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 Tutorial
11 --------
12
13 The tutorial provides some information about the examples described below.
14 See the docs/tutorial.html file in the distribution for more details.
15
16 Reference
17 ---------
18
19 A description of the different mechanisms provided by the pprocess module can
20 be found in the reference document. See the docs/reference.html file in the
21 distribution for more details.
22
23 Quick Start
24 -----------
25
26 Try running the simple examples. For example:
27
28 PYTHONPATH=. python examples/simple_create.py
29
30 (These examples show in different ways how limited number of processes can be
31 used to perform a parallel computation. The simple.py, simple1.py, simple2.py
32 and simple_map.py programs are sequential versions of the other programs.)
33
34 The following table summarises the features used in the programs:
35
36 Program (.py) pmap MakeParallel manage start create Map Queue Exchange
37 ------------- ---- ------------ ------ ----- ------ --- ----- --------
38 simple_create_map Yes Yes
39 simple_create_queue Yes Yes
40 simple_create Yes Yes
41 simple_managed_map Yes Yes Yes
42 simple_managed_queue Yes Yes Yes
43 simple_managed Yes Yes Yes
44 simple_pmap Yes
45 simple_pmap_iter Yes
46 simple_start_queue Yes Yes Yes
47 simple_start Yes Yes
48
49 The simplest parallel programs are simple_pmap.py and simple_pmap_iter.py
50 which employ the pmap function resembling the built-in map function in
51 Python.
52
53 Other simple programs are those employing the Queue class, together with those
54 using the manage method which associates functions or callables with Queue or
55 Exchange objects for convenient invocation of those functions and the
56 management of their communications.
57
58 The most technically involved program is simple_start.py which uses the
59 Exchange class together with a calculation function which is aware of the
60 parallel environment and which communicates over the supplied communications
61 channel directly to the creating process.
62
63 It should be noted that with the exception of simple_start.py, those examples
64 employing calculation functions (as opposed to doing a calculation inline in a
65 loop body) all use MakeParallel to make those functions parallel-aware, thus
66 permitting the conversion of "normal" functions to a form usable in the
67 parallel environment.
68
69 Reusable Processes
70 ------------------
71
72 An additional example not listed above, simple_managed_map_reusable.py,
73 employs the MakeReusable class instead of MakeParallel in order to demonstrate
74 reusable processes and channels:
75
76 PYTHONPATH=. python examples/simple_managed_map_reusable.py
77
78 Continuous Process Communications
79 ---------------------------------
80
81 Another example not listed above, simple_continuous_queue.py, employs
82 continuous communications to monitor output from created processes:
83
84 PYTHONPATH=. python examples/simple_continuous_queue.py
85
86 Persistent Processes
87 --------------------
88
89 A number of persistent variants of some of the above examples employ a
90 persistent or background process which can be started by one process and
91 contacted later by another in order to collect the results of a computation.
92 For example:
93
94 PYTHONPATH=. python examples/simple_persistent_managed.py --start
95 PYTHONPATH=. python examples/simple_persistent_managed.py --reconnect
96
97 PYTHONPATH=. python examples/simple_background_queue.py --start
98 PYTHONPATH=. python examples/simple_background_queue.py --reconnect
99
100 PYTHONPATH=. python examples/simple_persistent_queue.py --start
101 PYTHONPATH=. python examples/simple_persistent_queue.py --reconnect
102
103 Parallel Raytracing with PyGmy
104 ------------------------------
105
106 The PyGmy raytracer modified to use pprocess can be run to investigate the
107 potential for speed increases in "real world" programs:
108
109 cd examples/PyGmy
110 PYTHONPATH=../..:. python scene.py
111
112 (This should produce a file called test.tif - a TIFF file containing a
113 raytraced scene image.)
114
115 Examples from the Concurrency SIG
116 ---------------------------------
117
118 PYTHONPATH=. python examples/concurrency-sig/bottles.py
119 PYTHONPATH=. python examples/concurrency-sig/bottles_heartbeat.py
120
121 Test Programs
122 -------------
123
124 There are some elementary tests:
125
126 PYTHONPATH=. python tests/create_loop.py
127 PYTHONPATH=. python tests/start_loop.py
128
129 (Simple loop demonstrations which use two different ways of creating and
130 starting the parallel processes.)
131
132 PYTHONPATH=. python tests/start_indexer.py <directory>
133
134 (A text indexing demonstration, where <directory> should be a directory
135 containing text files to be indexed, although HTML files will also work well
136 enough. After indexing the files, a prompt will appear, words or word
137 fragments can be entered, and matching words and their locations will be
138 shown. Run the program without arguments to see more information.)
139
140 Contact, Copyright and Licence Information
141 ------------------------------------------
142
143 The current Web page for pprocess at the time of release is:
144
145 http://www.boddie.org.uk/python/pprocess.html
146
147 The author can be contacted at the following e-mail address:
148
149 paul@boddie.org.uk
150
151 Copyright and licence information can be found in the docs directory - see
152 docs/COPYING.txt, docs/lgpl-3.0.txt and docs/gpl-3.0.txt for more information.
153
154 For the PyGmy raytracer example, different copyright and licence information
155 is provided in the docs directory - see docs/COPYING-PyGmy.txt and
156 docs/LICENCE-PyGmy.txt for more information.
157
158 Dependencies
159 ------------
160
161 This software depends on standard library features which are stated as being
162 available only on "UNIX"; it has only been tested repeatedly on a GNU/Linux
163 system, and occasionally on systems running OpenSolaris.
