priority_queue.h

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/***************************************************************************
 * include/stxxl/bits/containers/priority_queue.h
 *
 * Implements a data structure from "Peter Sanders. Fast Priority Queues for
 * Cached Memory. ALENEX'99" for external memory.
 *
 * Part of the STXXL. See http://stxxl.sourceforge.net
 *
 * Copyright (C) 1999 Peter Sanders <[email protected]>
 * Copyright (C) 2003, 2004, 2007 Roman Dementiev <[email protected]>
 * Copyright (C) 2007-2009 Johannes Singler <[email protected]>
 * Copyright (C) 2007-2010 Andreas Beckmann <[email protected]>
 * Copyright (C) 2014 Timo Bingmann <[email protected]>
 *
 * Distributed under the Boost Software License, Version 1.0.
 * (See accompanying file LICENSE_1_0.txt or copy at
 * http://www.boost.org/LICENSE_1_0.txt)
 **************************************************************************/

#ifndef STXXL_CONTAINERS_PRIORITY_QUEUE_HEADER
#define STXXL_CONTAINERS_PRIORITY_QUEUE_HEADER

#include <stxxl/bits/containers/pq_helpers.h>
#include <stxxl/bits/containers/pq_mergers.h>
#include <stxxl/bits/containers/pq_ext_merger.h>
#include <stxxl/bits/containers/pq_losertree.h>

STXXL_BEGIN_NAMESPACE

/*
 KNBufferSize1 = 32;
 KNN = 512; // length of group 1 sequences
 KNKMAX = 64; // maximal arity
 LogKNKMAX = 6; // ceil(log KNKMAX)
 KNLevels = 4; // overall capacity >= KNN*KNKMAX^KNLevels
 */

// internal memory consumption >= N_*(KMAX_^IntLevels_) + ext

template <
 class ValueType,
 class CompareType,
 unsigned BufferSize1_ = 32, // equalize procedure call overheads etc.
 unsigned N_ = 512, // length of group 1 sequences
 unsigned IntKMAX_ = 64, // maximal arity for internal mergers
 unsigned IntLevels_ = 4, // number of internal groups
 unsigned BlockSize_ = (2* 1024* 1024), // external block size
 unsigned ExtKMAX_ = 64, // maximal arity for external mergers
 unsigned ExtLevels_ = 2, // number of external groups
 class AllocStr_ = STXXL_DEFAULT_ALLOC_STRATEGY
 >
struct priority_queue_config
{
 typedef ValueType value_type;
 typedef CompareType comparator_type;
 typedef AllocStr_ alloc_strategy_type;
 enum
 {
 delete_buffer_size = BufferSize1_,
 N = N_,
 IntKMAX = IntKMAX_,
 num_int_groups = IntLevels_,
 num_ext_groups = ExtLevels_,
 BlockSize = BlockSize_,
 ExtKMAX = ExtKMAX_,
 element_size = sizeof(ValueType)
 };
};

STXXL_END_NAMESPACE

namespace std {

template <class BlockType,
 class CompareType,
 unsigned Arity,
 class AllocStr>
void swap(stxxl::priority_queue_local::ext_merger<BlockType, CompareType, Arity, AllocStr>& a,
 stxxl::priority_queue_local::ext_merger<BlockType, CompareType, Arity, AllocStr>& b)
{
 a.swap(b);
}
template <class ValueType, class CompareType, unsigned KNKMAX>
void swap(stxxl::priority_queue_local::loser_tree<ValueType, CompareType, KNKMAX>& a,
 stxxl::priority_queue_local::loser_tree<ValueType, CompareType, KNKMAX>& b)
{
 a.swap(b);
}

} // namespace std

STXXL_BEGIN_NAMESPACE

//! External priority queue data structure \n
//! <b> Introduction </b> to priority queue container: see \ref tutorial_pqueue tutorial. \n
//! <b> Design and Internals </b> of priority queue container: see \ref design_pqueue.
template <class ConfigType>
class priority_queue : private noncopyable
{
public:
 typedef ConfigType Config;
 enum
 {
 delete_buffer_size = Config::delete_buffer_size,
 N = Config::N,
 IntKMAX = Config::IntKMAX,
 num_int_groups = Config::num_int_groups,
 num_ext_groups = Config::num_ext_groups,
 total_num_groups = Config::num_int_groups + Config::num_ext_groups,
 BlockSize = Config::BlockSize,
 ExtKMAX = Config::ExtKMAX
 };

 //! The type of object stored in the priority_queue.
 typedef typename Config::value_type value_type;
 //! Comparison object.
 typedef typename Config::comparator_type comparator_type;
 typedef typename Config::alloc_strategy_type alloc_strategy_type;
 //! An unsigned integral type (64 bit).
 typedef stxxl::uint64 size_type;
 //! Type of the block used in disk-memory transfers
 typedef typed_block<BlockSize, value_type> block_type;
 typedef read_write_pool<block_type> pool_type;

protected:
 typedef priority_queue_local::internal_priority_queue<value_type, std::vector<value_type>, comparator_type>
 insert_heap_type;

 typedef priority_queue_local::loser_tree<
 value_type,
 comparator_type,
 IntKMAX> int_merger_type;

 typedef priority_queue_local::ext_merger<
 block_type,
 comparator_type,
 ExtKMAX,
 alloc_strategy_type> ext_merger_type;

 int_merger_type int_mergers[num_int_groups];
 pool_type* pool;
 bool pool_owned;
 ext_merger_type** ext_mergers;

