_concurrent_queue_impl.h

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/*
    Copyright (c) 2005-2020 Intel Corporation

    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 __TBB__concurrent_queue_impl_H
#define __TBB__concurrent_queue_impl_H

#ifndef __TBB_concurrent_queue_H
#error Do not #include this internal file directly; use public TBB headers instead.
#endif

#include "../tbb_stddef.h"
#include "../tbb_machine.h"
#include "../atomic.h"
#include "../spin_mutex.h"
#include "../cache_aligned_allocator.h"
#include "../tbb_exception.h"
#include "../tbb_profiling.h"
#include <new>
#include __TBB_STD_SWAP_HEADER
#include <iterator>

namespace tbb {

#if !__TBB_TEMPLATE_FRIENDS_BROKEN

// forward declaration
namespace strict_ppl {
template<typename T, typename A> class concurrent_queue;
}

template<typename T, typename A> class concurrent_bounded_queue;

#endif

namespace strict_ppl {

namespace internal {

using namespace tbb::internal;

typedef size_t ticket;

template<typename T> class micro_queue ;
template<typename T> class micro_queue_pop_finalizer ;
template<typename T> class concurrent_queue_base_v3;
template<typename T> struct concurrent_queue_rep;


struct concurrent_queue_rep_base : no_copy {
    template<typename T> friend class micro_queue;
    template<typename T> friend class concurrent_queue_base_v3;

protected:
    static const size_t phi = 3;

public:
    // must be power of 2
    static const size_t n_queue = 8;

    struct page {
        page* next;
        uintptr_t mask;
    };

    atomic<ticket> head_counter;
    char pad1[NFS_MaxLineSize-sizeof(atomic<ticket>)];
    atomic<ticket> tail_counter;
    char pad2[NFS_MaxLineSize-sizeof(atomic<ticket>)];

    size_t items_per_page;

    size_t item_size;

    atomic<size_t> n_invalid_entries;

    char pad3[NFS_MaxLineSize-sizeof(size_t)-sizeof(size_t)-sizeof(atomic<size_t>)];
} ;

inline bool is_valid_page(const concurrent_queue_rep_base::page* p) {
    return uintptr_t(p)>1;
}


class concurrent_queue_page_allocator
{
    template<typename T> friend class micro_queue ;
    template<typename T> friend class micro_queue_pop_finalizer ;
protected:
    virtual ~concurrent_queue_page_allocator() {}
private:
    virtual concurrent_queue_rep_base::page* allocate_page() = 0;
    virtual void deallocate_page( concurrent_queue_rep_base::page* p ) = 0;
} ;

#if _MSC_VER && !defined(__INTEL_COMPILER)
// unary minus operator applied to unsigned type, result still unsigned
#pragma warning( push )
#pragma warning( disable: 4146 )
#endif


template<typename T>
class micro_queue : no_copy {
public:
    typedef void (*item_constructor_t)(T* location, const void* src);
private:
    typedef concurrent_queue_rep_base::page page;

    class destroyer: no_copy {
        T& my_value;
    public:
        destroyer( T& value ) : my_value(value) {}
        ~destroyer() {my_value.~T();}
    };

    void copy_item( page& dst, size_t dindex, const void* src, item_constructor_t construct_item ) {
        construct_item( &get_ref(dst, dindex), src );
    }

    void copy_item( page& dst, size_t dindex, const page& src, size_t sindex,
        item_constructor_t construct_item )
    {
        T& src_item = get_ref( const_cast<page&>(src), sindex );
        construct_item( &get_ref(dst, dindex), static_cast<const void*>(&src_item) );
    }

    void assign_and_destroy_item( void* dst, page& src, size_t index ) {
        T& from = get_ref(src,index);
        destroyer d(from);
        *static_cast<T*>(dst) = tbb::internal::move( from );
    }

    void spin_wait_until_my_turn( atomic<ticket>& counter, ticket k, concurrent_queue_rep_base& rb ) const ;

public:
    friend class micro_queue_pop_finalizer<T>;

    struct padded_page: page {
        padded_page();
        void operator=( const padded_page& );
        T last;
    };

    static T& get_ref( page& p, size_t index ) {
        return (&static_cast<padded_page*>(static_cast<void*>(&p))->last)[index];
    }

    atomic<page*> head_page;
    atomic<ticket> head_counter;

    atomic<page*> tail_page;
    atomic<ticket> tail_counter;

