...one of the most highly regarded and expertly designed C++ library projects in the world. — Herb Sutter and Andrei Alexandrescu , C++ Coding Standards

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;
    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);
          Constructor
explicit buffered_channel( std::size_t capacity);
                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
                elements, otherwise it is considered to be full.
                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.
                If channel is closed, returns closed.
                Otherwise 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.
Throws:
                Exceptions thrown by copy- or move-operations.
                If channel is closed, returns closed.
                Otherwise 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.
Throws:
                Exceptions thrown by copy- or move-operations.
                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).
Throws:
                Exceptions thrown by copy- or move-operations.
                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).
Throws:
                fiber_error if *this
                is closed or by copy- or move-operations.
Error conditions:
                std::errc::operation_not_permitted
                If channel is empty, returns empty.
                If channel is closed, returns closed.
                Otherwise it returns success
                and va contains the
                dequeued value.
Throws:
                Exceptions thrown by copy- or move-operations.
template< typename Rep, typename Period >
channel_op_status pop_wait_for(
    value_type & va,
    std::chrono::duration< Rep, Period > const& timeout_duration)
                Accepts std::chrono::duration and internally computes
                a timeout time as (system time + timeout_duration).
                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 the computed timeout time (return value
                timeout).
Throws:
                timeout-related exceptions or by copy- or move-operations.
template< typename Clock, typename Duration >
channel_op_status pop_wait_until(
    value_type & va,
    std::chrono::time_point< Clock, Duration > const& timeout_time)
                Clock,
                Duration >.
                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 the passed time_point
                (return value timeout).
Throws:
                timeout-related exceptions or by copy- or move-operations.
        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)