 // one delete buffer for each tree => group buffer
 value_type group_buffers[total_num_groups][N + 1]; // tree->group_buffers->delete_buffer (extra space for sentinel)
 value_type* group_buffer_current_mins[total_num_groups]; // group_buffer_current_mins[i] is current start of group_buffers[i], end is group_buffers[i] + N

 // overall delete buffer
 value_type delete_buffer[delete_buffer_size + 1];
 value_type* delete_buffer_current_min; // current start of delete_buffer
 value_type* delete_buffer_end; // end of delete_buffer

 comparator_type cmp;

 // insert buffer
 insert_heap_type insert_heap;

 // how many groups are active
 unsigned_type num_active_groups;

 // total size not counting insert_heap and delete_buffer
 size_type size_;

private:
 void init();

 void refill_delete_buffer();
 size_type refill_group_buffer(unsigned_type k);

 unsigned_type make_space_available(unsigned_type level);
 void empty_insert_heap();

 value_type get_supremum() const { return cmp.min_value(); } //{ return group_buffers[0][KNN].key; }
 unsigned_type current_delete_buffer_size() const { return delete_buffer_end - delete_buffer_current_min; }
 unsigned_type current_group_buffer_size(unsigned_type i) const { return &(group_buffers[i][N]) - group_buffer_current_mins[i]; }

public:
 //! \name Constructors/Destructors
 //! \{

 //! Constructs external priority queue object.
 //! \param pool_ pool of blocks that will be used
 //! for data writing and prefetching for the disk<->memory transfers
 //! happening in the priority queue. Larger pool size
 //! helps to speed up operations.
 priority_queue(pool_type& pool_);

 //! Constructs external priority queue object.
 //! \param p_pool_ pool of blocks that will be used
 //! for data prefetching for the disk<->memory transfers
 //! happening in the priority queue. Larger pool size
 //! helps to speed up operations.
 //! \param w_pool_ pool of blocks that will be used
 //! for writing data for the memory<->disk transfers
 //! happening in the priority queue. Larger pool size
 //! helps to speed up operations.
 STXXL_DEPRECATED(
 priority_queue(prefetch_pool<block_type>& p_pool_, write_pool<block_type>& w_pool_)
 );

 //! Constructs external priority queue object.
 //! \param p_pool_mem memory (in bytes) for prefetch pool that will be used
 //! for data prefetching for the disk<->memory transfers
 //! happening in the priority queue. Larger pool size
 //! helps to speed up operations.
 //! \param w_pool_mem memory (in bytes) for buffered write pool that will be used
 //! for writing data for the memory<->disk transfers
 //! happening in the priority queue. Larger pool size
 //! helps to speed up operations.
 priority_queue(unsigned_type p_pool_mem, unsigned_type w_pool_mem);

 virtual ~priority_queue();

 //! \}

#if 0

 //! swap this priority queue with another one.
 //! Implementation correctness is questionable.
 void swap(priority_queue& obj)
 {
 //swap_1D_arrays(int_mergers,obj.int_mergers,num_int_groups); // does not work in g++ 3.4.3 :( bug?
 for (unsigned_type i = 0; i < num_int_groups; ++i)
 std::swap(int_mergers[i], obj.int_mergers[i]);

 //std::swap(pool,obj.pool);
 //std::swap(pool_owned, obj.pool_owned);
 std::swap(ext_mergers, obj.ext_mergers);
 for (unsigned_type i1 = 0; i1 < total_num_groups; ++i1)
 for (unsigned_type i2 = 0; i2 < (N + 1); ++i2)
 std::swap(group_buffers[i1][i2], obj.group_buffers[i1][i2]);

 STXXL_STATIC_ASSERT(false);
 // Shoot yourself in the foot: group_buffer_current_mins contains pointers into group_buffers ...
 // either recompute them or add/subtract (&this->group_buffers[0][0] - &obj->group_buffers[0][0])
 swap_1D_arrays(group_buffer_current_mins, obj.group_buffer_current_mins, total_num_groups);
 swap_1D_arrays(delete_buffer, obj.delete_buffer, delete_buffer_size + 1);
 std::swap(delete_buffer_current_min, obj.delete_buffer_current_min);
 std::swap(delete_buffer_end, obj.delete_buffer_end);
 std::swap(cmp, obj.cmp);
 std::swap(insert_heap, obj.insert_heap);
 std::swap(num_active_groups, obj.num_active_groups);
 std::swap(size_, obj.size_);
 }
#endif

 //! \name Capacity
 //! \{

 //! Returns number of elements contained.
 //! \return number of elements contained
 size_type size() const;

