DRTVWR-494: Defend LLInstanceTracker against multi-thread usage.

The previous implementation went to some effort to crash if anyone attempted
to create or destroy an LLInstanceTracker subclass instance during traversal.
That restriction is manageable within a single thread, but becomes unworkable
if it's possible that a given subclass might be used on more than one thread.

Remove LLInstanceTracker::instance_iter, beginInstances(), endInstances(),
also key_iter, beginKeys() and endKeys(). Instead, introduce key_snapshot()
and instance_snapshot(), the only means of iterating over LLInstanceTracker
instances. (These are intended to resemble functions, but in fact the current
implementation simply presents the classes.) Iterating over a captured
snapshot defends against container modifications during traversal. The term
'snapshot' reminds the coder that a new instance created during traversal will
not be considered. To defend against instance deletion during traversal, a
snapshot stores std::weak_ptrs which it lazily dereferences, skipping on the
fly any that have expired.

Dereferencing instance_snapshot::iterator gets you a reference rather than a
pointer. Because some use cases want to delete all existing instances, add an
instance_snapshot::deleteAll() method that extracts the pointer. Those cases
used to require explicitly copying instance pointers into a separate
container; instance_snapshot() now takes care of that. It remains the caller's
responsibility to ensure that all instances of that LLInstanceTracker subclass
were allocated on the heap.

Replace unkeyed static LLInstanceTracker::getInstance(T*) -- which returned
nullptr if that instance had been destroyed -- with new getWeak() method
returning std::weak_ptr<T>. Caller must detect expiration of that weak_ptr.

Adjust tests accordingly.

Use of std::weak_ptr to detect expired instances requires engaging
std::shared_ptr in the constructor. We now store shared_ptrs in the static
containers (std::map for keyed, std::set for unkeyed).

Make LLInstanceTrackerBase a template parameterized on the type of the static
data it manages. For that reason, hoist static data class declarations out of
the class definitions to an LLInstanceTrackerStuff namespace.

Remove the static atomic sIterationNestDepth and its methods incrementDepth(),
decrementDepth() and getDepth(), since they were used only to forbid creation
and destruction during traversal.

Add a std::mutex to static data. Introduce an internal LockStatic class that
locks the mutex while providing a pointer to static data, making that the only
way to access the static data.

The LLINSTANCETRACKER_DTOR_NOEXCEPT macro goes away because we no longer
expect ~LLInstanceTracker() to throw an exception in test programs.
That affects LLTrace::StatBase as well as LLInstanceTracker itself.

Adapt consumers to the new LLInstanceTracker API.

22 files changed, 548 insertions, 533 deletions

diff --git a/indra/llcommon/lleventtimer.cpp b/indra/llcommon/lleventtimer.cpp
index 0d96e03da4..3986dee3ac 100644
--- a/indra/llcommon/lleventtimer.cpp
+++ b/indra/llcommon/lleventtimer.cpp
@@ -58,9 +58,8 @@ LLEventTimer::~LLEventTimer()
 void LLEventTimer::updateClass() 
 {
 	std::list<LLEventTimer*> completed_timers;
-	for (instance_iter iter = beginInstances(); iter != endInstances(); ) 
+	for (auto& timer : instance_snapshot())
 	{
-		LLEventTimer& timer = *iter++;
 		F32 et = timer.mEventTimer.getElapsedTimeF32();
 		if (timer.mEventTimer.getStarted() && et > timer.mPeriod) {
 			timer.mEventTimer.reset();
diff --git a/indra/llcommon/llfasttimer.cpp b/indra/llcommon/llfasttimer.cpp
index 3d28cd15b0..08ea668964 100644
--- a/indra/llcommon/llfasttimer.cpp
+++ b/indra/llcommon/llfasttimer.cpp
@@ -193,27 +193,26 @@ TimeBlockTreeNode& BlockTimerStatHandle::getTreeNode() const
 
 void BlockTimer::bootstrapTimerTree()
 {
-	for (BlockTimerStatHandle::instance_tracker_t::instance_iter it = BlockTimerStatHandle::instance_tracker_t::beginInstances(), end_it = BlockTimerStatHandle::instance_tracker_t::endInstances(); 
-		it != end_it; 
-		++it)
+	for (auto& base : BlockTimerStatHandle::instance_snapshot())
 	{
-		BlockTimerStatHandle& timer = static_cast<BlockTimerStatHandle&>(*it);
+		// because of indirect derivation from LLInstanceTracker, have to downcast
+		BlockTimerStatHandle& timer = static_cast<BlockTimerStatHandle&>(base);
 		if (&timer == &BlockTimer::getRootTimeBlock()) continue;
 
 		// bootstrap tree construction by attaching to last timer to be on stack
 		// when this timer was called
 		if (timer.getParent() == &BlockTimer::getRootTimeBlock())
-{
+		{
 			TimeBlockAccumulator& accumulator = timer.getCurrentAccumulator();
 
 			if (accumulator.mLastCaller)
-	{
+			{
 				timer.setParent(accumulator.mLastCaller);
 				accumulator.mParent = accumulator.mLastCaller;
-		}
+			}
 			// no need to push up tree on first use, flag can be set spuriously
 			accumulator.mMoveUpTree = false;
-	}
+		}
 	}
 }
 
@@ -306,12 +305,10 @@ void BlockTimer::processTimes()
 	updateTimes();
 
 	// reset for next frame
-	for (BlockTimerStatHandle::instance_tracker_t::instance_iter it = BlockTimerStatHandle::instance_tracker_t::beginInstances(),
-			end_it = BlockTimerStatHandle::instance_tracker_t::endInstances();
-		it != end_it;
-		++it)
+	for (auto& base : BlockTimerStatHandle::instance_snapshot())
 	{
-		BlockTimerStatHandle& timer = static_cast<BlockTimerStatHandle&>(*it);
+		// because of indirect derivation from LLInstanceTracker, have to downcast
+		BlockTimerStatHandle& timer = static_cast<BlockTimerStatHandle&>(base);
 		TimeBlockAccumulator& accumulator = timer.getCurrentAccumulator();
 
 		accumulator.mLastCaller = NULL;
@@ -362,12 +359,10 @@ void BlockTimer::logStats()
 		LLSD sd;
 
 		{
-			for (BlockTimerStatHandle::instance_tracker_t::instance_iter it = BlockTimerStatHandle::instance_tracker_t::beginInstances(), 
-				end_it = BlockTimerStatHandle::instance_tracker_t::endInstances(); 
-				it != end_it; 
-			++it)
+			for (auto& base : BlockTimerStatHandle::instance_snapshot())
 			{
-				BlockTimerStatHandle& timer = static_cast<BlockTimerStatHandle&>(*it);
+				// because of indirect derivation from LLInstanceTracker, have to downcast
+				BlockTimerStatHandle& timer = static_cast<BlockTimerStatHandle&>(base);
 				LLTrace::PeriodicRecording& frame_recording = LLTrace::get_frame_recording();
 				sd[timer.getName()]["Time"] = (LLSD::Real) (frame_recording.getLastRecording().getSum(timer).value());	
 				sd[timer.getName()]["Calls"] = (LLSD::Integer) (frame_recording.getLastRecording().getSum(timer.callCount()));
diff --git a/indra/llcommon/llinstancetracker.cpp b/indra/llcommon/llinstancetracker.cpp
index 3f990f4869..accb4286e8 100644
--- a/indra/llcommon/llinstancetracker.cpp
+++ b/indra/llcommon/llinstancetracker.cpp
@@ -34,18 +34,5 @@
 // external library headers
 // other Linden headers
 
-void LLInstanceTrackerBase::StaticBase::incrementDepth()
-{
-	++sIterationNestDepth;
-}
-
-void LLInstanceTrackerBase::StaticBase::decrementDepth()
-{
-	llassert(sIterationNestDepth);
-	--sIterationNestDepth;
-}
-
-U32 LLInstanceTrackerBase::StaticBase::getDepth()
-{
-	return sIterationNestDepth;
-}
+// This .cpp file is required by our CMake test macro. It contributes no code
+// to the viewer.
diff --git a/indra/llcommon/llinstancetracker.h b/indra/llcommon/llinstancetracker.h
index 363d0bcbd5..76b201ad8c 100644
--- a/indra/llcommon/llinstancetracker.h
+++ b/indra/llcommon/llinstancetracker.h
@@ -28,354 +28,456 @@
 #ifndef LL_LLINSTANCETRACKER_H
 #define LL_LLINSTANCETRACKER_H
 
-#include <atomic>
 #include <map>
+#include <set>
+#include <vector>
 #include <typeinfo>
+#include <mutex>
+#include <memory>
+#include <type_traits>
 
