[/
          Copyright Oliver Kowalke 2013.
 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
]

[section:buffered_channel Buffered Channel]

__boost_fiber__ provides a bounded, buffered channel (MPMC queue) suitable to
synchonize fibers (running on same or different threads) via asynchronouss
message passing.

    typedef boost::fibers::buffered_channel< int > channel_t;

    void send( channel_t & chan) {
        for ( int i = 0; i < 5; ++i) {
            chan.push( i);
        }
        chan.close();
    }

    void recv( channel_t & chan) {
        int i;
        while ( boost::fibers::channel_op_status::success == chan.pop(i) ) {
            std::cout << "received " << i << std::endl;
        }
    }

    channel_t chan{ 2 };
    boost::fibers::fiber f1( std::bind( send, std::ref( chan) ) );
    boost::fibers::fiber f2( std::bind( recv, std::ref( chan) ) );

    f1.join();
    f2.join();

Class `buffered_channel` supports range-for syntax:

    typedef boost::fibers::buffered_channel< int > channel_t;

    void foo( channel_t & chan) {
        chan.push( 1);
        chan.push( 1);
        chan.push( 2);
        chan.push( 3);
        chan.push( 5);
        chan.push( 8);
        chan.push( 12);
        chan.close();
    }

    void bar( channel_t & chan) {
        for ( unsigned int value : chan) {
            std::cout << value << " ";
        }
        std::cout << std::endl;
    }


[template_heading buffered_channel]

        #include <boost/fiber/buffered_channel.hpp>

        namespace boost {
        namespace fibers {

        template< typename T >
        class buffered_channel {
        public:
            typedef T   value_type;

            class iterator;

            explicit buffered_channel( std::size_t capacity);

            buffered_channel( buffered_channel const& other) = delete; 
            buffered_channel & operator=( buffered_channel const& other) = delete; 

            void close() noexcept;

            channel_op_status push( value_type const& va);
            channel_op_status push( value_type && va);
            template< typename Rep, typename Period >
            channel_op_status push_wait_for(
                value_type const& va,
                std::chrono::duration< Rep, Period > const& timeout_duration);
            channel_op_status push_wait_for( value_type && va,
                std::chrono::duration< Rep, Period > const& timeout_duration);
            template< typename Clock, typename Duration >
            channel_op_status push_wait_until(
                value_type const& va,
                std::chrono::time_point< Clock, Duration > const& timeout_time);
            template< typename Clock, typename Duration >
            channel_op_status push_wait_until(
                value_type && va,
                std::chrono::time_point< Clock, Duration > const& timeout_time);
            channel_op_status try_push( value_type const& va);
            channel_op_status try_push( value_type && va);

            channel_op_status pop( value_type & va);
            value_type value_pop();
            template< typename Rep, typename Period >
            channel_op_status pop_wait_for(
                value_type & va,
                std::chrono::duration< Rep, Period > const& timeout_duration);
            template< typename Clock, typename Duration >
            channel_op_status pop_wait_until(
                value_type & va,
                std::chrono::time_point< Clock, Duration > const& timeout_time);
            channel_op_status try_pop( value_type & va);
        };

        template< typename T >
        buffered_channel< T >::iterator begin( buffered_channel< T > & chan);

        template< typename T >
        buffered_channel< T >::iterator end( buffered_channel< T > & chan);

        }}

[heading Constructor]

        explicit buffered_channel( std::size_t capacity);

[variablelist
[[Preconditions:] [`2<=capacity && 0==(capacity & (capacity-1))`]]
[[Effects:] [The constructor constructs an object of class `buffered_channel`
with an internal buffer of size `capacity`.]]
[[Throws:] [`fiber_error`]]
[[Error Conditions:] [
[*invalid_argument]: if `0==capacity || 0!=(capacity & (capacity-1))`.]]
[[Notes:] [A `push()`, `push_wait_for()` or `push_wait_until()` will not block
until the number of values in the channel becomes equal to `capacity`.
The channel can hold only `capacity - 1` elements, otherwise it is
considered to be full.]]
]

[member_heading buffered_channel..close]

        void close() noexcept;

[variablelist
[[Effects:] [Deactivates the channel. No values can be put after calling
`this->close()`. Fibers blocked in `this->pop()`, `this->pop_wait_for()`
or `this->pop_wait_until()` will return `closed`. Fibers blocked in
`this->value_pop()` will receive an exception.]]
[[Throws:] [Nothing.]]
[[Note:] [`close()` is like closing a pipe. It informs waiting consumers
that no more values will arrive.]]
]

[template buffered_channel_push_effects[enqueues] If channel is closed, returns
`closed`. [enqueues] the value in the channel, wakes up a fiber
blocked on `this->pop()`, `this->value_pop()`, `this->pop_wait_for()` or
`this->pop_wait_until()` and returns `success`. If the channel is full,
the fiber is blocked.]

