iSharkFly-Open
/
python-peps
mirror of https://github.com/python/peps.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

reSTify PEP 371 (#325)

This commit is contained in:
Huang Huang 2017-08-17 06:47:03 +08:00 committed by Brett Cannon
parent 0f7b74537f
commit dd454efb3a
1 changed files with 321 additions and 309 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

396
pep-0371.txt
View File

@ -6,64 +6,66 @@ Author: Jesse Noller <jnoller@gmail.com>,
Richard Oudkerk <r.m.oudkerk@googlemail.com> Richard Oudkerk <r.m.oudkerk@googlemail.com>
Status: Final Status: Final
Type: Standards Track Type: Standards Track
Content-Type: text/plain Content-Type: text/x-rst
Created: 06-May-2008 Created: 06-May-2008
Python-Version: 2.6 / 3.0 Python-Version: 2.6 / 3.0
Post-History: Post-History:
Abstract Abstract
========
This PEP proposes the inclusion of the pyProcessing [1] package This PEP proposes the inclusion of the ``pyProcessing`` [1]_ package
into the Python standard library, renamed to "multiprocessing". into the Python standard library, renamed to "multiprocessing".
The processing package mimics the standard library threading The ``processing`` package mimics the standard library ``threading``
module functionality to provide a process-based approach to module functionality to provide a process-based approach to
threaded programming allowing end-users to dispatch multiple threaded programming allowing end-users to dispatch multiple
tasks that effectively side-step the global interpreter lock. tasks that effectively side-step the global interpreter lock.
The package also provides server and client functionality The package also provides server and client functionality
(processing.Manager) to provide remote sharing and management of (``processing.Manager``) to provide remote sharing and management of
objects and tasks so that applications may not only leverage objects and tasks so that applications may not only leverage
multiple cores on the local machine, but also distribute objects multiple cores on the local machine, but also distribute objects
and tasks across a cluster of networked machines. and tasks across a cluster of networked machines.
While the distributed capabilities of the package are beneficial, While the distributed capabilities of the package are beneficial,
the primary focus of this PEP is the core threading-like API and the primary focus of this PEP is the core threading-like API and
capabilities of the package. capabilities of the package.
Rationale Rationale
=========
The current CPython interpreter implements the Global Interpreter The current CPython interpreter implements the Global Interpreter
Lock (GIL) and barring work in Python 3000 or other versions Lock (GIL) and barring work in Python 3000 or other versions
currently planned [2], the GIL will remain as-is within the currently planned [2]_, the GIL will remain as-is within the
CPython interpreter for the foreseeable future. While the GIL CPython interpreter for the foreseeable future. While the GIL
itself enables clean and easy to maintain C code for the itself enables clean and easy to maintain C code for the
interpreter and extensions base, it is frequently an issue for interpreter and extensions base, it is frequently an issue for
those Python programmers who are leveraging multi-core machines. those Python programmers who are leveraging multi-core machines.
The GIL itself prevents more than a single thread from running The GIL itself prevents more than a single thread from running
within the interpreter at any given point in time, effectively within the interpreter at any given point in time, effectively
removing Python's ability to take advantage of multi-processor removing Python's ability to take advantage of multi-processor
systems. systems.
The pyprocessing package offers a method to side-step the GIL The pyprocessing package offers a method to side-step the GIL
allowing applications within CPython to take advantage of allowing applications within CPython to take advantage of
multi-core architectures without asking users to completely change multi-core architectures without asking users to completely change
their programming paradigm (i.e.: dropping threaded programming their programming paradigm (i.e.: dropping threaded programming
for another "concurrent" approach - Twisted, Actors, etc). for another "concurrent" approach - Twisted, Actors, etc).
The Processing package offers CPython a "known API" which mirrors The Processing package offers CPython a "known API" which mirrors
albeit in a PEP 8 compliant manner, that of the threading API, albeit in a PEP 8 compliant manner, that of the threading API,
with known semantics and easy scalability. with known semantics and easy scalability.
In the future, the package might not be as relevant should the In the future, the package might not be as relevant should the
CPython interpreter enable "true" threading, however for some CPython interpreter enable "true" threading, however for some
applications, forking an OS process may sometimes be more applications, forking an OS process may sometimes be more
desirable than using lightweight threads, especially on those desirable than using lightweight threads, especially on those
platforms where process creation is fast and optimized. platforms where process creation is fast and optimized.
