queue

The queue() function reserves a slot for the current execution so you can serialize or limit concurrent runs of the same flow.

Interactive example

Syntax

function queue<
	GenericConcurrency extends number
>(
	params?: {
		concurrency?: GenericConcurrency;
	}
): AsyncGenerator

Parameters

• params.concurrency: Maximum number of simultaneous runs allowed for the same flow reference. The default is 1.

Return value

An async generator yielding a queue effect and returning a release function that must be called when the execution can free its slot, usually from a finally block.

Notes

• Internal state is stored in a WeakMap keyed by the executed flow reference.
• To share the same queue across calls, reuse the same flow created with F.create(...) or the same function returned by F.toFunction(...).
• If release() is never called, later runs remain blocked in the queue.
• If the same execution yields queue(...) multiple times, only the first encountered effect is applied by the runner.

See also

• calledByNext - Calls a callback when a later run replaces the current one
• throttling - Ignores or defers runs that happen too close together
• exec - Executes a nested flow inside the current flow