pprocess.py

#!/usr/bin/env python

"""
A simple parallel processing API for Python, inspired somewhat by the thread
module, slightly less by pypar, and slightly less still by pypvm.

Copyright (C) 2005, 2006, 2007, 2008, 2009 Paul Boddie <paul@boddie.org.uk>

This program is free software; you can redistribute it and/or modify it under
the terms of the GNU Lesser General Public License as published by the Free
Software Foundation; either version 3 of the License, or (at your option) any
later version.

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 Lesser General Public License for more
details.

You should have received a copy of the GNU Lesser General Public License along
with this program.  If not, see <http://www.gnu.org/licenses/>.
"""

__version__ = "0.5"

import os
import sys
import select
import socket
import platform
from StringIO import StringIO

try:
	import cPickle as pickle
except ImportError:
	import pickle

try:
	set
except NameError:
	from sets import Set as set

# Special values.

class Undefined: pass

# Communications.

class AcknowledgementError(Exception):
	pass

class Channel:

	"A communications channel."

	def __init__(self, pid, read_pipe, write_pipe):

		"""
		Initialise the channel with a process identifier 'pid', a 'read_pipe'
		from which messages will be received, and a 'write_pipe' into which
		messages will be sent.
		"""

		self.pid = pid
		self.read_pipe = read_pipe
		self.write_pipe = write_pipe

	def __del__(self):

		# Since signals don't work well with I/O, we close pipes and wait for
		# created processes upon finalisation.

		self.close()

	def close(self):

		"Explicitly close the channel."

		if self.read_pipe is not None:
			self.read_pipe.close()
			self.read_pipe = None
		if self.write_pipe is not None:
			self.write_pipe.close()
			self.write_pipe = None
		#self.wait(os.WNOHANG)

	def wait(self, options=0):

		"Wait for the created process, if any, to exit."

		if self.pid != 0:
			try:
				os.waitpid(self.pid, options)
			except OSError:
				pass

	def _send(self, obj):

		"Send the given object 'obj' through the channel."
		
		pickle.dump(obj, self.write_pipe)
		self.write_pipe.flush()

	def send(self, obj):

		"""
		Send the given object 'obj' through the channel. Then wait for an
		acknowledgement. (The acknowledgement makes the caller wait, thus
		preventing processes from exiting and disrupting the communications
		channel and losing data.)
		"""

		self._send(obj)
		if self._receive() != "OK":
			raise AcknowledgementError, obj

	def _receive(self):

		"Receive an object through the channel, returning the object."

		obj = pickle.load(self.read_pipe)
		if isinstance(obj, Exception):
			raise obj
		else:
			return obj

	def receive(self):

		"""
		Receive an object through the channel, returning the object. Send an
		acknowledgement of receipt. (The acknowledgement makes the sender wait,
		thus preventing processes from exiting and disrupting the communications
		channel and losing data.)
		"""

		try:
			obj = self._receive()
			return obj
		finally:
			self._send("OK")

class PersistentChannel(Channel):

	"""
	A persistent communications channel which can handle peer disconnection,
	acting as a server, meaning that this channel is associated with a specific
	address which can be contacted by other processes.
	"""

	def __init__(self, pid, endpoint, address):
		Channel.__init__(self, pid, None, None)
		self.endpoint = endpoint
		self.address = address
		self.poller = select.poll()

		# Listen for connections before this process is interested in
		# communicating. It is not desirable to wait for connections at this
		# point because this will block the process.

		self.endpoint.listen(1)

	def close(self):

		"Close the persistent channel and remove the socket file."

		Channel.close(self)
		try:
			os.unlink(self.address)
		except OSError:
			pass

	def _ensure_pipes(self):

		"Ensure that the channel is capable of communicating."

		if self.read_pipe is None or self.write_pipe is None:

			# Accept any incoming connections.

			endpoint, address = self.endpoint.accept()
			self.read_pipe = endpoint.makefile("r", 0)
			self.write_pipe = endpoint.makefile("w", 0)

			# Monitor the write pipe for error conditions.

			fileno = self.write_pipe.fileno()
			self.poller.register(fileno, select.POLLOUT | select.POLLHUP | select.POLLNVAL | select.POLLERR)

	def _reset_pipes(self):

		"Discard the existing connection."

