Gate

A Gate controls when entities are allowed to move on. It does no work and holds nothing of its own; it opens and closes, releasing entities while open and making them wait while closed. Use it for a barrier that follows a schedule, responds to a signal, or waits for downstream demand.

Open or closed to start

Default State sets whether the gate begins Normally Open or Normally Closed. From there, one or more mechanisms change its state during the run, and you can combine them.

Ways to open and close a gate

• On a schedule: open the gate during set time windows, or tie it to a shift calendar so entities move only during working hours.
• On a condition: give an open or close condition, a live expression over the model’s state. This is how a gate reacts to a signal: a condition such as Signal("Go").Active opens the gate the moment that signal is sent (see Signal).
• From action logic: open or close the gate directly with OpenGate, CloseGate, or ToggleGate from anywhere in the model. Once logic takes control this way, it keeps control for the rest of the run.
• On downstream demand: run the gate as a pull or Kanban control, or cap the work in progress downstream, so it releases only when the next step has room.

How many to release

While the gate is open, the Release Mode decides how many entities go through: one at a time, a set number, everything at once, at a limited rate, or within a repeating window.

Order and capacity

Entities that arrive while the gate is closed wait in the gate’s own queue. The Queue Order sets who leaves first, and a Queue Capacity makes the gate refuse new entities once full, backing them up upstream. The Blocking Mode decides what happens at the other end, when the gate is open but the next step has no room.

Reacting to open and close

On the Events tab you can run a short command list when the gate opens, closes, releases an entity, or blocks one, for counting or other side effects. These hooks take a small set of commands rather than the full action logic language, so read that article before writing one.

The gate’s other tabs

Every setting above has its own article:

• Gate Schedule: time windows and shift calendars
• Gate Flow Control: kanban cards and work-in-progress limits
• Gate Release: how many go through per opening
• Gate Events: the four hooks
• Gate Conditions: opening and closing from model state
• Gate Blocking: push, pull, and lookahead

Most of these tabs are hidden until you reveal them with the eye icon in the gate’s tab strip.