xpcom/build/IOInterposer.h

   1 /* This Source Code Form is subject to the terms of the Mozilla Public
   2  * License, v. 2.0. If a copy of the MPL was not distributed with this
   3  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   4
   5 #ifndef mozilla_IOInterposer_h
   6 #define mozilla_IOInterposer_h
   7
   8 #include "mozilla/Attributes.h"
   9 #include "mozilla/TimeStamp.h"
  10 #include "mozilla/XPCOM.h"
  11
  12 namespace mozilla {
  13
  14 /**
  15  * Interface for I/O interposer observers. This is separate from the
  16  * IOInterposer because we have multiple uses for these observations.
  17  */
  18 class IOInterposeObserver
  19 {
  20 public:
  21   enum Operation
  22   {
  23     OpNone = 0,
  24     OpCreateOrOpen = (1 << 0),
  25     OpRead = (1 << 1),
  26     OpWrite = (1 << 2),
  27     OpFSync = (1 << 3),
  28     OpStat = (1 << 4),
  29     OpClose = (1 << 5),
  30     OpNextStage = (1 << 6), // Meta - used when leaving startup, entering shutdown
  31     OpWriteFSync = (OpWrite | OpFSync),
  32     OpAll = (OpCreateOrOpen | OpRead | OpWrite | OpFSync | OpStat | OpClose),
  33     OpAllWithStaging = (OpAll | OpNextStage)
  34   };
  35
  36   /** A representation of an I/O observation  */
  37   class Observation
  38   {
  39   protected:
  40     /**
  41      * This constructor is for use by subclasses that are intended to take
  42      * timing measurements via RAII. The |aShouldReport| parameter may be
  43      * used to make the measurement and reporting conditional on the
  44      * satisfaction of an arbitrary predicate that was evaluated
  45      * in the subclass. Note that IOInterposer::IsObservedOperation() is
  46      * always ANDed with aShouldReport, so the subclass does not need to
  47      * include a call to that function explicitly.
  48      */
  49     Observation(Operation aOperation, const char* aReference,
  50                 bool aShouldReport = true);
  51
  52   public:
  53     /**
  54      * Since this constructor accepts start and end times, it does *not* take
  55      * its own timings, nor does it report itself.
  56      */
  57     Observation(Operation aOperation, const TimeStamp& aStart,
  58                 const TimeStamp& aEnd, const char* aReference);
  59
  60     /**
  61      * Operation observed, this is one of the individual Operation values.
  62      * Combinations of these flags are only used when registering observers.
  63      */
  64     Operation ObservedOperation() const { return mOperation; }
  65
  66     /**
  67      * Return the observed operation as a human-readable string.
  68      */
  69     const char* ObservedOperationString() const;
  70
  71     /** Time at which the I/O operation was started */
  72     TimeStamp Start() const { return mStart; }
  73
  74     /**
  75      * Time at which the I/O operation ended, for asynchronous methods this is
  76      * the time at which the call initiating the asynchronous request returned.
  77      */
  78     TimeStamp End() const { return mEnd; }
  79
  80     /**
  81      * Duration of the operation, for asynchronous I/O methods this is the
  82      * duration of the call initiating the asynchronous request.
  83      */
  84     TimeDuration Duration() const { return mEnd - mStart; }
  85
  86     /**
  87      * IO reference, function name or name of component (sqlite) that did IO
  88      * this is in addition the generic operation. This attribute may be platform
  89      * specific, but should only take a finite number of distinct values.
  90      * E.g. sqlite-commit, CreateFile, NtReadFile, fread, fsync, mmap, etc.
  91      * I.e. typically the platform specific function that did the IO.
  92      */
  93     const char* Reference() const { return mReference; }
  94
  95     /** Request filename associated with the I/O operation, null if unknown */
  96     virtual const char16_t* Filename() { return nullptr; }
  97
  98     virtual ~Observation() {}
  99
 100   protected:
 101     void
 102     Report();
 103
 104     Operation   mOperation;
 105     TimeStamp   mStart;
 106     TimeStamp   mEnd;
 107     const char* mReference;     // Identifies the source of the Observation
 108     bool        mShouldReport;  // Measure and report if true
 109   };
 110
 111   /**
 112    * Invoked whenever an implementation of the IOInterposeObserver should
 113    * observe aObservation. Implement this and do your thing...
 114    * But do consider if it is wise to use IO functions in this method, they are
 115    * likely to cause recursion :)
 116    * At least, see PoisonIOInterposer.h and register your handle as a debug file
 117    * even, if you don't initialize the poison IO interposer, someone else might.
 118    *
 119    * Remark: Observations may occur on any thread.
 120    */
 121   virtual void Observe(Observation& aObservation) = 0;
 122
 123   virtual ~IOInterposeObserver() {}
 124
 125 protected:
 126   /**
 127    * We don't use NS_IsMainThread() because we need to be able to determine the
 128    * main thread outside of XPCOM Initialization. IOInterposer observers should
 129    * call this function instead.