		fileno = self.write_pipe.fileno()
		self.poller.unregister(fileno)
		self.read_pipe = None
		self.write_pipe = None
		self.endpoint.listen(1)

	def _ensure_communication(self, timeout=None):

		"Ensure that sending and receiving are possible."

		while 1:
			self._ensure_pipes()
			fileno = self.write_pipe.fileno()
			fds = self.poller.poll(timeout)
			for fd, status in fds:
				if fd != fileno:
					continue
				if status & (select.POLLHUP | select.POLLNVAL | select.POLLERR):

					# Broken connection: discard it and start all over again.

					self._reset_pipes()
					break
			else:
				return

	def _send(self, obj):

		"Send the given object 'obj' through the channel."

		self._ensure_communication()
		Channel._send(self, obj)

	def _receive(self):

		"Receive an object through the channel, returning the object."

		self._ensure_communication()
		return Channel._receive(self)

# Management of processes and communications.

class Exchange:

	"""
	A communications exchange that can be used to detect channels which are
	ready to communicate. Subclasses of this class can define the 'store_data'
	method in order to enable the 'add_wait', 'wait' and 'finish' methods.

	Once exchanges are populated with active channels, use of the principal
	methods of the exchange typically cause the 'store' method to be invoked,
	resulting in the processing of any incoming data.
	"""

	def __init__(self, channels=None, limit=None, reuse=0, continuous=0, autoclose=1):

		"""
		Initialise the exchange with an optional list of 'channels'.

		If the optional 'limit' is specified, restrictions on the addition of
		new channels can be enforced and observed through the 'add_wait', 'wait'
		and 'finish' methods. To make use of these methods, create a subclass of
		this class and define a working 'store_data' method.

		If the optional 'reuse' parameter is set to a true value, channels and
		processes will be reused for waiting computations, but the callable will
		be invoked for each computation.

		If the optional 'continuous' parameter is set to a true value, channels
		and processes will be retained after receiving data sent from such
		processes, since it will be assumed that they will communicate more
		data.

		If the optional 'autoclose' parameter is set to a false value, channels
		will not be closed automatically when they are removed from the exchange
		- by default they are closed when removed.
		"""

		self.limit = limit
		self.reuse = reuse
		self.autoclose = autoclose
		self.continuous = continuous

		self.waiting = []
		self.readables = {}
		self.removed = []
		self.poller = select.poll()

		for channel in channels or []:
			self.add(channel)

	# Core methods, registering and reporting on channels.

	def add(self, channel):

		"Add the given 'channel' to the exchange."

		fileno = channel.read_pipe.fileno()
		self.readables[fileno] = channel
		self.poller.register(fileno, select.POLLIN | select.POLLHUP | select.POLLNVAL | select.POLLERR)

	def active(self):

		"Return a list of active channels."

		return self.readables.values()

	def ready(self, timeout=None):

		"""
		Wait for a period of time specified by the optional 'timeout' in
		milliseconds (or until communication is possible) and return a list of
		channels which are ready to be read from.
		"""

		fds = self.poller.poll(timeout)
		readables = []
		self.removed = []

		for fd, status in fds:
			channel = self.readables[fd]
			removed = 0

			# Remove ended/error channels.

			if status & (select.POLLHUP | select.POLLNVAL | select.POLLERR):
				self.remove(channel)
				self.removed.append(channel)
				removed = 1

			# Record readable channels.

			if status & select.POLLIN:
				if not (removed and self.autoclose):
					readables.append(channel)

		return readables

	def remove(self, channel):

		"""
		Remove the given 'channel' from the exchange.
		"""

		fileno = channel.read_pipe.fileno()
		del self.readables[fileno]
		self.poller.unregister(fileno)
		if self.autoclose:
			channel.close()
			channel.wait()

	# Enhanced exchange methods involving channel limits.

	def unfinished(self):

		"Return whether the exchange still has work scheduled or in progress."

		return self.active() or self.waiting

	def busy(self):

		"Return whether the exchange uses as many channels as it is allowed to."

		return self.limit is not None and len(self.active()) >= self.limit

	def add_wait(self, channel):

		"""
		Add the given 'channel' to the exchange, waiting if the limit on active
		channels would be exceeded by adding the channel.
		"""

		self.wait()
		self.add(channel)

	def wait(self):

		"""
		Test for the limit on channels, blocking and reading incoming data until
		the number of channels is below the limit.
		"""