For example, a simple threaded application: For example, a simple threaded application::
from threading import Thread as worker from threading import Thread as worker
@ -74,82 +76,85 @@ Rationale
t.start() t.start()
t.join() t.join()
The pyprocessing package mirrored the API so well, that with a The pyprocessing package mirrored the API so well, that with a
simple change of the import to: simple change of the import to::
from processing import process as worker from processing import process as worker
The code would now execute through the processing.process class. The code would now execute through the processing.process class.
Obviously, with the renaming of the API to PEP 8 compliance there Obviously, with the renaming of the API to PEP 8 compliance there
would be additional renaming which would need to occur within would be additional renaming which would need to occur within
user applications, however minor. user applications, however minor.
This type of compatibility means that, with a minor (in most cases) This type of compatibility means that, with a minor (in most cases)
change in code, users' applications will be able to leverage all change in code, users' applications will be able to leverage all
cores and processors on a given machine for parallel execution. cores and processors on a given machine for parallel execution.
In many cases the pyprocessing package is even faster than the In many cases the pyprocessing package is even faster than the
normal threading approach for I/O bound programs. This of course, normal threading approach for I/O bound programs. This of course,
takes into account that the pyprocessing package is in optimized C takes into account that the pyprocessing package is in optimized C
code, while the threading module is not. code, while the threading module is not.
The "Distributed" Problem The "Distributed" Problem
=========================
In the discussion on Python-Dev about the inclusion of this In the discussion on Python-Dev about the inclusion of this
package [3] there was confusion about the intentions this PEP with package [3]_ there was confusion about the intentions this PEP with
an attempt to solve the "Distributed" problem - frequently an attempt to solve the "Distributed" problem - frequently
comparing the functionality of this package with other solutions comparing the functionality of this package with other solutions
like MPI-based communication [4], CORBA, or other distributed like MPI-based communication [4]_, CORBA, or other distributed
object approaches [5]. object approaches [5]_.
The "distributed" problem is large and varied. Each programmer The "distributed" problem is large and varied. Each programmer
working within this domain has either very strong opinions about working within this domain has either very strong opinions about
their favorite module/method or a highly customized problem for their favorite module/method or a highly customized problem for
which no existing solution works. which no existing solution works.
The acceptance of this package does not preclude or recommend that The acceptance of this package does not preclude or recommend that
programmers working on the "distributed" problem not examine other programmers working on the "distributed" problem not examine other
solutions for their problem domain. The intent of including this solutions for their problem domain. The intent of including this
package is to provide entry-level capabilities for local package is to provide entry-level capabilities for local
concurrency and the basic support to spread that concurrency concurrency and the basic support to spread that concurrency
across a network of machines - although the two are not tightly across a network of machines - although the two are not tightly
coupled, the pyprocessing package could in fact, be used in coupled, the pyprocessing package could in fact, be used in
conjunction with any of the other solutions including MPI/etc. conjunction with any of the other solutions including MPI/etc.
If necessary - it is possible to completely decouple the local If necessary - it is possible to completely decouple the local
concurrency abilities of the package from the concurrency abilities of the package from the
network-capable/shared aspects of the package. Without serious network-capable/shared aspects of the package. Without serious
concerns or cause however, the author of this PEP does not concerns or cause however, the author of this PEP does not
recommend that approach. recommend that approach.
Performance Comparison Performance Comparison
======================
As we all know - there are "lies, damned lies, and benchmarks". As we all know - there are "lies, damned lies, and benchmarks".
These speed comparisons, while aimed at showcasing the performance These speed comparisons, while aimed at showcasing the performance
of the pyprocessing package, are by no means comprehensive or of the pyprocessing package, are by no means comprehensive or
applicable to all possible use cases or environments. Especially applicable to all possible use cases or environments. Especially
for those platforms with sluggish process forking timing. for those platforms with sluggish process forking timing.
All benchmarks were run using the following: All benchmarks were run using the following:
* 4 Core Intel Xeon CPU @ 3.00GHz
* 16 GB of RAM
* Python 2.5.2 compiled on Gentoo Linux (kernel 2.6.18.6)
* pyProcessing 0.52
All of the code for this can be downloaded from: * 4 Core Intel Xeon CPU @ 3.00GHz
http://jessenoller.com/code/bench-src.tgz * 16 GB of RAM
* Python 2.5.2 compiled on Gentoo Linux (kernel 2.6.18.6)
* pyProcessing 0.52
The basic method of execution for these benchmarks is in the All of the code for this can be downloaded from
run_benchmarks.py script, which is simply a wrapper to execute a http://jessenoller.com/code/bench-src.tgz
target function through a single threaded (linear), multi-threaded
(via threading), and multi-process (via pyprocessing) function for
a static number of iterations with increasing numbers of execution
loops and/or threads.