 130    */
 131   static bool IsMainThread();
 132 };
 133
 134 /**
 135  * These functions are responsible for ensuring that events are routed to the
 136  * appropriate observers.
 137  */
 138 namespace IOInterposer {
 139
 140 /**
 141  * This function must be called from the main-thread when no other threads are
 142  * running before any of the other methods on this class may be used.
 143  *
 144  * IO reports can however, safely assume that IsObservedOperation() will
 145  * return false until the IOInterposer is initialized.
 146  *
 147  * Remark, it's safe to call this method multiple times, so just call it when
 148  * you to utilize IO interposing.
 149  *
 150  * Using the IOInterposerInit class is preferred to calling this directly.
 151  */
 152 bool Init();
 153
 154 /**
 155  * This function must be called from the main thread, and furthermore
 156  * it must be called when no other threads are executing. Effectively
 157  * restricting us to calling it only during shutdown.
 158  *
 159  * Callers should take care that no other consumers are subscribed to events,
 160  * as these events will stop when this function is called.
 161  *
 162  * In practice, we don't use this method as the IOInterposer is used for
 163  * late-write checks.
 164  */
 165 void Clear();
 166
 167 /**
 168  * This function immediately disables IOInterposer functionality in a fast,
 169  * thread-safe manner. Primarily for use by the crash reporter.
 170  */
 171 void Disable();
 172
 173 /**
 174  * Report IO to registered observers.
 175  * Notice that the reported operation must be either OpRead, OpWrite or
 176  * OpFSync. You are not allowed to report an observation with OpWriteFSync or
 177  * OpAll, these are just auxiliary values for use with Register().
 178  *
 179  * If the IO call you're reporting does multiple things, write and fsync, you
 180  * can choose to call Report() twice once with write and once with FSync. You
 181  * may not call Report() with OpWriteFSync! The Observation::mOperation
 182  * attribute is meant to be generic, not perfect.
 183  *
 184  * Notice that there is no reason to report an observation with an operation
 185  * which is not being observed. Use IsObservedOperation() to check if the
 186  * operation you are about to report is being observed. This is especially
 187  * important if you are constructing expensive observations containing
 188  * filename and full-path.
 189  *
 190  * Remark: Init() must be called before any IO is reported. But
 191  * IsObservedOperation() will return false until Init() is called.
 192  */
 193 void Report(IOInterposeObserver::Observation& aObservation);
 194
 195 /**
 196  * Return whether or not an operation is observed. Reporters should not
 197  * report operations that are not being observed by anybody. This mechanism
 198  * allows us to avoid reporting I/O when no observers are registered.
 199  */
 200 bool IsObservedOperation(IOInterposeObserver::Operation aOp);
 201
 202 /**
 203  * Register IOInterposeObserver, the observer object will receive all
 204  * observations for the given operation aOp.
 205  *
 206  * Remark: Init() must be called before observers are registered.
 207  */
 208 void Register(IOInterposeObserver::Operation aOp,
 209               IOInterposeObserver* aObserver);
 210
 211 /**
 212  * Unregister an IOInterposeObserver for a given operation
 213  * Remark: It is always safe to unregister for all operations, even if yoú
 214  * didn't register for them all.
 215  * I.e. IOInterposer::Unregister(IOInterposeObserver::OpAll, aObserver)
 216  *
 217  * Remark: Init() must be called before observers are unregistered.
 218  */
 219 void Unregister(IOInterposeObserver::Operation aOp,
 220                 IOInterposeObserver* aObserver);
 221
 222 /**
 223  * Registers the current thread with the IOInterposer. This must be done to
 224  * ensure that per-thread data is created in an orderly fashion.
 225  * We could have written this to initialize that data lazily, however this
 226  * could have unintended consequences if a thread that is not aware of
 227  * IOInterposer was implicitly registered: its per-thread data would never
 228  * be deleted because it would not know to unregister itself.
 229  *
 230  * @param aIsMainThread true if IOInterposer should treat the current thread
 231  *                      as the main thread.
 232  */
 233 void RegisterCurrentThread(bool aIsMainThread = false);
 234
 235 /**
 236  * Unregisters the current thread with the IOInterposer. This is important
 237  * to call when a thread is shutting down because it cleans up data that
 238  * is stored in a TLS slot.
 239  */
 240 void UnregisterCurrentThread();
 241
 242 /**
 243  * Called to inform observers that the process has transitioned out of the
 244  * startup stage or into the shutdown stage. Main thread only.
 245  */
 246 void EnteringNextStage();
 247
 248 } // namespace IOInterposer
 249
 250 class IOInterposerInit
 251 {
 252 public:
 253   IOInterposerInit()
 254   {
 255   }
 256
 257   ~IOInterposerInit()
 258   {
 259   }
 260 };
 261
 262 } // namespace mozilla
 263
 264 #endif // mozilla_IOInterposer_h