		# If limited, block until channels have been closed.

		while self.busy():
			self.store()

	def finish(self):

		"""
		Finish the use of the exchange by waiting for all channels to complete.
		"""

		while self.unfinished():
			self.store()

	def store(self, timeout=None):

		"""
		For each ready channel, process the incoming data. If the optional
		'timeout' parameter (a duration in milliseconds) is specified, wait only
		for the specified duration if no channels are ready to provide data.
		"""

		# Either process input from active channels.

		if self.active():
			for channel in self.ready(timeout):
				self.store_data(channel)
				self.start_waiting(channel)

		# Or schedule new processes and channels.

		else:
			while self.waiting and not self.busy():
				callable, args, kw = self.waiting.pop()
				self.start(callable, *args, **kw)

	def store_data(self, channel):

		"""
		Store incoming data from the specified 'channel'. In subclasses of this
		class, such data could be stored using instance attributes.
		"""

		raise NotImplementedError, "store_data"

	# Support for the convenience methods.

	def _get_waiting(self, channel):

		"""
		Get waiting callable and argument information for new processes, given
		the reception of data on the given 'channel'.
		"""

		# For continuous channels, no scheduling is requested.

		if self.waiting and not self.continuous:

			# Schedule this callable and arguments.

			callable, args, kw = self.waiting.pop()

			# Try and reuse existing channels if possible.

			if self.reuse:

				# Re-add the channel - this may update information related to
				# the channel in subclasses.

				self.add(channel)
				channel.send((args, kw))

			else:
				return callable, args, kw

		# Where channels are being reused, but where no processes are waiting
		# any more, send a special value to tell them to quit.

		elif self.reuse:
			channel.send(None)

		return None

	def _set_waiting(self, callable, args, kw):

		"""
		Support process creation by returning whether the given 'callable' has
		been queued for later invocation.
		"""

		if self.busy():
			self.waiting.insert(0, (callable, args, kw))
			return 1
		else:
			return 0

	def _get_channel_for_process(self, channel):

		"""
		Support process creation by returning the given 'channel' to the
		creating process, and None to the created process.
		"""

		if channel.pid == 0:
			return channel
		else:
			self.add_wait(channel)
			return None

	# Methods for overriding, related to the convenience methods.

	def start_waiting(self, channel):

		"""
		Start a waiting process given the reception of data on the given
		'channel'.
		"""

		details = self._get_waiting(channel)
		if details is not None:
			callable, args, kw = details
			self.add(start(callable, *args, **kw))

	# Convenience methods.

	def start(self, callable, *args, **kw):

		"""
		Create a new process for the given 'callable' using any additional
		arguments provided. Then, monitor the channel created between this
		process and the created process.
		"""

		if self._set_waiting(callable, args, kw):
			return

		self.add_wait(start(callable, *args, **kw))

	def create(self):

		"""
		Create a new process and return the created communications channel to
		the created process. In the creating process, return None - the channel
		receiving data from the created process will be automatically managed by
		this exchange.
		"""

		channel = create()
		return self._get_channel_for_process(channel)

	def manage(self, callable):

		"""
		Wrap the given 'callable' in an object which can then be called in the
		same way as 'callable', but with new processes and communications
		managed automatically.
		"""

		return ManagedCallable(callable, self)

class Persistent:

	"""
	A mix-in class providing methods to exchanges for the management of
	persistent communications.
	"""

	def start_waiting(self, channel):

		"""
		Start a waiting process given the reception of data on the given
		'channel'.
		"""

		details = self._get_waiting(channel)
		if details is not None:
			callable, args, kw = details
			self.add(start_persistent(channel.address, callable, *args, **kw))

	def start(self, address, callable, *args, **kw):

		"""
		Create a new process, located at the given 'address', for the given
		'callable' using any additional arguments provided. Then, monitor the
		channel created between this process and the created process.
		"""

		if self._set_waiting(callable, args, kw):
			return

		start_persistent(address, callable, *args, **kw)

	def create(self, address):

		"""
		Create a new process, located at the given 'address', and return the
		created communications channel to the created process. In the creating
		process, return None - the channel receiving data from the created
		process will be automatically managed by this exchange.
		"""

		channel = create_persistent(address)
		return self._get_channel_for_process(channel)

	def manage(self, address, callable):

