The Queue

When a user wants an asset that isn't currently available, they can get in line for it. Queues are processed in strict FIFO (First In, First Out) order.

Directed queues

There is not one queue per stablecoin — there is one queue per direction. A position in the USDC → USDS queue is someone offering USDC and waiting for USDS. The USDS → USDC queue is a different queue, holding the opposite side.

That distinction is what makes peer matching work: a swap looks at the exact-opposite queue first and settles against it directly, moving no protocol reserves at all.

How it works

Getting in line happens as part of a swap: whatever cannot be filled instantly is escrowed as a new position at the tail of the queue. The escrow is the offer asset — the token the user put in, not a receipt. Your spot is held until either:

• The asset you want arrives and you receive it
• You leave the line and take your offer asset back

If you leave, you can immediately swap or withdraw against whatever is available. If you want back in line, you join at the tail.

Queue USDC → USDS:
  Position 1: Alice offers 500 USDC, wants USDS
  Position 2: Bob offers 1,000 USDC, wants USDS
  Position 3: Carol offers 600 USDC, wants USDS

800 USDS becomes available:
  → Alice receives 500 USDS (position closes, her 500 USDC enters reserves)
  → Bob receives 300 USDS (still in line for 700 more)
  → Carol still waiting

Queue USDC → USDS (after):
  Position 1: Bob offers 700 USDC
  Position 2: Carol offers 600 USDC

Partial fills

Positions can be partially filled. When this happens:

• The user receives the partial amount immediately
• The position stays in the queue for the remainder, keeping its place in line
• The QueueFilled event reports both the filled and the remaining amounts

FIFO is enforced against reserves

A queue does not just wait for someone to walk in with the right token. Before any swapper is allowed to touch protocol reserves on that route, the protocol settles the queue ahead of them, in order. Only if that queue is then empty does the swapper reach reserves.

How much settles per transaction

A single swap or deposit settles at most 8 positions inline, oldest first. That bound exists so one user's transaction is never forced to walk an arbitrarily long queue — it is a gas-safety limit, not a limit on how deep a queue can get.

With 100 positions waiting, a swap settles the 8 oldest and the other 92 stay queued, in order. They drain through subsequent swaps and deposits, or explicitly:

dollarStore.processQueue(offerAsset, wantAsset, maxPositions);

processQueue is permissionless and you choose the bound, so a keeper can pass a large number and drain as much as their gas allows. Nothing gets stuck. Note there is no reward for calling it — the protocol charges no fees, so it pays none either. The incentive to call it is having an order in that queue, or wanting the route unblocked so your own swap can reach reserves.

FIFO is per queue, not global

Each directed queue is strict FIFO by arrival. There is no global clock across queues, including queues that want the same asset.

USDS → USDT    Alice, queued a week ago
USDC → USDT    Bob, queued today

Both are waiting for USDT, but they are two separate queues — one per hub asset offered. When USDT liquidity arrives, the auto-settlement walks the hub assets in the pool's own order, so if USDC comes before USDS in that order, Bob settles before Alice despite arriving later.

Alice is not stuck, though. She can drain her own queue directly at any time:

dollarStore.processQueue(USDS, USDT, maxPositions);

and a USDS → USDT swap from anyone else matches against her position too. Only the automatic settlement follows pool order; every other path respects her queue's own FIFO.

If ordering against other pairs matters to you, treat processQueue as the tool that puts you back in control rather than waiting for the automatic path.

Leaving the queue

Users can leave at any time:

dollarStore.cancelQueue(positionId);

Cancelling returns the escrowed offer asset and is an exit path — it works even while the protocol is paused. If the transfer back fails (for example a token blacklist), the escrow is converted into the canonical receipt instead of bricking the position: DLRS on the hub, receipt shares on a spoke.

Queue limits

Parameter	Value	Purpose
Max positions per directed queue	150	Prevents unbounded gas costs
Min order (base)	$500	Prevents spam at low queue depth
Min order scaling	10x per 25 positions	Higher minimums as the queue grows

Minimum order scaling

The minimum order size increases as that queue gets deeper:

Queue positions	Minimum order
0-24	$500
25-49	$5,000
50-74	$50,000
75-99	$500,000
100-124	$5,000,000
125-149	$50,000,000

This prevents queue spam and ensures positions are meaningful at scale. The minimum is waived for the first position of an empty queue, so a route can always be opened. Read the current value with getMinimumOrderSize(offerAsset, wantAsset).