# Queues

Operation:

- Think of a Queue as a line of items awaiting entry into some process or activity (e.g., grocery store checkout line, airport ticket counter line).

- Queues are FIFO (first in - first out) in their operation. Stuff enters the queue, and remains in line, waiting its turn to exit the Queue.

- Multiple inflows are allowed (Uniflows only). The contents of each inflow are given their own slot or element in the Queue.

- The Queue exerts no behind the scenes control over its inflows. Any control from a Queue to its inflows must be explicitly represented in the inflow logic.

- The software prioritizes multiple inflows into a Queue. See Chapter 14 for inflow prioritization schemes.

Modeling Dialog Operations: The Queue's Modeling Dialog is easy to define, as shown in Figure 4-34.

Figure 4-34 Queue Dialog

Outflow Dialog Operations: Multiple Queue outflows are allowed-all must be Uniflows.

- The Queue "wants" to flow everything through its outflows. As such, its flows are constrained only when there is an Inflow limited and/or Capacity constrained Conveyor, or an Oven, immediately downstream.

- Unit conversion is possible in flows that connect Queues to other stocks. Unit conversion works as illustrated in Figure 4-17.

- When multiple outflows are drawn from a Queue, it is possible to designate one or more of the outflows as "overflow" in their dialogs. When a higher-priority flow is blocked because of capacity constraints, the flow will be routed through the overflow. A sample overflow designation is shown in Figure 4-35.

- Chapter 14 discusses the prioritization scheme employed by the software when there are multiple outflows from a Queue.

Figure 4-35 Queue Outflow Overflow Dialog