		"""
		Using the given 'address', publish the given 'callable' in an object
		which can then be called in the same way as 'callable', but with new
		processes and communications managed automatically.
		"""

		return PersistentCallable(address, callable, self)

	def connect(self, address):

		"Connect to a process which is contactable via the given 'address'."

		channel = connect_persistent(address)
		self.add_wait(channel)

class ManagedCallable:

	"A callable managed by an exchange."

	def __init__(self, callable, exchange):

		"""
		Wrap the given 'callable', using the given 'exchange' to monitor the
		channels created for communications between this and the created
		processes. Note that the 'callable' must be parallel-aware (that is,
		have a 'channel' parameter). Use the MakeParallel class to wrap other
		kinds of callable objects.
		"""

		self.callable = callable
		self.exchange = exchange

	def __call__(self, *args, **kw):

		"Invoke the callable with the supplied arguments."

		self.exchange.start(self.callable, *args, **kw)

class PersistentCallable:

	"A callable which sets up a persistent communications channel."

	def __init__(self, address, callable, exchange):

		"""
		Using the given 'address', wrap the given 'callable', using the given
		'exchange' to monitor the channels created for communications between
		this and the created processes, so that when it is called, a background
		process is started within which the 'callable' will run. Note that the
		'callable' must be parallel-aware (that is, have a 'channel' parameter).
		Use the MakeParallel class to wrap other kinds of callable objects.
		"""

		self.callable = callable
		self.exchange = exchange
		self.address = address

	def __call__(self, *args, **kw):

		"Invoke the callable with the supplied arguments."

		self.exchange.start(self.address, self.callable, *args, **kw)

class BackgroundCallable:

	"""
	A callable which sets up a persistent communications channel, but is
	unmanaged by an exchange.
	"""

	def __init__(self, address, callable):

		"""
		Using the given 'address', wrap the given 'callable'. This object can
		then be invoked, but the wrapped callable will be run in a background
		process. Note that the 'callable' must be parallel-aware (that is, have
		a 'channel' parameter). Use the MakeParallel class to wrap other kinds
		of callable objects.
		"""

		self.callable = callable
		self.address = address

	def __call__(self, *args, **kw):

		"Invoke the callable with the supplied arguments."

		start_persistent(self.address, self.callable, *args, **kw)

# Abstractions and utilities.

class Map(Exchange):

	"An exchange which can be used like the built-in 'map' function."

	def __init__(self, *args, **kw):
		Exchange.__init__(self, *args, **kw)
		self.init()

	def init(self):

		"Remember the channel addition order to order output."

		self.channel_number = 0
		self.channels = {}
		self.results = []
		self.current_index = 0

	def add(self, channel):

		"Add the given 'channel' to the exchange."

		Exchange.add(self, channel)
		self.channels[channel] = self.channel_number
		self.channel_number += 1

	def start(self, callable, *args, **kw):

		"""
		Create a new process for the given 'callable' using any additional
		arguments provided. Then, monitor the channel created between this
		process and the created process.
		"""

		self.results.append(Undefined) # placeholder
		Exchange.start(self, callable, *args, **kw)

	def create(self):

		"""
		Create a new process and return the created communications channel to
		the created process. In the creating process, return None - the channel
		receiving data from the created process will be automatically managed by
		this exchange.
		"""

		self.results.append(Undefined) # placeholder
		return Exchange.create(self)

	def __call__(self, callable, sequence):

		"Wrap and invoke 'callable' for each element in the 'sequence'."

		if not isinstance(callable, MakeParallel):
			wrapped = MakeParallel(callable)
		else:
			wrapped = callable

		self.init()

		# Start processes for each element in the sequence.

		for i in sequence:
			self.start(wrapped, i)

		# Access to the results occurs through this object.

		return self

	def store_data(self, channel):

		"Accumulate the incoming data, associating results with channels."

		data = channel.receive()
		self.results[self.channels[channel]] = data
		del self.channels[channel]

	def __iter__(self):
		return self

	def next(self):

		"Return the next element in the map."

		try:
			return self._next()
		except IndexError:
			pass

		while self.unfinished():
			self.store()
			try:
				return self._next()
			except IndexError:
				pass
		else:
			raise StopIteration

	def __getitem__(self, i):

		"Return element 'i' from the map."

