text: /*
   * Copyright (C) 2005 The Android Open Source Project
   *
   * Licensed under the Apache License, Version 2.0 (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.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  #define LOG_TAG "RefBase"
  // #define LOG_NDEBUG 0
  
  #include <utils/RefBase.h>
  
  #include <utils/CallStack.h>
  
  #ifndef __unused
  #define __unused __attribute__((__unused__))
  #endif
  
  // compile with refcounting debugging enabled
  #define DEBUG_REFS                      0
  
  // whether ref-tracking is enabled by default, if not, trackMe(true, false)
  // needs to be called explicitly
  #define DEBUG_REFS_ENABLED_BY_DEFAULT   0
  
  // whether callstack are collected (significantly slows things down)
  #define DEBUG_REFS_CALLSTACK_ENABLED    1
  
  // folder where stack traces are saved when DEBUG_REFS is enabled
  // this folder needs to exist and be writable
  #define DEBUG_REFS_CALLSTACK_PATH       "/data/debug"
  
  // log all reference counting operations
  #define PRINT_REFS                      0
  
  // ---------------------------------------------------------------------------
  
  namespace android {
  
  // Observations, invariants, etc:
  
  // By default, obects are destroyed when the last strong reference disappears
  // or, if the object never had a strong reference, when the last weak reference
  // disappears.
  //
  // OBJECT_LIFETIME_WEAK changes this behavior to retain the object
  // unconditionally until the last reference of either kind disappears.  The
  // client ensures that the extendObjectLifetime call happens before the dec
  // call that would otherwise have deallocated the object, or before an
  // attemptIncStrong call that might rely on it.  We do not worry about
  // concurrent changes to the object lifetime.
  //
  // AttemptIncStrong will succeed if the object has a strong reference, or if it
  // has a weak reference and has never had a strong reference.
  // AttemptIncWeak really does succeed only if there is already a WEAK
  // reference, and thus may fail when attemptIncStrong would succeed.
  //
  // mStrong is the strong reference count.  mWeak is the weak reference count.
  // Between calls, and ignoring memory ordering effects, mWeak includes strong
  // references, and is thus >= mStrong.
  //
  // A weakref_impl holds all the information, including both reference counts,
  // required to perform wp<> operations.  Thus these can continue to be performed
  // after the RefBase object has been destroyed.
  //
  // A weakref_impl is allocated as the value of mRefs in a RefBase object on
  // construction.
  // In the OBJECT_LIFETIME_STRONG case, it is normally deallocated in decWeak,
  // and hence lives as long as the last weak reference. (It can also be
  // deallocated in the RefBase destructor iff the strong reference count was
  // never incremented and the weak count is zero, e.g.  if the RefBase object is
  // explicitly destroyed without decrementing the strong count.  This should be
  // avoided.) In this case, the RefBase destructor should be invoked from
  // decStrong.
  // In the OBJECT_LIFETIME_WEAK case, the weakref_impl is always deallocated in
  // the RefBase destructor, which is always invoked by decWeak. DecStrong
  // explicitly avoids the deletion in this case.
  //
  // Memory ordering:
  // The client must ensure that every inc() call, together with all other
  // accesses to the object, happens before the corresponding dec() call.
  //
  // We try to keep memory ordering constraints on atomics as weak as possible,
  // since memory fences or ordered memory accesses are likely to be a major
  // performance cost for this code. All accesses to mStrong, mWeak, and mFlags
  // explicitly relax memory ordering in some way.
  //
  // The only operations that are not memory_order_relaxed are reference count
  // decrements. All reference count decrements are release operations.  In
  // addition, the final decrement leading the deallocation is followed by an
  // acquire fence, which we can view informally as also turning it into an
  // acquire operation.  (See 29.8p4 [atomics.fences] for details. We could
  // alternatively use acq_rel operations for all decrements. This is probably
  // slower on most current (2016) hardware, especially on ARMv7, but that may
  // not be true indefinitely.)
  //
  // This convention ensures that the second-to-last decrement synchronizes with
  // (in the language of 1.10 in the C++ standard) the final decrement of a
  // reference count. Since reference counts are only updated using atomic
  // read-modify-write operations, this also extends to any earlier decrements.
  // (See "release sequence" in 1.10.)
  //
  // Since all operations on an object happen before the corresponding reference
  // count decrement, and all reference count decrements happen before the final
  // one, we are guaranteed that all other object accesses happen before the
  // object is destroyed.
  