The run_benchmarks.py script executes each function 100 times, The basic method of execution for these benchmarks is in the
picking the best run of that 100 iterations via the timeit module. run_benchmarks.py script, which is simply a wrapper to execute a
target function through a single threaded (linear), multi-threaded
(via threading), and multi-process (via pyprocessing) function for
a static number of iterations with increasing numbers of execution
loops and/or threads.
First, to identify the overhead of the spawning of the workers, we The run_benchmarks.py script executes each function 100 times,
execute a function which is simply a pass statement (empty): picking the best run of that 100 iterations via the timeit module.
First, to identify the overhead of the spawning of the workers, we
execute a function which is simply a pass statement (empty)::
cmd: python run_benchmarks.py empty_func.py cmd: python run_benchmarks.py empty_func.py
Importing empty_func Importing empty_func
@ -170,12 +175,12 @@ Performance Comparison
threaded (8 threads) 0.007990 seconds threaded (8 threads) 0.007990 seconds
processes (8 procs) 0.005512 seconds processes (8 procs) 0.005512 seconds
As you can see, process forking via the pyprocessing package is As you can see, process forking via the pyprocessing package is
faster than the speed of building and then executing the threaded faster than the speed of building and then executing the threaded
version of the code. version of the code.
The second test calculates 50000 Fibonacci numbers inside of each The second test calculates 50000 Fibonacci numbers inside of each
thread (isolated and shared nothing): thread (isolated and shared nothing)::
cmd: python run_benchmarks.py fibonacci.py cmd: python run_benchmarks.py fibonacci.py
Importing fibonacci Importing fibonacci
@ -196,8 +201,8 @@ Performance Comparison
threaded (8 threads) 1.596824 seconds threaded (8 threads) 1.596824 seconds
processes (8 procs) 0.417899 seconds processes (8 procs) 0.417899 seconds
The third test calculates the sum of all primes below 100000, The third test calculates the sum of all primes below 100000,
again sharing nothing. again sharing nothing::
cmd: run_benchmarks.py crunch_primes.py cmd: run_benchmarks.py crunch_primes.py
Importing crunch_primes Importing crunch_primes
@ -218,18 +223,18 @@ Performance Comparison
threaded (8 threads) 5.109192 seconds threaded (8 threads) 5.109192 seconds
processes (8 procs) 1.077939 seconds processes (8 procs) 1.077939 seconds
The reason why tests two and three focused on pure numeric The reason why tests two and three focused on pure numeric
crunching is to showcase how the current threading implementation crunching is to showcase how the current threading implementation
does hinder non-I/O applications. Obviously, these tests could be does hinder non-I/O applications. Obviously, these tests could be
improved to use a queue for coordination of results and chunks of improved to use a queue for coordination of results and chunks of
work but that is not required to show the performance of the work but that is not required to show the performance of the
package and core processing.process module. package and core processing.process module.
The next test is an I/O bound test. This is normally where we see The next test is an I/O bound test. This is normally where we see
a steep improvement in the threading module approach versus a a steep improvement in the threading module approach versus a
single-threaded approach. In this case, each worker is opening a single-threaded approach. In this case, each worker is opening a
descriptor to lorem.txt, randomly seeking within it and writing descriptor to lorem.txt, randomly seeking within it and writing
lines to /dev/null: lines to /dev/null::
cmd: python run_benchmarks.py file_io.py cmd: python run_benchmarks.py file_io.py
Importing file_io Importing file_io
@ -250,14 +255,14 @@ Performance Comparison
threaded (8 threads) 2.437204 seconds threaded (8 threads) 2.437204 seconds
processes (8 procs) 0.203438 seconds processes (8 procs) 0.203438 seconds
As you can see, pyprocessing is still faster on this I/O operation As you can see, pyprocessing is still faster on this I/O operation
than using multiple threads. And using multiple threads is slower than using multiple threads. And using multiple threads is slower
than the single threaded execution itself. than the single threaded execution itself.