    spin_mutex page_mutex;

    void push( const void* item, ticket k, concurrent_queue_base_v3<T>& base,
        item_constructor_t construct_item ) ;

    bool pop( void* dst, ticket k, concurrent_queue_base_v3<T>& base ) ;

    micro_queue& assign( const micro_queue& src, concurrent_queue_base_v3<T>& base,
        item_constructor_t construct_item ) ;

    page* make_copy( concurrent_queue_base_v3<T>& base, const page* src_page, size_t begin_in_page,
        size_t end_in_page, ticket& g_index, item_constructor_t construct_item ) ;

    void invalidate_page_and_rethrow( ticket k ) ;
};

template<typename T>
void micro_queue<T>::spin_wait_until_my_turn( atomic<ticket>& counter, ticket k, concurrent_queue_rep_base& rb ) const {
    for( atomic_backoff b(true);;b.pause() ) {
        ticket c = counter;
        if( c==k ) return;
        else if( c&1 ) {
            ++rb.n_invalid_entries;
            throw_exception( eid_bad_last_alloc );
        }
    }
}

template<typename T>
void micro_queue<T>::push( const void* item, ticket k, concurrent_queue_base_v3<T>& base,
    item_constructor_t construct_item )
{
    k &= -concurrent_queue_rep_base::n_queue;
    page* p = NULL;
    size_t index = modulo_power_of_two( k/concurrent_queue_rep_base::n_queue, base.my_rep->items_per_page);
    if( !index ) {
        __TBB_TRY {
            concurrent_queue_page_allocator& pa = base;
            p = pa.allocate_page();
        } __TBB_CATCH (...) {
            ++base.my_rep->n_invalid_entries;
            invalidate_page_and_rethrow( k );
        }
        p->mask = 0;
        p->next = NULL;
    }

    if( tail_counter != k ) spin_wait_until_my_turn( tail_counter, k, *base.my_rep );
    call_itt_notify(acquired, &tail_counter);

    if( p ) {
        spin_mutex::scoped_lock lock( page_mutex );
        page* q = tail_page;
        if( is_valid_page(q) )
            q->next = p;
        else
            head_page = p;
        tail_page = p;
    } else {
        p = tail_page;
    }

    __TBB_TRY {
        copy_item( *p, index, item, construct_item );
        // If no exception was thrown, mark item as present.
        itt_hide_store_word(p->mask,  p->mask | uintptr_t(1)<<index);
        call_itt_notify(releasing, &tail_counter);
        tail_counter += concurrent_queue_rep_base::n_queue;
    } __TBB_CATCH (...) {
        ++base.my_rep->n_invalid_entries;
        call_itt_notify(releasing, &tail_counter);
        tail_counter += concurrent_queue_rep_base::n_queue;
        __TBB_RETHROW();
    }
}

template<typename T>
bool micro_queue<T>::pop( void* dst, ticket k, concurrent_queue_base_v3<T>& base ) {
    k &= -concurrent_queue_rep_base::n_queue;
    if( head_counter!=k ) spin_wait_until_eq( head_counter, k );
    call_itt_notify(acquired, &head_counter);
    if( tail_counter==k ) spin_wait_while_eq( tail_counter, k );
    call_itt_notify(acquired, &tail_counter);
    page *p = head_page;
    __TBB_ASSERT( p, NULL );
    size_t index = modulo_power_of_two( k/concurrent_queue_rep_base::n_queue, base.my_rep->items_per_page );
    bool success = false;
    {
        micro_queue_pop_finalizer<T> finalizer( *this, base, k+concurrent_queue_rep_base::n_queue, index==base.my_rep->items_per_page-1 ? p : NULL );
        if( p->mask & uintptr_t(1)<<index ) {
            success = true;
            assign_and_destroy_item( dst, *p, index );
        } else {
            --base.my_rep->n_invalid_entries;
        }
    }
    return success;
}

template<typename T>
micro_queue<T>& micro_queue<T>::assign( const micro_queue<T>& src, concurrent_queue_base_v3<T>& base,
    item_constructor_t construct_item )
{
    head_counter = src.head_counter;
    tail_counter = src.tail_counter;