  
  #define INITIAL_STRONG_VALUE (1<<28)
  
  #define MAX_COUNT 0xfffff
  
  // Test whether the argument is a clearly invalid strong reference count.
  // Used only for error checking on the value before an atomic decrement.
  // Intended to be very cheap.
  // Note that we cannot just check for excess decrements by comparing to zero
  // since the object would be deallocated before that.
  #define BAD_STRONG(c) \
          ((c) == 0 || ((c) & (~(MAX_COUNT | INITIAL_STRONG_VALUE))) != 0)
  
  // Same for weak counts.
  #define BAD_WEAK(c) ((c) == 0 || ((c) & (~MAX_COUNT)) != 0)
  
  // ---------------------------------------------------------------------------
  
  class RefBase::weakref_impl : public RefBase::weakref_type
  {
  public:
      std::atomic<int32_t>    mStrong;
      std::atomic<int32_t>    mWeak;
      RefBase* const          mBase;
      std::atomic<int32_t>    mFlags;
  
  #if !DEBUG_REFS
  
      explicit weakref_impl(RefBase* base)
          : mStrong(INITIAL_STRONG_VALUE)
          , mWeak(0)
          , mBase(base)
          , mFlags(0)
      {
      }
  
      void addStrongRef(const void* /*id*/) { }
      void removeStrongRef(const void* /*id*/) { }
      void renameStrongRefId(const void* /*old_id*/, const void* /*new_id*/) { }
      void addWeakRef(const void* /*id*/) { }
      void removeWeakRef(const void* /*id*/) { }
      void renameWeakRefId(const void* /*old_id*/, const void* /*new_id*/) { }
      void printRefs() const { }
      void trackMe(bool, bool) { }
  
  #else
  
      weakref_impl(RefBase* base)
          : mStrong(INITIAL_STRONG_VALUE)
          , mWeak(0)
          , mBase(base)
          , mFlags(0)
          , mStrongRefs(NULL)
          , mWeakRefs(NULL)
          , mTrackEnabled(!!DEBUG_REFS_ENABLED_BY_DEFAULT)
          , mRetain(false)
      {
      }
      
      ~weakref_impl()
      {
          bool dumpStack = false;
          if (!mRetain && mStrongRefs != NULL) {
              dumpStack = true;
              ALOGE("Strong references remain:");
              ref_entry* refs = mStrongRefs;
              while (refs) {
                  char inc = refs->ref >= 0 ? '+' : '-';
                  ALOGD("\t%c ID %p (ref %d):", inc, refs->id, refs->ref);
  #if DEBUG_REFS_CALLSTACK_ENABLED
                  refs->stack.log(LOG_TAG);
  #endif
                  refs = refs->next;
              }
          }
  
          if (!mRetain && mWeakRefs != NULL) {
              dumpStack = true;
              ALOGE("Weak references remain!");
              ref_entry* refs = mWeakRefs;
              while (refs) {
                  char inc = refs->ref >= 0 ? '+' : '-';
                  ALOGD("\t%c ID %p (ref %d):", inc, refs->id, refs->ref);
  #if DEBUG_REFS_CALLSTACK_ENABLED
                  refs->stack.log(LOG_TAG);
  #endif
                  refs = refs->next;
              }
          }
          if (dumpStack) {
              ALOGE("above errors at:");
              CallStack stack(LOG_TAG);
          }
      }
  
      void addStrongRef(const void* id) {
          //ALOGD_IF(mTrackEnabled,
          //        "addStrongRef: RefBase=%p, id=%p", mBase, id);
          addRef(&mStrongRefs, id, mStrong.load(std::memory_order_relaxed));
      }
  
      void removeStrongRef(const void* id) {
          //ALOGD_IF(mTrackEnabled,
          //        "removeStrongRef: RefBase=%p, id=%p", mBase, id);
          if (!mRetain) {
              removeRef(&mStrongRefs, id);
          } else {
              addRef(&mStrongRefs, id, -mStrong.load(std::memory_order_relaxed));
          }
      }
  
      void renameStrongRefId(const void* old_id, const void* new_id) {
          //ALOGD_IF(mTrackEnabled,
          //        "renameStrongRefId: RefBase=%p, oid=%p, nid=%p",
          //        mBase, old_id, new_id);
          renameRefsId(mStrongRefs, old_id, new_id);
      }
  
      void addWeakRef(const void* id) {
          addRef(&mWeakRefs, id, mWeak.load(std::memory_order_relaxed));
      }
  
      void removeWeakRef(const void* id) {
          if (!mRetain) {
              removeRef(&mWeakRefs, id);
          } else {
              addRef(&mWeakRefs, id, -mWeak.load(std::memory_order_relaxed));
          }
      }
  
      void renameWeakRefId(const void* old_id, const void* new_id) {
          renameRefsId(mWeakRefs, old_id, new_id);
      }
  
      void trackMe(bool track, bool retain)
      { 
          mTrackEnabled = track;
          mRetain = retain;
      }
  
      void printRefs() const
      {
          String8 text;
  
