    // Copyright (C) 2006  Davis E. King (davis@dlib.net)
    // License: Boost Software License   See LICENSE.txt for the full license.
    #undef DLIB_PIPE_KERNEl_ABSTRACT_
    #ifdef DLIB_PIPE_KERNEl_ABSTRACT_

    #include "../threads.h"

    namespace dlib
    {

        template <
            typename T
            >
        class pipe
        {
            /*!
                REQUIREMENTS ON T
                    T must be swappable by a global swap()
                    T must have a default constructor

                INITIAL VALUE
                    size() == 0
                    is_enabled() == true
                    is_enqueue_enabled() == true
                    is_dequeue_enabled() == true

                WHAT THIS OBJECT REPRESENTS
                    This is a first in first out queue with a fixed maximum size containing
                    items of type T.  It is suitable for passing objects between threads.

                THREAD SAFETY
                    All methods of this class are thread safe.  You may call them from any
                    thread and any number of threads my call them at once.
            !*/

        public:

            typedef T type;

            explicit pipe (
                size_t maximum_size
            );
            /*!
                ensures
                    - #*this is properly initialized
                    - #max_size() == maximum_size
                throws
                    - std::bad_alloc
                    - dlib::thread_error
            !*/

            virtual ~pipe (
            );
            /*!
                ensures
                    - any resources associated with *this have been released
                    - disables (i.e. sets is_enabled() == false) this object so that
                      all calls currently blocking on it will return immediately.
            !*/

            void enable (
            );
            /*!
                ensures
                    - #is_enabled() == true
            !*/

            void disable (
            );
            /*!
                ensures
                    - #is_enabled() == false
                    - causes all current and future calls to enqueue(), dequeue(),
                      enqueue_or_timeout() and dequeue_or_timeout() to not block but
                      to return false immediately until enable() is called.
                    - causes all current and future calls to wait_until_empty() and
                      wait_for_num_blocked_dequeues() to not block but return
                      immediately until enable() is called.
            !*/

            bool is_enabled (
            ) const;
            /*!
                ensures
                    - returns true if this pipe is currently enabled, false otherwise.
            !*/

            void empty (
            );
            /*!
                ensures
                    - #size() == 0
            !*/

            void wait_until_empty (
            ) const;
            /*!
                ensures
                    - blocks until one of the following is the case:
                        - size() == 0
                        - is_enabled() == false
                        - is_dequeue_enabled() == false
            !*/

            void wait_for_num_blocked_dequeues (
               unsigned long num
            ) const;
            /*!
                ensures
                    - blocks until one of the following is the case:
                        - size() == 0 and the number of threads blocked on calls
                          to dequeue() and dequeue_or_timeout() is greater than
                          or equal to num.
                        - is_enabled() == false
                        - is_dequeue_enabled() == false
            !*/

            bool is_enqueue_enabled (
            ) const;
            /*!
                ensures
                    - returns true if the enqueue() and enqueue_or_timeout() functions are
                      currently enabled, returns false otherwise.  (note that the higher
                      level is_enabled() function can overrule this one.  So if
                      is_enabled() == false then enqueue functions are still disabled even
                      if is_enqueue_enabled() returns true.  But if is_enqueue_enabled() == false
                      then enqueue functions are always disabled no matter the state of
                      is_enabled())
            !*/

            void disable_enqueue (
            );
            /*!
                ensures
                    - #is_enqueue_enabled() == false
                    - causes all current and future calls to enqueue() and
                      enqueue_or_timeout() to not block but to return false
                      immediately until enable_enqueue() is called.
            !*/

            void enable_enqueue (
            );
            /*!
                ensures
                    - #is_enqueue_enabled() == true
            !*/

            bool is_dequeue_enabled (
            ) const;
            /*!
                ensures
                    - returns true if the dequeue() and dequeue_or_timeout() functions are
                      currently enabled, returns false otherwise.  (note that the higher
                      level is_enabled() function can overrule this one.  So if
                      is_enabled() == false then dequeue functions are still disabled even
                      if is_dequeue_enabled() returns true.  But if is_dequeue_enabled() == false
                      then dequeue functions are always disabled no matter the state of
                      is_enabled())
            !*/

            void disable_dequeue (
            );
            /*!
                ensures
                    - #is_dequeue_enabled() == false
                    - causes all current and future calls to dequeue() and
                      dequeue_or_timeout() to not block but to return false
                      immediately until enable_dequeue() is called.
            !*/

