foundationdb/flow/IndexedSet.h

/*
 * IndexedSet.h
 *
 * This source file is part of the FoundationDB open source project
 *
 * Copyright 2013-2018 Apple Inc. and the FoundationDB project authors
 *
 * 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.
 */

#ifndef FLOW_INDEXEDSET_H
#define FLOW_INDEXEDSET_H
#pragma once

#include "flow/Arena.h"
#include "flow/Platform.h"
#include "flow/FastAlloc.h"
#include "flow/Trace.h"
#include "flow/Error.h"

#include <deque>
#include <vector>

// IndexedSet<T, Metric> is similar to a std::set<T>, with the following additional features:
//   - Each element in the set is associated with a value of type Metric
//   - sumTo() and sumRange() can report the sum of the metric values associated with a
//     contiguous range of elements in O(lg N) time
//   - index() can be used to find an element having a given sumTo() in O(lg N) time
//   - Search functions (find(), lower_bound(), etc) can accept a type comparable to T instead of T
//     (e.g. StringRef when T is std::string or Standalone<StringRef>).  This can save a lot of needless
//     copying at query time for read-mostly sets with string keys.
//   - iterators are not const; the responsibility of not changing the order lies with the caller
//   - the size() function is missing; if the metric being used is a count sumTo(end()) will do instead
// A number of STL compatibility features are missing and should be added as needed.
// T must define operator <, which must define a total order.  Unlike std::set,
//     a user-defined predicate is not currently supported as a template parameter.
// Metric is required to have operators + and - and <, and behavior is undefined if
//     the sum of metrics for all elements of a set overflows the Metric type.

// Map<Key,Value> is similar to a std::map<Key,Value>, except that it inherits the search key type
//     flexibility of IndexedSet<>, uses MapPair<Key,Value> by default instead of pair<Key,Value>
//     (use iterator->key instead of iterator->first), and uses FastAllocator for nodes.

template <class T>
class Future;

class Void;

class StringRef;

template <class T, class Metric>
struct IndexedSet{
	typedef T value_type;
	typedef T key_type;

private: // Forward-declare IndexedSet::Node because Clang is much stricter about this ordering.
	struct Node : FastAllocated<Node> {
		// Here, and throughout all code that indirectly instantiates a Node, we rely on forwarding
		// references so that we don't need to maintain the set of 2^arity lvalue and rvalue reference
		// combinations, but still take advantage of move constructors when available (or required).
		template <class T_, class Metric_>
		Node(T_&& data, Metric_&& m, Node* parent=0) : data(std::forward<T_>(data)), total(std::forward<Metric_>(m)), parent(parent), balance(0) {
			child[0] = child[1] = NULL;
		}
		~Node(){
			delete child[0];
			delete child[1];
		}

		T data;
		signed char balance;	// right height - left height
		Metric total;			// this + child[0] + child[1]
		Node *child[2];			// left, right
		Node *parent;
	};

public:
	struct iterator{
		typename IndexedSet::Node *i;
		iterator() : i(0) {};
		iterator(typename IndexedSet::Node *n) : i(n) {};
		T& operator*() { return i->data; };
		T* operator->() { return &i->data; }
		void operator++();
		void decrementNonEnd();
		bool operator == ( const iterator& r ) const { return i == r.i; }
		bool operator != ( const iterator& r ) const { return i != r.i; }
		// following two methods are for memory storage engine(KeyValueStoreMemory class) use only
		// in order to have same interface as radixtree
		StringRef& getKey(uint8_t* dummyContent) const { return i->data.key; }
		StringRef& getValue() const { return i->data.value; }
	};

	IndexedSet() : root(NULL) {};
	~IndexedSet() { delete root; }
	IndexedSet(IndexedSet&& r) BOOST_NOEXCEPT : root(r.root) { r.root = NULL; }
	IndexedSet& operator=(IndexedSet&& r) BOOST_NOEXCEPT { delete root; root = r.root; r.root = 0; return *this; }

	iterator begin() const;
	iterator end() const { return iterator(); }
	iterator previous(iterator i) const;
	iterator lastItem() const;

	bool empty() const { return !root; }
	void clear() { delete root; root = NULL; }
	void swap( IndexedSet& r ) { std::swap( root, r.root ); }

	// Place data in the set with the given metric.  If an item equal to data is already in the set and,
	//   replaceExisting == true, it will be overwritten (and its metric will be replaced)
	template <class T_, class Metric_>
	iterator insert(T_ &&data, Metric_ &&metric, bool replaceExisting = true);

	// Insert all items from data into set. All items will use metric. If an item equal to data is already in the set and,
	//   replaceExisting == true, it will be overwritten (and its metric will be replaced). returns the number of items inserted.
	int insert(const std::vector<std::pair<T,Metric>>& data, bool replaceExisting = true);

	// Increase the metric for the given item by the given amount.  Inserts data into the set if it
	//   doesn't exist. Returns the new sum.
	template <class T_, class Metric_>
	Metric addMetric( T_ && data, Metric_ && metric );

	// Remove the data item, if any, which is equal to key
	template <class Key>
	void erase(const Key &key) { erase( find(key) ); }

	// Erase the indicated item.  No effect if item == end().
	// SOMEDAY: Return ++item
	void erase(iterator item);