          {
              Mutex::Autolock _l(mMutex);
              char buf[128];
              snprintf(buf, sizeof(buf),
                       "Strong references on RefBase %p (weakref_type %p):\n",
                       mBase, this);
              text.append(buf);
              printRefsLocked(&text, mStrongRefs);
              snprintf(buf, sizeof(buf),
                       "Weak references on RefBase %p (weakref_type %p):\n",
                       mBase, this);
              text.append(buf);
              printRefsLocked(&text, mWeakRefs);
          }
  
          {
              char name[100];
              snprintf(name, sizeof(name), DEBUG_REFS_CALLSTACK_PATH "/%p.stack",
                       this);
              int rc = open(name, O_RDWR | O_CREAT | O_APPEND, 644);
              if (rc >= 0) {
                  write(rc, text.string(), text.length());
                  close(rc);
                  ALOGD("STACK TRACE for %p saved in %s", this, name);
              }
              else ALOGE("FAILED TO PRINT STACK TRACE for %p in %s: %s", this,
                        name, strerror(errno));
          }
      }
  
  private:
      struct ref_entry
      {
          ref_entry* next;
          const void* id;
  #if DEBUG_REFS_CALLSTACK_ENABLED
          CallStack stack;
  #endif
          int32_t ref;
      };
  
      void addRef(ref_entry** refs, const void* id, int32_t mRef)
      {
          if (mTrackEnabled) {
              AutoMutex _l(mMutex);
  
              ref_entry* ref = new ref_entry;
              // Reference count at the time of the snapshot, but before the
              // update.  Positive value means we increment, negative--we
              // decrement the reference count.
              ref->ref = mRef;
              ref->id = id;
  #if DEBUG_REFS_CALLSTACK_ENABLED
              ref->stack.update(2);
  #endif
              ref->next = *refs;
              *refs = ref;
          }
      }
  
      void removeRef(ref_entry** refs, const void* id)
      {
          if (mTrackEnabled) {
              AutoMutex _l(mMutex);
              
              ref_entry* const head = *refs;
              ref_entry* ref = head;
              while (ref != NULL) {
                  if (ref->id == id) {
                      *refs = ref->next;
                      delete ref;
                      return;
                  }
                  refs = &ref->next;
                  ref = *refs;
              }
  
              ALOGE("RefBase: removing id %p on RefBase %p"
                      "(weakref_type %p) that doesn't exist!",
                      id, mBase, this);
  
              ref = head;
              while (ref) {
                  char inc = ref->ref >= 0 ? '+' : '-';
                  ALOGD("\t%c ID %p (ref %d):", inc, ref->id, ref->ref);
                  ref = ref->next;
              }
  
              CallStack stack(LOG_TAG);
          }
      }
  
      void renameRefsId(ref_entry* r, const void* old_id, const void* new_id)
      {
          if (mTrackEnabled) {
              AutoMutex _l(mMutex);
              ref_entry* ref = r;
              while (ref != NULL) {
                  if (ref->id == old_id) {
                      ref->id = new_id;
                  }
                  ref = ref->next;
              }
          }
      }
  
      void printRefsLocked(String8* out, const ref_entry* refs) const
      {
          char buf[128];
          while (refs) {
              char inc = refs->ref >= 0 ? '+' : '-';
              snprintf(buf, sizeof(buf), "\t%c ID %p (ref %d):\n",
                       inc, refs->id, refs->ref);
              out->append(buf);
  #if DEBUG_REFS_CALLSTACK_ENABLED
              out->append(refs->stack.toString("\t\t"));
  #else
              out->append("\t\t(call stacks disabled)");
  #endif
              refs = refs->next;
          }
      }
  
      mutable Mutex mMutex;
      ref_entry* mStrongRefs;
      ref_entry* mWeakRefs;
  
      bool mTrackEnabled;
      // Collect stack traces on addref and removeref, instead of deleting the stack references
      // on removeref that match the address ones.
      bool mRetain;
  
