⚙️ What is Concurrency?
Concurrency is the ability of a system to handle multiple tasks at the same time. In distributed systems, it means multiple operations or processes executing independently and potentially in parallel—either on the same machine (multi-threaded) or across multiple machines (distributed).
🧠 Concurrency vs. Parallelism
| Concept | Definition | Example |
|---|---|---|
| Concurrency | Tasks make progress independently (may or may not run in parallel) | A web server handling many client requests |
| Parallelism | Tasks actually run simultaneously on multiple CPUs | Matrix multiplication using multiple cores |
All parallel programs are concurrent, but not all concurrent programs are parallel.
🔁 Concurrency in Distributed Systems
In distributed systems (like Temporal, databases, cloud services), concurrency allows:
- Handling multiple requests from clients
- Executing multiple workflows in parallel
- Scaling up to use multiple CPUs/nodes
- Non-blocking I/O for better resource use
🚨 Challenges of Concurrency
-
Race conditions → Two operations interfere with each other (e.g., two users withdrawing from the same bank account)
-
Deadlocks → Two or more operations wait on each other indefinitely
-
Consistency problems → Especially when multiple operations modify shared data
-
Non-determinism → Harder to test and debug when the execution order changes
🔐 Tools & Strategies for Managing Concurrency
- Locks/Mutexes: Ensure only one process accesses shared data
- Semaphores: Control access to a limited number of resources
- Transactions: In databases, to ensure atomic and isolated updates
- Message Queues: Decouple producers and consumers
- Workflow engines (e.g., Temporal): Manage concurrent execution with built-in control