-#include "llstringtable.h"
 #include <boost/iterator/transform_iterator.hpp>
 #include <boost/iterator/indirect_iterator.hpp>
+#include <boost/iterator/filter_iterator.hpp>
 
-// As of 2017-05-06, as far as nat knows, only clang supports __has_feature().
-// Unfortunately VS2013's preprocessor shortcut logic doesn't prevent it from
-// producing (fatal) warnings for defined(__clang__) && __has_feature(...).
-// Have to work around that.
-#if ! defined(__clang__)
-#define __has_feature(x) 0
-#endif // __clang__
-
-#if defined(LL_TEST_llinstancetracker) && __has_feature(cxx_noexcept)
-// ~LLInstanceTracker() performs llassert_always() validation. That's fine in
-// production code, since the llassert_always() is implemented as an LL_ERRS
-// message, which will crash-with-message. In our integration test executable,
-// though, this llassert_always() throws an exception instead so we can test
-// error conditions and continue running the test. However -- as of C++11,
-// destructors are implicitly noexcept(true). Unless we mark
-// ~LLInstanceTracker() noexcept(false), the test executable crashes even on
-// the ATTEMPT to throw.
-#define LLINSTANCETRACKER_DTOR_NOEXCEPT noexcept(false)
-#else
-// If we're building for production, or in fact building *any other* test, or
-// we're using a compiler that doesn't support __has_feature(), or we're not
-// compiling with a C++ version that supports noexcept -- don't specify it.
-#define LLINSTANCETRACKER_DTOR_NOEXCEPT
-#endif
-
+/*****************************************************************************
+*   LLInstanceTrackerBase
+*****************************************************************************/
 /**
  * Base class manages "class-static" data that must actually have singleton
  * semantics: one instance per process, rather than one instance per module as
  * sometimes happens with data simply declared static.
  */
+namespace LLInstanceTrackerStuff
+{
+    struct StaticBase
+    {
+        // We need to be able to lock static data while manipulating it.
+        typedef std::mutex mutex_t;
+        mutex_t mMutex;
+    };
+} // namespace LLInstanceTrackerStuff
+
+template <class Static>
 class LL_COMMON_API LLInstanceTrackerBase
 {
 protected:
-    /// It's not essential to derive your STATICDATA (for use with
-    /// getStatic()) from StaticBase; it's just that both known
-    /// implementations do.
-    struct StaticBase
+    typedef Static StaticData;
+
+    // Instantiate this class to obtain a pointer to the canonical static
+    // instance of class Static while holding a lock on that instance. Use of
+    // Static::mMutex presumes either that Static is derived from StaticBase,
+    // or that Static declares some other suitable mMutex.
+    class LockStatic
     {
-        StaticBase():
-            sIterationNestDepth(0)
+        typedef std::unique_lock<decltype(Static::mMutex)> lock_t;
+    public:
+        LockStatic():
+            mData(getStatic()),
+            mLock(mData->mMutex)
         {}
-
-		void incrementDepth();
-		void decrementDepth();
-		U32 getDepth();
-	private:
-#ifdef LL_WINDOWS
-		std::atomic_uint32_t sIterationNestDepth;
-#else
-		std::atomic_uint sIterationNestDepth;
-#endif
-	};
+        Static* get() const { return mData; }
+        operator Static*() const { return get(); }
+        Static* operator->() const { return get(); }
+        // sometimes we must explicitly unlock...
+        void unlock()
+        {
+            // but once we do, access is no longer permitted
+            mData = nullptr;
+            mLock.unlock();
+        }
+    protected:
+        Static* mData;
+        lock_t mLock;
+    private:
+        Static* getStatic()
+        {
+            static Static sData;
+            return &sData;
+        }
+    };
 };
 
-LL_COMMON_API void assert_main_thread();
-
+/*****************************************************************************
+*   LLInstanceTracker with key
+*****************************************************************************/
 enum EInstanceTrackerAllowKeyCollisions
 {
-	LLInstanceTrackerErrorOnCollision,
-	LLInstanceTrackerReplaceOnCollision
+    LLInstanceTrackerErrorOnCollision,
+    LLInstanceTrackerReplaceOnCollision
 };
 
+namespace LLInstanceTrackerStuff
+{
+    template <typename KEY, typename VALUE>
+    struct StaticMap: public StaticBase
+    {
+        typedef std::map<KEY, VALUE> InstanceMap;
+        InstanceMap mMap;
+    };
+} // LLInstanceTrackerStuff
+
 /// This mix-in class adds support for tracking all instances of the specified class parameter T
 /// The (optional) key associates a value of type KEY with a given instance of T, for quick lookup
 /// If KEY is not provided, then instances are stored in a simple set
 /// @NOTE: see explicit specialization below for default KEY==void case
-/// @NOTE: this class is not thread-safe unless used as read-only
-template<typename T, typename KEY = void, EInstanceTrackerAllowKeyCollisions KEY_COLLISION_BEHAVIOR = LLInstanceTrackerErrorOnCollision>
-class LLInstanceTracker : public LLInstanceTrackerBase
+template<typename T, typename KEY = void,
+         EInstanceTrackerAllowKeyCollisions KEY_COLLISION_BEHAVIOR = LLInstanceTrackerErrorOnCollision>
+class LLInstanceTracker :
+    public LLInstanceTrackerBase<LLInstanceTrackerStuff::StaticMap<KEY, std::shared_ptr<T>>>
 {
-	typedef LLInstanceTracker<T, KEY> self_t;
-	typedef typename std::multimap<KEY, T*> InstanceMap;
-	struct StaticData: public StaticBase
-	{
-		InstanceMap sMap;
-	};
-	static StaticData& getStatic() { static StaticData sData; return sData;}
-	static InstanceMap& getMap_() { return getStatic().sMap; }
+    typedef LLInstanceTrackerBase<LLInstanceTrackerStuff::StaticMap<KEY, std::shared_ptr<T>>> super;
+    using typename super::StaticData;
+    using typename super::LockStatic;
+    typedef typename StaticData::InstanceMap InstanceMap;
 
