Class Queue

We refer to queues and resources interchangeably. Resources are just Queues with limited capacity. Seizing a resource is the same as entering a Queue, and releasing a resource is the same as leaving a Quue.

Queues can be seized and released by entities while the simulation runs using the Entity.enterQueue and Entity.leaveQueue methods.

When that happens, the simulation collects aggregate statistics about the number of entities in the queue and the amount of time they spent there.

For example, the script below causes entities to enter a waiting queue, seize one capacity unit of a server queue, leave the waiting queue, undergo a delay that represents the service, then leave the server:

class Customer extends Entity<BarberShop> {
    service = new Uniform(15 - 3, 15 + 3);
    async script() {
        const shop = this.simulation;
        await this.enterQueue(shop.qWait); // enter the line (unlimited capacity)
        await this.enterQueue(shop.qJoe); // seize Joe the barber (capacity == 1)
        this.leaveQueue(shop.qWait); // leave the line
        await this.delay(this.service.sample()); // get a haircut
        this.leaveQueue(shop.qJoe); // free Joe        
    }
}

Queue statistics can be obtained at the end of the simulation by inspecting the queue's grossPop and grossDwell Tally objects.

You can also generate complete reports on queue utilization using the Simulation.getStatsTable method.

In addition to the Entity.enterQueue and Entity.leaveQueue methods, SimScript has an Entity.seize method that provides a shorter way to instruct entities to enter one or more waiting queues (unlimited capacity), seize a resource (limited capacity), undergo a delay, and leave the waiting queues.

For example, the code below uses the Entity.seize method to perform the same tasks as the script listed above:

class Customer extends Entity<BarberShop> {
    service = new Uniform(15 - 3, 15 + 3);
    async script() {
        const shop = this.simulation;

        // seize method: enter the line, seize the barber, leave the line,
        // get a haircut, release the barber
        await this.seize(shop.qJoe, this.service.sample(), shop.qWait);
    }
}