 //! Returns true if queue has no elements.
 //! \return \b true if queue has no elements, \b false otherwise
 bool empty() const { return (size() == 0); }

 //! \}

 //! \name Operators
 //! \{

 //! Returns "largest" element.
 //!
 //! Returns a const reference to the element at the top of the
 //! priority_queue. The element at the top is guaranteed to be the largest
 //! element in the \b priority queue, as determined by the comparison
 //! function \b comparator_type (the same as the second parameter of
 //! PRIORITY_QUEUE_GENERATOR utility class). That is, for every other
 //! element \b x in the priority_queue, \b comparator_type(Q.top(), x) is
 //! false. Precondition: \c empty() is false.
 const value_type & top() const;

 //! \}

 //! \name Modifiers
 //! \{

 //! Removes the element at the top.
 //!
 //! Removes the element at the top of the priority_queue, that is, the
 //! largest element in the \b priority_queue. Precondition: \c empty() is
 //! \b false. Postcondition: \c size() will be decremented by 1.
 void pop();

 //! Inserts x into the priority_queue.
 //!
 //! Inserts x into the priority_queue. Postcondition: \c size() will be
 //! incremented by 1.
 void push(const value_type& obj);

 //! \}

 //! \name Miscellaneous
 //! \{

 //! Number of bytes consumed by the \b priority_queue from the internal
 //! memory not including pools (see the constructor)
 unsigned_type mem_cons() const
 {
 unsigned_type dynam_alloc_mem = 0;
 //dynam_alloc_mem += w_pool.mem_cons();
 //dynam_alloc_mem += p_pool.mem_cons();
 for (int i = 0; i < num_int_groups; ++i)
 dynam_alloc_mem += int_mergers[i].mem_cons();

 for (int i = 0; i < num_ext_groups; ++i)
 dynam_alloc_mem += ext_mergers[i]->mem_cons();

 return (sizeof(*this) +
 sizeof(ext_merger_type) * num_ext_groups +
 dynam_alloc_mem);
 }

 void dump_sizes() const;
 void dump_params() const;

 //! \}
};

template <class ConfigType>
inline typename priority_queue<ConfigType>::size_type
priority_queue<ConfigType>::size() const
{
 return size_ +
 insert_heap.size() - 1 +
 (delete_buffer_end - delete_buffer_current_min);
}

template <class ConfigType>
inline const typename priority_queue<ConfigType>::value_type &
priority_queue<ConfigType>::top() const
{
 assert(!insert_heap.empty());

 const typename priority_queue<ConfigType>::value_type& t = insert_heap.top();
 if (/*(!insert_heap.empty()) && */ cmp(*delete_buffer_current_min, t))
 return t;
 else
 return *delete_buffer_current_min;
}

template <class ConfigType>
inline void priority_queue<ConfigType>::pop()
{
 //STXXL_VERBOSE1("priority_queue::pop()");
 assert(!insert_heap.empty());

 if (/*(!insert_heap.empty()) && */ cmp(*delete_buffer_current_min, insert_heap.top()))
 insert_heap.pop();
 else
 {
 assert(delete_buffer_current_min < delete_buffer_end);
 ++delete_buffer_current_min;
 if (delete_buffer_current_min == delete_buffer_end)
 refill_delete_buffer();
 }
}

template <class ConfigType>
inline void priority_queue<ConfigType>::push(const value_type& obj)
{
 //STXXL_VERBOSE3("priority_queue::push("<< obj <<")");
 assert(int_mergers->not_sentinel(obj));
 if (insert_heap.size() == N + 1)
 empty_insert_heap();

 assert(!insert_heap.empty());

 insert_heap.push(obj);
}

////////////////////////////////////////////////////////////////

template <class ConfigType>
priority_queue<ConfigType>::priority_queue(pool_type& pool_)
 : pool(&pool_),
 pool_owned(false),
 delete_buffer_end(delete_buffer + delete_buffer_size),
 insert_heap(N + 2),
 num_active_groups(0), size_(0)
{
 STXXL_VERBOSE_PQ("priority_queue(pool)");
 init();
}

// DEPRECATED
template <class ConfigType>
priority_queue<ConfigType>::priority_queue(prefetch_pool<block_type>& p_pool_, write_pool<block_type>& w_pool_)
 : pool(new pool_type(p_pool_, w_pool_)),
 pool_owned(true),
 delete_buffer_end(delete_buffer + delete_buffer_size),
 insert_heap(N + 2),
 num_active_groups(0), size_(0)
{
 STXXL_VERBOSE_PQ("priority_queue(p_pool, w_pool)");
 init();
}

template <class ConfigType>
priority_queue<ConfigType>::priority_queue(unsigned_type p_pool_mem, unsigned_type w_pool_mem)
 : pool(new pool_type(p_pool_mem / BlockSize, w_pool_mem / BlockSize)),
 pool_owned(true),
 delete_buffer_end(delete_buffer + delete_buffer_size),
 insert_heap(N + 2),
 num_active_groups(0), size_(0)
{
 STXXL_VERBOSE_PQ("priority_queue(pool sizes)");
 init();
}