	// Erase all data items x for which begin<=x<end
	template <class Key>
	void erase(const Key& begin, const Key& end) { erase( lower_bound(begin), lower_bound(end) ); }

	// Erase data items with a deferred (async) free process. The data structure has the items removed
	//  synchronously with the invocation of this method so any subsequent call will see this new state.
	template <class Key>
	Future<Void> eraseAsync(const Key& begin, const Key& end);

	// Erase the items in the indicated range.
	void erase(iterator begin, iterator end);

	// Erase data items with a deferred (async) free process. The data structure has the items removed
	//  synchronously with the invocation of this method so any subsequent call will see this new state.
	Future<Void> eraseAsync(iterator begin, iterator end);

	// Returns the number of items equal to key (either 0 or 1)
	template <class Key>
	int count(const Key &key) const { return find(key) != end(); }

	// Returns x such that key==*x, or end()
	template <class Key>
	iterator find(const Key &key) const;

	// Returns the smallest x such that *x>=key, or end()
	template <class Key>
	iterator lower_bound(const Key &key) const;

	// Returns the smallest x such that *x>key, or end()
	template <class Key>
	iterator upper_bound(const Key &key) const;

	// Returns the largest x such that *x<=key, or end()
	template <class Key>
	iterator lastLessOrEqual( const Key &key ) const;

	// Returns smallest x such that sumTo(x+1) > metric, or end()
	template <class M>
	iterator index( M const& metric ) const;

	// Return the metric inserted with item x
	Metric getMetric(iterator x) const; 

	// Return the sum of getMetric(x) for begin()<=x<to
	Metric sumTo(iterator to) const;

	// Return the sum of getMetric(x) for begin<=x<end
	Metric sumRange(iterator begin, iterator end) const { return sumTo(end) - sumTo(begin); }

	// Return the sum of getMetric(x) for all x s.t. begin <= *x && *x < end
	template <class Key> 
	Metric sumRange(const Key& begin, const Key& end) const { return sumRange(lower_bound(begin), lower_bound(end)); }

	// Return the amount of memory used by an entry in the IndexedSet
	static int getElementBytes() { return sizeof(Node); }

private:
	// Copy operations unimplemented.  SOMEDAY: Implement and make public.
	IndexedSet( const IndexedSet& );  
	IndexedSet& operator=( const IndexedSet& );

	Node *root;

	Metric eraseHalf(Node* start, Node* end, int eraseDir, int& heightDelta, std::vector<Node*>& toFree);
	void erase( iterator begin, iterator end, std::vector<Node*>& toFree );

	void replacePointer( Node* oldNode, Node* newNode ) {
		if (oldNode->parent)
			oldNode->parent->child[ oldNode->parent->child[1] == oldNode ] = newNode;
		else
			root = newNode;
		if (newNode)
			newNode->parent = oldNode->parent;
	}

	// direction 0 = left, 1 = right
	template <int direction>
	static void moveIterator(Node* &i){
		if (i->child[0^direction]) {
			i = i->child[0^direction];
			while (i->child[1^direction])
				i = i->child[1^direction];
		} else {
			while (i->parent && i->parent->child[0^direction] == i)
				i = i->parent;
			i = i->parent;
		}
	}

public: // but testonly
	std::pair<int, int> testonly_assertBalanced(Node*n=0, int d=0, bool a=true);
};

class NoMetric {
public:
	NoMetric() {}
	NoMetric(int) {} // NoMetric(1)
	NoMetric operator+(NoMetric const&) const { return NoMetric(); }
	NoMetric operator-(NoMetric const&) const { return NoMetric(); }
	bool operator<(NoMetric const&) const { return false; }
};

template <class Key, class Value>
class MapPair {
public:
	Key key;
	Value value;

	template <class Key_, class Value_>
	MapPair( Key_&& key, Value_&& value ) : key(std::forward<Key_>(key)), value(std::forward<Value_>(value)) {}
	void operator= ( MapPair const& rhs ) { key = rhs.key; value = rhs.value; }
	MapPair( MapPair const& rhs ) : key(rhs.key), value(rhs.value) {}

	MapPair(MapPair&& r) BOOST_NOEXCEPT  : key(std::move(r.key)), value(std::move(r.value)) {}
	void operator=(MapPair&& r) BOOST_NOEXCEPT { key = std::move(r.key); value = std::move(r.value); }

	int compare(MapPair<Key, Value> const& r) const { return ::compare(key, r.key); }
	template <class CompatibleWithKey>
	int compare(CompatibleWithKey const& r) const {
		return ::compare(key, r);
	}
	bool operator<(MapPair<Key,Value> const& r) const { return key < r.key; }
	bool operator<=(MapPair<Key,Value> const& r) const { return key <= r.key; }
	bool operator==(MapPair<Key,Value> const& r) const { return key == r.key; }
	bool operator!=(MapPair<Key,Value> const& r) const { return key != r.key; }