    const page* srcp = src.head_page;
    if( is_valid_page(srcp) ) {
        ticket g_index = head_counter;
        __TBB_TRY {
            size_t n_items  = (tail_counter-head_counter)/concurrent_queue_rep_base::n_queue;
            size_t index = modulo_power_of_two( head_counter/concurrent_queue_rep_base::n_queue, base.my_rep->items_per_page );
            size_t end_in_first_page = (index+n_items<base.my_rep->items_per_page)?(index+n_items):base.my_rep->items_per_page;

            head_page = make_copy( base, srcp, index, end_in_first_page, g_index, construct_item );
            page* cur_page = head_page;

            if( srcp != src.tail_page ) {
                for( srcp = srcp->next; srcp!=src.tail_page; srcp=srcp->next ) {
                    cur_page->next = make_copy( base, srcp, 0, base.my_rep->items_per_page, g_index, construct_item );
                    cur_page = cur_page->next;
                }

                __TBB_ASSERT( srcp==src.tail_page, NULL );
                size_t last_index = modulo_power_of_two( tail_counter/concurrent_queue_rep_base::n_queue, base.my_rep->items_per_page );
                if( last_index==0 ) last_index = base.my_rep->items_per_page;

                cur_page->next = make_copy( base, srcp, 0, last_index, g_index, construct_item );
                cur_page = cur_page->next;
            }
            tail_page = cur_page;
        } __TBB_CATCH (...) {
            invalidate_page_and_rethrow( g_index );
        }
    } else {
        head_page = tail_page = NULL;
    }
    return *this;
}

template<typename T>
void micro_queue<T>::invalidate_page_and_rethrow( ticket k ) {
    // Append an invalid page at address 1 so that no more pushes are allowed.
    page* invalid_page = (page*)uintptr_t(1);
    {
        spin_mutex::scoped_lock lock( page_mutex );
        itt_store_word_with_release(tail_counter, k+concurrent_queue_rep_base::n_queue+1);
        page* q = tail_page;
        if( is_valid_page(q) )
            q->next = invalid_page;
        else
            head_page = invalid_page;
        tail_page = invalid_page;
    }
    __TBB_RETHROW();
}

template<typename T>
concurrent_queue_rep_base::page* micro_queue<T>::make_copy( concurrent_queue_base_v3<T>& base,
    const concurrent_queue_rep_base::page* src_page, size_t begin_in_page, size_t end_in_page,
    ticket& g_index, item_constructor_t construct_item )
{
    concurrent_queue_page_allocator& pa = base;
    page* new_page = pa.allocate_page();
    new_page->next = NULL;
    new_page->mask = src_page->mask;
    for( ; begin_in_page!=end_in_page; ++begin_in_page, ++g_index )
        if( new_page->mask & uintptr_t(1)<<begin_in_page )
            copy_item( *new_page, begin_in_page, *src_page, begin_in_page, construct_item );
    return new_page;
}

template<typename T>
class micro_queue_pop_finalizer: no_copy {
    typedef concurrent_queue_rep_base::page page;
    ticket my_ticket;
    micro_queue<T>& my_queue;
    page* my_page;
    concurrent_queue_page_allocator& allocator;
public:
    micro_queue_pop_finalizer( micro_queue<T>& queue, concurrent_queue_base_v3<T>& b, ticket k, page* p ) :
        my_ticket(k), my_queue(queue), my_page(p), allocator(b)
    {}
    ~micro_queue_pop_finalizer() ;
};

template<typename T>
micro_queue_pop_finalizer<T>::~micro_queue_pop_finalizer() {
    page* p = my_page;
    if( is_valid_page(p) ) {
        spin_mutex::scoped_lock lock( my_queue.page_mutex );
        page* q = p->next;
        my_queue.head_page = q;
        if( !is_valid_page(q) ) {
            my_queue.tail_page = NULL;
        }
    }
    itt_store_word_with_release(my_queue.head_counter, my_ticket);
    if( is_valid_page(p) ) {
        allocator.deallocate_page( p );
    }
}