template <class ConfigType>
void priority_queue<ConfigType>::init()
{
 assert(!cmp(cmp.min_value(), cmp.min_value())); // verify strict weak ordering

 ext_mergers = new ext_merger_type*[num_ext_groups];
 for (unsigned_type j = 0; j < num_ext_groups; ++j) {
 ext_mergers[j] = new ext_merger_type;
 ext_mergers[j]->set_pool(pool);
 }

 value_type sentinel = cmp.min_value();
 insert_heap.push(sentinel); // always keep the sentinel
 delete_buffer[delete_buffer_size] = sentinel; // sentinel
 delete_buffer_current_min = delete_buffer_end; // empty
 for (unsigned_type i = 0; i < total_num_groups; i++)
 {
 group_buffers[i][N] = sentinel; // sentinel
 group_buffer_current_mins[i] = &(group_buffers[i][N]); // empty
 }
}

template <class ConfigType>
priority_queue<ConfigType>::~priority_queue()
{
 STXXL_VERBOSE_PQ("~priority_queue()");
 if (pool_owned)
 delete pool;

 for (unsigned_type j = 0; j < num_ext_groups; ++j)
 delete ext_mergers[j];
 delete[] ext_mergers;
}

//--------------------- Buffer refilling -------------------------------

// refill group_buffers[j] and return number of elements found
template <class ConfigType>
typename priority_queue<ConfigType>::size_type
priority_queue<ConfigType>::refill_group_buffer(unsigned_type group)
{
 STXXL_VERBOSE_PQ("refill_group_buffer(" << group << ")");

 value_type* target;
 size_type length;
 size_type group_size = (group < num_int_groups) ?
 int_mergers[group].size() :
 ext_mergers[group - num_int_groups]->size(); // elements left in segments
 unsigned_type left_elements = group_buffers[group] + N - group_buffer_current_mins[group]; //elements left in target buffer
 if (group_size + left_elements >= size_type(N))
 { // buffer will be filled completely
 target = group_buffers[group];
 length = N - left_elements;
 }
 else
 {
 target = group_buffers[group] + N - group_size - left_elements;
 length = group_size;
 }

 if (length > 0)
 {
 // shift remaininig elements to front
 memmove(target, group_buffer_current_mins[group], left_elements * sizeof(value_type));
 group_buffer_current_mins[group] = target;

 // fill remaining space from group
 if (group < num_int_groups)
 int_mergers[group].multi_merge(target + left_elements,
 (unsigned_type)length);
 else
 ext_mergers[group - num_int_groups]->multi_merge(
 target + left_elements,
 target + left_elements + length);
 }

 //STXXL_MSG(length + left_elements);
 //std::copy(target,target + length + left_elements,std::ostream_iterator<value_type>(std::cout, "\n"));
#if STXXL_CHECK_ORDER_IN_SORTS
 priority_queue_local::invert_order<typename Config::comparator_type, value_type, value_type> inv_cmp(cmp);
 if (!stxxl::is_sorted(group_buffer_current_mins[group], group_buffers[group] + N, inv_cmp))
 {
 STXXL_VERBOSE_PQ("refill_grp... length: " << length << " left_elements: " << left_elements);
 for (value_type* v = group_buffer_current_mins[group] + 1; v < group_buffer_current_mins[group] + left_elements; ++v)
 {
 if (inv_cmp(*v, *(v - 1)))
 {
 STXXL_MSG("Error in buffer " << group << " at position " << (v - group_buffer_current_mins[group] - 1) << "/" << (v - group_buffer_current_mins[group]) << " " << *(v - 2) << " " << *(v - 1) << " " << *v << " " << *(v + 1));
 }
 }
 assert(false);
 }
#endif

 return length + left_elements;
}

template <class ConfigType>
void priority_queue<ConfigType>::refill_delete_buffer()
{
 STXXL_VERBOSE_PQ("refill_delete_buffer()");

 size_type total_group_size = 0;
 //num_active_groups is <= 4
 for (unsigned_type i = num_active_groups; i > 0; )
 {
 --i;
 if ((group_buffers[i] + N) - group_buffer_current_mins[i] < delete_buffer_size)
 {
 size_type length = refill_group_buffer(i);
 // max active level dry now?
 if (length == 0 && unsigned(i) == num_active_groups - 1)
 --num_active_groups;

 total_group_size += length;
 }
 else
 total_group_size += delete_buffer_size; // actually only a sufficient lower bound
 }

 size_type length;
 if (total_group_size >= delete_buffer_size) // buffer can be filled completely
 {
 length = delete_buffer_size; // amount to be copied
 size_ -= size_type(delete_buffer_size); // amount left in group_buffers
 }
 else
 {
 length = total_group_size;
 assert(size_ == length); // trees and group_buffers get empty
 size_ = 0;
 }

 priority_queue_local::invert_order<typename Config::comparator_type, value_type, value_type> inv_cmp(cmp);