//private: MapPair( const MapPair& );
};

template <class Key, class Value, class CompatibleWithKey>
inline int compare(CompatibleWithKey const& l, MapPair<Key, Value> const& r) {
	return compare(l, r.key);
}

template <class Key, class Value>
inline MapPair<typename std::decay<Key>::type, typename std::decay<Value>::type> mapPair(Key&& key, Value&& value) { return MapPair<typename std::decay<Key>::type, typename std::decay<Value>::type>(std::forward<Key>(key), std::forward<Value>(value)); }

template <class Key, class Value, class CompatibleWithKey>
bool operator<(MapPair<Key, Value> const& l, CompatibleWithKey const& r) { return l.key < r; }

template <class Key, class Value, class CompatibleWithKey>
bool operator<(CompatibleWithKey const& l, MapPair<Key, Value> const& r) { return l < r.key; }

template <class Key, class Value, class Pair = MapPair<Key,Value>, class Metric=NoMetric >
class Map {
public:
	typedef typename IndexedSet<Pair,Metric>::iterator iterator;

	Map() {}
	iterator begin() const { return set.begin(); }
	iterator end() const { return set.end(); }
	iterator lastItem() const { return set.lastItem(); }
	iterator previous(iterator i) const { return set.previous(i); }
	bool empty() const { return set.empty(); }

	Value& operator[]( const Key& key ) { 
		iterator i = set.insert( Pair(key, Value()), Metric(1), false );
		return i->value;
	}

	Value& get( const Key& key, Metric m = Metric(1) ) { 
		iterator i = set.insert( Pair(key, Value()), m, false );
		return i->value;
	}

	iterator insert( const Pair& p, bool replaceExisting = true, Metric m = Metric(1) ) { return set.insert(p, m, replaceExisting); }
	iterator insert( Pair && p, bool replaceExisting = true, Metric m = Metric(1) ) { return set.insert(std::move(p), m, replaceExisting); }
	int insert( const std::vector<std::pair<MapPair<Key,Value>, Metric>>& pairs, bool replaceExisting = true) { return set.insert(pairs, replaceExisting); }
	
	template <class KeyCompatible>
	void erase( KeyCompatible const& k ) { set.erase(k); }
	void erase( iterator b, iterator e ) { set.erase(b,e); }
	void erase( iterator x ) { set.erase(x); }
	void clear() { set.clear(); }
	Metric size() const {
		static_assert(!std::is_same<Metric, NoMetric>::value, "size() on Map with NoMetric is not valid!");
		return sumTo(end());
	}

	template <class KeyCompatible>
	iterator find( KeyCompatible const& k ) const { return set.find(k); }
	template <class KeyCompatible>
	iterator lower_bound( KeyCompatible const& k ) const { return set.lower_bound(k); }
	template <class KeyCompatible>
	iterator upper_bound( KeyCompatible const& k ) const { return set.upper_bound(k); }
	template <class KeyCompatible>
	iterator lastLessOrEqual( KeyCompatible const& k ) const { return set.lastLessOrEqual(k); }
	template <class M> 
	iterator index( M const& metric ) const { return set.index(metric); }
	Metric getMetric(iterator x) const { return set.getMetric(x); }
	Metric sumTo(iterator to) const { return set.sumTo(to); }
	Metric sumRange(iterator begin, iterator end) const { return set.sumRange(begin,end); }
	template <class KeyCompatible> 
	Metric sumRange(const KeyCompatible& begin, const KeyCompatible& end) const { return set.sumRange(begin,end); }

	static int getElementBytes() { return IndexedSet< Pair, Metric >::getElementBytes(); }

	Map(Map&& r) BOOST_NOEXCEPT : set(std::move(r.set)) {}
	void operator=(Map&& r) BOOST_NOEXCEPT { set = std::move(r.set); }

private:
	Map( Map<Key,Value,Pair> const& ); // unimplemented
	void operator=( Map<Key,Value,Pair> const& ); // unimplemented

	IndexedSet< Pair, Metric > set;
};

/////////////////////// implementation //////////////////////////

template <class T, class Metric>
void IndexedSet<T,Metric>::iterator::operator++(){
	moveIterator<1>(i);
}

template <class T, class Metric>
void IndexedSet<T,Metric>::iterator::decrementNonEnd(){
	moveIterator<0>(i);
}

template <class Node>
void ISRotate(Node*& oldRootRef, int d) {
	Node *oldRoot = oldRootRef;
	Node *newRoot = oldRoot->child[1-d];

	// metrics
	auto orTotal = oldRoot->total - newRoot->total;
	if (newRoot->child[d])
		orTotal = orTotal + newRoot->child[d]->total;
	newRoot->total = oldRoot->total;
	oldRoot->total = orTotal;

	//pointers
	oldRoot->child[1-d] = newRoot->child[d];
	if (oldRoot->child[1-d]) oldRoot->child[1-d]->parent = oldRoot;
	newRoot->child[d] = oldRoot;
	newRoot->parent = oldRoot->parent;
	oldRoot->parent = newRoot;
	oldRootRef = newRoot;
}

template <class Node>
void ISAdjustBalance(Node* root, int d, int bal) {
	Node *n = root->child[d];
	Node *nn = n->child[1-d];

	if ( !nn->balance )
		root->balance = n->balance = 0;
	else if ( nn->balance == bal ) {
		root->balance = -bal;
		n->balance = 0;
	} else {
		root->balance = 0;
		n->balance = bal;
	}
	nn->balance = 0;
}