#if _MSC_VER && !defined(__INTEL_COMPILER)
#pragma warning( pop )
#endif // warning 4146 is back

template<typename T> class concurrent_queue_iterator_rep ;
template<typename T> class concurrent_queue_iterator_base_v3;


template<typename T>
struct concurrent_queue_rep : public concurrent_queue_rep_base {
    micro_queue<T> array[n_queue];

    static size_t index( ticket k ) {
        return k*phi%n_queue;
    }

    micro_queue<T>& choose( ticket k ) {
        // The formula here approximates LRU in a cache-oblivious way.
        return array[index(k)];
    }
};


template<typename T>
class concurrent_queue_base_v3: public concurrent_queue_page_allocator {
private:
    concurrent_queue_rep<T>* my_rep;

    friend struct concurrent_queue_rep<T>;
    friend class micro_queue<T>;
    friend class concurrent_queue_iterator_rep<T>;
    friend class concurrent_queue_iterator_base_v3<T>;

protected:
    typedef typename concurrent_queue_rep<T>::page page;

private:
    typedef typename micro_queue<T>::padded_page padded_page;
    typedef typename micro_queue<T>::item_constructor_t item_constructor_t;

    virtual page *allocate_page() __TBB_override {
        concurrent_queue_rep<T>& r = *my_rep;
        size_t n = sizeof(padded_page) + (r.items_per_page-1)*sizeof(T);
        return reinterpret_cast<page*>(allocate_block ( n ));
    }

    virtual void deallocate_page( concurrent_queue_rep_base::page *p ) __TBB_override {
        concurrent_queue_rep<T>& r = *my_rep;
        size_t n = sizeof(padded_page) + (r.items_per_page-1)*sizeof(T);
        deallocate_block( reinterpret_cast<void*>(p), n );
    }

    virtual void *allocate_block( size_t n ) = 0;

    virtual void deallocate_block( void *p, size_t n ) = 0;

protected:
    concurrent_queue_base_v3();

    virtual ~concurrent_queue_base_v3() {
#if TBB_USE_ASSERT
        size_t nq = my_rep->n_queue;
        for( size_t i=0; i<nq; i++ )
            __TBB_ASSERT( my_rep->array[i].tail_page==NULL, "pages were not freed properly" );
#endif /* TBB_USE_ASSERT */
        cache_aligned_allocator<concurrent_queue_rep<T> >().deallocate(my_rep,1);
    }

    void internal_push( const void* src, item_constructor_t construct_item ) {
         concurrent_queue_rep<T>& r = *my_rep;
         ticket k = r.tail_counter++;
         r.choose(k).push( src, k, *this, construct_item );
    }


    bool internal_try_pop( void* dst ) ;

    size_t internal_size() const ;

    bool internal_empty() const ;

    /* note that the name may be misleading, but it remains so due to a historical accident. */
    void internal_finish_clear() ;

    void internal_throw_exception() const {
        throw_exception( eid_bad_alloc );
    }

    void assign( const concurrent_queue_base_v3& src, item_constructor_t construct_item ) ;

#if __TBB_CPP11_RVALUE_REF_PRESENT
    void internal_swap( concurrent_queue_base_v3& src ) {
        std::swap( my_rep, src.my_rep );
    }
#endif /* __TBB_CPP11_RVALUE_REF_PRESENT */
};

template<typename T>
concurrent_queue_base_v3<T>::concurrent_queue_base_v3() {
    const size_t item_size = sizeof(T);
    my_rep = cache_aligned_allocator<concurrent_queue_rep<T> >().allocate(1);
    __TBB_ASSERT( (size_t)my_rep % NFS_GetLineSize()==0, "alignment error" );
    __TBB_ASSERT( (size_t)&my_rep->head_counter % NFS_GetLineSize()==0, "alignment error" );
    __TBB_ASSERT( (size_t)&my_rep->tail_counter % NFS_GetLineSize()==0, "alignment error" );
    __TBB_ASSERT( (size_t)&my_rep->array % NFS_GetLineSize()==0, "alignment error" );
    memset(static_cast<void*>(my_rep),0,sizeof(concurrent_queue_rep<T>));
    my_rep->item_size = item_size;
    my_rep->items_per_page = item_size<=  8 ? 32 :
                             item_size<= 16 ? 16 :
                             item_size<= 32 ?  8 :
                             item_size<= 64 ?  4 :
                             item_size<=128 ?  2 :
                             1;
}

template<typename T>
bool concurrent_queue_base_v3<T>::internal_try_pop( void* dst ) {
    concurrent_queue_rep<T>& r = *my_rep;
    ticket k;
    do {
        k = r.head_counter;
        for(;;) {
            if( (ptrdiff_t)(r.tail_counter-k)<=0 ) {
                // Queue is empty
                return false;
            }
            // Queue had item with ticket k when we looked.  Attempt to get that item.
            ticket tk=k;
#if defined(_MSC_VER) && defined(_Wp64)
    #pragma warning (push)
    #pragma warning (disable: 4267)
#endif
            k = r.head_counter.compare_and_swap( tk+1, tk );
#if defined(_MSC_VER) && defined(_Wp64)
    #pragma warning (pop)
#endif
            if( k==tk )
                break;
            // Another thread snatched the item, retry.
        }
    } while( !r.choose( k ).pop( dst, k, *this ) );
    return true;
}

