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1# Coroutine implementation using Python threads.
2#
3# Combines ideas from Guido's Generator module, and from the coroutine
4# features of Icon and Simula 67.
5#
6# To run a collection of functions as coroutines, you need to create
7# a Coroutine object to control them:
8#    co = Coroutine()
9# and then 'create' a subsidiary object for each function in the
10# collection:
11#    cof1 = co.create(f1 [, arg1, arg2, ...]) # [] means optional,
12#    cof2 = co.create(f2 [, arg1, arg2, ...]) #... not list
13#    cof3 = co.create(f3 [, arg1, arg2, ...])
14# etc.  The functions need not be distinct; 'create'ing the same
15# function multiple times gives you independent instances of the
16# function.
17#
18# To start the coroutines running, use co.tran on one of the create'd
19# functions; e.g., co.tran(cof2).  The routine that first executes
20# co.tran is called the "main coroutine".  It's special in several
21# respects:  it existed before you created the Coroutine object; if any of
22# the create'd coroutines exits (does a return, or suffers an unhandled
23# exception), EarlyExit error is raised in the main coroutine; and the
24# co.detach() method transfers control directly to the main coroutine
25# (you can't use co.tran() for this because the main coroutine doesn't
26# have a name ...).
27#
28# Coroutine objects support these methods:
29#
30# handle = .create(func [, arg1, arg2, ...])
31#    Creates a coroutine for an invocation of func(arg1, arg2, ...),
32#    and returns a handle ("name") for the coroutine so created.  The
33#    handle can be used as the target in a subsequent .tran().
34#
35# .tran(target, data=None)
36#    Transfer control to the create'd coroutine "target", optionally
37#    passing it an arbitrary piece of data. To the coroutine A that does
38#    the .tran, .tran acts like an ordinary function call:  another
39#    coroutine B can .tran back to it later, and if it does A's .tran
40#    returns the 'data' argument passed to B's tran.  E.g.,
41#
42#    in coroutine coA   in coroutine coC    in coroutine coB
43#      x = co.tran(coC)   co.tran(coB)        co.tran(coA,12)
44#      print x # 12
45#
46#    The data-passing feature is taken from Icon, and greatly cuts
47#    the need to use global variables for inter-coroutine communication.
48#
49# .back( data=None )
50#    The same as .tran(invoker, data=None), where 'invoker' is the
51#    coroutine that most recently .tran'ed control to the coroutine
52#    doing the .back.  This is akin to Icon's "&source".
53#
54# .detach( data=None )
55#    The same as .tran(main, data=None), where 'main' is the
56#    (unnameable!) coroutine that started it all.  'main' has all the
57#    rights of any other coroutine:  upon receiving control, it can
58#    .tran to an arbitrary coroutine of its choosing, go .back to
59#    the .detach'er, or .kill the whole thing.
60#
61# .kill()
62#    Destroy all the coroutines, and return control to the main
63#    coroutine.  None of the create'ed coroutines can be resumed after a
64#    .kill().  An EarlyExit exception does a .kill() automatically.  It's
65#    a good idea to .kill() coroutines you're done with, since the
66#    current implementation consumes a thread for each coroutine that
67#    may be resumed.
68
69import thread
70import sync
71
72class _CoEvent:
73    def __init__(self, func):
74        self.f = func
75        self.e = sync.event()
76
77    def __repr__(self):
78        if self.f is None:
79            return 'main coroutine'
80        else:
81            return 'coroutine for func ' + self.f.func_name
82
83    def __hash__(self):
84        return id(self)
85
86    def __cmp__(x,y):
87        return cmp(id(x), id(y))
88
89    def resume(self):
90        self.e.post()
91
92    def wait(self):
93        self.e.wait()
94        self.e.clear()
95
96class Killed(Exception): pass
97class EarlyExit(Exception): pass
98
99class Coroutine:
100    def __init__(self):
101        self.active = self.main = _CoEvent(None)
102        self.invokedby = {self.main: None}
103        self.killed = 0
104        self.value  = None
105        self.terminated_by = None
106
107    def create(self, func, *args):
108        me = _CoEvent(func)
109        self.invokedby[me] = None
110        thread.start_new_thread(self._start, (me,) + args)
111        return me
112
113    def _start(self, me, *args):
114        me.wait()
115        if not self.killed:
116            try:
117                try:
118                    apply(me.f, args)
119                except Killed:
120                    pass
121            finally:
122                if not self.killed:
123                    self.terminated_by = me
124                    self.kill()
125
126    def kill(self):
127        if self.killed:
128            raise TypeError, 'kill() called on dead coroutines'
129        self.killed = 1
130        for coroutine in self.invokedby.keys():
131            coroutine.resume()
132
133    def back(self, data=None):
134        return self.tran( self.invokedby[self.active], data )
135
136    def detach(self, data=None):
137        return self.tran( self.main, data )
138
139    def tran(self, target, data=None):
140        if not self.invokedby.has_key(target):
141            raise TypeError, '.tran target %r is not an active coroutine' % (target,)
142        if self.killed:
143            raise TypeError, '.tran target %r is killed' % (target,)
144        self.value = data
145        me = self.active
146        self.invokedby[target] = me
147        self.active = target
148        target.resume()
149
150        me.wait()
151        if self.killed:
152            if self.main is not me:
153                raise Killed
154            if self.terminated_by is not None:
155                raise EarlyExit, '%r terminated early' % (self.terminated_by,)
156
157        return self.value
158
159# end of module
160