1 Introduction
2 ------------
3
4 The pprocess module provides elementary support for parallel programming in
5 Python using a fork-based process creation model in conjunction with a
6 channel-based communications model implemented using socketpair and poll. On
7 systems with multiple CPUs or multicore CPUs, processes should take advantage
8 of as many CPUs or cores as the operating system permits.
9
10 Quick Start
11 -----------
12
13 Try running the simple examples. For example:
14
15 PYTHONPATH=. python examples/simple_create.py
16
17 (These examples show in different ways how limited number of processes can be
18 used to perform a parallel computation. The simple.py, simple1.py, simple2.py
19 and simple_map.py programs are sequential versions of the other programs.)
20
21 The following table summarises the features used in the programs:
22
23 Program (.py) pmap MakeParallel manage start create Map Queue Exchange
24 ------------- ---- ------------ ------ ----- ------ --- ----- --------
25 simple_create_map Yes Yes
26 simple_create_queue Yes Yes
27 simple_create Yes Yes
28 simple_managed_map Yes Yes Yes
29 simple_managed_queue Yes Yes Yes
30 simple_managed Yes Yes Yes
31 simple_pmap Yes
32 simple_start_queue Yes Yes Yes
33 simple_start Yes Yes
34
35 The simplest parallel program is simple_pmap.py which employs the pmap
36 function resembling the built-in map function in Python.
37
38 Other simple programs are those employing the Queue class, together with those
39 using the manage method which associates functions or callables with Queue or
40 Exchange objects for convenient invocation of those functions and the
41 management of their communications.
42
43 The most technically involved program is simple_start.py which uses the
44 Exchange class together with a calculation function which is aware of the
45 parallel environment and which communicates over the supplied communications
46 channel directly to the creating process.
47
48 It should be noted that with the exception of simple_start.py, those examples
49 employing calculation functions (as opposed to doing a calculation inline in a
50 loop body) all use MakeParallel to make those functions parallel-aware, thus
51 permitting the conversion of "normal" functions to a form usable in the
52 parallel environment.
53
54 An additional example not listed above, simple_managed_map_reusable.py,
55 employs the MakeReusable class instead of MakeParallel in order to demonstrate
56 reusable processes and channels.
57
58 The tutorial provides some information about the examples: docs/tutorial.xhtml
59
60 Parallel Raytracing with PyGmy
61 ------------------------------
62
63 The PyGmy raytracer modified to use pprocess can be run to investigate the
64 potential for speed increases in "real world" programs:
65
66 cd examples/PyGmy
67 PYTHONPATH=../..:. python scene.py
68
69 (This should produce a file called test.tif - a TIFF file containing a
70 raytraced scene image.)
71
72 Test Programs
73 -------------
74
75 There are some elementary tests:
76
77 PYTHONPATH=. python tests/create_loop.py
78 PYTHONPATH=. python tests/start_loop.py
79
80 (Simple loop demonstrations which use two different ways of creating and
81 starting the parallel processes.)
82
83 PYTHONPATH=. python tests/start_indexer.py <directory>
84
85 (A text indexing demonstration, where <directory> should be a directory
86 containing text files to be indexed, although HTML files will also work well
87 enough. After indexing the files, a prompt will appear, words or word
88 fragments can be entered, and matching words and their locations will be
89 shown. Run the program without arguments to see more information.)
90
91 Contact, Copyright and Licence Information
92 ------------------------------------------
93
94 No Web page has yet been made available for this work, but the author can be
95 contacted at the following e-mail address:
96
97 paul@boddie.org.uk
98
99 Copyright and licence information can be found in the docs directory - see
100 docs/COPYING.txt, docs/lgpl-3.0.txt and docs/gpl-3.0.txt for more information.
101
102 For the PyGmy raytracer example, different copyright and licence information
103 is provided in the docs directory - see docs/COPYING-PyGmy.txt and
104 docs/LICENCE-PyGmy.txt for more information.
105
106 Dependencies
107 ------------
108
109 This software depends on standard library features which are stated as being
110 available only on "UNIX"; it has only been tested on a GNU/Linux system.