		try:
			return self._get(i)
		except IndexError:
			pass

		while self.unfinished():
			self.store()
			try:
				return self._get(i)
			except IndexError:
				pass
		else:
			raise IndexError, i

	# Helper methods for the above access methods.

	def _next(self):
		result = self._get(self.current_index)
		self.current_index += 1
		return result

	def _get(self, i):
		result = self.results[i]
		if result is Undefined or isinstance(i, slice) and Undefined in result:
			raise IndexError, i
		return result

class Queue(Exchange):

	"""
	An exchange acting as a queue, making data from created processes available
	in the order in which it is received.
	"""

	def __init__(self, *args, **kw):
		Exchange.__init__(self, *args, **kw)
		self.queue = []

	def store_data(self, channel):

		"Accumulate the incoming data, associating results with channels."

		data = channel.receive()
		self.queue.insert(0, data)

	def __iter__(self):
		return self

	def next(self):

		"Return the next element in the queue."

		if self.queue:
			return self.queue.pop()

		while self.unfinished():
			self.store()
			if self.queue:
				return self.queue.pop()
		else:
			raise StopIteration

	def __len__(self):

		"Return the current length of the queue."

		return len(self.queue)

class MakeParallel:

	"A wrapper around functions making them able to communicate results."

	def __init__(self, callable):

		"""
		Initialise the wrapper with the given 'callable'. This object will then
		be able to accept a 'channel' parameter when invoked, and to forward the
		result of the given 'callable' via the channel provided back to the
		invoking process.
		"""

		self.callable = callable

	def __call__(self, channel, *args, **kw):

		"Invoke the callable and return its result via the given 'channel'."

		channel.send(self.callable(*args, **kw))

class MakeReusable(MakeParallel):

	"""
	A wrapper around functions making them able to communicate results in a
	reusable fashion.
	"""

	def __call__(self, channel, *args, **kw):

		"Invoke the callable and return its result via the given 'channel'."

		channel.send(self.callable(*args, **kw))
		t = channel.receive()
		while t is not None:
			args, kw = t
			channel.send(self.callable(*args, **kw))
			t = channel.receive()

# Persistent variants.

class PersistentExchange(Persistent, Exchange):

	"An exchange which manages persistent communications."

	pass

class PersistentQueue(Persistent, Queue):

	"A queue which manages persistent communications."

	pass

# Convenience functions.

def BackgroundQueue(address):

	"""
	Connect to a process reachable via the given 'address', making the results
	of which accessible via a queue.
	"""

	queue = PersistentQueue(limit=1)
	queue.connect(address)
	return queue

def pmap(callable, sequence, limit=None):

	"""
	A parallel version of the built-in map function with an optional process
	'limit'. The given 'callable' should not be parallel-aware (that is, have a
	'channel' parameter) since it will be wrapped for parallel communications
	before being invoked.

	Return the processed 'sequence' where each element in the sequence is
	processed by a different process.
	"""

	mymap = Map(limit=limit)
	return mymap(callable, sequence)

# Utility functions.

_cpuinfo_fields = "processor", "physical id", "core id"

def _get_number_of_cores():

	"""
	Return the number of distinct, genuine processor cores. If the platform is
	not supported by this function, None is returned.
	"""

	try:
		f = open("/proc/cpuinfo")
		try:
			processors = set()

			# Use the _cpuinfo_field values as "digits" in a larger unique
			# core identifier.

			processor = [None, None, None]

			for line in f.xreadlines():
				for i, field in enumerate(_cpuinfo_fields):

					# Where the field is found, insert the value into the
					# appropriate location in the processor identifier.

					if line.startswith(field):
						t = line.split(":")
						processor[i] = int(t[1].strip())
						break

				# Where a new processor description is started, record the
				# identifier.

				if line.startswith("processor") and processor[0] is not None:
					processors.add(tuple(processor))
					processor = [None, None, None]

			# At the end of reading the file, add any unrecorded processors.

			if processor[0] is not None:
				processors.add(tuple(processor))

			return len(processors)

		finally:
			f.close()

	except OSError:
		return None

def _get_number_of_cores_solaris():

	"""
	Return the number of cores for OpenSolaris 2008.05 and possibly other
	editions of Solaris.
	"""

	f = os.popen("psrinfo -p")
	try:
		return int(f.read().strip())
	finally:
		f.close()

# Low-level functions.

def create_socketpair():

	"""
	Create a new process, returning a communications channel to both the
	creating process and the created process.
	"""

	parent, child = socket.socketpair()
	for s in [parent, child]:
		s.setblocking(1)

	pid = os.fork()
	if pid == 0:
		parent.close()
		return Channel(pid, child.makefile("r", 0), child.makefile("w", 0))
	else:
		child.close()
		return Channel(pid, parent.makefile("r", 0), parent.makefile("w", 0))

def create_pipes():

	"""
	Create a new process, returning a communications channel to both the
	creating process and the created process.