 public:
-	class instance_iter : public boost::iterator_facade<instance_iter, T, boost::forward_traversal_tag>
-	{
-	public:
-		typedef boost::iterator_facade<instance_iter, T, boost::forward_traversal_tag> super_t;
-		
-		instance_iter(const typename InstanceMap::iterator& it)
-		:	mIterator(it)
-		{
-			getStatic().incrementDepth();
-		}
-
-		~instance_iter()
-		{
-			getStatic().decrementDepth();
-		}
-
-
-	private:
-		friend class boost::iterator_core_access;
-
-		void increment() { mIterator++; }
-		bool equal(instance_iter const& other) const
-		{
-			return mIterator == other.mIterator;
-		}
-
-		T& dereference() const
-		{
-			return *(mIterator->second);
-		}
-
-		typename InstanceMap::iterator mIterator;
-	};
-
-	class key_iter : public boost::iterator_facade<key_iter, KEY, boost::forward_traversal_tag>
-	{
-	public:
-		typedef boost::iterator_facade<key_iter, KEY, boost::forward_traversal_tag> super_t;
-
-		key_iter(typename InstanceMap::iterator it)
-		:	mIterator(it)
-		{
-			getStatic().incrementDepth();
-		}
-
-		key_iter(const key_iter& other)
-		:	mIterator(other.mIterator)
-		{
-			getStatic().incrementDepth();
-		}
-
-		~key_iter()
-		{
-			getStatic().decrementDepth();
-		}
-
-
-	private:
-		friend class boost::iterator_core_access;
-
-		void increment() { mIterator++; }
-		bool equal(key_iter const& other) const
-		{
-			return mIterator == other.mIterator;
-		}
-
-		KEY& dereference() const
-		{
-			return const_cast<KEY&>(mIterator->first);
-		}
-
-		typename InstanceMap::iterator mIterator;
-	};
-
-	static T* getInstance(const KEY& k)
-	{
-		const InstanceMap& map(getMap_());
-		typename InstanceMap::const_iterator found = map.find(k);
-		return (found == map.end()) ? NULL : found->second;
-	}
-
-	static instance_iter beginInstances() 
-	{	
-		return instance_iter(getMap_().begin()); 
-	}
-
-	static instance_iter endInstances() 
-	{
-		return instance_iter(getMap_().end());
-	}
-
-	static S32 instanceCount() 
-	{ 
-		return getMap_().size(); 
-	}
-
-	static key_iter beginKeys()
-	{
-		return key_iter(getMap_().begin());
-	}
-	static key_iter endKeys()
-	{
-		return key_iter(getMap_().end());
-	}
+    // snapshot of std::pair<const KEY, std::shared_ptr<T>> pairs
+    class snapshot
+    {
+        // It's very important that what we store in this snapshot are
+        // weak_ptrs, NOT shared_ptrs. That's how we discover whether any
+        // instance has been deleted during the lifespan of a snapshot.
+        typedef std::vector<std::pair<const KEY, std::weak_ptr<T>>> VectorType;
+        // Dereferencing our iterator produces a std::shared_ptr for each
+        // instance that still exists. Since we store weak_ptrs, that involves
+        // two chained transformations:
+        // - a transform_iterator to lock the weak_ptr and return a shared_ptr
+        // - a filter_iterator to skip any shared_ptr that has become invalid.
+        // It is very important that we filter lazily, that is, during
+        // traversal. Any one of our stored weak_ptrs might expire during
+        // traversal.
+        typedef std::pair<const KEY, std::shared_ptr<T>> strong_pair;
+        // Note for future reference: nat has not yet had any luck (up to
+        // Boost 1.67) trying to use boost::transform_iterator with a hand-
+        // coded functor, only with actual functions. In my experience, an
+        // internal boost::result_of() operation fails, even with an explicit
+        // result_type typedef. But this works.
+        static strong_pair strengthen(typename VectorType::value_type& pair)
+        {
+            return { pair.first, pair.second.lock() };
+        }
+        static bool dead_skipper(const strong_pair& pair)
+        {
+            return bool(pair.second);
+        }
+
+    public:
+        snapshot():
+            // populate our vector with a snapshot of (locked!) InstanceMap
+            // note, this assigns pair<KEY, shared_ptr> to pair<KEY, weak_ptr>
+            mData(mLock->mMap.begin(), mLock->mMap.end())
+        {
+            // release the lock once we've populated mData
+            mLock.unlock();
+        }
+
+        // You can't make a transform_iterator (or anything else) that
+        // literally stores a C++ function (decltype(strengthen)) -- but you
+        // can make a transform_iterator based on a _function pointer._
+        typedef boost::transform_iterator<decltype(strengthen)*,
+                                          typename VectorType::iterator> strong_iterator;
+        typedef boost::filter_iterator<decltype(dead_skipper)*, strong_iterator> iterator;
+
+        iterator begin() { return make_iterator(mData.begin()); }
+        iterator end()   { return make_iterator(mData.end()); }
+
+    private:
+        iterator make_iterator(typename VectorType::iterator iter)
+        {
+            // transform_iterator only needs the base iterator and the transform.
+            // filter_iterator wants the predicate and both ends of the range.
+            return iterator(dead_skipper,
+                            strong_iterator(iter, strengthen),
+                            strong_iterator(mData.end(), strengthen));
+        }
+
+        LockStatic mLock;           // lock static data during construction
+        VectorType mData;
+    };
+
+    // iterate over this for references to each instance
+    class instance_snapshot: public snapshot
+    {
+    private:
+        static T& instance_getter(typename snapshot::iterator::reference pair)
+        {
+            return *pair.second;
+        }
+    public:
+        typedef boost::transform_iterator<decltype(instance_getter)*,
+                                          typename snapshot::iterator> iterator;
+        iterator begin() { return iterator(snapshot::begin(), instance_getter); }
+        iterator end()   { return iterator(snapshot::end(),   instance_getter); }
+
+        void deleteAll()
+        {
+            for (auto it(snapshot::begin()), end(snapshot::end()); it != end; ++it)
+            {
+                delete it->second.get();
+            }
+        }
+    };                   
+
+    // iterate over this for each key
+    class key_snapshot: public snapshot
+    {
+    private:
+        static KEY key_getter(typename snapshot::iterator::reference pair)
+        {
+            return pair.first;
+        }
+    public:
+        typedef boost::transform_iterator<decltype(key_getter)*,
+                                          typename snapshot::iterator> iterator;
+        iterator begin() { return iterator(snapshot::begin(), key_getter); }
+        iterator end()   { return iterator(snapshot::end(),   key_getter); }
+    };
+
+    static T* getInstance(const KEY& k)
+    {
+        LockStatic lock;
+        const InstanceMap& map(lock->mMap);
+        typename InstanceMap::const_iterator found = map.find(k);
+        return (found == map.end()) ? NULL : found->second.get();
+    }
+
+    static S32 instanceCount() 
+    { 
+        return LockStatic()->mMap.size(); 
+    }
 
 protected:
-	LLInstanceTracker(const KEY& key) 
-	{ 
-		// make sure static data outlives all instances
-		getStatic();
-		add_(key); 
-	}
-	virtual ~LLInstanceTracker() LLINSTANCETRACKER_DTOR_NOEXCEPT
-	{ 
-		// it's unsafe to delete instances of this type while all instances are being iterated over.
-		llassert_always(getStatic().getDepth() == 0);
-		remove_();
-	}
-	virtual void setKey(KEY key) { remove_(); add_(key); }
-	virtual const KEY& getKey() const { return mInstanceKey; }
+    LLInstanceTracker(const KEY& key) 
+    {
+        // We do not intend to manage the lifespan of this object with
+        // shared_ptr, so give it a no-op deleter. We store shared_ptrs in our
+        // InstanceMap specifically so snapshot can store weak_ptrs so we can
+        // detect deletions during traversals.
+        std::shared_ptr<T> ptr(static_cast<T*>(this), [](T*){});
+        LockStatic lock;
+        add_(lock, key, ptr);
+    }
+public:
+    virtual ~LLInstanceTracker()
+    {
+        LockStatic lock;
+        remove_(lock);
+    }
+protected:
+    virtual void setKey(KEY key)
+    {
+        LockStatic lock;
+        // Even though the shared_ptr we store in our map has a no-op deleter
+        // for T itself, letting the use count decrement to 0 will still
+        // delete the use-count object. Capture the shared_ptr we just removed
+        // and re-add it to the map with the new key.
+        auto ptr = remove_(lock);
+        add_(lock, key, ptr);
+    }
+public:
+    virtual const KEY& getKey() const { return mInstanceKey; }
 
 private:
-	LLInstanceTracker( const LLInstanceTracker& );
-	const LLInstanceTracker& operator=( const LLInstanceTracker& );
-
-	void add_(const KEY& key) 
-	{ 
-		mInstanceKey = key; 
-		InstanceMap& map = getMap_();
-		typename InstanceMap::iterator insertion_point_it = map.lower_bound(key);
-		if (insertion_point_it != map.end() 
-			&& insertion_point_it->first == key)
-		{ // found existing entry with that key
-			switch(KEY_COLLISION_BEHAVIOR)
-			{
-				case LLInstanceTrackerErrorOnCollision:
-				{
-					// use assert here instead of LL_ERRS(), otherwise the error will be ignored since this call is made during global object initialization
-					llassert_always_msg(false, "Instance with this same key already exists!");
-					break;
-				}
-				case LLInstanceTrackerReplaceOnCollision:
-				{
-					// replace pointer, but leave key (should have compared equal anyway)
-					insertion_point_it->second = static_cast<T*>(this);
-					break;
-				}
-				default:
-					break;
-			}
-		}
-		else
-		{ // new key
-			map.insert(insertion_point_it, std::make_pair(key, static_cast<T*>(this)));
-		}
-	}
-	void remove_()
-	{
-		InstanceMap& map = getMap_();
-		typename InstanceMap::iterator iter = map.find(mInstanceKey);
-		if (iter != map.end())
-		{
-			map.erase(iter);
-		}
-	}
+    LLInstanceTracker( const LLInstanceTracker& ) = delete;
+    LLInstanceTracker& operator=( const LLInstanceTracker& ) = delete;
+
+    // for logging
+    template <typename K>
+    static K report(K key) { return key; }
+    static std::string report(const std::string& key) { return "'" + key + "'"; }
+    static std::string report(const char* key) { return report(std::string(key)); }
+
+    // caller must instantiate LockStatic
+    void add_(LockStatic& lock, const KEY& key, const std::shared_ptr<T>& ptr) 
+    { 
+        mInstanceKey = key; 
+        InstanceMap& map = lock->mMap;
+        switch(KEY_COLLISION_BEHAVIOR)
+        {
+        case LLInstanceTrackerErrorOnCollision:
+        {
+            // map stores shared_ptr to self
+            auto pair = map.emplace(key, ptr);
+            if (! pair.second)
+            {
+                LL_ERRS("LLInstanceTracker") << "Instance with key " << report(key)
+                                             << " already exists!" << LL_ENDL;
+            }
+            break;
+        }
+        case LLInstanceTrackerReplaceOnCollision:
+            map[key] = ptr;
+            break;
+        default:
+            break;
+        }
+    }
+    std::shared_ptr<T> remove_(LockStatic& lock)
+    {
+        InstanceMap& map = lock->mMap;
+        typename InstanceMap::iterator iter = map.find(mInstanceKey);
+        if (iter != map.end())
+        {
+            auto ret = iter->second;
+            map.erase(iter);
+            return ret;
+        }
+        return {};
+    }
 
 private:
-	KEY mInstanceKey;
+    KEY mInstanceKey;
 };
 