 // now call simplified refill routines
 // which can make the assumption that
 // they find all they are asked in the buffers
 delete_buffer_current_min = delete_buffer_end - length;
 STXXL_VERBOSE_PQ("refill_del... Active groups = " << num_active_groups);
 switch (num_active_groups)
 {
 case 0:
 break;
 case 1:
 std::copy(group_buffer_current_mins[0], group_buffer_current_mins[0] + length, delete_buffer_current_min);
 group_buffer_current_mins[0] += length;
 break;
 case 2:
#if STXXL_PARALLEL && STXXL_PARALLEL_PQ_MULTIWAY_MERGE_DELETE_BUFFER
 {
 std::pair<value_type*, value_type*> seqs[2] =
 {
 std::make_pair(group_buffer_current_mins[0], group_buffers[0] + N),
 std::make_pair(group_buffer_current_mins[1], group_buffers[1] + N)
 };
 parallel::multiway_merge_sentinel(seqs, seqs + 2, delete_buffer_current_min, inv_cmp, length); //sequence iterators are progressed appropriately

 group_buffer_current_mins[0] = seqs[0].first;
 group_buffer_current_mins[1] = seqs[1].first;
 }
#else
 priority_queue_local::merge_iterator(
 group_buffer_current_mins[0],
 group_buffer_current_mins[1], delete_buffer_current_min, length, cmp);
#endif
 break;
 case 3:
#if STXXL_PARALLEL && STXXL_PARALLEL_PQ_MULTIWAY_MERGE_DELETE_BUFFER
 {
 std::pair<value_type*, value_type*> seqs[3] =
 {
 std::make_pair(group_buffer_current_mins[0], group_buffers[0] + N),
 std::make_pair(group_buffer_current_mins[1], group_buffers[1] + N),
 std::make_pair(group_buffer_current_mins[2], group_buffers[2] + N)
 };
 parallel::multiway_merge_sentinel(seqs, seqs + 3, delete_buffer_current_min, inv_cmp, length); //sequence iterators are progressed appropriately

 group_buffer_current_mins[0] = seqs[0].first;
 group_buffer_current_mins[1] = seqs[1].first;
 group_buffer_current_mins[2] = seqs[2].first;
 }
#else
 priority_queue_local::merge3_iterator(
 group_buffer_current_mins[0],
 group_buffer_current_mins[1],
 group_buffer_current_mins[2], delete_buffer_current_min, length, cmp);
#endif
 break;
 case 4:
#if STXXL_PARALLEL && STXXL_PARALLEL_PQ_MULTIWAY_MERGE_DELETE_BUFFER
 {
 std::pair<value_type*, value_type*> seqs[4] =
 {
 std::make_pair(group_buffer_current_mins[0], group_buffers[0] + N),
 std::make_pair(group_buffer_current_mins[1], group_buffers[1] + N),
 std::make_pair(group_buffer_current_mins[2], group_buffers[2] + N),
 std::make_pair(group_buffer_current_mins[3], group_buffers[3] + N)
 };
 parallel::multiway_merge_sentinel(seqs, seqs + 4, delete_buffer_current_min, inv_cmp, length); //sequence iterators are progressed appropriately

 group_buffer_current_mins[0] = seqs[0].first;
 group_buffer_current_mins[1] = seqs[1].first;
 group_buffer_current_mins[2] = seqs[2].first;
 group_buffer_current_mins[3] = seqs[3].first;
 }
#else
 priority_queue_local::merge4_iterator(
 group_buffer_current_mins[0],
 group_buffer_current_mins[1],
 group_buffer_current_mins[2],
 group_buffer_current_mins[3], delete_buffer_current_min, length, cmp); //side effect free
#endif
 break;
 default:
 STXXL_THROW2(std::runtime_error, "priority_queue<...>::refill_delete_buffer()",
 "Overflow! The number of buffers on 2nd level in stxxl::priority_queue is currently limited to 4");
 }

#if STXXL_CHECK_ORDER_IN_SORTS
 if (!stxxl::is_sorted(delete_buffer_current_min, delete_buffer_end, inv_cmp))
 {
 for (value_type* v = delete_buffer_current_min + 1; v < delete_buffer_end; ++v)
 {
 if (inv_cmp(*v, *(v - 1)))
 {
 STXXL_MSG("Error at position " << (v - delete_buffer_current_min - 1) << "/" << (v - delete_buffer_current_min) << " " << *(v - 1) << " " << *v);
 }
 }
 assert(false);
 }
#endif
 //std::copy(delete_buffer_current_min,delete_buffer_current_min + length,std::ostream_iterator<value_type>(std::cout, "\n"));
}

