Handling Race Conditions in Multi-Device Warehouse Fulfillment

One of the most complex engineering challenges in offline-first warehouse logistics is managing concurrency. When multiple warehouse workers are assigned overlapping fulfillment waves, a dangerous race condition emerges: what happens if two pickers scan the exact same item simultaneously while disconnected from the network?

Without strict concurrency controls, both devices will eventually sync their successful payloads back to Shopify, resulting in double-fulfillment, incorrect inventory counts, and lost revenue.

The Solution: Pessimistic Locking

WedgeRoam prevents double-fulfillment entirely by utilizing pessimistic locking to guarantee single-winner syncs at the cloud database level.

1. The Cloud as the Ultimate Source of Truth

While the mobile application caches data locally to maintain sub-50ms scan latency, the final state of an order is strictly governed by the central cloud database.

2. Sequential Transaction Processing

When a device attempts to sync an offline picking payload, the cloud database opens a sequential, pessimistic transaction block. It queries the item's current state and locks the row.

• If the item is marked as unfulfilled, the transaction succeeds, updates the row to "fulfilled," and releases the lock.
• If a second device (the "late sync") attempts to update the exact same item moments later, the transaction encounters the updated state and safely aborts.

3. Graceful Conflict Resolution

When a late sync is rejected, WedgeRoam’s architecture automatically pushes a conflict resolution payload back to the offending device. The device immediately:

1. Reverts the local UI state of the item.
2. Triggers a harsh error vibration (haptic feedback).
3. Highlights the item in red, instructing the picker to return it to the bin.

This robust engineering architecture provides Shopify merchants with absolute peace of mind, allowing them to deploy unlimited picking devices concurrently without fear of inventory corruption.