Merge pull request #187 from CiwPython/server-priorities

Server priorities

Author: geraintpalmer

CHANGES.rst

@@ -1,6 +1,10 @@
 History
 -------
 
+v2.2.3 (2021-01-27)
+~~~~~~~~~~~~~~~~~~~
+- Server priority functions implemented.
+
 v2.2.2 (2021-12-17)
 ~~~~~~~~~~~~~~~~~~~
 - State trackers now take objects not indices

ciw/import_params.py

@@ -42,7 +42,8 @@ def create_network(arrival_distributions=None,
                    service_distributions=None,
                    routing=None,
                    batching_distributions=None,
-                   ps_thresholds=None):
+                   ps_thresholds=None,
+                   server_priority_functions=None):
     """
     Takes in kwargs, creates dictionary.
     """
@@ -69,6 +70,8 @@ def create_network(arrival_distributions=None,
         params['batching_distributions'] = batching_distributions
     if ps_thresholds != None:
         params['ps_thresholds'] = ps_thresholds
+    if server_priority_functions != None:
+        params['server_priority_functions'] = server_priority_functions
 
     return create_network_from_dictionary(params)
 
@@ -160,7 +163,8 @@ def create_network_from_dictionary(params_input):
             class_change_matrices['Node ' + str(nd + 1)],
             schedules[nd],
             preempts[nd],
-            params['ps_thresholds'][nd]))
+            params['ps_thresholds'][nd],
+            params['server_priority_functions'][nd]))
     for clss in range(number_of_classes):
         if all(isinstance(f, types.FunctionType) for f in params['routing']):
             classes.append(CustomerClass(
@@ -229,7 +233,10 @@ def fill_out_dictionary(params_input):
             len(params['number_of_servers']))] for i in range(
             len(params['arrival_distributions']))},
         'ps_thresholds': [1 for _ in range(len(
-            params['number_of_servers']))]
+            params['number_of_servers']))],
+        'server_priority_functions' : [
+            None for _ in range(len(params['number_of_servers']))
+        ]
         }
 
     for a in default_dict:

ciw/network.py

@@ -13,7 +13,8 @@ def __init__(self,
                  class_change_matrix=None,
                  schedule=None,
                  preempt=False,
-                 ps_threshold=1):
+                 ps_threshold=1,
+                 server_priority_function=None):
         """
         Initialises the ServiceCentre object.
         """
@@ -23,6 +24,7 @@ def __init__(self,
         self.schedule = schedule
         self.preempt = preempt
         self.ps_threshold = ps_threshold
+        self.server_priority_function = server_priority_function
 
 
 class CustomerClass(object):

ciw/node.py

@@ -21,6 +21,7 @@ def __init__(self, id_, simulation):
         """
         self.simulation = simulation
         node = self.simulation.network.service_centres[id_ - 1]
+        self.server_priority_function = node.server_priority_function
         if node.schedule:
             raw_schedule = node.schedule
             self.cyclelength = self.increment_time(0, raw_schedule[-1][1])
@@ -124,7 +125,7 @@ def begin_service_if_possible_accept(self, next_individual):
             - Update the server's end date (only when servers are not infinite)
         """
         next_individual.arrival_date = self.get_now()
-        free_server = self.find_free_server()
+        free_server = self.find_free_server(next_individual)
         if free_server is not None or isinf(self.c):
             if not isinf(self.c):
                 self.attach_server(free_server, next_individual)
@@ -178,7 +179,7 @@ def begin_service_if_possible_change_shift(self):
                         srvr.next_end_service_date = ind.service_end_date
                         break
 
-    def begin_service_if_possible_release(self):
+    def begin_service_if_possible_release(self, next_individual):
         """
         Begins the service of the next individual (at point
         of previous individual's release)
@@ -188,7 +189,7 @@ def begin_service_if_possible_release(self):
           - give a start date and end date
           - attach server to individual
         """
-        srvr = self.find_free_server()
+        srvr = self.find_free_server(next_individual)
         if srvr is not None:
             if self.number_interrupted_individuals > 0:
                 self.begin_interrupted_individuals_service(srvr)
@@ -287,17 +288,27 @@ def detatch_server(self, server, individual):
         if server.offduty:
             self.kill_server(server)
 
-    def find_free_server(self):
+    def find_free_server(self, ind):
         """
         Finds a free server.
         """
         if isinf(self.c):
             return None
-        for svr in self.servers:
+        
+        if self.server_priority_function is None:
+            all_servers = self.servers
+        else:
+            all_servers = sorted(
+                self.servers, key=lambda srv: self.server_priority_function(srv, ind)
+            )
+
+        for svr in all_servers:
             if not svr.busy:
                 return svr
         return None
 
+
+
     def find_next_individual(self):
         """
         Finds the next individual that should now finish service.
@@ -418,7 +429,7 @@ def release(self, next_individual_index, next_node):
         self.write_individual_record(next_individual)
         self.simulation.statetracker.change_state_release(self,
             next_node, next_individual, next_individual.is_blocked)
-        self.begin_service_if_possible_release()
+        self.begin_service_if_possible_release(next_individual)
         next_node.accept(next_individual)
         self.release_blocked_individual()
 

ciw/processor_sharing.py

@@ -64,7 +64,7 @@ def begin_service_if_possible_accept(self, next_individual):
             next_individual.with_server = True
             self.update_all_service_end_dates()
 
-    def begin_service_if_possible_release(self):
+    def begin_service_if_possible_release(self, ind=None):
         """
         Begins the service of the next individual (at point
         of previous individual's release)

ciw/tests/test_node.py

@@ -251,7 +251,7 @@ def test_begin_service_if_possible_release_method(self):
         self.assertEqual(ind.service_start_date, False)
         self.assertEqual(ind.service_end_date, False)
         Q.current_time = 200.0
-        Q.transitive_nodes[0].begin_service_if_possible_release()
+        Q.transitive_nodes[0].begin_service_if_possible_release(ind)
         self.assertEqual(ind.arrival_date, 100.0)
         self.assertEqual(round(ind.service_time, 5), 0.03382)
         self.assertEqual(ind.service_start_date, 200.0)
@@ -266,9 +266,9 @@ def test_release_blocked_individual_method(self):
         N1.individuals = [[ciw.Individual(i) for i in range(N1.c + 3)]]
         N2.individuals = [[ciw.Individual(i + 100) for i in range(N2.c + 4)]]
         for ind in N1.all_individuals[:2]:
-            N1.attach_server(N1.find_free_server(), ind)
+            N1.attach_server(N1.find_free_server(ind), ind)
         for ind in N2.all_individuals[:1]:
-            N2.attach_server(N2.find_free_server(), ind)
+            N2.attach_server(N2.find_free_server(ind), ind)
 
         self.assertEqual([str(obs) for obs in N1.all_individuals],
             ['Individual 0',
@@ -722,3 +722,76 @@ def event_and_return_nextnode(simself, next_active_node):
             'ciw/tests/testing_parameters/params.yml')
         Q = AssertSim(N)
         Q.simulate_until_max_time(100)
+
+    def test_server_priority_function_allocate_to_less_busy(self):
+        """
+        Test the server priority function when we prioritise the server that was
+        less busy throughout the simulation.
+        """
+        def get_server_busy_time(server, ind):
+            return server.busy_time
+
+        ciw.seed(0)
+        Q = ciw.Simulation(ciw.create_network(
+                arrival_distributions=[ciw.dists.Exponential(1)],
+                service_distributions=[ciw.dists.Exponential(2)],
+                number_of_servers=[2],
+                server_priority_functions=[get_server_busy_time]
+            )
+        )
+        Q.simulate_until_max_time(1000)
+
+        expected_times = [245.07547532640024, 244.68396417751663]
+        for i, srv in enumerate(Q.nodes[1].servers):
+            self.assertEqual(srv.busy_time, expected_times[i])
+
+
+    def test_server_priority_function_allocate_to_last_server_first(self):
+        """
+        Test the server priority function when we prioritise the server with the
+        highest id number.
+        """
+        def get_server_busy_time(server, ind):
+            return -server.id_number
+
+        ciw.seed(0)
+        Q = ciw.Simulation(ciw.create_network(
+                arrival_distributions=[ciw.dists.Exponential(1)],
+                service_distributions=[ciw.dists.Exponential(2)],
+                number_of_servers=[2],
+                server_priority_functions=[get_server_busy_time]
