6. Resource bottlenecks and utilization

6.1. Overview

The objective here is to analyze how limited capacities affect throughput and schedule and show how queues behave when multiple entities compete for scarce capacity and how priority settings change the outcome.

6.2. Scenario

Three work crews request the same truck fleet, but capacity is only three units and the trucks arrive in batches. One crew waits with a higher priority to demonstrate preemption of the queue order.

6.3. Simulation code (priority bottleneck)

import simpm
from simpm.des import Entity, Environment, PriorityResource

def crew_one(env, entity: Entity, trucks: PriorityResource):
    print("Crew 1 wants 3 trucks at:", env.now)
    yield entity.get(trucks, 3, priority=1)
    print("Crew 1 got 3 trucks at:", env.now)

def crew_two(env, entity: Entity, trucks: PriorityResource):
    print("Crew 2 wants 2 trucks at:", env.now)
    yield entity.get(trucks, 2, priority=2)
    print("Crew 2 got 2 trucks at:", env.now)

def crew_three(env, entity: Entity, trucks: PriorityResource):
    # Arrives later but with higher priority (negative is highest)
    yield entity.do("wait", 1)
    print("Crew 3 wants 2 trucks at:", env.now)
    yield entity.get(trucks, 2, priority=-3)
    print("Crew 3 got 2 trucks at:", env.now)

def fleet_arrivals(env, entity: Entity, trucks: PriorityResource):
    # Trucks arrive gradually, freeing capacity
    yield entity.do("wait", 3)
    yield entity.add(trucks, 3)
    yield entity.do("wait", 3)
    yield entity.add(trucks, 2)
    yield entity.do("wait", 2)
    yield entity.add(trucks, 3)

env = Environment()
crew1 = Entity(env, "crew1")
crew2 = Entity(env, "crew2")
crew3 = Entity(env, "crew3")
fleet = Entity(env, "fleet")
trucks = PriorityResource(env, "Truck", init=0, capacity=3, print_actions=True)

env.process(crew_one(env, crew1, trucks))
env.process(crew_two(env, crew2, trucks))
env.process(crew_three(env, crew3, trucks))
env.process(fleet_arrivals(env, fleet, trucks))

simpm.run(env, dashboard=True)

6.4. What to look for

• Queue order – Crew 3 jumps ahead because it requests trucks with a higher priority even though it arrives later.

• Utilization – PriorityResource logs show when the three available trucks are idle versus allocated. Inspect status_log if you need time-stamped detail.

• Capacity sensitivity – Increase capacity or the add amounts to see how quickly the queue clears; decrease them to stress-test the bottleneck.

• Preemption vs. fairness – Switching to simpm.des.Resource (no priority) will force first-come-first-served behavior.