//--------------------------------------------------------------------

// check if space is available on level k and
// empty this level if necessary leading to a recursive call.
// return the level where space was finally available
template <class ConfigType>
unsigned_type priority_queue<ConfigType>::make_space_available(unsigned_type level)
{
 STXXL_VERBOSE_PQ("make_space_available(" << level << ")");
 unsigned_type finalLevel;
 assert(level < total_num_groups);
 assert(level <= num_active_groups);

 if (level == num_active_groups)
 ++num_active_groups;

 const bool spaceIsAvailable_ =
 (level < num_int_groups) ? int_mergers[level].is_space_available()
 : (ext_mergers[level - num_int_groups]->is_space_available());

 if (spaceIsAvailable_)
 {
 finalLevel = level;
 }
 else if (level == total_num_groups - 1)
 {
 size_type capacity = N;
 for (int i = 0; i < num_int_groups; ++i)
 capacity *= IntKMAX;
 for (int i = 0; i < num_ext_groups; ++i)
 capacity *= ExtKMAX;
 STXXL_ERRMSG("priority_queue OVERFLOW - all groups full, size=" << size() <<
 ", capacity(last externel group (" << num_int_groups + num_ext_groups - 1 << "))=" << capacity);
 dump_sizes();

 unsigned_type extLevel = level - num_int_groups;
 const size_type segmentSize = ext_mergers[extLevel]->size();
 STXXL_VERBOSE1("Inserting segment into last level external: " << level << " " << segmentSize);
 ext_merger_type* overflow_merger = new ext_merger_type;
 overflow_merger->set_pool(pool);
 overflow_merger->insert_segment(*ext_mergers[extLevel], segmentSize);
 std::swap(ext_mergers[extLevel], overflow_merger);
 delete overflow_merger;
 finalLevel = level;
 }
 else
 {
 finalLevel = make_space_available(level + 1);

 if (level < num_int_groups - 1) // from internal to internal tree
 {
 unsigned_type segmentSize = int_mergers[level].size();
 value_type* newSegment = new value_type[segmentSize + 1];
 int_mergers[level].multi_merge(newSegment, segmentSize); // empty this level

 newSegment[segmentSize] = delete_buffer[delete_buffer_size]; // sentinel
 // for queues where size << #inserts
 // it might make sense to stay in this level if
 // segmentSize < alpha * KNN * k^level for some alpha < 1
 int_mergers[level + 1].insert_segment(newSegment, segmentSize);
 }
 else
 {
 if (level == num_int_groups - 1) // from internal to external tree
 {
 const unsigned_type segmentSize = int_mergers[num_int_groups - 1].size();
 STXXL_VERBOSE_PQ("make_space... Inserting segment into first level external: " << level << " " << segmentSize);
 ext_mergers[0]->insert_segment(int_mergers[num_int_groups - 1], segmentSize);
 }
 else // from external to external tree
 {
 const size_type segmentSize = ext_mergers[level - num_int_groups]->size();
 STXXL_VERBOSE_PQ("make_space... Inserting segment into second level external: " << level << " " << segmentSize);
 ext_mergers[level - num_int_groups + 1]->insert_segment(*ext_mergers[level - num_int_groups], segmentSize);
 }
 }
 }
 return finalLevel;
}

// empty the insert heap into the main data structure
template <class ConfigType>
void priority_queue<ConfigType>::empty_insert_heap()
{
 STXXL_VERBOSE_PQ("empty_insert_heap()");
 assert(insert_heap.size() == (N + 1));

 const value_type sup = get_supremum();

 // build new segment
 value_type* newSegment = new value_type[N + 1];
 value_type* newPos = newSegment;

 // put the new data there for now
 //insert_heap.sortTo(newSegment);
 value_type* SortTo = newSegment;

 insert_heap.sort_to(SortTo);

 SortTo = newSegment + N;
 insert_heap.clear();
 insert_heap.push(*SortTo);

 assert(insert_heap.size() == 1);

 newSegment[N] = sup; // sentinel

 // copy the delete_buffer and group_buffers[0] to temporary storage
 // (the temporary can be eliminated using some dirty tricks)
 const unsigned_type tempSize = N + delete_buffer_size;
 value_type temp[tempSize + 1];
 unsigned_type sz1 = current_delete_buffer_size();
 unsigned_type sz2 = current_group_buffer_size(0);
 value_type* pos = temp + tempSize - sz1 - sz2;
 std::copy(delete_buffer_current_min, delete_buffer_current_min + sz1, pos);
 std::copy(group_buffer_current_mins[0], group_buffer_current_mins[0] + sz2, pos + sz1);
 temp[tempSize] = sup; // sentinel

 // refill delete_buffer
 // (using more complicated code it could be made somewhat fuller
 // in certain circumstances)
 priority_queue_local::merge_iterator(pos, newPos, delete_buffer_current_min, sz1, cmp);

 // refill group_buffers[0]
 // (as above we might want to take the opportunity
 // to make group_buffers[0] fuller)
 priority_queue_local::merge_iterator(pos, newPos, group_buffer_current_mins[0], sz2, cmp);

 // merge the rest to the new segment
 // note that merge exactly trips into the footsteps
 // of itself
 priority_queue_local::merge_iterator(pos, newPos, newSegment, (unsigned_type)N, cmp);

 // and insert it
 unsigned_type freeLevel = make_space_available(0);
 assert(freeLevel == 0 || int_mergers[0].size() == 0);
 int_mergers[0].insert_segment(newSegment, N);