164
165 New in pprocess 0.5 (Changes since pprocess 0.4)
166 ------------------------------------------------
167
168 * Added proper support in the Exchange class for continuous communications
169 between processes, providing examples: simple_continuous_queue.py and the
170 concurrency-sig directory.
171 * Changed the Map class to permit incremental access to received results
172 from completed parts of the sequence of inputs, also adding an iteration
173 interface.
174 * Added an example, simple_pmap_iter.py, to demonstrate iteration over maps.
175 * Fixed the get_number_of_cores function to work with /proc/cpuinfo where
176 the "physical id" field is missing.
177 * Tidied the Exchange class, adding distinct status methods: unfinished and
178 busy.
179
180 New in pprocess 0.4 (Changes since pprocess 0.3.1)
181 --------------------------------------------------
182
183 * Added support for persistent/background processes.
184 * Added a utility function to detect and return the number of processor
185 cores available.
186 * Added missing documentation stylesheet.
187 * Added support for Solaris using pipes instead of socket pairs, since
188 the latter do not apparently work properly with poll on Solaris.
189
190 New in pprocess 0.3.1 (Changes since pprocess 0.3)
191 --------------------------------------------------
192
193 * Moved the reference material out of the module docstring and into a
194 separate document, converting it to XHTML in the process.
195 * Fixed the project name in the setup script.
196
197 New in pprocess 0.3 (Changes since parallel 0.2.5)
198 --------------------------------------------------
199
200 * Added managed callables: wrappers around callables which cause them to be
201 automatically managed by the exchange from which they were acquired.
202 * Added MakeParallel: a wrapper instantiated around a normal function which
203 sends the result of that function over the supplied channel when invoked.
204 * Added MakeReusable: a wrapper like MakeParallel which can be used in
205 conjunction with the newly-added reuse capability of the Exchange class in
206 order to reuse processes and channels.
207 * Added a Map class which attempts to emulate the built-in map function,
208 along with a pmap function using this class.
209 * Added a Queue class which provides a simpler iterator-style interface to
210 data produced by created processes.
211 * Added a create method to the Exchange class and an exit convenience
212 function to the module.
213 * Changed the Exchange implementation to not block when attempting to start
214 new processes beyond the process limit: such requests are queued and
215 performed as running processes are completed. This permits programs using
216 the start method to proceed to consumption of results more quickly.
217 * Extended and updated the examples. Added a tutorial.
218 * Added Ubuntu Feisty (7.04) package support.
219
220 New in parallel 0.2.5 (Changes since parallel 0.2.4)
221 ----------------------------------------------------
222
223 * Added a start method to the Exchange class for more convenient creation of
224 processes.
225 * Relicensed under the LGPL (version 3 or later) - this also fixes the
226 contradictory situation where the GPL was stated in the pprocess module
227 (which was not, in fact, the intention) and the LGPL was stated in the
228 documentation.
229
230 New in parallel 0.2.4 (Changes since parallel 0.2.3)
231 ----------------------------------------------------
232
233 * Set buffer sizes to zero for the file object wrappers around sockets: this
234 may prevent deadlock issues.
235
236 New in parallel 0.2.3 (Changes since parallel 0.2.2)
237 ----------------------------------------------------
238
239 * Added convenient message exchanges, offering methods handling common
240 situations at the cost of having to define a subclass of Exchange.
241 * Added a simple example of performing a parallel computation.
242 * Improved the PyGmy raytracer example to use the newly added functionality.
243
244 New in parallel 0.2.2 (Changes since parallel 0.2.1)
245 ----------------------------------------------------
246
247 * Changed the status testing in the Exchange class, potentially fixing the
248 premature closure of channels before all data was read.
249 * Fixed the PyGmy raytracer example's process accounting by relying on the
250 possibly more reliable Exchange behaviour, whilst also preventing
251 erroneous creation of "out of bounds" processes.
252 * Added a removed attribute on the Exchange to record which channels were
253 removed in the last call to the ready method.
254
255 New in parallel 0.2.1 (Changes since parallel 0.2)
256 --------------------------------------------------
257
258 * Added a PyGmy raytracer example.
259 * Updated copyright and licensing details (FSF address, additional works).
260
261 New in parallel 0.2 (Changes since parallel 0.1)
262 ------------------------------------------------
263
264 * Changed the name of the included module from parallel to pprocess in order
265 to avoid naming conflicts with PyParallel.
266
267 Release Procedures
268 ------------------
269
270 Update the pprocess __version__ attribute and the setup.py file version field.
271 Change the version number and package filename/directory in the documentation.
272 Update the release notes (see above).
273 Check the release information in the PKG-INFO file.
274 Tag, export.
275 Archive, upload.
276 Update PyPI.
277
278 Making Packages
279 ---------------
280
281 To make Debian-based packages:
282
283 1. Create new package directories under packages if necessary.
284 2. Make a symbolic link in the distribution's root directory to keep the
285 Debian tools happy:
286
287 ln -s packages/ubuntu-hoary/python2.4-parallel-pprocess/debian/
288
289 Or:
290
291 ln -s packages/ubuntu-feisty/python-pprocess/debian/
292
293 3. Run the package builder:
294
295 dpkg-buildpackage -rfakeroot
296
297 4. Locate and tidy up the packages in the parent directory of the
298 distribution's root directory.