[member_heading buffered_channel..push]

        channel_op_status push( value_type const& va);
        channel_op_status push( value_type && va);

[variablelist
[[Effects:] [[buffered_channel_push_effects Otherwise enqueues]]]
[[Throws:] [Exceptions thrown by copy- or move-operations.]]
]

[template buffered_channel_try_push_effects[enqueues] If channel is closed, returns
`closed`. [enqueues] the value in the channel, wakes up a fiber
blocked on `this->pop()`, `this->value_pop()`, `this->pop_wait_for()` or
`this->pop_wait_until()` and returns `success`. If the channel is full,
it doesn't block and returns `full`.]

[member_heading buffered_channel..try_push]

        channel_op_status try_push( value_type const& va);
        channel_op_status try_push( value_type && va);

[variablelist
[[Effects:] [[buffered_channel_try_push_effects Otherwise enqueues]]]
[[Throws:] [Exceptions thrown by copy- or move-operations.]]
]

[template buffered_channel_pop[cls unblocking]
[member_heading [cls]..pop]

        channel_op_status pop( value_type & va);

[variablelist
[[Effects:] [Dequeues a value from the channel. If the channel is empty, the
fiber gets suspended until at least one new item is `push()`ed (return value
`success` and `va` contains dequeued value) or the channel gets `close()`d
(return value `closed`)[unblocking]]]
[[Throws:] [Exceptions thrown by copy- or move-operations.]]
]
]
[buffered_channel_pop buffered_channel .]

[template buffered_channel_value_pop[cls unblocking]
[member_heading [cls]..value_pop]

        value_type value_pop();

[variablelist
[[Effects:] [Dequeues a value from the channel. If the channel is empty, the
fiber gets suspended until at least one new item is `push()`ed or the channel
gets `close()`d (which throws an exception)[unblocking]]]
[[Throws:] [`fiber_error` if `*this` is closed or by copy- or move-operations.]]
[[Error conditions:] [`std::errc::operation_not_permitted`]]
]
]
[buffered_channel_value_pop buffered_channel .]

[template buffered_channel_try_pop[cls unblocking]
[member_heading [cls]..try_pop]

        channel_op_status try_pop( value_type & va);

[variablelist
[[Effects:] [If channel is empty, returns `empty`. If channel is closed,
returns `closed`. Otherwise it returns `success` and `va` contains the
dequeued value[unblocking]]]
[[Throws:] [Exceptions thrown by copy- or move-operations.]]
]
]
[buffered_channel_try_pop buffered_channel .]

[template buffered_channel_pop_wait_until_effects[endtime unblocking] If channel
is not empty, immediately dequeues a value from the channel. Otherwise
the fiber gets suspended until at least one new item is `push()`ed (return
value `success` and `va` contains dequeued value), or the channel gets
`close()`d (return value `closed`), or the system time reaches [endtime]
(return value `timeout`)[unblocking]]

[template buffered_channel_pop_wait_for[cls unblocking]
[member_heading [cls]..pop_wait_for]

        template< typename Rep, typename Period >
        channel_op_status pop_wait_for(
            value_type & va,
            std::chrono::duration< Rep, Period > const& timeout_duration)

[variablelist
[[Effects:] [Accepts `std::chrono::duration` and internally computes a timeout
time as (system time + `timeout_duration`).
[buffered_channel_pop_wait_until_effects the computed timeout time..[unblocking]]]]
[[Throws:] [timeout-related exceptions or by copy- or move-operations.]]
]
]
[buffered_channel_pop_wait_for buffered_channel .]

[template buffered_channel_pop_wait_until[cls unblocking]
[member_heading [cls]..pop_wait_until]

        template< typename Clock, typename Duration >
        channel_op_status pop_wait_until(
            value_type & va,
            std::chrono::time_point< Clock, Duration > const& timeout_time)

[variablelist
[[Effects:] [Accepts a `std::chrono::time_point< Clock, Duration >`.
[buffered_channel_pop_wait_until_effects the passed `time_point`..[unblocking]]]]
[[Throws:] [timeout-related exceptions or by copy- or move-operations.]]
]
]
[buffered_channel_pop_wait_until buffered_channel .]

[heading Non-member function `begin( buffered_channel< T > &)`]
    template< typename T >
    buffered_channel< T >::iterator begin( buffered_channel< T > &);

[variablelist
[[Returns:] [Returns a range-iterator (input-iterator).]]
]

[heading Non-member function `end( buffered_channel< T > &)`]
    template< typename T >
    buffered_channel< R >::iterator end( buffered_channel< T > &);

[variablelist
[[Returns:] [Returns an end range-iterator (input-iterator).]]
]

[endsect]