template <class Node>
int ISRebalance( Node*& root ) {
	// Pre: root is a tree having the BST, metric, and balance invariants but not (necessarily) the AVL invariant.  root->child[0] and root->child[1] are AVL.
	// Post: root is an AVL tree with the same nodes
	// Returns: the change in height of root
	// rebalance is O(1) if abs(root->balance)<=2, and probably O(log N) otherwise.  (The rare "still unbalanced" recursion is hard to analyze)
	//
	// The documentation of this function will be referencing the following tree (where
	// nodes A, C, E, and G represent subtrees of unspecified height). Thus for each node X, 
	// we know the value of balance(X), but not height(X).
	//
	// We will assume that balance(F) < 0 (so we will be rotating right).
	// Trees that rotate to the left will perform analagous operations.
	// 
	//         F
	//       /   \
	//      B     G
	//     / \
	//    A   D 
	//       / \
	//      C   E

	if (!root || (root->balance >= -1 && root->balance <= +1))
		return 0;

	int rebalanceDir = root->balance<0; // 1 if rotating right, 0 if rotating left
	auto* n = root->child[ 1-rebalanceDir ]; // Node B
	int bal = rebalanceDir ? +1 : -1; // 1 if rotating right, -1 if rotating left
	int rootBal = root->balance;

	// Depending on the balance at B, we will be required to do one or two rotations.
	// If balance(B) <= 0, then we do only one rotation (the second of the two).
	//
	// In a tree where balance(B) == +1, we are required to do both rotations.
	// The result of the first rotation will be:
	//
	//          F
	//        /   \
	//       D     G
	//      / \
	//     B   E 
	//    / \
	//   A   C
	//
	bool doubleRotation = n->balance == bal;
	if (doubleRotation) {
		int x = n->child[rebalanceDir]->balance; // balance of Node D
		ISRotate( root->child[1-rebalanceDir], 1-rebalanceDir); // Rotate at Node B

		// Change node pointed to by 'n' to prepare for the second rotation
		// After this first rotation, Node D will be the left child of the root
		n = root->child[1-rebalanceDir];

		// Compute the balance at the new root node D' of our rotation
		// We know that height(A) == max(height(C), height(E)) because B had balance of +1
		// If height(E) >= height(C), then height(E) == height(A) and balance(D') = -1
		// Otherwise height(C) == height(E) + 1, and therefore balance(D') = -2
		n->balance = ((x==-bal) ? -2 : -1)*bal; 

		// Compute the balance at the old root node B' of our rotation
		// As stated above, height(A) == max(height(C), height(E))
		// If height(C) >= height(E), then height(A) == height(C) and balance(B') = 0
		// Otherwise height(A) == height(E) == height(C) + 1, and therefore balance(B') = -1
		n->child[1-rebalanceDir]->balance = ((x==bal) ? -1 : 0)*bal;
	}

	// At this point, we perform the "second" rotation (which may actually be the first
	// if the "first" rotation was not performed). The rotation that is performed is the
	// same for both trees, but the result will be different depending on which tree we
	// started with:
	//
	//   If unrotated:       If once rotated:
	//
	//         B                      D
	//       /   \                  /   \
	//      A     F                B     F
	//           / \              / \   / \
	//          D   G            A   C E   G
	//         / \
	//        C   E
	//
	// The documentation for this second rotation will be based on the unrotated original tree.

	// Compute the balance at the new root node B'.
	// balance(B') = 1 + max(height(D), height(G)) - height(A) = 1 + max(height(D) - height(A), height(G) - height(A))
	// balance(B') = 1 + max(balance(B), height(G) - height(A))
	//
	// Now, we must find height(G) - height(A):
	// If height(A) >= height(D) (i.e. balance(B) <= 0), then
	// height(G) - height(A) = height(G) - height(B) + 1 = balance(F) + 1
	//
	// Otherwise, height(A) = height(D) - balance(B) = height(B) - 1 - balance(B), so
	// height(G) - height(A) = height(G) - height(B) + 1 + balance(B) = balance(F) + 1 + balance(B) 
	//
	// balance(B') = 1 + max(balance(B), balance(F) + 1 + max(balance(B), 0))
	//
	int nBal = n->balance * bal; // Direction corrected balance at Node B
	int newRootBalance = bal * (1 + std::max(nBal, bal * root->balance + 1 + std::max(nBal, 0)));

	// Compute the balance at the old root node F' (which becomes a child of the new root).
	// balance(F') = height(G) - height(D)
	//
	// If height(D) >= height(A) (i.e. balance(B) >= 0), then height(D) = height(B) - 1, so
	// balance(F') = height(G) - height(B) + 1 = balance(F) + 1
	//
	// Otherwise, height(D) = height(A) + balance(B) = height(B) - 1 + balance(B), so 
	// balance(F') = height(G) - height(B) + 1 - balance(B) = balance(F) + 1 - balance(B) 
	//
	// balance(F') = balance(F) + 1 - min(balance(B), 0)
	//
	int newChildBalance = root->balance + bal * (1 - std::min(nBal, 0));

	ISRotate( root, rebalanceDir );
	root->balance = newRootBalance;
	root->child[rebalanceDir]->balance = newChildBalance;

	// If the original tree is very unbalanced, the unbalance may have been "pushed" down into this subtree, so recursively rebalance that if necessary.
	int childHeightChange = ISRebalance(root->child[rebalanceDir]);
	root->balance += childHeightChange * bal;

	newRootBalance *= bal;

