Understanding Thread, Process, and Distributed Locks and Their Implementation

In distributed cluster development, traditional thread locks cannot cover all scenarios, so distributed locks are introduced.

Thread lock, Process lock, Distributed lock

Thread lock: familiar mechanism that synchronizes access to a method or code block so that only one thread executes the locked section at a time, while other threads may run non‑locked code.

Process lock: controls access to a shared resource across multiple processes on the same operating system, typically using OS semaphores.

Distributed lock: extends locking to processes running on different machines, requiring a third‑party storage to hold lock metadata.

What is a distributed lock and how to implement it?

Implementation relies on an external store (e.g., Redis or Zookeeper) to record a unique lock ID. A process checks the store; if the ID is absent it writes the ID and proceeds, otherwise it polls until the lock is released, then deletes the ID.

In Redis, the atomic command jedis.set(String key, String value, String nxxx, String expx, int time) should be used instead of separate get/set.

When to use distributed locks?

Thread, process, and distributed locks serve the same purpose—preventing concurrent conflicts—but differ in scope. Use the smallest viable lock; distributed locks add complexity and should be reserved for cross‑machine contention.

Practical considerations

Choosing the storage: Redis offers fast in‑memory operations and high availability, while Zookeeper provides strong consistency via the Paxos algorithm and built‑in watch notifications.

Distributed locks are not a universal solution; they must be designed with specific business requirements in mind, similar to cache or transaction strategies.