+/*****************************************************************************
+*   LLInstanceTracker without key
+*****************************************************************************/
+namespace LLInstanceTrackerStuff
+{
+    template <typename VALUE>
+    struct StaticSet: public StaticBase
+    {
+        typedef std::set<VALUE> InstanceSet;
+        InstanceSet mSet;
+    };
+} // LLInstanceTrackerStuff
+
+// TODO:
+// - For the case of omitted KEY template parameter, consider storing
+//   std::map<T*, std::shared_ptr<T>> instead of std::set<std::shared_ptr<T>>.
+//   That might let us share more of the implementation between KEY and
+//   non-KEY LLInstanceTracker subclasses.
+// - Even if not that, consider trying to unify the snapshot implementations.
+//   The trouble is that the 'iterator' published by each (and by their
+//   subclasses) must reflect the specific type of the callables that
+//   distinguish them. (Maybe make instance_snapshot() and key_snapshot()
+//   factory functions that pass lambdas to a factory function for the generic
+//   template class?)
+
 /// explicit specialization for default case where KEY is void
 /// use a simple std::set<T*>
 template<typename T, EInstanceTrackerAllowKeyCollisions KEY_COLLISION_BEHAVIOR>
-class LLInstanceTracker<T, void, KEY_COLLISION_BEHAVIOR> : public LLInstanceTrackerBase
+class LLInstanceTracker<T, void, KEY_COLLISION_BEHAVIOR> :
+    public LLInstanceTrackerBase<LLInstanceTrackerStuff::StaticSet<std::shared_ptr<T>>>
 {
-	typedef LLInstanceTracker<T, void> self_t;
-	typedef typename std::set<T*> InstanceSet;
-	struct StaticData: public StaticBase
-	{
-		InstanceSet sSet;
-	};
-	static StaticData& getStatic() { static StaticData sData; return sData; }
-	static InstanceSet& getSet_() { return getStatic().sSet; }
+    typedef LLInstanceTrackerBase<LLInstanceTrackerStuff::StaticSet<std::shared_ptr<T>>> super;
+    using typename super::StaticData;
+    using typename super::LockStatic;
+    typedef typename StaticData::InstanceSet InstanceSet;
 
 public:
+    /**
+     * Storing a dumb T* somewhere external is a bad idea, since
+     * LLInstanceTracker subclasses are explicitly destroyed rather than
+     * managed by smart pointers. It's legal to declare stack instances of an
+     * LLInstanceTracker subclass. But it's reasonable to store a
+     * std::weak_ptr<T>, which will become invalid when the T instance is
+     * destroyed.
+     */
+    std::weak_ptr<T> getWeak()
+    {
+        return mSelf;
+    }
+    
+    static S32 instanceCount() { return LockStatic()->mSet.size(); }
 
-	/**
-	 * Does a particular instance still exist? Of course, if you already have
-	 * a T* in hand, you need not call getInstance() to @em locate the
-	 * instance -- unlike the case where getInstance() accepts some kind of
-	 * key. Nonetheless this method is still useful to @em validate a
-	 * particular T*, since each instance's destructor removes itself from the
-	 * underlying set.
-	 */
-	static T* getInstance(T* k)
-	{
-		const InstanceSet& set(getSet_());
-		typename InstanceSet::const_iterator found = set.find(k);
-		return (found == set.end())? NULL : *found;
-	}
-	static S32 instanceCount() { return getSet_().size(); }
-
-	class instance_iter : public boost::iterator_facade<instance_iter, T, boost::forward_traversal_tag>
-	{
-	public:
-		instance_iter(const typename InstanceSet::iterator& it)
-		:	mIterator(it)
-		{
-			getStatic().incrementDepth();
-		}
-
-		instance_iter(const instance_iter& other)
-		:	mIterator(other.mIterator)
-		{
-			getStatic().incrementDepth();
-		}
-
-		~instance_iter()
-		{
-			getStatic().decrementDepth();
-		}
-
-	private:
-		friend class boost::iterator_core_access;
-
-		void increment() { mIterator++; }
-		bool equal(instance_iter const& other) const
-		{
-			return mIterator == other.mIterator;
-		}
-
-		T& dereference() const
-		{
-			return **mIterator;
-		}
-
-		typename InstanceSet::iterator mIterator;
-	};
-
-	static instance_iter beginInstances() {	return instance_iter(getSet_().begin()); }
-	static instance_iter endInstances() { return instance_iter(getSet_().end()); }
+    // snapshot of std::shared_ptr<T> pointers
+    class snapshot
+    {
+        // It's very important that what we store in this snapshot are
+        // weak_ptrs, NOT shared_ptrs. That's how we discover whether any
+        // instance has been deleted during the lifespan of a snapshot.
+        typedef std::vector<std::weak_ptr<T>> VectorType;
+        // Dereferencing our iterator produces a std::shared_ptr for each
+        // instance that still exists. Since we store weak_ptrs, that involves
+        // two chained transformations:
+        // - a transform_iterator to lock the weak_ptr and return a shared_ptr
+        // - a filter_iterator to skip any shared_ptr that has become invalid.
+        typedef std::shared_ptr<T> strong_ptr;
+        static strong_ptr strengthen(typename VectorType::value_type& ptr)
+        {
+            return ptr.lock();
+        }
+        static bool dead_skipper(const strong_ptr& ptr)
+        {
+            return bool(ptr);
+        }
+
+    public:
+        snapshot():
+            // populate our vector with a snapshot of (locked!) InstanceSet
+            // note, this assigns stored shared_ptrs to weak_ptrs for snapshot
+            mData(mLock->mSet.begin(), mLock->mSet.end())
+        {
+            // release the lock once we've populated mData
+            mLock.unlock();
+        }
+
+        typedef boost::transform_iterator<decltype(strengthen)*,
+                                          typename VectorType::iterator> strong_iterator;
+        typedef boost::filter_iterator<decltype(dead_skipper)*, strong_iterator> iterator;
+
+        iterator begin() { return make_iterator(mData.begin()); }
+        iterator end()   { return make_iterator(mData.end()); }
+
+    private:
+        iterator make_iterator(typename VectorType::iterator iter)
+        {
+            // transform_iterator only needs the base iterator and the transform.
+            // filter_iterator wants the predicate and both ends of the range.
+            return iterator(dead_skipper,
+                            strong_iterator(iter, strengthen),
+                            strong_iterator(mData.end(), strengthen));
+        }
+
+        LockStatic mLock;           // lock static data during construction
+        VectorType mData;
+    };
+
+    // iterate over this for references to each instance
+    struct instance_snapshot: public snapshot
+    {
+        typedef boost::indirect_iterator<typename snapshot::iterator> iterator;
+        iterator begin() { return iterator(snapshot::begin()); }
+        iterator end()   { return iterator(snapshot::end()); }
+
+        void deleteAll()
+        {
+            for (auto it(snapshot::begin()), end(snapshot::end()); it != end; ++it)
+            {
+                delete it->get();
+            }
+        }
+    };
 
 protected:
-	LLInstanceTracker()
-	{
-		// make sure static data outlives all instances
-		getStatic();
-		getSet_().insert(static_cast<T*>(this));
-	}
-	virtual ~LLInstanceTracker() LLINSTANCETRACKER_DTOR_NOEXCEPT
-	{
-		// it's unsafe to delete instances of this type while all instances are being iterated over.
-		llassert_always(getStatic().getDepth() == 0);
-		getSet_().erase(static_cast<T*>(this));
-	}
-
-	LLInstanceTracker(const LLInstanceTracker& other)
-	{
-		getSet_().insert(static_cast<T*>(this));
-	}
+    LLInstanceTracker()
+    {
+        // Since we do not intend for this shared_ptr to manage lifespan, give
+        // it a no-op deleter.
+        std::shared_ptr<T> ptr(static_cast<T*>(this), [](T*){});
+        // save corresponding weak_ptr for future reference
+        mSelf = ptr;
+        // Also store it in our class-static set to track this instance.
+        LockStatic()->mSet.emplace(ptr);
+    }
+public:
+    virtual ~LLInstanceTracker()
+    {
+        // convert weak_ptr to shared_ptr because that's what we store in our
+        // InstanceSet
+        LockStatic()->mSet.erase(mSelf.lock());
+    }
+protected:
+    LLInstanceTracker(const LLInstanceTracker& other):
+        LLInstanceTracker()
+    {}
+
+private:
+    // Storing a weak_ptr to self is a bit like deriving from
+    // std::enable_shared_from_this(), except more explicit.
+    std::weak_ptr<T> mSelf;
 };
 
