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<div class="section" id="module-cspthread">

<h1>CSP based on POSIX threads<a class="headerlink" href="#module-cspthread" title="Permalink to this headline">¶</a></h1>

<p>Communicating sequential processes, in Python.</p>

<p>When using CSP Python as a DSL, this module will normally be imported

via the statement &#8216;from csp.cspthread import <a href="#id1"><span class="problematic" id="id2">*</span></a>&#8216;.</p>

<p>Copyright (C) Sarah Mount, 2009.</p>

<p>This program is free software; you can redistribute it and/or

modify it under the terms of the GNU General Public License

as published by the Free Software Foundation; either version 2

of the License, or (at your option) any later version.</p>

<p>This program is distributed in the hope that it will be useful,

but WITHOUT ANY WARRANTY; without even the implied warranty of

MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

GNU General Public License for more details.</p>

<p>You should have rceeived a copy of the GNU General Public License

along with this program; if not, write to the Free Software

Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA</p>

<dl class="class">

<dt id="cspthread.CSPProcess">

<em class="property">class </em><tt class="descclassname">cspthread.</tt><tt class="descname">CSPProcess</tt><big>(</big><em>func</em>, <em>*args</em>, <em>**kwargs</em><big>)</big><a class="headerlink" href="#cspthread.CSPProcess" title="Permalink to this definition">¶</a></dt>

<dd><p>Implementation of CSP processes.

Not intended to be used in client code. Use &#64;process instead.</p>

<dl class="method">

<dt id="cspthread.CSPProcess.getPid">

<tt class="descname">getPid</tt><big>(</big><big>)</big><a class="headerlink" href="#cspthread.CSPProcess.getPid" title="Permalink to this definition">¶</a></dt>

<dd><p>Return thread ident.</p>

<p>The name of this method ensures that the CSPProcess interface

in this module is identical to the one defined in

cspprocess.py.</p>

<dl class="method">

<dt id="cspthread.CSPProcess.run">

<tt class="descname">run</tt><big>(</big><big>)</big><a class="headerlink" href="#cspthread.CSPProcess.run" title="Permalink to this definition">¶</a></dt>

<dd>Called automatically when the L{start} methods is called.</dd></dl>

<dl class="class">

<dt id="cspthread.CSPServer">

<em class="property">class </em><tt class="descclassname">cspthread.</tt><tt class="descname">CSPServer</tt><big>(</big><em>func</em>, <em>*args</em>, <em>**kwargs</em><big>)</big><a class="headerlink" href="#cspthread.CSPServer" title="Permalink to this definition">¶</a></dt>

<dd><p>Implementation of CSP server processes.

Not intended to be used in client code. Use &#64;forever instead.</p>

<dl class="method">

<dt id="cspthread.CSPServer.run">

<tt class="descname">run</tt><big>(</big><big>)</big><a class="headerlink" href="#cspthread.CSPServer.run" title="Permalink to this definition">¶</a></dt>

<dd>Called automatically when the L{start} methods is called.</dd></dl>

<dl class="class">

<dt id="cspthread.Alt">

<em class="property">class </em><tt class="descclassname">cspthread.</tt><tt class="descname">Alt</tt><big>(</big><em>*args</em><big>)</big><a class="headerlink" href="#cspthread.Alt" title="Permalink to this definition">¶</a></dt>

<dd><p>CSP select (OCCAM ALT) process.</p>

<p>What should happen if a guard is poisoned?</p>

<dl class="method">

<dt id="cspthread.Alt.fair_select">

<tt class="descname">fair_select</tt><big>(</big><big>)</big><a class="headerlink" href="#cspthread.Alt.fair_select" title="Permalink to this definition">¶</a></dt>

<dd>Select a guard to synchronise with. Do not select the

previously selected guard (unless it is the only guard

available).</dd></dl>

<dl class="method">

<dt id="cspthread.Alt.poison">

<tt class="descname">poison</tt><big>(</big><big>)</big><a class="headerlink" href="#cspthread.Alt.poison" title="Permalink to this definition">¶</a></dt>

