def check_non_blocking(net0):
"""
Checks if a workflow net is non-blocking
Parameters
-------------
net
Petri net
Returns
-------------
boolean
Boolean value
"""
net = deepcopy(net0)
petri_utils.decorate_transitions_prepostset(net)
graph, inv_dictionary = petri_utils.create_networkx_directed_graph(net)
dictionary = {y:x for x,y in inv_dictionary.items()}
source_place = [place for place in net.places if len(place.in_arcs) == 0][0]
for trans in net.transitions:
# transitions with 1 input arcs does not block
if len(trans.in_arcs) > 1:
places = [arc.source for arc in trans.in_arcs]
# search the top-right intersection between a path connecting the initial marking and the input places
# of such transition
#
# this exploration is based on heuristics; another option is to use the exploration provided in explore_path (that is based on alignments)
spaths = [[inv_dictionary[y] for y in nx.algorithms.shortest_paths.generic.shortest_path(graph, dictionary[source_place], dictionary[x])] for x in places]
spaths = [[y for y in x if type(y) is petrinet.PetriNet.Transition] for x in spaths]
trans_dict = {}
i = 0
while i < len(places):
p1 = places[i]
spath1 = spaths[i]
j = i + 1
while j < len(places):
p2 = places[j]
spath2 = spaths[j]
s1, s2 = [x for x in spath1 if x in spath2], [x for x in spath2 if x in spath1]
if len(s1) > 0 and len(s2) > 0 and s1[-1] == s2[-1]:
# there is an intersection
t = s1[-1]
if len(t.out_arcs) <= 1:
return False
else:
if t not in trans_dict:
trans_dict[t] = set()
trans_dict[t].add(p1)
trans_dict[t].add(p2)
else:
return False
j = j + 1
i = i + 1
# after checking if the intersecting transition has at least one exit,
# we check also that the number of outputs of the transition is at least the one expected
for t in trans_dict:
if len(t.out_arcs) < len(trans_dict[t]):
return False
return True
def check_loops_generating_tokens(net0):
"""
Check if the Petri net contains loops generating tokens
Parameters
------------
net0
Petri net
Returns
------------
boolean
Boolean value (True if the net has loops generating tokens)
"""
net = deepcopy(net0)
petri_utils.decorate_transitions_prepostset(net)
graph, inv_dictionary = petri_utils.create_networkx_directed_graph(net)
dictionary = {y:x for x,y in inv_dictionary.items()}
loops_trans = petri_utils.get_cycles_petri_net_transitions(net)
for loop in loops_trans:
m = petrinet.Marking()
for index, trans in enumerate(loop):
m = m + trans.add_marking
visited_couples = set()
while True:
changed_something = False
# if there are no places with positive marking replaying the loop, then we are fine
neg_places = [p for p in m if m[p] < 0]
pos_places = [p for p in m if m[p] > 0]
for p1 in pos_places:
# if there are no places with negative marking replaying the loop, then we are doomed
for p2 in neg_places:
if not ((p1, p2)) in visited_couples:
visited_couples.add((p1, p2))
# otherwise, do a check if there is a path in the workflow net between the two places
# this exploration is based on heuristics; indeed, since we can enter the cycle multiple times
# it does not really matter if we reach suddenly the optimal path
#
# another option is to use the exploration provided in explore_path (that is based on alignments)
spath = None
try:
spath = nx.algorithms.shortest_paths.generic.shortest_path(graph, dictionary[p1], dictionary[p2])
except:
pass
if spath is not None:
trans = [inv_dictionary[x] for x in spath if type(inv_dictionary[x]) is petrinet.PetriNet.Transition]
sec_m0 = petrinet.Marking()
for t in trans:
sec_m0 = sec_m0 + t.add_marking
sec_m = petrinet.Marking()
for place in m:
if place in sec_m0:
sec_m[place] = sec_m0[place]
m1 = m + sec_m
# the exploration is (in part) successful
if m1[p1] == 0:
m = m1
changed_something = True
break
if not changed_something:
break
if not changed_something:
break
# at this point, we have definitely created one token
if sum(m[place] for place in m) > 0:
return True
return False
