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# Coroutine implementation using Python threads.
#
# Combines ideas from Guido's Generator module, and from the coroutine
# features of Icon and Simula 67.
#
# To run a collection of functions as coroutines, you need to create
# a Coroutine object to control them:
# co = Coroutine()
# and then 'create' a subsidiary object for each function in the
# collection:
# cof1 = co.create(f1 [, arg1, arg2, ...]) # [] means optional,
# cof2 = co.create(f2 [, arg1, arg2, ...]) #... not list
# cof3 = co.create(f3 [, arg1, arg2, ...])
# etc. The functions need not be distinct; 'create'ing the same
# function multiple times gives you independent instances of the
# function.
#
# To start the coroutines running, use co.tran on one of the create'd
# functions; e.g., co.tran(cof2). The routine that first executes
# co.tran is called the "main coroutine". It's special in several
# respects: it existed before you created the Coroutine object; if any of
# the create'd coroutines exits (does a return, or suffers an unhandled
# exception), EarlyExit error is raised in the main coroutine; and the
# co.detach() method transfers control directly to the main coroutine
# (you can't use co.tran() for this because the main coroutine doesn't
# have a name ...).
#
# Coroutine objects support these methods:
#
# handle = .create(func [, arg1, arg2, ...])
# Creates a coroutine for an invocation of func(arg1, arg2, ...),
# and returns a handle ("name") for the coroutine so created. The
# handle can be used as the target in a subsequent .tran().
#
# .tran(target, data=None)
# Transfer control to the create'd coroutine "target", optionally
# passing it an arbitrary piece of data. To the coroutine A that does
# the .tran, .tran acts like an ordinary function call: another
# coroutine B can .tran back to it later, and if it does A's .tran
# returns the 'data' argument passed to B's tran. E.g.,
#
# in coroutine coA in coroutine coC in coroutine coB
# x = co.tran(coC) co.tran(coB) co.tran(coA,12)
# print x # 12
#
# The data-passing feature is taken from Icon, and greatly cuts
# the need to use global variables for inter-coroutine communication.
#
# .back( data=None )
# The same as .tran(invoker, data=None), where 'invoker' is the
# coroutine that most recently .tran'ed control to the coroutine
# doing the .back. This is akin to Icon's "&source".
#
# .detach( data=None )
# The same as .tran(main, data=None), where 'main' is the
# (unnameable!) coroutine that started it all. 'main' has all the
# rights of any other coroutine: upon receiving control, it can
# .tran to an arbitrary coroutine of its choosing, go .back to
# the .detach'er, or .kill the whole thing.
#
# .kill()
# Destroy all the coroutines, and return control to the main
# coroutine. None of the create'ed coroutines can be resumed after a
# .kill(). An EarlyExit exception does a .kill() automatically. It's
# a good idea to .kill() coroutines you're done with, since the
# current implementation consumes a thread for each coroutine that
# may be resumed.
import _thread as thread
import sync
class _CoEvent:
def __init__(self, func):
self.f = func
self.e = sync.event()
def __repr__(self):
if self.f is None:
return 'main coroutine'
else:
return 'coroutine for func ' + self.f.__name__
def __hash__(self):
return id(self)
def __cmp__(x,y):
return cmp(id(x), id(y))
def resume(self):
self.e.post()
def wait(self):
self.e.wait()
self.e.clear()
class Killed(Exception): pass
class EarlyExit(Exception): pass
class Coroutine:
def __init__(self):
self.active = self.main = _CoEvent(None)
self.invokedby = {self.main: None}
self.killed = 0
self.value = None
self.terminated_by = None
def create(self, func, *args):
me = _CoEvent(func)
self.invokedby[me] = None
thread.start_new_thread(self._start, (me,) + args)
return me
def _start(self, me, *args):
me.wait()
if not self.killed:
try:
try:
me.f(*args)
except Killed:
pass
finally:
if not self.killed:
self.terminated_by = me
self.kill()
def kill(self):
if self.killed:
raise TypeError('kill() called on dead coroutines')
self.killed = 1
for coroutine in self.invokedby.keys():
coroutine.resume()
def back(self, data=None):
return self.tran( self.invokedby[self.active], data )
def detach(self, data=None):
return self.tran( self.main, data )
def tran(self, target, data=None):
if target not in self.invokedby:
raise TypeError('.tran target %r is not an active coroutine' % (target,))
if self.killed:
raise TypeError('.tran target %r is killed' % (target,))
self.value = data
me = self.active
self.invokedby[target] = me
self.active = target
target.resume()
me.wait()
if self.killed:
if self.main is not me:
raise Killed
if self.terminated_by is not None:
raise EarlyExit('%r terminated early' % (self.terminated_by,))
return self.value
# end of module
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