	// Compute the change in height at the root
	// We will look at the single and double rotation cases separately
	//
	// If we did a single rotation, then height(A) >= height(D).
	// As a result, height(A) >= height(G) + 1; otherwise the tree would be balanced and we wouldn't do any rotations.
	// 
	// Then the original height of the tree is height(A) + 2, 
	// and the new height is max(height(D) + 2 + childHeightChange, height(A) + 1), so
	//
	// heightChange_single = max(height(D) + 2 + childHeightChange, height(A) + 1) - (height(A) + 2)
	// heightChange_single = max(height(D) - height(A) + childHeightChange, -1)
	// heightChange_single = max(balance(B) + childHeightChange, -1)
	//
	// If we did a double rotation, then height(D) = height(A) + 1 in the original tree.
	// As a result, height(D) >= height(G) + 1; otherwise the tree would be balanced and we wouldn't do any rotations.
	//
	// Then the original height of the tree is height(D) + 2,
	// and the new height is max(height(A), height(C), height(E), height(G)) + 2
	//
	// balance(B) == 1, so height(A) == max(height(C), height(E)).
	// Also, height(A) = height(D) - 1 >= height(G)
	// Therefore the new height is height(A) + 2
	//
	// heightChange_double = height(A) + 2 - (height(D) + 2)
	// heightChange_double = height(A) - height(D)
	// heightChange_double = -1
	//
	int heightChange = doubleRotation ? -1 : std::max(nBal + childHeightChange, -1);

	// If the root is still unbalanced, then it should at least be more balanced than before. Recursively rebalance the root until we get a balanced tree.
	if (root->balance <-1 || root->balance > +1) {
		ASSERT(abs(root->balance) < abs(rootBal));
		heightChange += ISRebalance(root);
	}

	return heightChange;
}

template <class Node>
Node* ISCommonSubtreeRoot(Node* first, Node* last) {
	// Finds the smallest common subtree of first and last and returns its root node

	//Find the depth of first and last
	int firstDepth=0, lastDepth=0;
	for(auto f = first; f; f=f->parent) firstDepth++;
	for(auto f = last; f; f=f->parent) lastDepth++;

	//Traverse up the tree from the deeper of first and last until f and l are at the same depth
	auto f = first, l = last;
	for(int i=firstDepth; i>lastDepth; i--) f = f->parent;
	for(int i=lastDepth; i>firstDepth; i--) l = l->parent;

	//Traverse up from f and l simultaneously until we reach a common node
	while (f != l) {
		f = f->parent;
		l = l->parent;
	}

	return f;
}

template <class T, class Metric>
typename IndexedSet<T,Metric>::iterator IndexedSet<T,Metric>::begin() const {
	Node *x = root;
	while (x && x->child[0])
		x = x->child[0];
	return x;
}

template <class T, class Metric>
typename IndexedSet<T,Metric>::iterator IndexedSet<T,Metric>::previous(typename IndexedSet<T,Metric>::iterator i) const {
	if (i==end())
		return lastItem();

	moveIterator<0>(i.i);
	return i;
}

template <class T, class Metric>
typename IndexedSet<T,Metric>::iterator IndexedSet<T,Metric>::lastItem() const {
	Node *x = root;
	while (x && x->child[1])
		x = x->child[1];
	return x;
}

template <class T, class Metric> template<class T_, class Metric_>
Metric IndexedSet<T,Metric>::addMetric(T_&& data, Metric_&& metric){
	auto i = find( data );
	if (i == end()) {
		insert( std::forward<T_>(data), std::forward<Metric_>(metric) );
		return metric;
	} else {
		Metric m = metric + getMetric(i);
		insert( std::forward<T_>(data), m );
		return m;
	}
}

template <class T, class Metric> template<class T_, class Metric_>
typename IndexedSet<T,Metric>::iterator IndexedSet<T,Metric>::insert(T_&& data, Metric_&& metric, bool replaceExisting){
	if (root == NULL){
		root = new Node(std::forward<T_>(data), std::forward<Metric_>(metric));
		return root;
	}
	Node *t = root;
	int d; // direction
	// traverse to find insert point
	while (true){
		int cmp = compare(data, t->data);
		if (cmp == 0) {
			Node *returnNode = t;
			if(replaceExisting) {
				t->data = std::forward<T_>(data);
				Metric delta = t->total;
				t->total = std::forward<Metric_>(metric);
				if (t->child[0]) t->total = t->total + t->child[0]->total;
				if (t->child[1]) t->total = t->total + t->child[1]->total;
				delta = t->total - delta;
				while (true) {
					t = t->parent;
					if (!t) break;
					t->total = t->total + delta;
				}
			}

			return returnNode;
		}
		d = cmp > 0;
		Node *nextT = t->child[d];
		if (!nextT) break;
		t = nextT;
	}

	Node *newNode = new Node(std::forward<T_>(data), std::forward<Metric_>(metric), t);
	t->child[d] = newNode;

	while (true){
		t->balance += d ? 1 : -1;
		t->total = t->total + metric;
		if (t->balance == 0)
			break;
		if (t->balance != 1 && t->balance != -1){
			Node** parent = t->parent ? &t->parent->child[t->parent->child[1]==t] : &root;
			//assert( *parent == t );

