This means there is no convenient way for them to remove themselves from the
 143 // static list of counters, and should an instance of either class be freed
 144 // before 'dump()' has walked over the list it will potentially walk over an
 145 // invalid pointer.
 146 //
 147 // This class is intended for use where the counter may possibly be deleted before
 148 // the program exits. Should this occur, the counter will print it's value to
 149 // stderr, and remove itself from the static list. Example:
 150 //
 151 // DeletableSamplingCounter* counter = new DeletableSamplingCounter("The Counter With No Name");
 152 // counter->count();
 153 // delete counter;
 154 //
 155 class DeletableSamplingCounter : public AbstractSamplingCounter {
 156 public:
 157     DeletableSamplingCounter(const char* name) { init(name); }
 158
 159     ~DeletableSamplingCounter()
 160     {
 161         if (!s_completed)
 162             dataFile("DeletableSamplingCounter \"%s\" deleted early (with count %lld)\n", m_name, m_counter);
 163         // Our m_referer pointer should know where the pointer to this node is,
 164         // and m_next should know that this node is the previous node in the list.
 165         ASSERT(*m_referer == this);
 166         ASSERT(m_next->m_referer == &m_next);
 167         // Remove this node from the list, and inform m_next that we have done so.
 168         m_next->m_referer = m_referer;
 169         *m_referer = m_next;
 170     }
 171 };
 172 #endif
 173
 174 } // namespace JSC
 175
 176 #endif // SamplingCounter_h
 177
 178