Finally, we will run a socket-based test to show network I/O Finally, we will run a socket-based test to show network I/O
performance. This function grabs a URL from a server on the LAN performance. This function grabs a URL from a server on the LAN
that is a simple error page from tomcat. It gets the page 100 that is a simple error page from tomcat. It gets the page 100
times. The network is silent, and a 10G connection: times. The network is silent, and a 10G connection::
cmd: python run_benchmarks.py url_get.py cmd: python run_benchmarks.py url_get.py
Importing url_get Importing url_get
@ -278,19 +283,19 @@ Performance Comparison
threaded (8 threads) 0.659298 seconds threaded (8 threads) 0.659298 seconds
processes (8 procs) 0.298625 seconds processes (8 procs) 0.298625 seconds
We finally see threaded performance surpass that of We finally see threaded performance surpass that of
single-threaded execution, but the pyprocessing package is still single-threaded execution, but the pyprocessing package is still
faster when increasing the number of workers. If you stay with faster when increasing the number of workers. If you stay with
one or two threads/workers, then the timing between threads and one or two threads/workers, then the timing between threads and
pyprocessing is fairly close. pyprocessing is fairly close.
One item of note however, is that there is an implicit overhead One item of note however, is that there is an implicit overhead
within the pyprocessing package's Queue implementation due to the within the pyprocessing package's ``Queue`` implementation due to the
object serialization. object serialization.
Alec Thomas provided a short example based on the Alec Thomas provided a short example based on the
run_benchmarks.py script to demonstrate this overhead versus the run_benchmarks.py script to demonstrate this overhead versus the
default Queue implementation: default ``Queue`` implementation::
cmd: run_bench_queue.py cmd: run_bench_queue.py
non_threaded (1 iters) 0.010546 seconds non_threaded (1 iters) 0.010546 seconds
@ -309,123 +314,130 @@ Performance Comparison
threaded (8 threads) 0.184254 seconds threaded (8 threads) 0.184254 seconds
processes (8 procs) 0.302999 seconds processes (8 procs) 0.302999 seconds
Additional benchmarks can be found in the pyprocessing package's Additional benchmarks can be found in the pyprocessing package's
source distribution's examples/ directory. The examples will be source distribution's examples/ directory. The examples will be
included in the package's documentation. included in the package's documentation.
Maintenance Maintenance
===========
Richard M. Oudkerk - the author of the pyprocessing package has Richard M. Oudkerk - the author of the pyprocessing package has
agreed to maintain the package within Python SVN. Jesse Noller agreed to maintain the package within Python SVN. Jesse Noller
has volunteered to also help maintain/document and test the has volunteered to also help maintain/document and test the
package. package.
API Naming API Naming
==========
While the aim of the package's API is designed to closely mimic that of While the aim of the package's API is designed to closely mimic that of
the threading and Queue modules as of python 2.x, those modules are not the threading and ``Queue`` modules as of python 2.x, those modules are not
PEP 8 compliant. It has been decided that instead of adding the package PEP 8 compliant. It has been decided that instead of adding the package
"as is" and therefore perpetuating the non-PEP 8 compliant naming, we "as is" and therefore perpetuating the non-PEP 8 compliant naming, we
will rename all APIs, classes, etc to be fully PEP 8 compliant. will rename all APIs, classes, etc to be fully PEP 8 compliant.
This change does affect the ease-of-drop in replacement for those using This change does affect the ease-of-drop in replacement for those using
the threading module, but that is an acceptable side-effect in the view the threading module, but that is an acceptable side-effect in the view
of the authors, especially given that the threading module's own API of the authors, especially given that the threading module's own API
will change. will change.
Issue 3042 in the tracker proposes that for Python 2.6 there will be Issue 3042 in the tracker proposes that for Python 2.6 there will be
two APIs for the threading module - the current one, and the PEP 8 two APIs for the threading module - the current one, and the PEP 8
compliant one. Warnings about the upcoming removal of the original compliant one. Warnings about the upcoming removal of the original
java-style API will be issued when -3 is invoked. java-style API will be issued when -3 is invoked.
In Python 3000, the threading API will become PEP 8 compliant, which In Python 3000, the threading API will become PEP 8 compliant, which
means that the multiprocessing module and the threading module will means that the multiprocessing module and the threading module will
again have matching APIs. again have matching APIs.
Timing/Schedule Timing/Schedule
===============
Some concerns have been raised about the timing/lateness of this Some concerns have been raised about the timing/lateness of this
PEP for the 2.6 and 3.0 releases this year, however it is felt by PEP for the 2.6 and 3.0 releases this year, however it is felt by
both the authors and others that the functionality this package both the authors and others that the functionality this package
offers surpasses the risk of inclusion. offers surpasses the risk of inclusion.
However, taking into account the desire not to destabilize However, taking into account the desire not to destabilize
Python-core, some refactoring of pyprocessing's code "into" Python-core, some refactoring of pyprocessing's code "into"
Python-core can be withheld until the next 2.x/3.x releases. This Python-core can be withheld until the next 2.x/3.x releases. This
means that the actual risk to Python-core is minimal, and largely means that the actual risk to Python-core is minimal, and largely
constrained to the actual package itself. constrained to the actual package itself.
