emacs/mps/design/testthr.txt

.. 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";
   <http://pubs.opengroup.org/onlinepubs/7990989775/xsh/threads.html>


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

- 2014-10-21 GDR_ Initial draft.

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


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

Copyright © 2014 Ravenbrook Limited. All rights reserved.
<http://www.ravenbrook.com/>. This is an open source license. Contact
Ravenbrook for commercial licensing options.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:

#. Redistributions of source code must retain the above copyright
   notice, this list of conditions and the following disclaimer.

#. Redistributions in binary form must reproduce the above copyright
   notice, this list of conditions and the following disclaimer in the
   documentation and/or other materials provided with the distribution.

#. Redistributions in any form must be accompanied by information on how
   to obtain complete source code for this software and any
   accompanying software that uses this software.  The source code must
   either be included in the distribution or be available for no more than
   the cost of distribution plus a nominal fee, and must be freely
   redistributable under reasonable conditions.  For an executable file,
   complete source code means the source code for all modules it contains.
   It does not include source code for modules or files that typically
   accompany the major components of the operating system on which the
   executable file runs.

**This software is provided by the copyright holders and contributors
"as is" and any express or implied warranties, including, but not
limited to, the implied warranties of merchantability, fitness for a
particular purpose, or non-infringement, are disclaimed.  In no event
shall the copyright holders and contributors be liable for any direct,
indirect, incidental, special, exemplary, or consequential damages
(including, but not limited to, procurement of substitute goods or
services; loss of use, data, or profits; or business interruption)
however caused and on any theory of liability, whether in contract,
strict liability, or tort (including negligence or otherwise) arising in
any way out of the use of this software, even if advised of the
possibility of such damage.**