environment/lib/python2.7/site-packages/IPython/parallel/controller/scheduler.py
def maybe_run(self, job):
        """check location dependencies, and run if they are met."""
        msg_id = job.msg_id
        self.log.debug("Attempting to assign task %s", msg_id)
        if not self.targets:
            # no engines, definitely can't run
            return False
        
        if job.follow or job.targets or job.blacklist or self.hwm:
            # we need a can_run filter
            def can_run(idx):
                # check hwm
                if self.hwm and self.loads[idx] == self.hwm:
                    return False
                target = self.targets[idx]
                # check blacklist
                if target in job.blacklist:
                    return False
                # check targets
                if job.targets and target not in job.targets:
                    return False
                # check follow
                return job.follow.check(self.completed[target], self.failed[target])

            indices = filter(can_run, range(len(self.targets)))

            if not indices:
                # couldn't run
                if job.follow.all:
                    # check follow for impossibility
                    dests = set()
                    relevant = set()
                    if job.follow.success:
                        relevant = self.all_completed
                    if job.follow.failure:
                        relevant = relevant.union(self.all_failed)
                    for m in job.follow.intersection(relevant):
                        dests.add(self.destinations[m])
                    if len(dests) > 1:
                        self.depending[msg_id] = job
                        self.fail_unreachable(msg_id)
                        return False
                if job.targets:
                    # check blacklist+targets for impossibility
                    job.targets.difference_update(job.blacklist)
                    if not job.targets or not job.targets.intersection(self.targets):
                        self.depending[msg_id] = job
                        self.fail_unreachable(msg_id)
                        return False
                return False
        else:
            indices = None

        self.submit_task(job, indices)
        return True
def maybe_run(self, job):
        """check location dependencies, and run if they are met."""
        msg_id = job.msg_id
        self.log.debug("Attempting to assign task %s", msg_id)
        if not self.targets:
            # no engines, definitely can't run
            return False
        
        if job.follow or job.targets or job.blacklist or self.hwm:
            # we need a can_run filter
            def can_run(idx):
                # check hwm
                if self.hwm and self.loads[idx] == self.hwm:
                    return False
                target = self.targets[idx]
                # check blacklist
                if target in job.blacklist:
                    return False
                # check targets
                if job.targets and target not in job.targets:
                    return False
                # check follow
                return job.follow.check(self.completed[target], self.failed[target])

            indices = filter(can_run, range(len(self.targets)))

            if not indices:
                # couldn't run
                if job.follow.all:
                    # check follow for impossibility
                    dests = set()
                    relevant = set()
                    if job.follow.success:
                        relevant = self.all_completed
                    if job.follow.failure:
                        relevant = relevant.union(self.all_failed)
                    for m in job.follow.intersection(relevant):
                        dests.add(self.destinations[m])
                    if len(dests) > 1:
                        self.depending[msg_id] = job
                        self.fail_unreachable(msg_id)
                        return False
                if job.targets:
                    # check blacklist+targets for impossibility
                    job.targets.difference_update(job.blacklist)
                    if not job.targets or not job.targets.intersection(self.targets):
                        self.depending[msg_id] = job
                        self.fail_unreachable(msg_id)
                        return False
                return False
        else:
            indices = None

        self.submit_task(job, indices)
        return True
check location dependencies, and run if they are met.