template<typename T>
size_t concurrent_queue_base_v3<T>::internal_size() const {
    concurrent_queue_rep<T>& r = *my_rep;
    __TBB_ASSERT( sizeof(ptrdiff_t)<=sizeof(size_t), NULL );
    ticket hc = r.head_counter;
    size_t nie = r.n_invalid_entries;
    ticket tc = r.tail_counter;
    __TBB_ASSERT( hc!=tc || !nie, NULL );
    ptrdiff_t sz = tc-hc-nie;
    return sz<0 ? 0 :  size_t(sz);
}

template<typename T>
bool concurrent_queue_base_v3<T>::internal_empty() const {
    concurrent_queue_rep<T>& r = *my_rep;
    ticket tc = r.tail_counter;
    ticket hc = r.head_counter;
    // if tc!=r.tail_counter, the queue was not empty at some point between the two reads.
    return tc==r.tail_counter && tc==hc+r.n_invalid_entries ;
}

template<typename T>
void concurrent_queue_base_v3<T>::internal_finish_clear() {
    concurrent_queue_rep<T>& r = *my_rep;
    size_t nq = r.n_queue;
    for( size_t i=0; i<nq; ++i ) {
        page* tp = r.array[i].tail_page;
        if( is_valid_page(tp) ) {
            __TBB_ASSERT( r.array[i].head_page==tp, "at most one page should remain" );
            deallocate_page( tp );
            r.array[i].tail_page = NULL;
        } else
            __TBB_ASSERT( !is_valid_page(r.array[i].head_page), "head page pointer corrupt?" );
    }
}

template<typename T>
void concurrent_queue_base_v3<T>::assign( const concurrent_queue_base_v3& src,
    item_constructor_t construct_item )
{
    concurrent_queue_rep<T>& r = *my_rep;
    r.items_per_page = src.my_rep->items_per_page;

    // copy concurrent_queue_rep data
    r.head_counter = src.my_rep->head_counter;
    r.tail_counter = src.my_rep->tail_counter;
    r.n_invalid_entries = src.my_rep->n_invalid_entries;

    // copy or move micro_queues
    for( size_t i = 0; i < r.n_queue; ++i )
        r.array[i].assign( src.my_rep->array[i], *this, construct_item);

    __TBB_ASSERT( r.head_counter==src.my_rep->head_counter && r.tail_counter==src.my_rep->tail_counter,
            "the source concurrent queue should not be concurrently modified." );
}

template<typename Container, typename Value> class concurrent_queue_iterator;

template<typename T>
class concurrent_queue_iterator_rep: no_assign {
    typedef typename micro_queue<T>::padded_page padded_page;
public:
    ticket head_counter;
    const concurrent_queue_base_v3<T>& my_queue;
    typename concurrent_queue_base_v3<T>::page* array[concurrent_queue_rep<T>::n_queue];
    concurrent_queue_iterator_rep( const concurrent_queue_base_v3<T>& queue ) :
        head_counter(queue.my_rep->head_counter),
        my_queue(queue)
    {
        for( size_t k=0; k<concurrent_queue_rep<T>::n_queue; ++k )
            array[k] = queue.my_rep->array[k].head_page;
    }

    bool get_item( T*& item, size_t k ) ;
};

template<typename T>
bool concurrent_queue_iterator_rep<T>::get_item( T*& item, size_t k ) {
    if( k==my_queue.my_rep->tail_counter ) {
        item = NULL;
        return true;
    } else {
        typename concurrent_queue_base_v3<T>::page* p = array[concurrent_queue_rep<T>::index(k)];
        __TBB_ASSERT(p,NULL);
        size_t i = modulo_power_of_two( k/concurrent_queue_rep<T>::n_queue, my_queue.my_rep->items_per_page );
        item = &micro_queue<T>::get_ref(*p,i);
        return (p->mask & uintptr_t(1)<<i)!=0;
    }
}


template<typename Value>
class concurrent_queue_iterator_base_v3 {

    concurrent_queue_iterator_rep<Value>* my_rep;

