Overview

Everblack Grackle is the coordination layer for your distributed system — fundamental synchronization primitives, served over a clean API, in a single self-contained binary.

Stop reinventing distributed locks on top of a database, or bending a key-value store into a semaphore. Grackle gives you the primitives directly, with the durability and safety guarantees you’d otherwise have to build (and debug) yourself.

The primitives

• Hierarchical locks — shared (read) or exclusive (write) locks whose names are /-separated paths. Lock users/123 and you’ve guarded its whole subtree — no need to enumerate every leaf. When an acquire is blocked, Grackle tells you who holds the lock and why.
• Weighted semaphores — bound concurrent access to a resource pool. Each acquire takes a configurable weight, so heavy and light work can share one pool of permits.
• Wait groups — fan-in for millions of jobs, the distributed equivalent of Go’s sync.WaitGroup: workers report jobs done, observers block until the group completes.
• Barriers — generational, reusable rendezvous points where a fleet of processes wait for each other and advance together, cycle after cycle.

Everything lives inside a namespace and is reached by name — no IDs to track, no resources to provision up front.

Why Grackle

• Safe by default. Lock and semaphore holds sit under a TTL lease that the holder heartbeats; wait groups carry an absolute deadline; idle barriers auto-delete. A crashed client never leaves a dangling lock or a wait group that blocks forever. Every operation is atomic and safe to retry.
• Durable and replicated. State is persisted and Raft-replicated for high availability, and sharded so it scales horizontally as your workload grows.
• Zero dependencies. One binary, embedded storage — no database, Kafka, Redis, or ZooKeeper to run alongside it. Start single-node, grow into a replicated, sharded cluster without changing your code.
• An API that does the heavy lifting. Responses are rich enough to act on — a failed lock acquire returns the current holders and the reason it was blocked, not just “no”. Consistent conventions across every primitive: opaque metadata on everything, optimistic-concurrency updates, cursor pagination.

Grackle is Open Source, under AGPL-3 License.

Get started with Grackle →