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Channels

Channels are a message system for communication between threads. Depending on the platform, channels may be built on top of various underlying systems. Intraprocess channels generally require only that the threads of a process share a memory space, while interprocess channels may use sockets or pipes.

Creating a Channel​

The Channel template is parameterized by the type of the message that will be sent across the channel, as well as the type of queue that will be used. The default queue type is a blocking ring buffer queue, but this can be replaced with another if desired, such as a lock-free queue. A Channel acts as a reference type, which is copyable. Every copy is a handle on the same channel, whose state is stored independently of any Channel instance on the heap. The state is freed when the reference count of the channel reaches 0. The InputChannel is a read-only version of Channel, and OutputChannel is an output-only version. Channel is a subclass which extends both of these.

Selecting from Multiple Channels​

The function Channel::Select allows for waiting on one of multiple channels to have a message. The call will block until a message is received from one of the channels.

Channel::Select([](auto&& channel, auto&& msg) {
    if (channel == channel1) {
        // For channel1 message
    } else if (channel == channel2) {
        // For channel2 message
    } else {
        // For channel3 message
    }
}, channel1, channel2, channel3);

The callback takes a reference to the channel as well as a reference to the message. The callback can be conditionally handled based on which channel received a message, or, in a constexpr context, the type of the message, assuming it differs between all channels (or some combination thereof).

Interprocess Channels​

Interprocess channels are a special case of Channel. These use the types SharedChannel or SharedNamedChannel. The SharedChannel should be constructed within SharedMemory so that it can be accessible to multiple processes. The SharedNamedChannel acts as a handle to a system-wide channel of a given name. It interacts with any other channel constructed with the same name on the same system. As with intraprocess channels, it is also possible to use SharedInputChannel/SharedNamedInputChannel and SharedOutputChannel/SharedNamedOutputChannel to get read-only or write-only versions of the channel.

info

Types used as messages for interprocess channels must be serializable with the Pion ser/des system.