			Node *n = t->child[d];
			int bal = d ? 1 : -1;
			if (n->balance == bal){
				t->balance = n->balance = 0;
			} else {
				ISAdjustBalance(t, d, bal);
				ISRotate(t->child[d], d);
			}
			ISRotate(*parent, 1-d);
			t = *parent;
			break;
		}
		if (!t->parent) break;

		d = t->parent->child[1] == t;
		t = t->parent;
	}
	while (true) {
		t = t->parent;
		if (!t) break;
		t->total = t->total + metric;
	}

	return newNode;
}

template <class T, class Metric>
int IndexedSet<T,Metric>::insert(const std::vector<std::pair<T,Metric>>& dataVector, bool replaceExisting) {
	int num_inserted = 0;
	Node *blockStart = NULL;
	Node *blockEnd = NULL;

	for(int i = 0; i < dataVector.size(); ++i) {
		Metric metric = dataVector[i].second;
		T data = std::move(dataVector[i].first);

		int d = 1; // direction
		if(blockStart == NULL || (blockEnd != NULL && data >= blockEnd->data)) {
			blockEnd = NULL;
			if (root == NULL) {
				root = new Node(std::move(data), metric);
				num_inserted++;
				blockStart = root;
				continue;
			}

			Node *t = root;
			// traverse to find insert point
			bool foundNode = false;
			while (true) {
				int cmp = compare(data, t->data);
				d = cmp > 0;
				if (d == 0)
					blockEnd = t;
				if (cmp == 0) {
					Node *returnNode = t;
					if(replaceExisting) {
						num_inserted++;
						t->data = std::move(data);
						Metric delta = t->total;
						t->total = metric;
						if (t->child[0]) t->total = t->total + t->child[0]->total;
						if (t->child[1]) t->total = t->total + t->child[1]->total;
						delta = t->total - delta;
						while (true) {
							t = t->parent;
							if (!t) break;
							t->total = t->total + delta;
						}
					}

					blockStart = returnNode;
					foundNode = true;
					break;
				}
				Node *nextT = t->child[d];
				if (!nextT) { 
					blockStart = t;
					break;
				}
				t = nextT;
			}

			if(foundNode)
				continue;
		}

		Node *t = blockStart;
		while(t->child[d]) {
			t = t->child[d];
			d = 0;
		}

		Node *newNode = new Node(std::move(data), metric, t);
		num_inserted++;

		t->child[d] = newNode;
		blockStart = newNode;

		while (true){
			t->balance += d ? 1 : -1;
			t->total = t->total + metric;
			if (t->balance == 0)
				break;
			if (t->balance != 1 && t->balance != -1){
				Node** parent = t->parent ? &t->parent->child[t->parent->child[1]==t] : &root;
				//assert( *parent == t );

				Node *n = t->child[d];
				int bal = d ? 1 : -1;
				if (n->balance == bal){
					t->balance = n->balance = 0;
				} else {
					ISAdjustBalance(t, d, bal);
					ISRotate(t->child[d], d);
				}
				ISRotate(*parent, 1-d);
				t = *parent;
				break;
			}
			if (!t->parent) break;

			d = t->parent->child[1] == t;
			t = t->parent;
		}
		while (true) {
			t = t->parent;
			if (!t) break;
			t->total = t->total + metric;
		}
	}
	return num_inserted;
}

template <class T, class Metric>
Metric IndexedSet<T, Metric>::eraseHalf(Node* start, Node* end, int eraseDir, int& heightDelta,
                                        std::vector<Node*>& toFree) {
	// Removes all nodes between start (inclusive) and end (exclusive) from the set, where start is equal to end or one of its descendants
	// eraseDir 1 means erase the right half (nodes > at) of the left subtree of end.  eraseDir 0 means the left half of the right subtree
	// toFree is extended with the roots of completely removed subtrees
	// heightDelta will be set to the change in height of the end node
	// Returns the amount that should be subtracted from end node's metric value (and, by extension, the metric values of all ancestors of the end node).
	//
	// The end node may be left unbalanced (AVL invariant broken)
	// The end node may be left with the incorrect metric total (the correct value is end->total = end->total + metricDelta)
	// scare quotes in comments mean the values when eraseDir==1 (when eraseDir==0, "left" means right etc)

	// metricDelta measures how much should be subtracted from the current node's metrics
	Metric metricDelta = 0;
	heightDelta = 0;

	int fromDir = 1 - eraseDir;

	// Begin removing nodes at start continuing up until we get to end
	while(start != end) {
		start->total = start->total - metricDelta;

		IndexedSet<T,Metric>::Node *parent = start->parent;

		// Obtain the child pointer to start, which rebalance will update with the new root of the subtree currently rooted at start
		IndexedSet<T,Metric>::Node *& node = parent->child[ parent->child[1] == start ];
		int nextDir = parent->child[1] == start;

		if (fromDir==eraseDir) {
			// The "right" subtree has been half-erased, and the "left" subtree doesn't need to be (nor does node).
			// But this node might be unbalanced by the shrinking "right" subtree. Rebalance and continue up.
			heightDelta += ISRebalance( node );
		} else {
			// The "left" subtree has been half-erased.  `start' and its "right" subtree will be completely erased,
			// leaving only the "left" subtree in its place (which is already AVL balanced).
			heightDelta += -1 - std::max<int>(0, node->balance * (eraseDir ? +1 : -1));
			metricDelta = metricDelta + start->total;

			// If there is a surviving subtree of start, then connect it to start->parent
			IndexedSet<T,Metric>::Node *n = node->child[fromDir];
			node = n; // This updates the appropriate child pointer of start->parent
			if (n) {
				metricDelta = metricDelta - n->total;
				n->parent = start->parent;
			}
			
			start->child[fromDir] = NULL;
			toFree.push_back( start );
		}

		int dir = (nextDir ? +1 : -1);
		int oldBalance = parent->balance;