111
112 New in parallel 0.3 (Changes since parallel 0.2.5)
113 --------------------------------------------------
114
115 * Added managed callables: wrappers around callables which cause them to be
116 automatically managed by the exchange from which they were acquired.
117 * Added MakeParallel: a wrapper instantiated around a normal function which
118 sends the result of that function over the supplied channel when invoked.
119 * Added MakeReusable: a wrapper like MakeParallel which can be used in
120 conjunction with the newly-added reuse capability of the Exchange class in
121 order to reuse processes and channels.
122 * Added a Map class which attempts to emulate the built-in map function,
123 along with a pmap function using this class.
124 * Added a Queue class which provides a simpler iterator-style interface to
125 data produced by created processes.
126 * Added a create method to the Exchange class and an exit convenience
127 function to the module.
128 * Changed the Exchange implementation to not block when attempting to start
129 new processes beyond the process limit: such requests are queued and
130 performed as running processes are completed. This permits programs using
131 the start method to proceed to consumption of results more quickly.
132 * Extended and updated the examples. Added a tutorial.
133 * Added Ubuntu Feisty (7.04) package support.
134
135 New in parallel 0.2.5 (Changes since parallel 0.2.4)
136 ----------------------------------------------------
137
138 * Added a start method to the Exchange class for more convenient creation of
139 processes.
140 * Relicensed under the LGPL (version 3 or later) - this also fixes the
141 contradictory situation where the GPL was stated in the pprocess module
142 (which was not, in fact, the intention) and the LGPL was stated in the
143 documentation.
144
145 New in parallel 0.2.4 (Changes since parallel 0.2.3)
146 ----------------------------------------------------
147
148 * Set buffer sizes to zero for the file object wrappers around sockets: this
149 may prevent deadlock issues.
150
151 New in parallel 0.2.3 (Changes since parallel 0.2.2)
152 ----------------------------------------------------
153
154 * Added convenient message exchanges, offering methods handling common
155 situations at the cost of having to define a subclass of Exchange.
156 * Added a simple example of performing a parallel computation.
157 * Improved the PyGmy raytracer example to use the newly added functionality.
158
159 New in parallel 0.2.2 (Changes since parallel 0.2.1)
160 ----------------------------------------------------
161
162 * Changed the status testing in the Exchange class, potentially fixing the
163 premature closure of channels before all data was read.
164 * Fixed the PyGmy raytracer example's process accounting by relying on the
165 possibly more reliable Exchange behaviour, whilst also preventing
166 erroneous creation of "out of bounds" processes.
167 * Added a removed attribute on the Exchange to record which channels were
168 removed in the last call to the ready method.
169
170 New in parallel 0.2.1 (Changes since parallel 0.2)
171 --------------------------------------------------
172
173 * Added a PyGmy raytracer example.
174 * Updated copyright and licensing details (FSF address, additional works).
175
176 New in parallel 0.2 (Changes since parallel 0.1)
177 ------------------------------------------------
178
179 * Changed the name of the included module from parallel to pprocess in order
180 to avoid naming conflicts with PyParallel.
181
182 Release Procedures
183 ------------------
184
185 Update the pprocess __version__ attribute.
186 Change the version number and package filename/directory in the documentation.
187 Update the release notes (see above).
188 Check the release information in the PKG-INFO file.
189 Tag, export.
190 Archive, upload.
191 Update PyPI.
192
193 Making Packages
194 ---------------
195
196 To make Debian-based packages:
197
198 1. Create new package directories under packages if necessary.
199 2. Make a symbolic link in the distribution's root directory to keep the
200 Debian tools happy:
201
202 ln -s packages/ubuntu-hoary/python2.4-parallel-pprocess/debian/
203
204 Or:
205
206 ln -s packages/ubuntu-feisty/python-pprocess/debian/
207
208 3. Run the package builder:
209
210 dpkg-buildpackage -rfakeroot
211
212 4. Locate and tidy up the packages in the parent directory of the
213 distribution's root directory.