Open Issues Open Issues
===========
* Confirm no "default" remote connection capabilities, if needed * Confirm no "default" remote connection capabilities, if needed
enable the remote security mechanisms by default for those enable the remote security mechanisms by default for those
classes which offer remote capabilities. classes which offer remote capabilities.
* Some of the API (Queue methods qsize(), task_done() and join()) * Some of the API (``Queue`` methods ``qsize()``, ``task_done()`` and ``join()``)
either need to be added, or the reason for their exclusion needs either need to be added, or the reason for their exclusion needs
to be identified and documented clearly. to be identified and documented clearly.
Closed Issues Closed Issues
=============
* The PyGILState bug patch submitted in issue 1683 by roudkerk * The ``PyGILState`` bug patch submitted in issue 1683 by roudkerk
must be applied for the package unit tests to work. must be applied for the package unit tests to work.
* Existing documentation has to be moved to ReST formatting. * Existing documentation has to be moved to ReST formatting.
* Reliance on ctypes: The pyprocessing package's reliance on * Reliance on ctypes: The ``pyprocessing`` package's reliance on
ctypes prevents the package from functioning on platforms where ctypes prevents the package from functioning on platforms where
ctypes is not supported. This is not a restriction of this ctypes is not supported. This is not a restriction of this
package, but rather of ctypes. package, but rather of ctypes.
* DONE: Rename top-level package from "pyprocessing" to * DONE: Rename top-level package from "pyprocessing" to
"multiprocessing". "multiprocessing".
* DONE: Also note that the default behavior of process spawning * DONE: Also note that the default behavior of process spawning
does not make it compatible with use within IDLE as-is, this does not make it compatible with use within IDLE as-is, this
will be examined as a bug-fix or "setExecutable" enhancement. will be examined as a bug-fix or "setExecutable" enhancement.
* DONE: Add in "multiprocessing.setExecutable()" method to override the * DONE: Add in "multiprocessing.setExecutable()" method to override the
default behavior of the package to spawn processes using the default behavior of the package to spawn processes using the
current executable name rather than the Python interpreter. Note current executable name rather than the Python interpreter. Note
that Mark Hammond has suggested a factory-style interface for that Mark Hammond has suggested a factory-style interface for
this[7]. this [7]_.
References References
==========
[1] PyProcessing home page .. [1] PyProcessing home page
http://pyprocessing.berlios.de/ http://pyprocessing.berlios.de/
[2] See Adam Olsen's "safe threading" project .. [2] See Adam Olsen's "safe threading" project
http://code.google.com/p/python-safethread/ http://code.google.com/p/python-safethread/
[3] See: Addition of "pyprocessing" module to standard lib. .. [3] See: Addition of "pyprocessing" module to standard lib.
https://mail.python.org/pipermail/python-dev/2008-May/079417.html https://mail.python.org/pipermail/python-dev/2008-May/079417.html
[4] http://mpi4py.scipy.org/ .. [4] http://mpi4py.scipy.org/
[5] See "Cluster Computing" .. [5] See "Cluster Computing"
http://wiki.python.org/moin/ParallelProcessing http://wiki.python.org/moin/ParallelProcessing
[6] The original run_benchmark.py code was published in Python .. [6] The original run_benchmark.py code was published in Python
Magazine in December 2007: "Python Threads and the Global Magazine in December 2007: "Python Threads and the Global
Interpreter Lock" by Jesse Noller. It has been modified for Interpreter Lock" by Jesse Noller. It has been modified for
this PEP. this PEP.
[7] http://groups.google.com/group/python-dev2/msg/54cf06d15cbcbc34 .. [7] http://groups.google.com/group/python-dev2/msg/54cf06d15cbcbc34
[8] Addition Python-Dev discussion .. [8] Addition Python-Dev discussion
https://mail.python.org/pipermail/python-dev/2008-June/080011.html https://mail.python.org/pipermail/python-dev/2008-June/080011.html
Copyright Copyright
=========
This document has been placed in the public domain. This document has been placed in the public domain.
..
Local Variables: Local Variables:
mode: indented-text mode: indented-text
indent-tabs-mode: nil indent-tabs-mode: nil
sentence-end-double-space: t sentence-end-double-space: t
fill-column: 70 fill-column: 70
coding: utf-8 coding: utf-8
End: End: