Gate Blocking

A gate’s Blocking tab decides how it hands entities to the next step, and what happens when that step has no room.

Blocking Mode

Mode	Behaviour
Push	Release immediately whenever the gate is open. If the next step is full, the entity blocks in place (the default)
Pull	Release only when a downstream step asks for one, by freeing capacity
Lookahead	Before releasing, check a named step for room and reserve a slot there

Push is the ordinary case and the right default. The gate lets go as soon as it opens, and back-pressure happens naturally when the destination fills up.

Pull inverts that. The gate holds everything until a downstream step signals that it has room, then lets exactly one through per signal. Use it to model a genuine pull system where the downstream step sets the pace. A pull gate is stocked with credits from the downstream capacity at the start of the run, so it is not stuck waiting for the first signal.

Lookahead sits between the two. Rather than releasing hopefully and blocking, the gate checks a step you name and reserves a place before it lets the entity go, so the entity is never stranded in transit.

Lookahead Target

Shown for Lookahead. The name of the activity or queue to check for room, typed in.

Type it exactly. This is a free text field, and a name that does not match anything in the model does not raise an error: the gate quietly behaves as Push instead, which looks like Lookahead simply having no effect. A blank target is caught as a model error, so it is specifically the misspelling that slips through. Copy the name from the element rather than retyping it.

What a Pull gate gives up

Running a gate as Pull means downstream demand governs it completely, so it cannot also be governed by anything else. A Pull gate cannot carry a schedule, an open or close condition, a Normally Closed default state, or the Windowed release mode. Those settings are hidden on the tab and cleared if they were already set.

Under kanban

With Kanban Pull Control on, the whole tab disappears. The card loop decides when an entity is released and the blocking mode never comes into play. See Gate Flow Control.