Boost C++ Libraries

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

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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 buffered_channel<>

#include <boost/fiber/buffered_channel.hpp>

namespace boost {
namespace fibers {

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

    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);
};

}}
Constructor
explicit buffered_channel( std::size_t capacity);

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 function close()

void close() noexcept;

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.

Member function push()

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

Effects:

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.

Throws:

Exceptions thrown by copy- or move-operations.

Member function try_push()

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

Effects:

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.

Throws:

Exceptions thrown by copy- or move-operations.

Member function pop()

channel_op_status pop( value_type & va);

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).

Throws:

Exceptions thrown by copy- or move-operations.

Member function value_pop()

value_type value_pop();

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).

Throws:

fiber_error if *this is closed or by copy- or move-operations.

Error conditions:

std::errc::operation_not_permitted

Member function try_pop()

channel_op_status try_pop( value_type & va);

Effects:

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.

Member function 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)

Effects:

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.

Member function 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)

Effects:

Accepts a std::chrono::time_point< 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.


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