I'm trying to simulate a bunch of tasks that all together belong to the same generic project.
Tasks have duration and precedence (represented by a list of tasks that have to be done before the current task).
For example:
/--->A --->B\
Start ---->C------->End
\--->D---->E/
That means tasks A, C and D can be executed at same time, but task B should be executed after task A, and task E after task D.
I wrote this code:
#!/usr/bin/python2.7
# -*- coding: utf-8 -*-
import simpy
class Task(object):
"""
Has an id i.e.: 'E',
duration i.e.: 5
a list with Task that precede the current
"""
def __init__(self, idTask, duration, env, previousTasks=None):
self.idTask = idTask
self.duration = duration
self.env = envs
self.completed = env.event()
self.action = env.process(self.run())
if previousTasks is None:
self.previousTasks = []
else:
self.previousTasks = previousTasks
def run(self):
while self.can_execute() and not self.completed.triggered:
print "Starting task %s at time %s" % (self.idTask, self.env.now)
yield self.env.timeout(self.duration)
print "Completed task %s in time %s" % (self.idTask, self.env.now)
self.completed.succeed(True)
def can_execute(self):
result = True
for task in self.previousTasks:
if not task.completed.triggered:
result = False
break
return result
if __name__ == "__main__":
env = simpy.Environment()
taskA = Task('A', 4, env)
taskB = Task('B', 5, env, [taskA])
env.run(until=20)
Completed attribute in Task object, is for having a way to know if current task is completed or finished. (I tried to do that with a boolean value with no different results.)
taskB has taskA as a precedent task. That means that taskB should start before taskA finishes, but this is the output when I run it:
% python tasks.py
Starting task A at time 0
Completed task A at time 4
%
I don't understand why taskB couldn't run.
SOLVED
I used "start_delayed" method, available in simpy.util module from Simpy. Depending on if the current task has previous tasks to be performed, the "action" of each task is a simple process or a delayed process.
Delay for each task is calculated in add_precedences and estimate_delays but is necessary to sum duration of previous tasks to the previous task of the current.
Here is the final code:
#!/usr/bin/python2.7
# -*- coding: utf-8 -*-
import simpy
from simpy.util import start_delayed
delays = {}
completed = []
class Task(object):
""" Has an id i.e.: 'E',
duration i.e.: 5
a list with Task that precede the current
"""
def __init__(self, id, duration, env, previousTasks=None):
self.id = id
self.duration = duration
self.env = env
if previousTasks is None:
self.previousTasks = []
else:
self.previousTasks = previousTasks
self.action = None
def run(self):
while True:
if delays[self.id] == self.env.now:
print "Start task: %s at time: %s" % (self.id, self.env.now)
yield self.env.timeout(self.duration)
completed.append(self.id)
print "Finish task: %s at time: %s" % (self.id, self.env.now)
else:
if self.id in completed:
self.env.exit()
def add_precedences(prevTask, durations):
if len(prevTask) == 0:
return 0
else:
durations.extend(map(lambda x: x.duration, prevTask))
for prev in prevTask:
add_precedences(prev.previousTasks, durations)
return sum(durations)
def estimate_delays(tasks):
result = {}
for task in tasks:
durations = []
total = (add_precedences(task.previousTasks, durations))
result.update({task.id: total})
return result
def set_action(tasks):
for task in tasks:
if delays[task.id] > 0:
task.action = start_delayed(task.env, task.run(), delays[task.id])
else:
task.action = env.process(task.run())
if __name__ == '__main__':
env = simpy.Environment()
taskA = Task('A', 4, env)
taskB = Task('B', 5, env, previousTasks=[taskA])
taskC = Task('C', 2, env, previousTasks=[taskB])
tasks = [taskA, taskB, taskC]
delays.update(estimate_delays(tasks))
set_action(tasks)
env.run(until=20)
In this case, the project has 3 tasks ('A','B','C') and here is the tree:
Start --->A--->B--->C--->End
B has to start at time: 4 (because that is the duration of A). And C, has to start at time: 9 (because that is the duration of B+A).
To know which task has already finished, I created a list that each task adds its own id. If its own id is on that list each task is removed from the environment.
I should do this as a comment, but I don't have the reputation to do so. Nevertheless, I think it might help with your problem.
I am not familiar with simpy but you might be confusing triggered and processed which is not allowing task B to execute; check this link: http://simpy.readthedocs.org/en/latest/api_reference/simpy.events.html#module-simpy.events