<dd><p>Poison the last selected guard and unlink from the guard list.</p>

<p>Sets self.last_selected to None.</p>

<dl class="method">

<dt id="cspthread.Alt.pri_select">

<tt class="descname">pri_select</tt><big>(</big><big>)</big><a class="headerlink" href="#cspthread.Alt.pri_select" title="Permalink to this definition">¶</a></dt>

<dd>Select a guard to synchronise with, in order of

&#8220;priority&#8221;. The guard with the lowest index in the L{guards}

list has the highest priority.</dd></dl>

<dl class="method">

<dt id="cspthread.Alt.select">

<tt class="descname">select</tt><big>(</big><big>)</big><a class="headerlink" href="#cspthread.Alt.select" title="Permalink to this definition">¶</a></dt>

<dd>Randomly select from ready guards.</dd></dl>

<dl class="class">

<dt id="cspthread.Par">

<em class="property">class </em><tt class="descclassname">cspthread.</tt><tt class="descname">Par</tt><big>(</big><em>*procs</em>, <em>**kwargs</em><big>)</big><a class="headerlink" href="#cspthread.Par" title="Permalink to this definition">¶</a></dt>

<dd><p>Run CSP processes in parallel.</p>

<dl class="method">

<dt id="cspthread.Par.getPid">

<tt class="descname">getPid</tt><big>(</big><big>)</big><a class="headerlink" href="#cspthread.Par.getPid" title="Permalink to this definition">¶</a></dt>

<dd><p>Return thread ident.</p>

<p>The name of this method ensures that the CSPProcess interface

in this module is identical to the one defined in

cspprocess.py.</p>

<dl class="method">

<dt id="cspthread.Par.start">

<tt class="descname">start</tt><big>(</big><big>)</big><a class="headerlink" href="#cspthread.Par.start" title="Permalink to this definition">¶</a></dt>

<dd>Start then synchronize with the execution of parallel processes.

Return when all parallel processes have returned.</dd></dl>

<dl class="method">

<dt id="cspthread.Par.terminate">

<tt class="descname">terminate</tt><big>(</big><big>)</big><a class="headerlink" href="#cspthread.Par.terminate" title="Permalink to this definition">¶</a></dt>

<dd>Terminate the execution of this process.</dd></dl>

<dl class="class">

<dt id="cspthread.Seq">

<em class="property">class </em><tt class="descclassname">cspthread.</tt><tt class="descname">Seq</tt><big>(</big><em>*procs</em><big>)</big><a class="headerlink" href="#cspthread.Seq" title="Permalink to this definition">¶</a></dt>

<dd><p>Run CSP processes sequentially.</p>

<dl class="method">

<dt id="cspthread.Seq.start">

<tt class="descname">start</tt><big>(</big><big>)</big><a class="headerlink" href="#cspthread.Seq.start" title="Permalink to this definition">¶</a></dt>

<dd>Start this process running.</dd></dl>

<dl class="method">

<dt id="cspthread.Seq.terminate">

<tt class="descname">terminate</tt><big>(</big><big>)</big><a class="headerlink" href="#cspthread.Seq.terminate" title="Permalink to this definition">¶</a></dt>

<dd>Terminate the execution of this process.</dd></dl>

<dl class="class">

<dt id="cspthread.Guard">

<em class="property">class </em><tt class="descclassname">cspthread.</tt><tt class="descname">Guard</tt><a class="headerlink" href="#cspthread.Guard" title="Permalink to this definition">¶</a></dt>

<dd><p>Abstract class to represent CSP guards.</p>

<p>All methods must be overridden in subclasses.</p>

<dl class="method">

<dt id="cspthread.Guard.disable">

<tt class="descname">disable</tt><big>(</big><big>)</big><a class="headerlink" href="#cspthread.Guard.disable" title="Permalink to this definition">¶</a></dt>

<dd>Roll back from an L{enable} call.</dd></dl>

<dl class="method">

<dt id="cspthread.Guard.enable">

<tt class="descname">enable</tt><big>(</big><big>)</big><a class="headerlink" href="#cspthread.Guard.enable" title="Permalink to this definition">¶</a></dt>

