This file is indexed.

/usr/include/firefox/nsExpirationTracker.h is in firefox-dev 11.0+build1-0ubuntu4.

This file is owned by root:root, with mode 0o644.

The actual contents of the file can be viewed below.

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is mozilla.org code.
 *
 * The Initial Developer of the Original Code is
 * Mozilla.
 * Portions created by the Initial Developer are Copyright (C) 2007
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   robert@ocallahan.org
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either of the GNU General Public License Version 2 or later (the "GPL"),
 * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
 * of those above. If you wish to allow use of your version of this file only
 * under the terms of either the GPL or the LGPL, and not to allow others to
 * use your version of this file under the terms of the MPL, indicate your
 * decision by deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL or the LGPL. If you do not delete
 * the provisions above, a recipient may use your version of this file under
 * the terms of any one of the MPL, the GPL or the LGPL.
 *
 * ***** END LICENSE BLOCK ***** */

#ifndef NSEXPIRATIONTRACKER_H_
#define NSEXPIRATIONTRACKER_H_

#include "prlog.h"
#include "nsTArray.h"
#include "nsITimer.h"
#include "nsCOMPtr.h"
#include "nsAutoPtr.h"
#include "nsComponentManagerUtils.h"
#include "nsIObserver.h"
#include "nsIObserverService.h"
#include "mozilla/Services.h"

/**
 * Data used to track the expiration state of an object. We promise that this
 * is 32 bits so that objects that includes this as a field can pad and align
 * efficiently.
 */
struct nsExpirationState {
  enum { NOT_TRACKED = (1U << 4) - 1,
         MAX_INDEX_IN_GENERATION = (1U << 28) - 1 };

  nsExpirationState() : mGeneration(NOT_TRACKED) {}
  bool IsTracked() { return mGeneration != NOT_TRACKED; }

  /**
   * The generation that this object belongs to, or NOT_TRACKED.
   */
  PRUint32 mGeneration:4;
  PRUint32 mIndexInGeneration:28;
};

/**
 * nsExpirationTracker can track the lifetimes and usage of a large number of
 * objects, and send a notification some window of time after a live object was
 * last used. This is very useful when you manage a large number of objects
 * and want to flush some after they haven't been used for a while.
 * nsExpirationTracker is designed to be very space and time efficient.
 * 
 * The type parameter T is the object type that we will track pointers to. T
 * must include an accessible method GetExpirationState() that returns a
 * pointer to an nsExpirationState associated with the object (preferably,
 * stored in a field of the object).
 * 
 * The parameter K is the number of generations that will be used. Increasing
 * the number of generations narrows the window within which we promise
 * to fire notifications, at a slight increase in space cost for the tracker.
 * We require 2 <= K <= nsExpirationState::NOT_TRACKED (currently 15).
 * 
 * To use this class, you need to inherit from it and override the
 * NotifyExpired() method.
 * 
 * The approach is to track objects in K generations. When an object is accessed
 * it moves from its current generation to the newest generation. Generations
 * are stored in a cyclic array; when a timer interrupt fires, we advance
 * the current generation pointer to effectively age all objects very efficiently.
 * By storing information in each object about its generation and index within its
 * generation array, we make removal of objects from a generation very cheap.
 * 
 * Future work:
 * -- Add a method to change the timer period?
 */
template <class T, PRUint32 K> class nsExpirationTracker {
  public:
    /**
     * Initialize the tracker.
     * @param aTimerPeriod the timer period in milliseconds. The guarantees
     * provided by the tracker are defined in terms of this period. If the
     * period is zero, then we don't use a timer and rely on someone calling
     * AgeOneGeneration explicitly.
     */
    nsExpirationTracker(PRUint32 aTimerPeriod)
      : mTimerPeriod(aTimerPeriod), mNewestGeneration(0),
        mInAgeOneGeneration(false) {
      PR_STATIC_ASSERT(K >= 2 && K <= nsExpirationState::NOT_TRACKED);
      mObserver = new ExpirationTrackerObserver();
      mObserver->Init(this);
    }
    ~nsExpirationTracker() {
      if (mTimer) {
        mTimer->Cancel();
      }
      mObserver->Destroy();
    }

    /**
     * Add an object to be tracked. It must not already be tracked. It will
     * be added to the newest generation, i.e., as if it was just used.
     * @return an error on out-of-memory
     */
    nsresult AddObject(T* aObj) {
      nsExpirationState* state = aObj->GetExpirationState();
      NS_ASSERTION(!state->IsTracked(), "Tried to add an object that's already tracked");
      nsTArray<T*>& generation = mGenerations[mNewestGeneration];
      PRUint32 index = generation.Length();
      if (index > nsExpirationState::MAX_INDEX_IN_GENERATION) {
        NS_WARNING("More than 256M elements tracked, this is probably a problem");
        return NS_ERROR_OUT_OF_MEMORY;
      }
      if (index == 0) {
        // We might need to start the timer
        nsresult rv = CheckStartTimer();
        if (NS_FAILED(rv))
          return rv;
      }
      if (!generation.AppendElement(aObj))
        return NS_ERROR_OUT_OF_MEMORY;
      state->mGeneration = mNewestGeneration;
      state->mIndexInGeneration = index;
      return NS_OK;
    }