		// The change in height from removing nodes should never increase our height
		ASSERT(heightDelta <= 0);
		parent->balance += heightDelta * dir;

		// Compute the change in height of start's parent based on its change in balance.
		// Because we can only be (possibly) shrinking one subtree of parent: 
		//   If we were originally heavier on the shrunken size (oldBalance * dir > 0), then the change in height is at most abs(oldBalance) == oldBalance * dir.
		//   If we were lighter on the shrunken side, then height cannot change.
		int maxHeightChange = std::max(oldBalance * dir, 0);
		int balanceChange = (oldBalance - parent->balance) * dir;
		heightDelta = -std::min(maxHeightChange, balanceChange);

		start = parent;
		fromDir = nextDir;
	}

	return metricDelta;
}

template <class T, class Metric>
void IndexedSet<T,Metric>::erase( typename IndexedSet<T,Metric>::iterator begin, typename IndexedSet<T,Metric>::iterator end, std::vector<Node*>& toFree ) {
	// Removes all nodes in the set between first and last, inclusive.
	// toFree is extended with the roots of completely removed subtrees.

	ASSERT(!end.i || (begin.i && (::compare(*begin, *end) <= 0)));

	if(begin == end)
		return;
	
	IndexedSet<T,Metric>::Node* first = begin.i;
	IndexedSet<T,Metric>::Node* last = previous(end).i; 

	IndexedSet<T,Metric>::Node* subRoot = ISCommonSubtreeRoot(first, last);

	Metric metricDelta = 0;
	int leftHeightDelta = 0;
	int rightHeightDelta = 0;
	
	// Erase all matching nodes that descend from subRoot, by first erasing descendants of subRoot->child[0] and then erasing the descendants of subRoot->child[1]
	// subRoot is not removed from the tree at this time
	metricDelta = metricDelta + eraseHalf(first, subRoot, 1, leftHeightDelta, toFree);
	metricDelta = metricDelta + eraseHalf(last, subRoot, 0, rightHeightDelta, toFree);

	// Change in the height of subRoot due to past activity, before subRoot is rebalanced. subRoot->balance already reflects changes in height to its children.
	int heightDelta = leftHeightDelta + rightHeightDelta; 

	// Rebalance and update metrics for all nodes from subRoot up to the root
	for(auto p = subRoot; p != NULL; p = p->parent) {
		p->total = p->total - metricDelta;

		auto& pc = p->parent ? p->parent->child[p->parent->child[1]==p] : root;
		heightDelta += ISRebalance(pc);
		p = pc;

		// Update the balance and compute heightDelta for p->parent
		if (p->parent) {
			int oldb = p->parent->balance;
			int dir = (p->parent->child[1]==p ? +1 : -1);
			p->parent->balance += heightDelta * dir;

			heightDelta = (std::max(p->parent->balance*dir, 0) - std::max(oldb*dir, 0));
		}
	}

	// Erase the subRoot using the single node erase implementation
	erase( IndexedSet<T,Metric>::iterator(subRoot) );
}

template <class T, class Metric>
void IndexedSet<T,Metric>::erase(iterator toErase) {
	Node* rebalanceNode;
	int rebalanceDir;

	{
		// Find the node to erase
		Node* t = toErase.i;
		if (!t) return;

		if (!t->child[0] || !t->child[1]) {
			Metric tMetric = t->total;
			if (t->child[0]) tMetric = tMetric - t->child[0]->total;
			if (t->child[1]) tMetric = tMetric - t->child[1]->total;
			for( Node* p = t->parent; p; p = p->parent )
				p->total = p->total - tMetric;
			rebalanceNode = t->parent;
			if (rebalanceNode) rebalanceDir = rebalanceNode->child[1] == t;
			int d = !t->child[0];  // Only one child, on this side (or no children!)
			replacePointer(t, t->child[d]);
			t->child[d] = 0;
			delete t;
		} else {  // Remove node with two children
			Node* predecessor = t->child[0];
			while ( predecessor->child[1] )
				predecessor = predecessor->child[1];
			rebalanceNode = predecessor->parent;
			if (rebalanceNode == t) rebalanceNode = predecessor;
			if (rebalanceNode) rebalanceDir = rebalanceNode->child[1] == predecessor;

			Metric tMetric = t->total - t->child[0]->total - t->child[1]->total;
			if (predecessor->child[0]) predecessor->total = predecessor->total - predecessor->child[0]->total;
			for( Node* p = predecessor->parent; p != t; p = p->parent )
				p->total = p->total - predecessor->total;
			for( Node* p = t->parent; p; p = p->parent )
				p->total = p->total - tMetric;