<dd>Prepare for, but do not commit to a synchronisation.</dd></dl>

<dl class="method">

<dt id="cspthread.Guard.is_selectable">

<tt class="descname">is_selectable</tt><big>(</big><big>)</big><a class="headerlink" href="#cspthread.Guard.is_selectable" title="Permalink to this definition">¶</a></dt>

<dd>Should return C{True} if this guard can be selected by an L{Alt}.</dd></dl>

<dl class="method">

<dt id="cspthread.Guard.poison">

<tt class="descname">poison</tt><big>(</big><big>)</big><a class="headerlink" href="#cspthread.Guard.poison" title="Permalink to this definition">¶</a></dt>

<dd>Terminate all processes attached to this guard.</dd></dl>

<dl class="method">

<dt id="cspthread.Guard.select">

<tt class="descname">select</tt><big>(</big><big>)</big><a class="headerlink" href="#cspthread.Guard.select" title="Permalink to this definition">¶</a></dt>

<dd>Commit to a synchronisation started by L{enable}.</dd></dl>

<dl class="class">

<dt id="cspthread.Channel">

<em class="property">class </em><tt class="descclassname">cspthread.</tt><tt class="descname">Channel</tt><a class="headerlink" href="#cspthread.Channel" title="Permalink to this definition">¶</a></dt>

<dd><p>CSP Channel objects.</p>

<p>In python-csp there are two sorts of channel. In JCSP terms these

are Any2Any, Alting channels. However, each channel creates an

operating system level pipe. Since this is a file object the

number of channels a program can create is limited to the maximum

number of files the operating system allows to be open at any one

time. To avoid this bottleneck use L{FileChannel} objects, which

close the file descriptor used for IPC after every read or write

operations. Read and write operations are, however, over 20 time

slower when performed on L{FileChannel} objects.</p>

<p>Subclasses of C{Channel} must call L{_setup()} in their

constructor and override L{put}, L{get}, L{__del__},

L{__getstate__} and L{__setstate__}, the latter two methods for

pickling.</p>

<dl class="method">

<dt id="cspthread.Channel.disable">

<tt class="descname">disable</tt><big>(</big><big>)</big><a class="headerlink" href="#cspthread.Channel.disable" title="Permalink to this definition">¶</a></dt>

<dd><p>Disable this channel for Alt selection.</p>

<p>MUST be called after L{enable} if this channel is not selected.</p>

<dl class="method">

<dt id="cspthread.Channel.enable">

<tt class="descname">enable</tt><big>(</big><big>)</big><a class="headerlink" href="#cspthread.Channel.enable" title="Permalink to this definition">¶</a></dt>

<dd><p>Enable a read for an Alt select.</p>

<p>MUST be called before L{select()} or L{is_selectable()}.</p>

<dl class="method">

<dt id="cspthread.Channel.get">

<tt class="descname">get</tt><big>(</big><big>)</big><a class="headerlink" href="#cspthread.Channel.get" title="Permalink to this definition">¶</a></dt>

<dd>Get a Python object from a process-safe store.</dd></dl>

<dl class="method">

<dt id="cspthread.Channel.is_selectable">

<tt class="descname">is_selectable</tt><big>(</big><big>)</big><a class="headerlink" href="#cspthread.Channel.is_selectable" title="Permalink to this definition">¶</a></dt>

<dd>Test whether Alt can select this channel.</dd></dl>

<dl class="method">

<dt id="cspthread.Channel.poison">

<tt class="descname">poison</tt><big>(</big><big>)</big><a class="headerlink" href="#cspthread.Channel.poison" title="Permalink to this definition">¶</a></dt>

<dd>Poison a channel causing all processes using it to terminate.</dd></dl>

<dl class="method">

<dt id="cspthread.Channel.put">

<tt class="descname">put</tt><big>(</big><em>item</em><big>)</big><a class="headerlink" href="#cspthread.Channel.put" title="Permalink to this definition">¶</a></dt>

<dd>Put C{item} on a process-safe store.</dd></dl>

<dl class="method">

<dt id="cspthread.Channel.read">

<tt class="descname">read</tt><big>(</big><big>)</big><a class="headerlink" href="#cspthread.Channel.read" title="Permalink to this definition">¶</a></dt>