    template<typename C, typename T, typename U>
    friend bool operator==( const concurrent_queue_iterator<C,T>& i, const concurrent_queue_iterator<C,U>& j );

    template<typename C, typename T, typename U>
    friend bool operator!=( const concurrent_queue_iterator<C,T>& i, const concurrent_queue_iterator<C,U>& j );
protected:
    Value* my_item;

    concurrent_queue_iterator_base_v3() : my_rep(NULL), my_item(NULL) {
#if __TBB_GCC_OPTIMIZER_ORDERING_BROKEN
        __TBB_compiler_fence();
#endif
    }

    concurrent_queue_iterator_base_v3( const concurrent_queue_iterator_base_v3& i )
    : my_rep(NULL), my_item(NULL) {
        assign(i);
    }

    concurrent_queue_iterator_base_v3& operator=( const concurrent_queue_iterator_base_v3& i ) {
        assign(i);
        return *this;
    }

    concurrent_queue_iterator_base_v3( const concurrent_queue_base_v3<Value>& queue ) ;

    void assign( const concurrent_queue_iterator_base_v3<Value>& other ) ;

    void advance() ;

    ~concurrent_queue_iterator_base_v3() {
        cache_aligned_allocator<concurrent_queue_iterator_rep<Value> >().deallocate(my_rep, 1);
        my_rep = NULL;
    }
};

template<typename Value>
concurrent_queue_iterator_base_v3<Value>::concurrent_queue_iterator_base_v3( const concurrent_queue_base_v3<Value>& queue ) {
    my_rep = cache_aligned_allocator<concurrent_queue_iterator_rep<Value> >().allocate(1);
    new( my_rep ) concurrent_queue_iterator_rep<Value>(queue);
    size_t k = my_rep->head_counter;
    if( !my_rep->get_item(my_item, k) ) advance();
}

template<typename Value>
void concurrent_queue_iterator_base_v3<Value>::assign( const concurrent_queue_iterator_base_v3<Value>& other ) {
    if( my_rep!=other.my_rep ) {
        if( my_rep ) {
            cache_aligned_allocator<concurrent_queue_iterator_rep<Value> >().deallocate(my_rep, 1);
            my_rep = NULL;
        }
        if( other.my_rep ) {
            my_rep = cache_aligned_allocator<concurrent_queue_iterator_rep<Value> >().allocate(1);
            new( my_rep ) concurrent_queue_iterator_rep<Value>( *other.my_rep );
        }
    }
    my_item = other.my_item;
}

template<typename Value>
void concurrent_queue_iterator_base_v3<Value>::advance() {
    __TBB_ASSERT( my_item, "attempt to increment iterator past end of queue" );
    size_t k = my_rep->head_counter;
    const concurrent_queue_base_v3<Value>& queue = my_rep->my_queue;
#if TBB_USE_ASSERT
    Value* tmp;
    my_rep->get_item(tmp,k);
    __TBB_ASSERT( my_item==tmp, NULL );
#endif /* TBB_USE_ASSERT */
    size_t i = modulo_power_of_two( k/concurrent_queue_rep<Value>::n_queue, queue.my_rep->items_per_page );
    if( i==queue.my_rep->items_per_page-1 ) {
        typename concurrent_queue_base_v3<Value>::page*& root = my_rep->array[concurrent_queue_rep<Value>::index(k)];
        root = root->next;
    }
    // advance k
    my_rep->head_counter = ++k;
    if( !my_rep->get_item(my_item, k) ) advance();
}


template<typename T> struct tbb_remove_cv {typedef T type;};
template<typename T> struct tbb_remove_cv<const T> {typedef T type;};
template<typename T> struct tbb_remove_cv<volatile T> {typedef T type;};
template<typename T> struct tbb_remove_cv<const volatile T> {typedef T type;};


template<typename Container, typename Value>
class concurrent_queue_iterator: public concurrent_queue_iterator_base_v3<typename tbb_remove_cv<Value>::type>,
        public std::iterator<std::forward_iterator_tag,Value> {
#if !__TBB_TEMPLATE_FRIENDS_BROKEN
    template<typename T, class A>
    friend class ::tbb::strict_ppl::concurrent_queue;
#else
public:
#endif
    explicit concurrent_queue_iterator( const concurrent_queue_base_v3<typename tbb_remove_cv<Value>::type>& queue ) :
        concurrent_queue_iterator_base_v3<typename tbb_remove_cv<Value>::type>(queue)
    {
    }

public:
    concurrent_queue_iterator() {}

    concurrent_queue_iterator( const concurrent_queue_iterator<Container,typename Container::value_type>& other ) :
        concurrent_queue_iterator_base_v3<typename tbb_remove_cv<Value>::type>(other)
    {}

    concurrent_queue_iterator& operator=( const concurrent_queue_iterator<Container,typename Container::value_type>& other ) {
        concurrent_queue_iterator_base_v3<typename tbb_remove_cv<Value>::type>::operator=(other);
        return *this;
    }