 #endif
diff --git a/indra/llcommon/llleaplistener.cpp b/indra/llcommon/llleaplistener.cpp
index fa5730f112..f50bacb1e8 100644
--- a/indra/llcommon/llleaplistener.cpp
+++ b/indra/llcommon/llleaplistener.cpp
@@ -228,13 +228,11 @@ void LLLeapListener::getAPIs(const LLSD& request) const
 {
     Response reply(LLSD(), request);
 
-    for (LLEventAPI::instance_iter eai(LLEventAPI::beginInstances()),
-             eaend(LLEventAPI::endInstances());
-         eai != eaend; ++eai)
+    for (auto& ea : LLEventAPI::instance_snapshot())
     {
         LLSD info;
-        info["desc"] = eai->getDesc();
-        reply[eai->getName()] = info;
+        info["desc"] = ea.getDesc();
+        reply[ea.getName()] = info;
     }
 }
 
diff --git a/indra/llcommon/llthreadlocalstorage.cpp b/indra/llcommon/llthreadlocalstorage.cpp
index 8cef05caac..d8a063e8d5 100644
--- a/indra/llcommon/llthreadlocalstorage.cpp
+++ b/indra/llcommon/llthreadlocalstorage.cpp
@@ -93,11 +93,9 @@ void LLThreadLocalPointerBase::initAllThreadLocalStorage()
 {
 	if (!sInitialized)
 	{
-		for (LLInstanceTracker<LLThreadLocalPointerBase>::instance_iter it = beginInstances(), end_it = endInstances();
-			it != end_it;
-			++it)
+		for (auto& base : instance_snapshot())
 		{
-			(*it).initStorage();
+			base.initStorage();
 		}
 		sInitialized = true;
 	}
@@ -108,11 +106,9 @@ void LLThreadLocalPointerBase::destroyAllThreadLocalStorage()
 {
 	if (sInitialized)
 	{
-		//for (LLInstanceTracker<LLThreadLocalPointerBase>::instance_iter it = beginInstances(), end_it = endInstances();
-		//	it != end_it;
-		//	++it)
+		//for (auto& base : instance_snapshot())
 		//{
-		//	(*it).destroyStorage();
+		//	base.destroyStorage();
 		//}
 		sInitialized = false;
 	}
diff --git a/indra/llcommon/lltrace.h b/indra/llcommon/lltrace.h
index 79ff55b739..0d0cd6f581 100644
--- a/indra/llcommon/lltrace.h
+++ b/indra/llcommon/lltrace.h
@@ -57,7 +57,7 @@ class StatBase
 {
 public:
 	StatBase(const char* name, const char* description);
-	virtual ~StatBase() LLINSTANCETRACKER_DTOR_NOEXCEPT	{}
+	virtual ~StatBase()	{}
 	virtual const char* getUnitLabel() const;
 
 	const std::string& getName() const { return mName; }
diff --git a/indra/llcommon/lltracethreadrecorder.cpp b/indra/llcommon/lltracethreadrecorder.cpp
index 181fc2f058..025dc57044 100644
--- a/indra/llcommon/lltracethreadrecorder.cpp
+++ b/indra/llcommon/lltracethreadrecorder.cpp
@@ -28,6 +28,7 @@
 #include "lltracethreadrecorder.h"
 #include "llfasttimer.h"
 #include "lltrace.h"
+#include "llstl.h"
 
 namespace LLTrace
 {
@@ -64,16 +65,15 @@ void ThreadRecorder::init()
 	activate(&mThreadRecordingBuffers);
 
 	// initialize time block parent pointers
-	for (BlockTimerStatHandle::instance_tracker_t::instance_iter it = BlockTimerStatHandle::instance_tracker_t::beginInstances(), end_it = BlockTimerStatHandle::instance_tracker_t::endInstances(); 
-		it != end_it; 
-		++it)
+	for (auto& base : BlockTimerStatHandle::instance_snapshot())
 	{
-		BlockTimerStatHandle& time_block = static_cast<BlockTimerStatHandle&>(*it);
-		TimeBlockTreeNode& tree_node = mTimeBlockTreeNodes[it->getIndex()];
+		// because of indirect derivation from LLInstanceTracker, have to downcast
+		BlockTimerStatHandle& time_block = static_cast<BlockTimerStatHandle&>(base);
+		TimeBlockTreeNode& tree_node = mTimeBlockTreeNodes[time_block.getIndex()];
 		tree_node.mBlock = &time_block;
 		tree_node.mParent = &root_time_block;
 
-		it->getCurrentAccumulator().mParent = &root_time_block;
+		time_block.getCurrentAccumulator().mParent = &root_time_block;
 	}
 
 	mRootTimer = new BlockTimer(root_time_block);
diff --git a/indra/llcommon/tests/llinstancetracker_test.cpp b/indra/llcommon/tests/llinstancetracker_test.cpp
index d94fc0c56d..9b89159625 100644
--- a/indra/llcommon/tests/llinstancetracker_test.cpp
+++ b/indra/llcommon/tests/llinstancetracker_test.cpp
@@ -41,7 +41,6 @@
 #include <boost/scoped_ptr.hpp>
 // other Linden headers
 #include "../test/lltut.h"
-#include "wrapllerrs.h"
 
 struct Badness: public std::runtime_error
 {
@@ -112,24 +111,22 @@ namespace tut
     void object::test<2>()
     {
         ensure_equals(Unkeyed::instanceCount(), 0);
-        Unkeyed* dangling = NULL;
+        std::weak_ptr<Unkeyed> dangling;
         {
             Unkeyed one;
             ensure_equals(Unkeyed::instanceCount(), 1);
-            Unkeyed* found = Unkeyed::getInstance(&one);
-            ensure_equals(found, &one);
+            std::weak_ptr<Unkeyed> found = one.getWeak();
+            ensure(! found.expired());
             {
                 boost::scoped_ptr<Unkeyed> two(new Unkeyed);
                 ensure_equals(Unkeyed::instanceCount(), 2);
-                Unkeyed* found = Unkeyed::getInstance(two.get());
-                ensure_equals(found, two.get());
             }
             ensure_equals(Unkeyed::instanceCount(), 1);
-            // store an unwise pointer to a temp Unkeyed instance
-            dangling = &one;
+            // store a weak pointer to a temp Unkeyed instance
+            dangling = found;
         } // make that instance vanish
         // check the now-invalid pointer to the destroyed instance
-        ensure("getInstance(T*) failed to track destruction", ! Unkeyed::getInstance(dangling));
+        ensure("weak_ptr<Unkeyed> failed to track destruction", dangling.expired());
         ensure_equals(Unkeyed::instanceCount(), 0);
     }
 
@@ -142,7 +139,8 @@ namespace tut
         // reimplement LLInstanceTracker using, say, a hash map instead of a
         // std::map. We DO insist that every key appear exactly once.
         typedef std::vector<std::string> StringVector;
-        StringVector keys(Keyed::beginKeys(), Keyed::endKeys());
+        auto snap = Keyed::key_snapshot();
+        StringVector keys(snap.begin(), snap.end());
         std::sort(keys.begin(), keys.end());
         StringVector::const_iterator ki(keys.begin());
         ensure_equals(*ki++, "one");
@@ -153,17 +151,15 @@ namespace tut
         ensure("didn't reach end", ki == keys.end());
 
         // Use a somewhat different approach to order independence with
-        // beginInstances(): explicitly capture the instances we know in a
+        // instance_snapshot(): explicitly capture the instances we know in a
         // set, and delete them as we iterate through.
         typedef std::set<Keyed*> InstanceSet;
         InstanceSet instances;
         instances.insert(&one);
         instances.insert(&two);
         instances.insert(&three);
-        for (Keyed::instance_iter ii(Keyed::beginInstances()), iend(Keyed::endInstances());
-             ii != iend; ++ii)
+        for (auto& ref : Keyed::instance_snapshot())
         {
-            Keyed& ref = *ii;
             ensure_equals("spurious instance", instances.erase(&ref), 1);
         }
         ensure_equals("unreported instance", instances.size(), 0);
@@ -180,11 +176,10 @@ namespace tut
         instances.insert(&two);
         instances.insert(&three);
 