            void enable_dequeue (
            );
            /*!
                ensures
                    - #is_dequeue_enabled() == true
            !*/

            size_t max_size (
            ) const;
            /*!
                ensures
                    - returns the maximum number of objects of type T that this
                      pipe can contain.
            !*/

            size_t size (
            ) const;
            /*!
                ensures
                    - returns the number of objects of type T that this
                      object currently contains.
            !*/

            bool enqueue (
                T& item
            );
            /*!
                ensures
                    - if (size() == max_size()) then
                        - this call to enqueue() blocks until one of the following is the case:
                            - there is room in the pipe for another item
                            - max_size() == 0 and another thread is trying to dequeue from this
                              pipe and we can pass our item object directly to that thread.
                            - someone calls disable()
                            - someone calls disable_enqueue()
                    - else
                        - this call does not block.
                    - if (this call to enqueue() returns true) then
                        - #is_enabled() == true
                        - #is_enqueue_enabled() == true
                        - if (max_size() == 0) then
                            - using global swap, item was passed directly to a
                              thread attempting to dequeue from this pipe
                        - else
                            - using global swap, item was added into this pipe.
                        - #item is in an undefined but valid state for its type
                    - else
                        - item was NOT added into the pipe
                        - #item == item (i.e. the value of item is unchanged)
            !*/

            bool enqueue (T&& item) { return enqueue(item); }
            /*!
                enable enqueueing from rvalues
            !*/

            bool enqueue_or_timeout (
                T& item,
                unsigned long timeout
            );
            /*!
                ensures
                    - if (size() == max_size() && timeout > 0) then
                        - this call to enqueue_or_timeout() blocks until one of the following is the case:
                            - there is room in the pipe to add another item
                            - max_size() == 0 and another thread is trying to dequeue from this pipe
                              and we can pass our item object directly to that thread.
                            - someone calls disable()
                            - someone calls disable_enqueue()
                            - timeout milliseconds passes
                    - else
                        - this call does not block.
                    - if (this call to enqueue() returns true) then
                        - #is_enabled() == true
                        - #is_enqueue_enabled() == true
                        - if (max_size() == 0) then
                            - using global swap, item was passed directly to a
                              thread attempting to dequeue from this pipe
                        - else
                            - using global swap, item was added into this pipe.
                        - #item is in an undefined but valid state for its type
                    - else
                        - item was NOT added into the pipe
                        - #item == item (i.e. the value of item is unchanged)
            !*/

            bool enqueue_or_timeout (T&& item, unsigned long timeout) { return enqueue_or_timeout(item,timeout); }
            /*!
                enable enqueueing from rvalues
            !*/

            bool dequeue (
                T& item
            );
            /*!
                ensures
                    - if (size() == 0) then
                        - this call to dequeue() blocks until one of the following is the case:
                            - there is something in the pipe we can dequeue
                            - max_size() == 0 and another thread is trying to enqueue an item
                              onto this pipe and we can receive our item directly from that thread.
                            - someone calls disable()
                            - someone calls disable_dequeue()
                    - else
                        - this call does not block.
                    - if (this call to dequeue() returns true) then
                        - #is_enabled() == true
                        - #is_dequeue_enabled() == true
                        - the oldest item that was enqueued into this pipe has been
                          swapped into #item.
                    - else
                        - nothing was dequeued from this pipe.
                        - #item == item (i.e. the value of item is unchanged)
            !*/

            bool dequeue_or_timeout (
                T& item,
                unsigned long timeout
            );
            /*!
                ensures
                    - if (size() == 0 && timeout > 0) then
                        - this call to dequeue_or_timeout() blocks until one of the following is the case:
                            - there is something in the pipe we can dequeue
                            - max_size() == 0 and another thread is trying to enqueue an item onto this
                              pipe and we can receive our item directly from that thread.
                            - someone calls disable()
                            - someone calls disable_dequeue()
                            - timeout milliseconds passes
                    - else
                        - this call does not block.
                    - if (this call to dequeue_or_timeout() returns true) then
                        - #is_enabled() == true
                        - #is_dequeue_enabled() == true
                        - the oldest item that was enqueued into this pipe has been
                          swapped into #item.
                    - else
                        - nothing was dequeued from this pipe.
                        - #item == item (i.e. the value of item is unchanged)
            !*/

        private:

            // restricted functions
            pipe(const pipe&);        // copy constructor
            pipe& operator=(const pipe&);    // assignment operator

        };

    }

    #endif // DLIB_PIPE_KERNEl_ABSTRACT_