Semaphore

Throttles parallelism: at most Slots records at a time may run through the components behind Output; further records wait until a slot is free. Use it in front of resources that must not be called by too many threads at once (APIs with rate limits, databases).

Pins

Pin	Kind	Types	Description
Input	input	any	Record that requests a slot.
Output	output	same as input	Called with the same record and metadata while the slot is held.

Configuration

Field	Type	Default	Description
Slots	integer (1-65535)	4	Required. Maximum number of records processed in parallel. Values below 1 are treated as 1.
Lock	string (max 256)	Universal	Name of the semaphore. Must not be empty.

Behaviour

• For each record the calling thread waits for a free slot of the semaphore named Lock, calls Output synchronously and releases the slot when the downstream branch has finished, also when it throws. Exceptions are passed back to the caller.
• The semaphore is created on start (or on first use for a Lock name computed by an expression) with the Slots value at that moment.
• Waiting is blocking and has no timeout.

Notes

• Semaphores are per component: two Semaphore components with the same Lock name do not share slots. Use one Semaphore component in front of the protected branch.
• Within one component, different Lock values (set by an expression) get independent semaphores, which allows throttling per key (e.g. per customer).
• Changing Slots takes effect only after the flow is restarted.
• Slots = 1 serializes the branch (one record at a time).
• Only the synchronous part of the branch is protected; work handed to other threads (queues, async components) is not counted.
• An empty Lock makes the component fail when the flow starts.

Example

{ "Slots": 2, "Lock": "CrmApi" }

Queue → Semaphore → Http client → ...