+            )
+        )
+        Q.simulate_until_max_time(1000)
+
+        expected_times = [158.68745586286119, 331.0719836410557]
+        for i, srv in enumerate(Q.nodes[1].servers):
+            self.assertEqual(srv.busy_time, expected_times[i])
+
+    def test_server_priority_function_two_nodes(self):
+        """
+        Test the server priority function with two nodes that each has a 
+        different priority rule.
+        """
+        def prioritise_less_busy(srv, ind):
+            return srv.busy_time
+
+        def prioritise_highest_id(srv, ind):
+            return -srv.id_number
+
+        ciw.seed(0)
+        Q = ciw.Simulation(ciw.create_network(
+                arrival_distributions=[ciw.dists.Exponential(1), ciw.dists.Exponential(1)],
+                service_distributions=[ciw.dists.Exponential(2), ciw.dists.Exponential(2)],
+                number_of_servers=[2, 2],
+                routing=[[0, 0], [0, 0]],
+                server_priority_functions=[prioritise_less_busy, prioritise_highest_id]
+            )
+        )
+        Q.simulate_until_max_time(1000)
+        expected_times_node_1 = [256.2457715650031, 257.59339967047254]
+        expected_times_node_2 = [157.35577182806387, 356.41473247082365]
+
+        for i, (srv_1, srv_2) in enumerate(zip(Q.nodes[1].servers, Q.nodes[2].servers)):
+            self.assertEqual(srv_1.busy_time, expected_times_node_1[i])
+            self.assertEqual(srv_2.busy_time, expected_times_node_2[i])

ciw/tests/test_state_tracker.py

@@ -59,7 +59,7 @@ def test_base_release_method_within_simulation(self):
         inds = [ciw.Individual(i) for i in range(5)]
         N.individuals = [inds]
         for ind in N.all_individuals:
-            srvr = N.find_free_server()
+            srvr = N.find_free_server(ind)
             N.attach_server(srvr, ind)
         self.assertEqual(Q.statetracker.state, None)
         Q.current_time = 43.11
@@ -154,7 +154,7 @@ def test_systempop_release_method_within_simulation(self):
         inds = [ciw.Individual(i) for i in range(5)]
         N.individuals = [inds]
         for ind in N.individuals[0]:
-            srvr = N.find_free_server()
+            srvr = N.find_free_server(ind)
             N.attach_server(srvr, ind)
         Q.statetracker.state = 14
         self.assertEqual(Q.statetracker.state, 14)
@@ -252,7 +252,7 @@ def test_nodepop_release_method_within_simulation(self):
         inds = [ciw.Individual(i) for i in range(5)]
         N.individuals = [inds]
         for ind in N.individuals[0]:
-            srvr = N.find_free_server()
+            srvr = N.find_free_server(ind)
             N.attach_server(srvr, ind)
         Q.statetracker.state = [5, 3, 6, 0]
         self.assertEqual(Q.statetracker.state, [5, 3, 6, 0])
@@ -348,7 +348,7 @@ def test_nodeclassmatrix_release_method_within_simulation(self):
         inds = [ciw.Individual(i) for i in range(5)]
         N.individuals = [inds]
         for ind in N.individuals[0]:
-            srvr = N.find_free_server()
+            srvr = N.find_free_server(ind)
             N.attach_server(srvr, ind)
         Q.statetracker.state = [[3, 2, 1], [1, 1, 1], [3, 1, 2], [0, 0, 0]]
         self.assertEqual(Q.statetracker.state, [[3, 2, 1], [1, 1, 1], [3, 1, 2], [0, 0, 0]])
@@ -443,7 +443,7 @@ def test_naive_release_method_within_simulation(self):
         inds = [ciw.Individual(i) for i in range(5)]
         N.individuals = [inds]
         for ind in N.individuals[0]:
-            srvr = N.find_free_server()
+            srvr = N.find_free_server(ind)
             N.attach_server(srvr, ind)
         Q.statetracker.state = [[4, 1], [3, 0], [5, 1], [0, 0]]
         self.assertEqual(Q.statetracker.state, [[4, 1], [3, 0], [5, 1], [0, 0]])
@@ -595,7 +595,7 @@ def test_matrix_release_method_within_simulation(self):
         inds = [ciw.Individual(i) for i in range(5)]
         N.individuals = [inds]
         for ind in N.individuals[0]:
-            srvr = N.find_free_server()
+            srvr = N.find_free_server(ind)
             N.attach_server(srvr, ind)
         Q.statetracker.state = [[[[],  [2], [], []],
                                  [[],  [],  [], []],

ciw/version.py

@@ -1 +1 @@
-__version__ = "2.2.2"
+__version__ = "2.2.3"

docs/Guides/index.rst

@@ -20,6 +20,7 @@ Contents:
    batching.rst
    baulking.rst
    server_schedule.rst
+   server_priority.rst
    dynamic_customerclasses.rst
    state_trackers.rst
    deadlock.rst