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