-		for (Unkeyed::instance_iter ii(Unkeyed::beginInstances()), iend(Unkeyed::endInstances()); ii != iend; ++ii)
-		{
-			Unkeyed& ref = *ii;
-			ensure_equals("spurious instance", instances.erase(&ref), 1);
-		}
+        for (auto& ref : Unkeyed::instance_snapshot())
+        {
+            ensure_equals("spurious instance", instances.erase(&ref), 1);
+        }
 
         ensure_equals("unreported instance", instances.size(), 0);
     }
@@ -192,49 +187,49 @@ namespace tut
     template<> template<>
     void object::test<5>()
     {
-        set_test_name("delete Keyed with outstanding instance_iter");
-        std::string what;
-        Keyed* keyed = new Keyed("delete Keyed with outstanding instance_iter");
-        {
-            WrapLLErrs wrapper;
-            Keyed::instance_iter i(Keyed::beginInstances());
-            what = wrapper.catch_llerrs([&keyed](){
-                    delete keyed;
-                });
-        }
-        ensure(! what.empty());
+        std::string desc("delete Keyed with outstanding instance_snapshot");
+        set_test_name(desc);
+        Keyed* keyed = new Keyed(desc);
+        // capture a snapshot but do not yet traverse it
+        auto snapshot = Keyed::instance_snapshot();
+        // delete the one instance
+        delete keyed;
+        // traversing the snapshot should reflect the deletion
+        // avoid ensure_equals() because it requires the ability to stream the
+        // two values to std::ostream
+        ensure(snapshot.begin() == snapshot.end());
     }
 
     template<> template<>
     void object::test<6>()
     {
-        set_test_name("delete Keyed with outstanding key_iter");
-        std::string what;
-        Keyed* keyed = new Keyed("delete Keyed with outstanding key_it");
-        {
-            WrapLLErrs wrapper;
-            Keyed::key_iter i(Keyed::beginKeys());
-            what = wrapper.catch_llerrs([&keyed](){
-                    delete keyed;
-                });
-        }
-        ensure(! what.empty());
+        std::string desc("delete Keyed with outstanding key_snapshot");
+        set_test_name(desc);
+        Keyed* keyed = new Keyed(desc);
+        // capture a snapshot but do not yet traverse it
+        auto snapshot = Keyed::key_snapshot();
+        // delete the one instance
+        delete keyed;
+        // traversing the snapshot should reflect the deletion
+        // avoid ensure_equals() because it requires the ability to stream the
+        // two values to std::ostream
+        ensure(snapshot.begin() == snapshot.end());
     }
 
     template<> template<>
     void object::test<7>()
     {
-        set_test_name("delete Unkeyed with outstanding instance_iter");
+        set_test_name("delete Unkeyed with outstanding instance_snapshot");
         std::string what;
         Unkeyed* unkeyed = new Unkeyed;
-        {
-            WrapLLErrs wrapper;
-            Unkeyed::instance_iter i(Unkeyed::beginInstances());
-            what = wrapper.catch_llerrs([&unkeyed](){
-                    delete unkeyed;
-                });
-        }
-        ensure(! what.empty());
+        // capture a snapshot but do not yet traverse it
+        auto snapshot = Unkeyed::instance_snapshot();
+        // delete the one instance
+        delete unkeyed;
+        // traversing the snapshot should reflect the deletion
+        // avoid ensure_equals() because it requires the ability to stream the
+        // two values to std::ostream
+        ensure(snapshot.begin() == snapshot.end());
     }
 
     template<> template<>
@@ -246,11 +241,9 @@ namespace tut
         // We can't use the iterator-range InstanceSet constructor because
         // beginInstances() returns an iterator that dereferences to an
         // Unkeyed&, not an Unkeyed*.
-        for (Unkeyed::instance_iter uki(Unkeyed::beginInstances()),
-                                    ukend(Unkeyed::endInstances());
-             uki != ukend; ++uki)
+        for (auto& ref : Unkeyed::instance_snapshot())
         {
-            existing.insert(&*uki);
+            existing.insert(&ref);
         }
         try
         {
@@ -273,11 +266,9 @@ namespace tut
         // instances was also present in the original set. If that's not true,
         // it's because our new Unkeyed ended up in the updated set despite
         // its constructor exception.
-        for (Unkeyed::instance_iter uki(Unkeyed::beginInstances()),
-                                    ukend(Unkeyed::endInstances());
-             uki != ukend; ++uki)
+        for (auto& ref : Unkeyed::instance_snapshot())
         {
-            ensure("failed to remove instance", existing.find(&*uki) != existing.end());
+            ensure("failed to remove instance", existing.find(&ref) != existing.end());
         }
     }
 } // namespace tut
diff --git a/indra/llcommon/tests/llleap_test.cpp b/indra/llcommon/tests/llleap_test.cpp
index bf0a74d10d..9d71e327d8 100644
--- a/indra/llcommon/tests/llleap_test.cpp
+++ b/indra/llcommon/tests/llleap_test.cpp
@@ -49,24 +49,28 @@ const size_t BUFFERED_LENGTH = 1023*1024; // try wrangling just under a megabyte
 
 #endif
 
-void waitfor(const std::vector<LLLeap*>& instances, int timeout=60)
+// capture std::weak_ptrs to LLLeap instances so we can tell when they expire
+typedef std::vector<std::weak_ptr<LLLeap>> LLLeapVector;
+
+void waitfor(const LLLeapVector& instances, int timeout=60)
 {
     int i;
     for (i = 0; i < timeout; ++i)
     {
         // Every iteration, test whether any of the passed LLLeap instances
         // still exist (are still running).
-        std::vector<LLLeap*>::const_iterator vli(instances.begin()), vlend(instances.end());
-        for ( ; vli != vlend; ++vli)
+        bool found = false;
+        for (auto& ptr : instances)
         {
-            // getInstance() returns NULL if it's terminated/gone, non-NULL if
-            // it's still running
-            if (LLLeap::getInstance(*vli))
+            if (! ptr.expired())
+            {
+                found = true;
                 break;
+            }
         }
         // If we made it through all of 'instances' without finding one that's
         // still running, we're done.
-        if (vli == vlend)
+        if (! found)
         {
 /*==========================================================================*|
             std::cout << instances.size() << " LLLeap instances terminated in "
@@ -86,8 +90,8 @@ void waitfor(const std::vector<LLLeap*>& instances, int timeout=60)
 
 void waitfor(LLLeap* instance, int timeout=60)
 {
-    std::vector<LLLeap*> instances;
-    instances.push_back(instance);
+    LLLeapVector instances;
+    instances.push_back(instance->getWeak());
     waitfor(instances, timeout);
 }
 
@@ -218,11 +222,11 @@ namespace tut
         NamedTempFile script("py",
                              "import time\n"
                              "time.sleep(1)\n");
-        std::vector<LLLeap*> instances;
+        LLLeapVector instances;
         instances.push_back(LLLeap::create(get_test_name(),
-                                           sv(list_of(PYTHON)(script.getName()))));
+                                           sv(list_of(PYTHON)(script.getName())))->getWeak());
         instances.push_back(LLLeap::create(get_test_name(),
-                                           sv(list_of(PYTHON)(script.getName()))));
+                                           sv(list_of(PYTHON)(script.getName())))->getWeak());
         // In this case we're simply establishing that two LLLeap instances
         // can coexist without throwing exceptions or bombing in any other
         // way. Wait for them to terminate.
diff --git a/indra/llrender/llgl.cpp b/indra/llrender/llgl.cpp
index c0f0cec80b..a24de45fde 100644
--- a/indra/llrender/llgl.cpp
+++ b/indra/llrender/llgl.cpp
@@ -2376,9 +2376,8 @@ void LLGLNamePool::release(GLuint name)
 //static
 void LLGLNamePool::upkeepPools()
 {
-	for (tracker_t::instance_iter iter = beginInstances(); iter != endInstances(); ++iter)
+	for (auto& pool : instance_snapshot())
 	{
-		LLGLNamePool & pool = *iter;
 		pool.upkeep();
 	}
 }
@@ -2386,9 +2385,8 @@ void LLGLNamePool::upkeepPools()
 //static
 void LLGLNamePool::cleanupPools()
 {
-	for (tracker_t::instance_iter iter = beginInstances(); iter != endInstances(); ++iter)
+	for (auto& pool : instance_snapshot())
 	{
-		LLGLNamePool & pool = *iter;
 		pool.cleanup();
 	}
 }
diff --git a/indra/llui/llconsole.cpp b/indra/llui/llconsole.cpp
index 5f50e46233..7817d99aef 100644
--- a/indra/llui/llconsole.cpp
+++ b/indra/llui/llconsole.cpp
@@ -369,9 +369,9 @@ LLConsole::Paragraph::Paragraph (LLWString str, const LLColor4 &color, F32 add_t
 // static
 void LLConsole::updateClass()
 {	
-	for (instance_iter it = beginInstances(); it != endInstances(); ++it)
+	for (auto& con : instance_snapshot())
 	{
-		it->update();
+		con.update();
 	} 
 }
 