    Value& operator*() const {
        return *static_cast<Value*>(this->my_item);
    }

    Value* operator->() const {return &operator*();}

    concurrent_queue_iterator& operator++() {
        this->advance();
        return *this;
    }

    Value* operator++(int) {
        Value* result = &operator*();
        operator++();
        return result;
    }
}; // concurrent_queue_iterator


template<typename C, typename T, typename U>
bool operator==( const concurrent_queue_iterator<C,T>& i, const concurrent_queue_iterator<C,U>& j ) {
    return i.my_item==j.my_item;
}

template<typename C, typename T, typename U>
bool operator!=( const concurrent_queue_iterator<C,T>& i, const concurrent_queue_iterator<C,U>& j ) {
    return i.my_item!=j.my_item;
}

} // namespace internal


} // namespace strict_ppl

namespace internal {

class concurrent_queue_rep;
class concurrent_queue_iterator_rep;
class concurrent_queue_iterator_base_v3;
template<typename Container, typename Value> class concurrent_queue_iterator;


class concurrent_queue_base_v3: no_copy {
private:
    concurrent_queue_rep* my_rep;

    friend class concurrent_queue_rep;
    friend struct micro_queue;
    friend class micro_queue_pop_finalizer;
    friend class concurrent_queue_iterator_rep;
    friend class concurrent_queue_iterator_base_v3;
protected:
    struct page {
        page* next;
        uintptr_t mask;
    };

    ptrdiff_t my_capacity;

    size_t items_per_page;

    size_t item_size;

    enum copy_specifics { copy, move };

#if __TBB_PROTECTED_NESTED_CLASS_BROKEN
public:
#endif
    template<typename T>
    struct padded_page: page {
        padded_page();
        void operator=( const padded_page& );
        T last;
    };

private:
    virtual void copy_item( page& dst, size_t index, const void* src ) = 0;
    virtual void assign_and_destroy_item( void* dst, page& src, size_t index ) = 0;
protected:
    __TBB_EXPORTED_METHOD concurrent_queue_base_v3( size_t item_size );
    virtual __TBB_EXPORTED_METHOD ~concurrent_queue_base_v3();

    void __TBB_EXPORTED_METHOD internal_push( const void* src );

    void __TBB_EXPORTED_METHOD internal_pop( void* dst );

    void __TBB_EXPORTED_METHOD internal_abort();

    bool __TBB_EXPORTED_METHOD internal_push_if_not_full( const void* src );


    bool __TBB_EXPORTED_METHOD internal_pop_if_present( void* dst );

    ptrdiff_t __TBB_EXPORTED_METHOD internal_size() const;

    bool __TBB_EXPORTED_METHOD internal_empty() const;

    void __TBB_EXPORTED_METHOD internal_set_capacity( ptrdiff_t capacity, size_t element_size );

    virtual page *allocate_page() = 0;

    virtual void deallocate_page( page *p ) = 0;

    /* note that the name may be misleading, but it remains so due to a historical accident. */
    void __TBB_EXPORTED_METHOD internal_finish_clear() ;

    void __TBB_EXPORTED_METHOD internal_throw_exception() const;

    void __TBB_EXPORTED_METHOD assign( const concurrent_queue_base_v3& src ) ;