			// Replace t with predecessor
			replacePointer( predecessor, predecessor->child[0] );
			replacePointer( t, predecessor );
			predecessor->balance = t->balance;
			for(int i=0; i<2; i++) {
				Node* c = predecessor->child[i] = t->child[i];
				if (c) {
					c->parent = predecessor;
					predecessor->total = predecessor->total + c->total;
					t->child[i] = 0;
				}
			}
			delete t;
		}
	}

	if (!rebalanceNode) return;

	while (true) {
		rebalanceNode->balance += rebalanceDir ? -1 : +1;

		if ( rebalanceNode->balance < -1 || rebalanceNode->balance > +1 ) {
			Node** parent = rebalanceNode->parent ? &rebalanceNode->parent->child[rebalanceNode->parent->child[1]==rebalanceNode] : &root;
			Node* n = rebalanceNode->child[ 1-rebalanceDir ];
			int bal = rebalanceDir ? +1 : -1;
			if (n->balance == -bal) {
				rebalanceNode->balance = n->balance = 0;
				ISRotate( *parent, rebalanceDir );
			} else if (n->balance == bal) {
				ISAdjustBalance( rebalanceNode, 1-rebalanceDir, -bal );
				ISRotate( rebalanceNode->child[1-rebalanceDir], 1-rebalanceDir);
				ISRotate( *parent, rebalanceDir );
			} else {  // n->balance == 0
				rebalanceNode->balance = -bal;
				n->balance = bal;
				ISRotate( *parent, rebalanceDir );
				break;
			}
			rebalanceNode = *parent;
		} else if ( rebalanceNode->balance )	// +/- 1, we are done
			break;

		if (!rebalanceNode->parent) break;
		rebalanceDir = rebalanceNode->parent->child[1] == rebalanceNode;
		rebalanceNode = rebalanceNode->parent;
	}
}

// Returns x such that key==*x, or end()
template <class T, class Metric>
template <class Key>
typename IndexedSet<T,Metric>::iterator IndexedSet<T,Metric>::find(const Key &key) const {
	Node* t = root;
	while (t){
		int cmp = compare(key, t->data);
		if (cmp == 0) return iterator(t);
		t = t->child[cmp > 0];
	}
	return end();
}

// Returns the smallest x such that *x>=key, or end()
template <class T, class Metric>
template <class Key>
typename IndexedSet<T,Metric>::iterator IndexedSet<T,Metric>::lower_bound(const Key &key) const {
	Node* t = root;
	if (!t) return iterator();
	bool less;
	while (true) {
		less = t->data < key;
		Node* n = t->child[less];
		if (!n) break;
		t = n;
	}

	if (less) moveIterator<1>(t);

	return iterator(t);
}

// Returns the smallest x such that *x>key, or end()
template <class T, class Metric>
template <class Key>
typename IndexedSet<T,Metric>::iterator IndexedSet<T,Metric>::upper_bound(const Key &key) const {
	Node* t = root;
	if (!t) return iterator();
	bool not_less;
	while (true) {
		not_less = !(key < t->data);
		Node* n = t->child[not_less];
		if (!n) break;
		t = n;
	}

	if (not_less) moveIterator<1>(t);

	return iterator(t);
}

template <class T, class Metric>
template <class Key>
typename IndexedSet<T,Metric>::iterator IndexedSet<T,Metric>::lastLessOrEqual(const Key &key) const {
	iterator i = upper_bound(key);
	if (i == begin()) return end();
	return previous(i);
}

// Returns first x such that metric < sum(begin(), x+1), or end()
template <class T, class Metric>
template <class M>
typename IndexedSet<T,Metric>::iterator IndexedSet<T,Metric>::index( M const& metric ) const
{
	M m = metric;
	Node* t = root;
	while (t) {
		if (t->child[0] && m < t->child[0]->total)
			t = t->child[0];
		else {
			m = m - t->total;
			if (t->child[1])
				m = m + t->child[1]->total;
			if (m < M())
				return iterator(t);
			t = t->child[1];
		}
	}
	return end();
}

template <class T, class Metric>
Metric IndexedSet<T,Metric>::getMetric(typename IndexedSet<T,Metric>::iterator x) const {
	Metric m = x.i->total;
	for(int i=0; i<2; i++)
		if (x.i->child[i]) 
			m = m - x.i->child[i]->total;
	return m;
}

template <class T, class Metric>
Metric IndexedSet<T,Metric>::sumTo(typename IndexedSet<T,Metric>::iterator end) const {
	if (!end.i)
		return root ? root->total : Metric();

	Metric m = end.i->child[0] ? end.i->child[0]->total : Metric();
	for(Node* p = end.i; p->parent; p=p->parent) {
		if (p->parent->child[1] == p) {
			m = m - p->total;
			m = m + p->parent->total;
		}
	}
	return m;
}

#include "flow/flow.h"
#include "flow/IndexedSet.actor.h"

template <class T, class Metric>
void IndexedSet<T,Metric>::erase(typename IndexedSet<T,Metric>::iterator begin, typename IndexedSet<T,Metric>::iterator end) {
	std::vector<IndexedSet<T,Metric>::Node*> toFree;
	erase(begin, end, toFree);

	ISFreeNodes(toFree, true);
}

template <class T, class Metric>
template <class Key>
Future<Void> IndexedSet<T, Metric>::eraseAsync(const Key &begin, const Key &end) {
	return eraseAsync(lower_bound(begin), lower_bound(end) ); 
}

template <class T, class Metric>
Future<Void> IndexedSet<T, Metric>::eraseAsync(typename IndexedSet<T,Metric>::iterator begin, typename IndexedSet<T,Metric>::iterator end) {
	std::vector<IndexedSet<T,Metric>::Node*> toFree;
	erase(begin, end, toFree);

	return uncancellable(ISFreeNodes(toFree, false));
}

#endif