diff --git a/indra/llui/lllayoutstack.cpp b/indra/llui/lllayoutstack.cpp
index 4a464b3507..4aae1e374b 100644
--- a/indra/llui/lllayoutstack.cpp
+++ b/indra/llui/lllayoutstack.cpp
@@ -636,10 +636,10 @@ void LLLayoutStack::createResizeBar(LLLayoutPanel* panelp)
 //static 
 void LLLayoutStack::updateClass()
 {
-	for (instance_iter it = beginInstances(); it != endInstances(); ++it)
+	for (auto& layout : instance_snapshot())
 	{
-		it->updateLayout();
-		it->mAnimatedThisFrame = false;
+		layout.updateLayout();
+		layout.mAnimatedThisFrame = false;
 	}
 }
 
diff --git a/indra/llui/llnotificationslistener.cpp b/indra/llui/llnotificationslistener.cpp
index be26416cbb..e73ba1fbe9 100644
--- a/indra/llui/llnotificationslistener.cpp
+++ b/indra/llui/llnotificationslistener.cpp
@@ -127,18 +127,16 @@ void LLNotificationsListener::listChannels(const LLSD& params) const
 {
     LLReqID reqID(params);
     LLSD response(reqID.makeResponse());
-    for (LLNotificationChannel::instance_iter cmi(LLNotificationChannel::beginInstances()),
-                                              cmend(LLNotificationChannel::endInstances());
-         cmi != cmend; ++cmi)
+    for (auto& cm : LLNotificationChannel::instance_snapshot())
     {
         LLSD channelInfo, parents;
-        BOOST_FOREACH(const std::string& parent, cmi->getParents())
+        for (const std::string& parent : cm.getParents())
         {
             parents.append(parent);
         }
         channelInfo["parents"] = parents;
         channelInfo["parent"] = parents.size()? parents[0] : "";
-        response[cmi->getName()] = channelInfo;
+        response[cm.getName()] = channelInfo;
     }
     LLEventPumps::instance().obtain(params["reply"]).post(response);
 }
diff --git a/indra/llwindow/llwindow.cpp b/indra/llwindow/llwindow.cpp
index 1b24250618..40e297bac1 100644
--- a/indra/llwindow/llwindow.cpp
+++ b/indra/llwindow/llwindow.cpp
@@ -457,9 +457,9 @@ LLCoordCommon LL_COORD_TYPE_WINDOW::convertToCommon() const
 {
 	const LLCoordWindow& self = LLCoordWindow::getTypedCoords(*this);
 
-	LLWindow* windowp = &(*LLWindow::beginInstances());
+	auto windowit = LLWindow::instance_snapshot().begin();
 	LLCoordGL out;
-	windowp->convertCoords(self, &out);
+	windowit->convertCoords(self, &out);
 	return out.convert();
 }
 
@@ -467,18 +467,18 @@ void LL_COORD_TYPE_WINDOW::convertFromCommon(const LLCoordCommon& from)
 {
 	LLCoordWindow& self = LLCoordWindow::getTypedCoords(*this);
 
-	LLWindow* windowp = &(*LLWindow::beginInstances());
+	auto windowit = LLWindow::instance_snapshot().begin();
 	LLCoordGL from_gl(from);
-	windowp->convertCoords(from_gl, &self);
+	windowit->convertCoords(from_gl, &self);
 }
 
 LLCoordCommon LL_COORD_TYPE_SCREEN::convertToCommon() const
 {
 	const LLCoordScreen& self = LLCoordScreen::getTypedCoords(*this);
 
-	LLWindow* windowp = &(*LLWindow::beginInstances());
+	auto windowit = LLWindow::instance_snapshot().begin();
 	LLCoordGL out;
-	windowp->convertCoords(self, &out);
+	windowit->convertCoords(self, &out);
 	return out.convert();
 }
 
@@ -486,7 +486,7 @@ void LL_COORD_TYPE_SCREEN::convertFromCommon(const LLCoordCommon& from)
 {
 	LLCoordScreen& self = LLCoordScreen::getTypedCoords(*this);
 
-	LLWindow* windowp = &(*LLWindow::beginInstances());
+	auto windowit = LLWindow::instance_snapshot().begin();
 	LLCoordGL from_gl(from);
-	windowp->convertCoords(from_gl, &self);
+	windowit->convertCoords(from_gl, &self);
 }
diff --git a/indra/llxml/llcontrol.h b/indra/llxml/llcontrol.h
index de0d366492..39e1d3e615 100644
--- a/indra/llxml/llcontrol.h
+++ b/indra/llxml/llcontrol.h
@@ -200,8 +200,6 @@ public:
 	LLControlGroup(const std::string& name);
 	~LLControlGroup();
 	void cleanup();
-	
-	typedef LLInstanceTracker<LLControlGroup, std::string>::instance_iter instance_iter;
 
 	LLControlVariablePtr getControl(const std::string& name);
 
diff --git a/indra/newview/llappviewer.cpp b/indra/newview/llappviewer.cpp
index b232a8c3bb..a76ac58724 100644
--- a/indra/newview/llappviewer.cpp
+++ b/indra/newview/llappviewer.cpp
@@ -1681,24 +1681,9 @@ bool LLAppViewer::cleanup()
 		gDirUtilp->deleteFilesInDir(logdir, "*-*-*-*-*.dmp");
 	}
 
-	{
-		// Kill off LLLeap objects. We can find them all because LLLeap is derived
-		// from LLInstanceTracker. But collect instances first: LLInstanceTracker
-		// specifically forbids adding/deleting instances while iterating.
-		std::vector<LLLeap*> leaps;
-		leaps.reserve(LLLeap::instanceCount());
-		for (LLLeap::instance_iter li(LLLeap::beginInstances()), lend(LLLeap::endInstances());
-			 li != lend; ++li)
-		{
-			leaps.push_back(&*li);
-		}
-		// Okay, now trash them all. We don't have to NULL or erase the entry
-		// in 'leaps' because the whole vector is going away momentarily.
-		BOOST_FOREACH(LLLeap* leap, leaps)
-		{
-			delete leap;
-		}
-	} // destroy 'leaps'
+	// Kill off LLLeap objects. We can find them all because LLLeap is derived
+	// from LLInstanceTracker.
+	LLLeap::instance_snapshot().deleteAll();
 
 	//flag all elements as needing to be destroyed immediately
 	// to ensure shutdown order
@@ -2858,12 +2843,11 @@ bool LLAppViewer::initConfiguration()
 
 	// Let anyone else who cares know that we've populated our settings
 	// variables.
-	for (LLControlGroup::key_iter ki(LLControlGroup::beginKeys()), kend(LLControlGroup::endKeys());
-		 ki != kend; ++ki)
+	for (const auto& key : LLControlGroup::key_snapshot())
 	{
 		// For each named instance of LLControlGroup, send an event saying
 		// we've initialized an LLControlGroup instance by that name.
-		LLEventPumps::instance().obtain("LLControlGroup").post(LLSDMap("init", *ki));
+		LLEventPumps::instance().obtain("LLControlGroup").post(LLSDMap("init", key));
 	}
 
 	return true; // Config was successful.
diff --git a/indra/newview/llchathistory.cpp b/indra/newview/llchathistory.cpp
index 1099d4bc09..4131af828e 100644
--- a/indra/newview/llchathistory.cpp
+++ b/indra/newview/llchathistory.cpp
@@ -1344,10 +1344,8 @@ void LLChatHistory::appendMessage(const LLChat& chat, const LLSD &args, const LL
 				// We don't want multiple friendship offers to appear, this code checks if there are previous offers
 				// by iterating though all panels.
 				// Note: it might be better to simply add a "pending offer" flag somewhere
-				for (LLToastNotifyPanel::instance_iter ti(LLToastNotifyPanel::beginInstances())
-					, tend(LLToastNotifyPanel::endInstances()); ti != tend; ++ti)
+				for (auto& panel : LLToastNotifyPanel::instance_snapshot())
 				{
-					LLToastNotifyPanel& panel = *ti;
 					LLIMToastNotifyPanel * imtoastp = dynamic_cast<LLIMToastNotifyPanel *>(&panel);
 					const std::string& notification_name = panel.getNotificationName();
 					if (notification_name == "OfferFriendship"
diff --git a/indra/newview/llimprocessing.cpp b/indra/newview/llimprocessing.cpp
index c3375a3779..c1dcc61010 100644
--- a/indra/newview/llimprocessing.cpp
+++ b/indra/newview/llimprocessing.cpp
@@ -1404,10 +1404,8 @@ void LLIMProcessing::processNewMessage(LLUUID from_id,
             payload["sender"] = sender.getIPandPort();
 