    /**
     * Remove an object from the tracker. It must currently be tracked.
     */
    void RemoveObject(T* aObj) {
      nsExpirationState* state = aObj->GetExpirationState();
      NS_ASSERTION(state->IsTracked(), "Tried to remove an object that's not tracked");
      nsTArray<T*>& generation = mGenerations[state->mGeneration];
      PRUint32 index = state->mIndexInGeneration;
      NS_ASSERTION(generation.Length() > index &&
                   generation[index] == aObj, "Object is lying about its index");
      // Move the last object to fill the hole created by removing aObj
      PRUint32 last = generation.Length() - 1;
      T* lastObj = generation[last];
      generation[index] = lastObj;
      lastObj->GetExpirationState()->mIndexInGeneration = index;
      generation.RemoveElementAt(last);
      state->mGeneration = nsExpirationState::NOT_TRACKED;
      // We do not check whether we need to stop the timer here. The timer
      // will check that itself next time it fires. Checking here would not
      // be efficient since we'd need to track all generations. Also we could
      // thrash by incessantly creating and destroying timers if someone
      // kept adding and removing an object from the tracker.
    }

    /**
     * Notify that an object has been used.
     * @return an error if we lost the object from the tracker...
     */
    nsresult MarkUsed(T* aObj) {
      nsExpirationState* state = aObj->GetExpirationState();
      if (mNewestGeneration == state->mGeneration)
        return NS_OK;
      RemoveObject(aObj);
      return AddObject(aObj);
    }

    /**
     * The timer calls this, but it can also be manually called if you want
     * to age objects "artifically". This can result in calls to NotifyExpired.
     */
    void AgeOneGeneration() {
      if (mInAgeOneGeneration) {
        NS_WARNING("Can't reenter AgeOneGeneration from NotifyExpired");
        return;
      }
      
      mInAgeOneGeneration = true;
      PRUint32 reapGeneration = 
        mNewestGeneration > 0 ? mNewestGeneration - 1 : K - 1;
      nsTArray<T*>& generation = mGenerations[reapGeneration];
      // The following is rather tricky. We have to cope with objects being
      // removed from this generation either because of a call to RemoveObject
      // (or indirectly via MarkUsed) inside NotifyExpired. Fortunately no
      // objects can be added to this generation because it's not the newest
      // generation. We depend on the fact that RemoveObject can only cause
      // the indexes of objects in this generation to *decrease*, not increase.
      // So if we start from the end and work our way backwards we are guaranteed
      // to see each object at least once.
      PRUint32 index = generation.Length();
      for (;;) {
        // Objects could have been removed so index could be outside
        // the array
        index = NS_MIN(index, generation.Length());
        if (index == 0)
          break;
        --index;
        NotifyExpired(generation[index]);
      }
      // Any leftover objects from reapGeneration just end up in the new
      // newest-generation. This is bad form, though, so warn if there are any.
      if (!generation.IsEmpty()) {
        NS_WARNING("Expired objects were not removed or marked used");
      }
      // Free excess memory used by the generation array, since we probably
      // just removed most or all of its elements.
      generation.Compact();
      mNewestGeneration = reapGeneration;
      mInAgeOneGeneration = false;
    }

    /**
     * This just calls AgeOneGeneration K times. Under normal circumstances this
     * will result in all objects getting NotifyExpired called on them, but
     * if NotifyExpired itself marks some objects as used, then those objects
     * might not expire. This would be a good thing to call if we get into
     * a critically-low memory situation.
     */
    void AgeAllGenerations() {
      PRUint32 i;
      for (i = 0; i < K; ++i) {
        AgeOneGeneration();
      }
    }
    
    class Iterator {
    private:
      nsExpirationTracker<T,K>* mTracker;
      PRUint32                  mGeneration;
      PRUint32                  mIndex;
    public:
      Iterator(nsExpirationTracker<T,K>* aTracker)
        : mTracker(aTracker), mGeneration(0), mIndex(0) {}
      T* Next() {
        while (mGeneration < K) {
          nsTArray<T*>* generation = &mTracker->mGenerations[mGeneration];
          if (mIndex < generation->Length()) {
            ++mIndex;
            return (*generation)[mIndex - 1];
          }
          ++mGeneration;
          mIndex = 0;
        }
        return nsnull;
      }
    };
    
    friend class Iterator;

    bool IsEmpty() {
      for (PRUint32 i = 0; i < K; ++i) {
        if (!mGenerations[i].IsEmpty())
          return false;
      }
      return true;
    }