 // get rid of invalid level 2 buffers
 // by inserting them into tree 0 (which is almost empty in this case)
 if (freeLevel > 0)
 {
 for (int_type i = freeLevel; i >= 0; i--)
 {
 // reverse order not needed
 // but would allow immediate refill

 newSegment = new value_type[current_group_buffer_size(i) + 1]; // with sentinel
 std::copy(group_buffer_current_mins[i], group_buffer_current_mins[i] + current_group_buffer_size(i) + 1, newSegment);
 int_mergers[0].insert_segment(newSegment, current_group_buffer_size(i));
 group_buffer_current_mins[i] = group_buffers[i] + N; // empty
 }
 }

 // update size
 size_ += size_type(N);

 // special case if the tree was empty before
 if (delete_buffer_current_min == delete_buffer_end)
 refill_delete_buffer();
}

template <class ConfigType>
void priority_queue<ConfigType>::dump_sizes() const
{
 unsigned_type capacity = N;
 STXXL_MSG("pq::size()\t= " << size());
 STXXL_MSG(" insert_heap\t= " << insert_heap.size() - 1 << "/" << capacity);
 STXXL_MSG(" delete_buffer\t= " << (delete_buffer_end - delete_buffer_current_min) << "/" << delete_buffer_size);
 for (int i = 0; i < num_int_groups; ++i) {
 capacity *= IntKMAX;
 STXXL_MSG(" grp " << i << " int" <<
 " grpbuf=" << current_group_buffer_size(i) <<
 " size=" << int_mergers[i].size() << "/" << capacity <<
 " (" << (int)((double)int_mergers[i].size() * 100.0 / (double)capacity) << "%)" <<
 " space=" << int_mergers[i].is_space_available());
 }
 for (int i = 0; i < num_ext_groups; ++i) {
 capacity *= ExtKMAX;
 STXXL_MSG(" grp " << i + num_int_groups << " ext" <<
 " grpbuf=" << current_group_buffer_size(i + num_int_groups) <<
 " size=" << ext_mergers[i]->size() << "/" << capacity <<
 " (" << (int)((double)ext_mergers[i]->size() * 100.0 / (double)capacity) << "%)" <<
 " space=" << ext_mergers[i]->is_space_available());
 }
 dump_params();
}

template <class ConfigType>
void priority_queue<ConfigType>::dump_params() const
{
 STXXL_MSG("params: delete_buffer_size=" << delete_buffer_size << " N=" << N << " IntKMAX=" << IntKMAX << " num_int_groups=" << num_int_groups << " ExtKMAX=" << ExtKMAX << " num_ext_groups=" << num_ext_groups << " BlockSize=" << BlockSize);
}

namespace priority_queue_local {

struct Parameters_for_priority_queue_not_found_Increase_IntMem
{
 enum { fits = false };
 typedef Parameters_for_priority_queue_not_found_Increase_IntMem result;
};

struct dummy
{
 enum { fits = false };
 typedef dummy result;
};

template <internal_size_type ElementSize, internal_size_type IntMem,
 external_size_type MaxItems, internal_size_type BlockSize,
 unsigned_type m_, bool stop = false>
struct find_B_m
{
 typedef find_B_m<ElementSize, IntMem,
 MaxItems, BlockSize, m_, stop> self_type;

 //! element size
 static const internal_size_type element_size = ElementSize;
 //! internal memory size of PQ
 static const internal_size_type intmem = IntMem;
 //! block size (iterates from 8 MiB downwards)
 static const internal_size_type B = BlockSize;

 //! number of blocks that fit into internal memory (M)
 static const internal_size_type k = IntMem / BlockSize;
 //! number of blocks fitting into buffers of mergers (arity of both
 //! mergers), increased from 1 to 2048 ?-tb
 static const internal_size_type m = m_;
 //! remaining blocks, (freely moving, not necessarily unused) ?-tb
 static const int_type c = k - m_;

 // memory occupied by block must be at least 10 times larger than size of ext sequence

 //! calculated boolean whether the configuration fits into internal memory.
 static const external_size_type fits =
 // need some temporary constant-size internal blocks
 (c > 10) &&
 // satisfy items requirement
 (((k - m) * m * (m * B / (ElementSize * 4 * 1024))) >= MaxItems) &&
 // if we have two ext mergers their degree must be at least 64=m/2
 ((MaxItems < ((k - m) * m / (2 * ElementSize)) * 1024) || m >= 128);

 static const unsigned_type step = 1;

 //! if not fits, recurse into configuration with +step more internal buffers
 typedef typename find_B_m<ElementSize, IntMem, MaxItems, B,
 m + step, fits || (m + step >= k)>::result candidate1;
 //! if not fits, recurse into configuration with block size halved.
 typedef typename find_B_m<ElementSize, IntMem, MaxItems, B / 2,
 1, fits || candidate1::fits>::result candidate2;

 //! return a fitting configuration.
 typedef typename IF<fits, self_type, typename IF<candidate1::fits, candidate1, candidate2>::result>::result result;
};

