.. zephyr:code-sample:: sockets-socketpair
   :name: Socketpair
   :relevant-api: bsd_sockets

   Implement communication between threads using socket pairs.

Overview
********

The sockets/socketpair sample application for Zephyr demonstrates a
multi-threaded application communicating over pairs of unnamed,
connected UNIX-domain sockets. The pairs of sockets are created with
socketpair(2), as you might have guessed. Such sockets are compatible
with the BSD Sockets API, and therefore the purpose of this sample
is also to reinforce that it is possible to develop a sockets
application portable to both POSIX and Zephyr.

The source code for this sample application can be found at:
:zephyr_file:`samples/net/sockets/socketpair`.

Requirements
************

None

Building and Running
********************

Build the Zephyr version of the sockets/echo application like this:

.. zephyr-app-commands::
   :zephyr-app: samples/net/sockets/socketpair
   :board: <board_to_use>
   :goals: build
   :compact:

After the sample starts, several client threads are spawned. Each client
thread sends a fixed number of messages to the server (main).

.. code-block:: console

    *** Booting Zephyr OS build v3.3.0-rc1-97-g432ff20a72e1 ***
    setting-up
    Alpha: socketpair: 4 <=> 3
    Bravo: socketpair: 6 <=> 5
    Charlie: socketpair: 8 <=> 7
    main: read 'Alpha' on fd 4
    main: read 'Bravo' on fd 6
    main: read 'Charlie' on fd 8
    main: read 'Alpha' on fd 4
    main: read 'Bravo' on fd 6
    main: read 'Charlie' on fd 8
    main: read 'Alpha' on fd 4
    main: read 'Bravo' on fd 6
    main: read 'Charlie' on fd 8
    tearing-down
    SUCCESS

Running application on POSIX Host
=================================

The same application source code can be built for a POSIX system, e.g.
Linux.

To build:

.. code-block:: console

    $ make -f Makefile.host

To run:

.. code-block:: console

    ./socketpair_example
    setting-up
    Alpha: socketpair: 3 <=> 4
    Bravo: socketpair: 5 <=> 6
    Charlie: socketpair: 7 <=> 8
    main: read 'Alpha' on fd 3
    main: read 'Bravo' on fd 5
    main: read 'Charlie' on fd 7
    main: read 'Alpha' on fd 3
    main: read 'Alpha' on fd 3
    main: read 'Bravo' on fd 5
    main: read 'Charlie' on fd 7
    main: read 'Bravo' on fd 5
    main: read 'Charlie' on fd 7
    tearing-down
    SUCCESS

As can be seen, the behavior of the application is approximately the same as
the Zephyr version.