             bool add_notification = true;
-            for (LLToastNotifyPanel::instance_iter ti(LLToastNotifyPanel::beginInstances())
-                , tend(LLToastNotifyPanel::endInstances()); ti != tend; ++ti)
+            for (auto& panel : LLToastNotifyPanel::instance_snapshot())
             {
-                LLToastNotifyPanel& panel = *ti;
                 const std::string& notification_name = panel.getNotificationName();
                 if (notification_name == "OfferFriendship" && panel.isControlPanelEnabled())
                 {
diff --git a/indra/newview/llscenemonitor.cpp b/indra/newview/llscenemonitor.cpp
index 5ab0013055..2c0c38dc75 100644
--- a/indra/newview/llscenemonitor.cpp
+++ b/indra/newview/llscenemonitor.cpp
@@ -559,16 +559,14 @@ void LLSceneMonitor::dumpToFile(std::string file_name)
 
 
 	typedef StatType<CountAccumulator> trace_count;
-	for (trace_count::instance_iter it = trace_count::beginInstances(), end_it = trace_count::endInstances();
-		it != end_it;
-		++it)
+	for (auto& it : trace_count::instance_snapshot())
 	{
 		std::ostringstream row;
 		row << std::setprecision(10);
 
-		row << it->getName();
+		row << it.getName();
 
-		const char* unit_label = it->getUnitLabel();
+		const char* unit_label = it.getUnitLabel();
 		if(unit_label[0])
 		{
 			row << "(" << unit_label << ")";
@@ -579,8 +577,8 @@ void LLSceneMonitor::dumpToFile(std::string file_name)
 		for (S32 frame = 1; frame <= frame_count; frame++)
 		{
 			Recording& recording = scene_load_recording.getPrevRecording(frame_count - frame);
-			samples += recording.getSampleCount(*it);
-			row << ", " << recording.getSum(*it);
+			samples += recording.getSampleCount(it);
+			row << ", " << recording.getSum(it);
 		}
 
 		row << '\n';
@@ -593,15 +591,13 @@ void LLSceneMonitor::dumpToFile(std::string file_name)
 
 	typedef StatType<EventAccumulator> trace_event;
 
-	for (trace_event::instance_iter it = trace_event::beginInstances(), end_it = trace_event::endInstances();
-		it != end_it;
-		++it)
+	for (auto& it : trace_event::instance_snapshot())
 	{
 		std::ostringstream row;
 		row << std::setprecision(10);
-		row << it->getName();
+		row << it.getName();
 
-		const char* unit_label = it->getUnitLabel();
+		const char* unit_label = it.getUnitLabel();
 		if(unit_label[0])
 		{
 			row << "(" << unit_label << ")";
@@ -612,8 +608,8 @@ void LLSceneMonitor::dumpToFile(std::string file_name)
 		for (S32 frame = 1; frame <= frame_count; frame++)
 		{
 			Recording& recording = scene_load_recording.getPrevRecording(frame_count - frame);
-			samples += recording.getSampleCount(*it);
-			F64 mean = recording.getMean(*it);
+			samples += recording.getSampleCount(it);
+			F64 mean = recording.getMean(it);
 			if (llisnan(mean))
 			{
 				row << ", n/a";
@@ -634,15 +630,13 @@ void LLSceneMonitor::dumpToFile(std::string file_name)
 
 	typedef StatType<SampleAccumulator> trace_sample;
 
-	for (trace_sample::instance_iter it = trace_sample::beginInstances(), end_it = trace_sample::endInstances();
-		it != end_it;
-		++it)
+	for (auto& it : trace_sample::instance_snapshot())
 	{
 		std::ostringstream row;
 		row << std::setprecision(10);
-		row << it->getName();
+		row << it.getName();
 
-		const char* unit_label = it->getUnitLabel();
+		const char* unit_label = it.getUnitLabel();
 		if(unit_label[0])
 		{
 			row << "(" << unit_label << ")";
@@ -653,8 +647,8 @@ void LLSceneMonitor::dumpToFile(std::string file_name)
 		for (S32 frame = 1; frame <= frame_count; frame++)
 		{
 			Recording& recording = scene_load_recording.getPrevRecording(frame_count - frame);
-			samples += recording.getSampleCount(*it);
-			F64 mean = recording.getMean(*it);
+			samples += recording.getSampleCount(it);
+			F64 mean = recording.getMean(it);
 			if (llisnan(mean))
 			{
 				row << ", n/a";
@@ -674,15 +668,13 @@ void LLSceneMonitor::dumpToFile(std::string file_name)
 	}
 
 	typedef StatType<MemAccumulator> trace_mem;
-	for (trace_mem::instance_iter it = trace_mem::beginInstances(), end_it = trace_mem::endInstances();
-		it != end_it;
-		++it)
+	for (auto& it : trace_mem::instance_snapshot())
 	{
-		os << it->getName() << "(KiB)";
+		os << it.getName() << "(KiB)";
 
 		for (S32 frame = 1; frame <= frame_count; frame++)
 		{
-			os << ", " << scene_load_recording.getPrevRecording(frame_count - frame).getMax(*it).valueInUnits<LLUnits::Kilobytes>();
+			os << ", " << scene_load_recording.getPrevRecording(frame_count - frame).getMax(it).valueInUnits<LLUnits::Kilobytes>();
 		}
 
 		os << '\n';
diff --git a/indra/newview/lltoast.cpp b/indra/newview/lltoast.cpp
index 870e0d94f0..bf56a10d4d 100644
--- a/indra/newview/lltoast.cpp
+++ b/indra/newview/lltoast.cpp
@@ -612,11 +612,8 @@ S32	LLToast::notifyParent(const LLSD& info)
 //static
 void LLToast::updateClass()
 {
-	for (LLInstanceTracker<LLToast>::instance_iter iter = LLInstanceTracker<LLToast>::beginInstances(); 
-			iter != LLInstanceTracker<LLToast>::endInstances(); ) 
+	for (auto& toast : LLInstanceTracker<LLToast>::instance_snapshot())
 	{
-		LLToast& toast = *iter++;
-		
 		toast.updateHoveredState();
 	}
 }
@@ -624,22 +621,6 @@ void LLToast::updateClass()
 // static 
 void LLToast::cleanupToasts()
 {
-	LLToast * toastp = NULL;
-
-	while (LLInstanceTracker<LLToast>::instanceCount() > 0)
-	{
-		{	// Need to scope iter to allow deletion
-			LLInstanceTracker<LLToast>::instance_iter iter = LLInstanceTracker<LLToast>::beginInstances(); 
-			toastp = &(*iter);
-		}
-
-		//LL_INFOS() << "Cleaning up toast id " << toastp->getNotificationID() << LL_ENDL;
-
-		// LLToast destructor will remove it from the LLInstanceTracker.
-		if (!toastp)
-			break;		// Don't get stuck in the loop if a null pointer somehow got on the list
-
-		delete toastp;
-	}
+	LLInstanceTracker<LLToast>::instance_snapshot().deleteAll();
 }
 
diff --git a/indra/newview/llviewercontrollistener.cpp b/indra/newview/llviewercontrollistener.cpp
index d2484b2b23..3443bb644a 100644
--- a/indra/newview/llviewercontrollistener.cpp
+++ b/indra/newview/llviewercontrollistener.cpp
@@ -50,11 +50,9 @@ LLViewerControlListener::LLViewerControlListener()
 	std::ostringstream groupnames;
 	groupnames << "[\"group\"] is one of ";
 	const char* delim = "";
-	for (LLControlGroup::key_iter cgki(LLControlGroup::beginKeys()),
-								  cgkend(LLControlGroup::endKeys());
-		 cgki != cgkend; ++cgki)
+	for (const auto& key : LLControlGroup::key_snapshot())
 	{
-		groupnames << delim << '"' << *cgki << '"';
+		groupnames << delim << '"' << key << '"';
 		delim = ", ";
 	}
 	groupnames << '\n';
@@ -181,11 +179,9 @@ void LLViewerControlListener::groups(LLSD const & request)
 {
 	// No Info, we're not looking up either a group or a control name.
 	Response response(LLSD(), request);
-	for (LLControlGroup::key_iter cgki(LLControlGroup::beginKeys()),
-								  cgkend(LLControlGroup::endKeys());
-		 cgki != cgkend; ++cgki)
+	for (const auto& key : LLControlGroup::key_snapshot())
 	{
-		response["groups"].append(*cgki);
+		response["groups"].append(key);
 	}
 }