.. mode: -*- rst -*-

Multi-threaded testing
======================

:Tag: design.mps.testthr
:Author: Gareth Rees
:Date: 2014-10-21
:Status: complete design
:Revision: $Id$
:Copyright: See section `Copyright and License`_.
:Index terms: pair: threads; testing


Introduction
------------

_`.intro`: This is the design of the multi-threaded testing module
in the Memory Pool System.

_`.readership`: Any MPS developer.

_`.overview`: The MPS is designed to work in a multi-threaded
environment (see design.mps.thread-safety_) and this needs to be
tested on all supported platforms. The multi-threaded testing module
provides an interface for creating and joining threads, so that
multi-threaded test cases are portable to all platforms on which the
MPS runs.

.. _design.mps.thread-safety: thread-safety


Requirements
------------

_`.req.create`: The module must provide an interface for creating
threads and running code in them. (Because there is no such interface
in the Standard C Library.)

_`.req.join`: The module must provide an interface for joining a
running thread: that is, waiting for the thread to finish and
collecting a result. (Because we want to be able to test that the MPS
behaves correctly when interacting with a finished thread.)

_`.req.portable`: The module must be easily portable to all the
platforms on which the MPS runs.

_`.req.usable`: The module must be simple to use, not requiring
elaborate setup or tear-down or error handling. (Because we want test
cases to be easy to write.)


Implementation
--------------

_`.impl.posix`: To meet `.req.portable`_ and `.req.usable`_, the
module presents an interface that is essentially identical to the
POSIX Threads interface [pthreads]_, except for the names. On POSIX
platforms the implementation is trivial; on Windows it is
necessary to translate the concepts back and forth.

_`.impl.storage`: To meet `.req.usable`_, the module defines the
``testthr_t`` type in the header ``testthr.h`` (even though this
requires an ``#if``), so that test cases can easily declare variables
and allocate storage for thread identifiers.

_`.impl.error`: To meet `.req.usable`_, the module does not propagate
error codes, but calls ``error()`` from the test library if anything
goes wrong. There is thus no need for the test cases to check result
codes.


Interface
---------

``typedef testthr_t``

The type of thread identifiers.

``typedef void *(*testthr_routine_t)(void *)``

The type of a function that can be called when a thread is created.

``void testthr_create(testthr_t *thread_o, testthr_routine_t start, void *arg)``

Create a thread. Store the identifier of the newly created thread in
``*thread_o``, and call ``start()``, passing ``arg`` as the single
parameter.

``void testthr_join(testthr_t *thread, void **result_o)``

Wait for a thread to complete. Suspend execution of the calling thread
until the target thread terminates (if necessary), and if ``result_o``
is non-NULL, update ``*result_o`` with the return value of the
thread's ``start()`` function.


References
----------

.. [pthreads]
   The Open Group;
   "The Single UNIX Specification, Version 2---Threads";
   <https://pubs.opengroup.org/onlinepubs/7990989775/xsh/threads.html>


Document History
----------------

- 2014-10-21 GDR_ Initial draft.

.. _GDR: https://www.ravenbrook.com/consultants/gdr/


Copyright and License
---------------------

Copyright © 2014–2020 `Ravenbrook Limited <https://www.ravenbrook.com/>`_.

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