  #endif
  };
  
  // ---------------------------------------------------------------------------
  
  void RefBase::incStrong(const void* id) const
  {
      weakref_impl* const refs = mRefs;
      refs->incWeak(id);
      
      refs->addStrongRef(id);
      const int32_t c = refs->mStrong.fetch_add(1, std::memory_order_relaxed);
      if (c != INITIAL_STRONG_VALUE)  {
          return;
      }
  
      int32_t old = refs->mStrong.fetch_sub(INITIAL_STRONG_VALUE,
              std::memory_order_relaxed);
      // A decStrong() must still happen after us.
      refs->mBase->onFirstRef();
  }
  
  void RefBase::decStrong(const void* id) const
  {
      weakref_impl* const refs = mRefs;
      refs->removeStrongRef(id);
      const int32_t c = refs->mStrong.fetch_sub(1, std::memory_order_release);
      if (c == 1) {
          std::atomic_thread_fence(std::memory_order_acquire);
          refs->mBase->onLastStrongRef(id);
          int32_t flags = refs->mFlags.load(std::memory_order_relaxed);
          if ((flags&OBJECT_LIFETIME_MASK) == OBJECT_LIFETIME_STRONG) {
              delete this;
              // The destructor does not delete refs in this case.
          }
      }
      // Note that even with only strong reference operations, the thread
      // deallocating this may not be the same as the thread deallocating refs.
      // That's OK: all accesses to this happen before its deletion here,
      // and all accesses to refs happen before its deletion in the final decWeak.
      // The destructor can safely access mRefs because either it's deleting
      // mRefs itself, or it's running entirely before the final mWeak decrement.
      //
      // Since we're doing atomic loads of `flags`, the static analyzer assumes
      // they can change between `delete this;` and `refs->decWeak(id);`. This is
      // not the case. The analyzer may become more okay with this patten when
      // https://bugs.llvm.org/show_bug.cgi?id=34365 gets resolved. NOLINTNEXTLINE
      refs->decWeak(id);
  }
  
  void RefBase::forceIncStrong(const void* id) const
  {
      // Allows initial mStrong of 0 in addition to INITIAL_STRONG_VALUE.
      // TODO: Better document assumptions.
      weakref_impl* const refs = mRefs;
      refs->incWeak(id);
      
      refs->addStrongRef(id);
      const int32_t c = refs->mStrong.fetch_add(1, std::memory_order_relaxed);
  #if PRINT_REFS
      ALOGD("forceIncStrong of %p from %p: cnt=%d\n", this, id, c);
  #endif
  
      switch (c) {
      case INITIAL_STRONG_VALUE:
          refs->mStrong.fetch_sub(INITIAL_STRONG_VALUE,
                  std::memory_order_relaxed);
          // fall through...
      case 0:
          refs->mBase->onFirstRef();
      }
  }
  
  int32_t RefBase::getStrongCount() const
  {
      // Debugging only; No memory ordering guarantees.
      return mRefs->mStrong.load(std::memory_order_relaxed);
  }
  
  RefBase* RefBase::weakref_type::refBase() const
  {
      return static_cast<const weakref_impl*>(this)->mBase;
  }
  
  void RefBase::weakref_type::incWeak(const void* id)
  {
      weakref_impl* const impl = static_cast<weakref_impl*>(this);
      impl->addWeakRef(id);
      const int32_t c = impl->mWeak.fetch_add(1,
              std::memory_order_relaxed);
  }
  
  
  void RefBase::weakref_type::decWeak(const void* id)
  {
      weakref_impl* const impl = static_cast<weakref_impl*>(this);
      impl->removeWeakRef(id);
      const int32_t c = impl->mWeak.fetch_sub(1, std::memory_order_release);
      if (c != 1) return;
      atomic_thread_fence(std::memory_order_acquire);
  