	This function uses pipes instead of a socket pair, since some platforms
	seem to have problems with poll and such socket pairs.
	"""

	pr, cw = os.pipe()
	cr, pw = os.pipe()

	pid = os.fork()
	if pid == 0:
		os.close(pr)
		os.close(pw)
		return Channel(pid, os.fdopen(cr, "r", 0), os.fdopen(cw, "w", 0))
	else:
		os.close(cr)
		os.close(cw)
		return Channel(pid, os.fdopen(pr, "r", 0), os.fdopen(pw, "w", 0))

if platform.system() == "SunOS":
	create = create_pipes
	get_number_of_cores = _get_number_of_cores_solaris
else:
	create = create_socketpair
	get_number_of_cores = _get_number_of_cores

def create_persistent(address):

	"""
	Create a new process, returning a persistent communications channel between
	the creating process and the created process. This channel can be
	disconnected from the creating process and connected to another process, and
	thus can be used to collect results from daemon processes.

	In order to be able to reconnect to created processes, the 'address' of the
	communications endpoint for the created process needs to be provided. This
	should be a filename.
	"""

	parent = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
	child = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
	child.bind(address)

	for s in [parent, child]:
		s.setblocking(1)

	pid = os.fork()
	if pid == 0:
		parent.close()
		return PersistentChannel(pid, child, address)
	else:
		child.close()
		#parent.connect(address)
		return Channel(pid, parent.makefile("r", 0), parent.makefile("w", 0))

def connect_persistent(address):

	"""
	Connect via a persistent channel to an existing created process, reachable
	at the given 'address'.
	"""

	parent = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
	parent.setblocking(1)
	parent.connect(address)
	return Channel(0, parent.makefile("r", 0), parent.makefile("w", 0))

def exit(channel):

	"""
	Terminate a created process, closing the given 'channel'.
	"""

	channel.close()
	os._exit(0)

def start(callable, *args, **kw):

	"""
	Create a new process which shall start running in the given 'callable'.
	Additional arguments to the 'callable' can be given as additional arguments
	to this function.

	Return a communications channel to the creating process. For the created
	process, supply a channel as the 'channel' parameter in the given 'callable'
	so that it may send data back to the creating process.
	"""

	channel = create()
	if channel.pid == 0:
		try:
			try:
				callable(channel, *args, **kw)
			except:
				exc_type, exc_value, exc_traceback = sys.exc_info()
				channel.send(exc_value)
		finally:
			exit(channel)
	else:
		return channel

def start_persistent(address, callable, *args, **kw):

	"""
	Create a new process which shall be reachable using the given 'address' and
	which will start running in the given 'callable'. Additional arguments to
	the 'callable' can be given as additional arguments to this function.

	Return a communications channel to the creating process. For the created
	process, supply a channel as the 'channel' parameter in the given 'callable'
	so that it may send data back to the creating process.

	Note that the created process employs a channel which is persistent: it can
	withstand disconnection from the creating process and subsequent connections
	from other processes.
	"""

	channel = create_persistent(address)
	if channel.pid == 0:
		close_streams()
		try:
			try:
				callable(channel, *args, **kw)
			except:
				exc_type, exc_value, exc_traceback = sys.exc_info()
				channel.send(exc_value)
		finally:
			exit(channel)
	else:
		return channel

def close_streams():

	"""
	Close streams which keep the current process attached to any creating
	processes.
	"""

	os.close(sys.stdin.fileno())
	os.close(sys.stdout.fileno())
	os.close(sys.stderr.fileno())

def waitall():

	"Wait for all created processes to terminate."

	try:
		while 1:
			os.wait()
	except OSError:
		pass

# vim: tabstop=4 expandtab shiftwidth=4