<dd>Read (and return) a Python object from this channel.</dd></dl>

<dl class="method">

<dt id="cspthread.Channel.resume">

<tt class="descname">resume</tt><big>(</big><big>)</big><a class="headerlink" href="#cspthread.Channel.resume" title="Permalink to this definition">¶</a></dt>

<dd>Resume this mobile channel after migrating between processes.</dd></dl>

<dl class="method">

<dt id="cspthread.Channel.select">

<tt class="descname">select</tt><big>(</big><big>)</big><a class="headerlink" href="#cspthread.Channel.select" title="Permalink to this definition">¶</a></dt>

<dd>Complete a Channel read for an Alt select.</dd></dl>

<dl class="method">

<dt id="cspthread.Channel.suspend">

<tt class="descname">suspend</tt><big>(</big><big>)</big><a class="headerlink" href="#cspthread.Channel.suspend" title="Permalink to this definition">¶</a></dt>

<dd>Suspend this mobile channel before migrating between processes.</dd></dl>

<dl class="method">

<dt id="cspthread.Channel.write">

<tt class="descname">write</tt><big>(</big><em>obj</em><big>)</big><a class="headerlink" href="#cspthread.Channel.write" title="Permalink to this definition">¶</a></dt>

<dd>Write a Python object to this channel.</dd></dl>

<dl class="class">

<dt id="cspthread.FileChannel">

<em class="property">class </em><tt class="descclassname">cspthread.</tt><tt class="descname">FileChannel</tt><a class="headerlink" href="#cspthread.FileChannel" title="Permalink to this definition">¶</a></dt>

<dd><p>Channel objects using files on disk.</p>

<p>C{FileChannel} objects close their files after each read or write

operation. The advantage of this is that client code can create as

many C{FileChannel} objects as it wishes (unconstrained by the

operating system&#8217;s maximum number of open files). In return there

is a performance hit &#8211; reads and writes are around 10 x slower on

C{FileChannel} objects compared to L{Channel} objects.</p>

<dl class="method">

<dt id="cspthread.FileChannel.get">

<tt class="descname">get</tt><big>(</big><big>)</big><a class="headerlink" href="#cspthread.FileChannel.get" title="Permalink to this definition">¶</a></dt>

<dd>Get a Python object from a process-safe store.</dd></dl>

<dl class="method">

<dt id="cspthread.FileChannel.put">

<tt class="descname">put</tt><big>(</big><em>item</em><big>)</big><a class="headerlink" href="#cspthread.FileChannel.put" title="Permalink to this definition">¶</a></dt>

<dd>Put C{item} on a process-safe store.</dd></dl>

<dl class="method">

<dt id="cspthread.FileChannel.resume">

<tt class="descname">resume</tt><big>(</big><big>)</big><a class="headerlink" href="#cspthread.FileChannel.resume" title="Permalink to this definition">¶</a></dt>

<dd>Suspend this mobile channel after migrating between processes.</dd></dl>

<dl class="method">

<dt id="cspthread.FileChannel.suspend">

<tt class="descname">suspend</tt><big>(</big><big>)</big><a class="headerlink" href="#cspthread.FileChannel.suspend" title="Permalink to this definition">¶</a></dt>

<dd>Suspend this mobile channel before migrating between processes.</dd></dl>

<dl class="function">

<dt id="cspthread.process">

<tt class="descclassname">cspthread.</tt><tt class="descname">process</tt><big>(</big><em>func</em><big>)</big><a class="headerlink" href="#cspthread.process" title="Permalink to this definition">¶</a></dt>

<dd><p>Decorator to turn a function into a CSP process.</p>

<p>Note that the function itself will not be a CSPProcess object, but

will generate a CSPProcess object when called.</p>

<dl class="function">

<dt id="cspthread.forever">

<tt class="descclassname">cspthread.</tt><tt class="descname">forever</tt><big>(</big><em>func</em><big>)</big><a class="headerlink" href="#cspthread.forever" title="Permalink to this definition">¶</a></dt>

<dd><p>Decorator to turn a function into a CSP server process.</p>

<p>It is preferable to use this rather than &#64;process, to enable the

CSP tracer to terminate correctly and produce a CSP model, or

other debugging information.</p>

<div class="section" id="indices-and-tables">

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