      int32_t flags = impl->mFlags.load(std::memory_order_relaxed);
      if ((flags&OBJECT_LIFETIME_MASK) == OBJECT_LIFETIME_STRONG) {
          // This is the regular lifetime case. The object is destroyed
          // when the last strong reference goes away. Since weakref_impl
          // outlives the object, it is not destroyed in the dtor, and
          // we'll have to do it here.
          if (impl->mStrong.load(std::memory_order_relaxed)
                  == INITIAL_STRONG_VALUE) {
              // Decrementing a weak count to zero when object never had a strong
              // reference.  We assume it acquired a weak reference early, e.g.
              // in the constructor, and will eventually be properly destroyed,
              // usually via incrementing and decrementing the strong count.
              // Thus we no longer do anything here.  We log this case, since it
              // seems to be extremely rare, and should not normally occur. We
              // used to deallocate mBase here, so this may now indicate a leak.
          } else {
              // ALOGV("Freeing refs %p of old RefBase %p\n", this, impl->mBase);
              delete impl;
          }
      } else {
          // This is the OBJECT_LIFETIME_WEAK case. The last weak-reference
          // is gone, we can destroy the object.
          impl->mBase->onLastWeakRef(id);
          delete impl->mBase;
      }
  }
  
  bool RefBase::weakref_type::attemptIncStrong(const void* id)
  {
      incWeak(id);
      
      weakref_impl* const impl = static_cast<weakref_impl*>(this);
      int32_t curCount = impl->mStrong.load(std::memory_order_relaxed);
  
      while (curCount > 0 && curCount != INITIAL_STRONG_VALUE) {
          // we're in the easy/common case of promoting a weak-reference
          // from an existing strong reference.
          if (impl->mStrong.compare_exchange_weak(curCount, curCount+1,
                  std::memory_order_relaxed)) {
              break;
          }
          // the strong count has changed on us, we need to re-assert our
          // situation. curCount was updated by compare_exchange_weak.
      }
      
      if (curCount <= 0 || curCount == INITIAL_STRONG_VALUE) {
          // we're now in the harder case of either:
          // - there never was a strong reference on us
          // - or, all strong references have been released
          int32_t flags = impl->mFlags.load(std::memory_order_relaxed);
          if ((flags&OBJECT_LIFETIME_MASK) == OBJECT_LIFETIME_STRONG) {
              // this object has a "normal" life-time, i.e.: it gets destroyed
              // when the last strong reference goes away
              if (curCount <= 0) {
                  // the last strong-reference got released, the object cannot
                  // be revived.
                  decWeak(id);
                  return false;
              }
  
              // here, curCount == INITIAL_STRONG_VALUE, which means
              // there never was a strong-reference, so we can try to
              // promote this object; we need to do that atomically.
              while (curCount > 0) {
                  if (impl->mStrong.compare_exchange_weak(curCount, curCount+1,
                          std::memory_order_relaxed)) {
                      break;
                  }
                  // the strong count has changed on us, we need to re-assert our
                  // situation (e.g.: another thread has inc/decStrong'ed us)
                  // curCount has been updated.
              }
  
              if (curCount <= 0) {
                  // promote() failed, some other thread destroyed us in the
                  // meantime (i.e.: strong count reached zero).
                  decWeak(id);
                  return false;
              }
          } else {
              // this object has an "extended" life-time, i.e.: it can be
              // revived from a weak-reference only.
              // Ask the object's implementation if it agrees to be revived
              if (!impl->mBase->onIncStrongAttempted(FIRST_INC_STRONG, id)) {
                  // it didn't so give-up.
                  decWeak(id);
                  return false;
              }
              // grab a strong-reference, which is always safe due to the
              // extended life-time.
              curCount = impl->mStrong.fetch_add(1, std::memory_order_relaxed);
              // If the strong reference count has already been incremented by
              // someone else, the implementor of onIncStrongAttempted() is holding
              // an unneeded reference.  So call onLastStrongRef() here to remove it.
              // (No, this is not pretty.)  Note that we MUST NOT do this if we
              // are in fact acquiring the first reference.
              if (curCount != 0 && curCount != INITIAL_STRONG_VALUE) {
                  impl->mBase->onLastStrongRef(id);
              }
          }
      }
      
      impl->addStrongRef(id);
  
  #if PRINT_REFS
      ALOGD("attemptIncStrong of %p from %p: cnt=%d\n", this, id, curCount);
  #endif
  