  protected:
    /**
     * This must be overridden to catch notifications. It is called whenever
     * we detect that an object has not been used for at least (K-1)*mTimerPeriod
     * milliseconds. If timer events are not delayed, it will be called within
     * roughly K*mTimerPeriod milliseconds after the last use. (Unless AgeOneGeneration
     * or AgeAllGenerations have been called to accelerate the aging process.)
     * 
     * NOTE: These bounds ignore delays in timer firings due to actual work being
     * performed by the browser. We use a slack timer so there is always at least
     * mTimerPeriod milliseconds between firings, which gives us (K-1)*mTimerPeriod
     * as a pretty solid lower bound. The upper bound is rather loose, however.
     * If the maximum amount by which any given timer firing is delayed is D, then
     * the upper bound before NotifyExpired is called is K*(mTimerPeriod + D).
     * 
     * The NotifyExpired call is expected to remove the object from the tracker,
     * but it need not. The object (or other objects) could be "resurrected"
     * by calling MarkUsed() on them, or they might just not be removed.
     * Any objects left over that have not been resurrected or removed
     * are placed in the new newest-generation, but this is considered "bad form"
     * and should be avoided (we'll issue a warning). (This recycling counts
     * as "a use" for the purposes of the expiry guarantee above...)
     * 
     * For robustness and simplicity, we allow objects to be notified more than
     * once here in the same timer tick.
     */
    virtual void NotifyExpired(T* aObj) = 0;

  private:
    class ExpirationTrackerObserver;
    nsRefPtr<ExpirationTrackerObserver> mObserver;
    nsTArray<T*>       mGenerations[K];
    nsCOMPtr<nsITimer> mTimer;
    PRUint32           mTimerPeriod;
    PRUint32           mNewestGeneration;
    bool               mInAgeOneGeneration;

    /**
     * Whenever "memory-pressure" is observed, it calls AgeAllGenerations()
     * to minimize memory usage.
     */
    class ExpirationTrackerObserver : public nsIObserver {
    public:
      void Init(nsExpirationTracker<T,K> *obj) {
        mOwner = obj;
        nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
        if (obs) {
          obs->AddObserver(this, "memory-pressure", false);
        }
      }
      void Destroy() {
        nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
        if (obs)
          obs->RemoveObserver(this, "memory-pressure");
      }
      NS_DECL_ISUPPORTS
      NS_DECL_NSIOBSERVER
    private:
      nsExpirationTracker<T,K> *mOwner;
    };
  
    static void TimerCallback(nsITimer* aTimer, void* aThis) {
      nsExpirationTracker* tracker = static_cast<nsExpirationTracker*>(aThis);
      tracker->AgeOneGeneration();
      // Cancel the timer if we have no objects to track
      if (tracker->IsEmpty()) {
        tracker->mTimer->Cancel();
        tracker->mTimer = nsnull;
      }
    }

    nsresult CheckStartTimer() {
      if (mTimer || !mTimerPeriod)
        return NS_OK;
      mTimer = do_CreateInstance("@mozilla.org/timer;1");
      if (!mTimer)
        return NS_ERROR_OUT_OF_MEMORY;
      mTimer->InitWithFuncCallback(TimerCallback, this, mTimerPeriod,
                                   nsITimer::TYPE_REPEATING_SLACK);
      return NS_OK;
    }
};

template<class T, PRUint32 K>
NS_IMETHODIMP
nsExpirationTracker<T, K>::ExpirationTrackerObserver::Observe(nsISupports     *aSubject,
                                                              const char      *aTopic,
                                                              const PRUnichar *aData)
{
  if (!strcmp(aTopic, "memory-pressure"))
    mOwner->AgeAllGenerations();
  return NS_OK;
}

template <class T, PRUint32 K>
NS_IMETHODIMP_(nsrefcnt)
nsExpirationTracker<T,K>::ExpirationTrackerObserver::AddRef(void)
{
  NS_PRECONDITION(PRInt32(mRefCnt) >= 0, "illegal refcnt");
  NS_ASSERT_OWNINGTHREAD_AND_NOT_CCTHREAD(ExpirationTrackerObserver);
  ++mRefCnt;
  NS_LOG_ADDREF(this, mRefCnt, "ExpirationTrackerObserver", sizeof(*this));
  return mRefCnt;
}

template <class T, PRUint32 K>
NS_IMETHODIMP_(nsrefcnt)
nsExpirationTracker<T,K>::ExpirationTrackerObserver::Release(void)
{
  NS_PRECONDITION(0 != mRefCnt, "dup release");
  NS_ASSERT_OWNINGTHREAD_AND_NOT_CCTHREAD(ExpirationTrackerObserver);
  --mRefCnt;
  NS_LOG_RELEASE(this, mRefCnt, "ExpirationTrackerObserver");
  if (mRefCnt == 0) {
    NS_ASSERT_OWNINGTHREAD(ExpirationTrackerObserver);
    mRefCnt = 1; /* stabilize */
    delete (this);
    return 0;
  }
  return mRefCnt;
}

template <class T, PRUint32 K>
NS_IMETHODIMP
nsExpirationTracker<T,K>::ExpirationTrackerObserver::QueryInterface(REFNSIID aIID, 
                                                                    void** aInstancePtr)
{
  NS_ASSERTION(aInstancePtr,
               "QueryInterface requires a non-NULL destination!");            
  nsresult rv = NS_ERROR_FAILURE;
  NS_INTERFACE_TABLE1(ExpirationTrackerObserver, nsIObserver)
  return rv;
}

#endif /*NSEXPIRATIONTRACKER_H_*/