// specialization for the case when no valid parameters are found
template <internal_size_type ElementSize, internal_size_type IntMem,
 external_size_type MaxItems, bool stop>
struct find_B_m<ElementSize, IntMem, MaxItems, 2048, 1, stop>
{
 enum { fits = false };
 typedef Parameters_for_priority_queue_not_found_Increase_IntMem result;
};

// to speedup search
template <internal_size_type ElementSize, internal_size_type IntMem,
 external_size_type MaxItems, unsigned_type BlockSize,
 unsigned_type m_>
struct find_B_m<ElementSize, IntMem, MaxItems, BlockSize, m_, true>
{
 enum { fits = false };
 typedef dummy result;
};

// start search
template <internal_size_type ElementSize, internal_size_type IntMem,
 external_size_type MaxItems>
struct find_settings
{
 // start from block size (8*1024*1024) bytes
 typedef typename find_B_m<ElementSize, IntMem,
 MaxItems, (8* 1024* 1024), 1>::result result;
};

struct Parameters_not_found_Try_to_change_the_Tune_parameter
{
 typedef Parameters_not_found_Try_to_change_the_Tune_parameter result;
};

template <unsigned_type AI_, unsigned_type X_, unsigned_type CriticalSize>
struct compute_N
{
 typedef compute_N<AI_, X_, CriticalSize> Self;

 static const unsigned_type X = X_;
 static const unsigned_type AI = AI_;
 static const unsigned_type N = X / (AI * AI); // two stage internal

 typedef typename IF<(N >= CriticalSize), Self, typename compute_N<AI / 2, X, CriticalSize>::result>::result result;
};

template <unsigned_type X_, unsigned_type CriticalSize_>
struct compute_N<1, X_, CriticalSize_>
{
 typedef Parameters_not_found_Try_to_change_the_Tune_parameter result;
};

} // namespace priority_queue_local

//! \}

//! \addtogroup stlcont
//! \{

//! Priority queue type generator. \n
//! <b> Introduction </b> to priority queue container: see \ref tutorial_pqueue tutorial. \n
//! <b> Design and Internals </b> of priority queue container: see \ref design_pqueue.
//!
//! \tparam ValueType type of the contained objects (POD with no references to internal memory)
//!
//! \tparam CompareType the comparator type used to determine whether one element is
//! smaller than another element.
//!
//! \tparam IntMemory upper limit for internal memory consumption in bytes.
//!
//! \tparam MaxItems upper limit for number of elements contained in the priority queue (in 1024 units). <BR>
//! Example: if you are sure that priority queue contains no more than
//! one million elements in a time, then the right parameter is (1000000 / 1024) = 976.
//!
//! \tparam Tune tuning parameter for meta-program search. <BR>
//! Try to play with it if the code does not compile (larger than default
//! values might help). Code does not compile if no suitable internal
//! parameters were found for given IntMemory and MaxItems. It might also
//! happen that given IntMemory is too small for given MaxItems, try larger
//! values.
template <class ValueType,
 class CompareType,
 internal_size_type IntMemory,
 external_size_type MaxItems,
 unsigned Tune = 6>
class PRIORITY_QUEUE_GENERATOR
{
public:
 // actual calculation of B, m, k and element_size
 typedef typename priority_queue_local::find_settings<sizeof(ValueType), IntMemory, MaxItems>::result settings;
 enum {
 B = settings::B,
 m = settings::m,
 X = B * (settings::k - m) / settings::element_size, // interpretation of result
 Buffer1Size = 32 // fixed
 };
 // derivation of N, AI, AE
 typedef typename priority_queue_local::compute_N<(1 << Tune), X, 4* Buffer1Size>::result ComputeN;
 enum
 {
 N = ComputeN::N,
 AI = ComputeN::AI,
 AE = (m / 2 < 2) ? 2 : (m / 2) // at least 2
 };

 // Estimation of maximum internal memory consumption (in bytes)
 static const unsigned_type EConsumption = X * settings::element_size + settings::B * AE + ((MaxItems / X) / AE) * settings::B * 1024;

 /*
 unsigned BufferSize1_ = 32, // equalize procedure call overheads etc.
 unsigned N_ = 512, // bandwidth
 unsigned IntKMAX_ = 64, // maximal arity for internal mergers
 unsigned IntLevels_ = 4,
 unsigned BlockSize = (2*1024*1024),
 unsigned ExtKMAX_ = 64, // maximal arity for external mergers
 unsigned ExtLevels_ = 2,
 */
 typedef priority_queue<priority_queue_config<ValueType, CompareType, Buffer1Size, N, AI, 2, B, AE, 2> > result;
};

//! \}

STXXL_END_NAMESPACE

namespace std {

template <class ConfigType>
void swap(stxxl::priority_queue<ConfigType>& a,
 stxxl::priority_queue<ConfigType>& b)
{
 a.swap(b);
}

} // namespace std

#endif // !STXXL_CONTAINERS_PRIORITY_QUEUE_HEADER
// vim: et:ts=4:sw=4