      // curCount is the value of mStrong before we incremented it.
      // Now we need to fix-up the count if it was INITIAL_STRONG_VALUE.
      // This must be done safely, i.e.: handle the case where several threads
      // were here in attemptIncStrong().
      // curCount > INITIAL_STRONG_VALUE is OK, and can happen if we're doing
      // this in the middle of another incStrong.  The subtraction is handled
      // by the thread that started with INITIAL_STRONG_VALUE.
      if (curCount == INITIAL_STRONG_VALUE) {
          impl->mStrong.fetch_sub(INITIAL_STRONG_VALUE,
                  std::memory_order_relaxed);
      }
  
      return true;
  }
  
  bool RefBase::weakref_type::attemptIncWeak(const void* id)
  {
      weakref_impl* const impl = static_cast<weakref_impl*>(this);
  
      int32_t curCount = impl->mWeak.load(std::memory_order_relaxed);
      while (curCount > 0) {
          if (impl->mWeak.compare_exchange_weak(curCount, curCount+1,
                  std::memory_order_relaxed)) {
              break;
          }
          // curCount has been updated.
      }
  
      if (curCount > 0) {
          impl->addWeakRef(id);
      }
  
      return curCount > 0;
  }
  
  int32_t RefBase::weakref_type::getWeakCount() const
  {
      // Debug only!
      return static_cast<const weakref_impl*>(this)->mWeak
              .load(std::memory_order_relaxed);
  }
  
  void RefBase::weakref_type::printRefs() const
  {
      static_cast<const weakref_impl*>(this)->printRefs();
  }
  
  void RefBase::weakref_type::trackMe(bool enable, bool retain)
  {
      static_cast<weakref_impl*>(this)->trackMe(enable, retain);
  }
  
  RefBase::weakref_type* RefBase::createWeak(const void* id) const
  {
      mRefs->incWeak(id);
      return mRefs;
  }
  
  RefBase::weakref_type* RefBase::getWeakRefs() const
  {
      return mRefs;
  }
  
  RefBase::RefBase()
      : mRefs(new weakref_impl(this))
  {
  }
  
  RefBase::~RefBase()
  {
      int32_t flags = mRefs->mFlags.load(std::memory_order_relaxed);
      // Life-time of this object is extended to WEAK, in
      // which case weakref_impl doesn't out-live the object and we
      // can free it now.
      if ((flags & OBJECT_LIFETIME_MASK) == OBJECT_LIFETIME_WEAK) {
          // It's possible that the weak count is not 0 if the object
          // re-acquired a weak reference in its destructor
          if (mRefs->mWeak.load(std::memory_order_relaxed) == 0) {
              delete mRefs;
          }
      } else if (mRefs->mStrong.load(std::memory_order_relaxed)
              == INITIAL_STRONG_VALUE) {
          // We never acquired a strong reference on this object.
          // TODO: Always report if we get here. Currently MediaMetadataRetriever
          // C++ objects are inconsistently managed and sometimes get here.
          // There may be other cases, but we believe they should all be fixed.
          delete mRefs;
      }
      // For debugging purposes, clear mRefs.  Ineffective against outstanding wp's.
      const_cast<weakref_impl*&>(mRefs) = NULL;
  }
  
  void RefBase::extendObjectLifetime(int32_t mode)
  {
      // Must be happens-before ordered with respect to construction or any
      // operation that could destroy the object.
      mRefs->mFlags.fetch_or(mode, std::memory_order_relaxed);
  }
  
  void RefBase::onFirstRef()
  {
  }
  
  void RefBase::onLastStrongRef(const void* /*id*/)
  {
  }
  
  bool RefBase::onIncStrongAttempted(uint32_t flags, const void* /*id*/)
  {
      return (flags&FIRST_INC_STRONG) ? true : false;
  }
  
  void RefBase::onLastWeakRef(const void* /*id*/)
  {
  }
  
  // ---------------------------------------------------------------------------
  
  #if DEBUG_REFS
  void RefBase::renameRefs(size_t n, const ReferenceRenamer& renamer) {
      for (size_t i=0 ; i<n ; i++) {
          renamer(i);
      }
  }
  #else
  void RefBase::renameRefs(size_t /*n*/, const ReferenceRenamer& /*renamer*/) { }
  #endif
  
  void RefBase::renameRefId(weakref_type* ref,
          const void* old_id, const void* new_id) {
      weakref_impl* const impl = static_cast<weakref_impl*>(ref);
      impl->renameStrongRefId(old_id, new_id);
      impl->renameWeakRefId(old_id, new_id);
  }
  
  void RefBase::renameRefId(RefBase* ref,
          const void* old_id, const void* new_id) {
      ref->mRefs->renameStrongRefId(old_id, new_id);
      ref->mRefs->renameWeakRefId(old_id, new_id);
  }
  
  }; // namespace android
  