#if __TBB_CPP11_RVALUE_REF_PRESENT
    void internal_swap( concurrent_queue_base_v3& src ) {
        std::swap( my_capacity, src.my_capacity );
        std::swap( items_per_page, src.items_per_page );
        std::swap( item_size, src.item_size );
        std::swap( my_rep, src.my_rep );
    }
#endif /* __TBB_CPP11_RVALUE_REF_PRESENT */

    void internal_insert_item( const void* src, copy_specifics op_type );

    bool internal_insert_if_not_full( const void* src, copy_specifics op_type );

    void internal_assign( const concurrent_queue_base_v3& src, copy_specifics op_type );
private:
    virtual void copy_page_item( page& dst, size_t dindex, const page& src, size_t sindex ) = 0;
};


class concurrent_queue_base_v8: public concurrent_queue_base_v3 {
protected:
    concurrent_queue_base_v8( size_t item_sz ) : concurrent_queue_base_v3( item_sz ) {}

    void __TBB_EXPORTED_METHOD move_content( concurrent_queue_base_v8& src ) ;

    bool __TBB_EXPORTED_METHOD internal_push_move_if_not_full( const void* src );

    void __TBB_EXPORTED_METHOD internal_push_move( const void* src );
private:
    friend struct micro_queue;
    virtual void move_page_item( page& dst, size_t dindex, const page& src, size_t sindex ) = 0;
    virtual void move_item( page& dst, size_t index, const void* src ) = 0;
};


class concurrent_queue_iterator_base_v3 {

    concurrent_queue_iterator_rep* my_rep;

    template<typename C, typename T, typename U>
    friend bool operator==( const concurrent_queue_iterator<C,T>& i, const concurrent_queue_iterator<C,U>& j );

    template<typename C, typename T, typename U>
    friend bool operator!=( const concurrent_queue_iterator<C,T>& i, const concurrent_queue_iterator<C,U>& j );

    void initialize( const concurrent_queue_base_v3& queue, size_t offset_of_data );
protected:
    void* my_item;

    concurrent_queue_iterator_base_v3() : my_rep(NULL), my_item(NULL) {}

    concurrent_queue_iterator_base_v3( const concurrent_queue_iterator_base_v3& i ) : my_rep(NULL), my_item(NULL) {
        assign(i);
    }

    concurrent_queue_iterator_base_v3& operator=( const concurrent_queue_iterator_base_v3& i ) {
        assign(i);
        return *this;
    }


    __TBB_EXPORTED_METHOD concurrent_queue_iterator_base_v3( const concurrent_queue_base_v3& queue );

    __TBB_EXPORTED_METHOD concurrent_queue_iterator_base_v3( const concurrent_queue_base_v3& queue, size_t offset_of_data );

    void __TBB_EXPORTED_METHOD assign( const concurrent_queue_iterator_base_v3& i );

    void __TBB_EXPORTED_METHOD advance();

    __TBB_EXPORTED_METHOD ~concurrent_queue_iterator_base_v3();
};

typedef concurrent_queue_iterator_base_v3 concurrent_queue_iterator_base;


template<typename Container, typename Value>
class concurrent_queue_iterator: public concurrent_queue_iterator_base,
        public std::iterator<std::forward_iterator_tag,Value> {

#if !__TBB_TEMPLATE_FRIENDS_BROKEN
    template<typename T, class A>
    friend class ::tbb::concurrent_bounded_queue;
#else
public:
#endif

    explicit concurrent_queue_iterator( const concurrent_queue_base_v3& queue ) :
        concurrent_queue_iterator_base_v3(queue,__TBB_offsetof(concurrent_queue_base_v3::padded_page<Value>,last))
    {
    }

public:
    concurrent_queue_iterator() {}

    concurrent_queue_iterator( const concurrent_queue_iterator<Container,typename Container::value_type>& other ) :
        concurrent_queue_iterator_base_v3(other)
    {}

    concurrent_queue_iterator& operator=( const concurrent_queue_iterator<Container,typename Container::value_type>& other ) {
        concurrent_queue_iterator_base_v3::operator=(other);
        return *this;
    }

    Value& operator*() const {
        return *static_cast<Value*>(my_item);
    }

    Value* operator->() const {return &operator*();}

    concurrent_queue_iterator& operator++() {
        advance();
        return *this;
    }

    Value* operator++(int) {
        Value* result = &operator*();
        operator++();
        return result;
    }
}; // concurrent_queue_iterator


template<typename C, typename T, typename U>
bool operator==( const concurrent_queue_iterator<C,T>& i, const concurrent_queue_iterator<C,U>& j ) {
    return i.my_item==j.my_item;
}

template<typename C, typename T, typename U>
bool operator!=( const concurrent_queue_iterator<C,T>& i, const concurrent_queue_iterator<C,U>& j ) {
    return i.my_item!=j.my_item;
}

} // namespace internal;


} // namespace tbb

#endif /* __TBB__concurrent_queue_impl_H */