CSP based on OS processes¶
Communicating sequential processes, in Python.
When using CSP Python as a DSL, this module will normally be imported via the statement ‘from csp.cspprocess import *‘.
Copyright (C) Sarah Mount, 2008.
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- class cspprocess.CSPProcess(func, *args, **kwargs)¶
Implementation of CSP processes. Not intended to be used in client code. Use @process instead.
- run()¶
- Called automatically when the L{start} methods is called.
- class cspprocess.CSPServer(func, *args, **kwargs)¶
Implementation of CSP server processes. Not intended to be used in client code. Use @forever instead.
- run()¶
- Called automatically when the L{start} methods is called.
- class cspprocess.Alt(*args)¶
CSP select (OCCAM ALT) process.
What should happen if a guard is poisoned?
- fair_select()¶
- Select a guard to synchronise with. Do not select the previously selected guard (unless it is the only guard available).
- poison()¶
Poison the last selected guard and unlink from the guard list.
Sets self.last_selected to None.
- pri_select()¶
- Select a guard to synchronise with, in order of “priority”. The guard with the lowest index in the L{guards} list has the highest priority.
- select()¶
- Randomly select from ready guards.
- class cspprocess.Par(*procs, **kwargs)¶
Run CSP processes in parallel.
- start(timeout=None)¶
- Start then synchronize with the execution of parallel processes. Return when all parallel processes have returned.
- terminate()¶
- Terminate the execution of this process.
- class cspprocess.Seq(*procs)¶
Run CSP processes sequentially.
- start()¶
- Start this process running.
- stop()¶
Terminate the execution of this process.
FIXME: Remove this method.
- class cspprocess.Guard¶
Abstract class to represent CSP guards.
All methods must be overridden in subclasses.
- disable()¶
- Roll back from an L{enable} call.
- enable()¶
- Prepare for, but do not commit to a synchronisation.
- is_selectable()¶
- Should return C{True} if this guard can be selected by an L{Alt}.
- poison()¶
- Terminate all processes attached to this guard.
- select()¶
- Commit to a synchronisation started by L{enable}.
- class cspprocess.Channel¶
CSP Channel objects.
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.
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.
- disable()¶
Disable this channel for Alt selection.
MUST be called after L{enable} if this channel is not selected.
- enable()¶
Enable a read for an Alt select.
MUST be called before L{select()} or L{is_selectable()}.
- get()¶
- Get a Python object from a process-safe store.
- is_selectable()¶
- Test whether Alt can select this channel.
- poison()¶
- Poison a channel causing all processes using it to terminate.
- put(item)¶
- Put C{item} on a process-safe store.
- read()¶
- Read (and return) a Python object from this channel.
- resume()¶
- Resume this mobile channel after migrating between processes.
- select()¶
- Complete a Channel read for an Alt select.
- suspend()¶
- Suspend this mobile channel before migrating between processes.
- write(obj)¶
- Write a Python object to this channel.
- class cspprocess.FileChannel¶
Channel objects using files on disk.
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’s maximum number of open files). In return there is a performance hit – reads and writes are around 10 x slower on C{FileChannel} objects compared to L{Channel} objects.
- get()¶
- Get a Python object from a process-safe store.
- put(item)¶
- Put C{item} on a process-safe store.
- resume()¶
- Suspend this mobile channel after migrating between processes.
- suspend()¶
- Suspend this mobile channel before migrating between processes.
- cspprocess.process(func)¶
Decorator to turn a function into a CSP process.
Note that the function itself will not be a CSPProcess object, but will generate a CSPProcess object when called.
- cspprocess.forever(func)¶
Decorator to turn a function into a CSP server process.
It is preferable to use this rather than @process, to enable the CSP tracer to terminate correctly and produce a CSP model, or other debugging information.
