What is Concurrency?

Concurrency is the ability of a program to deal with multiple tasks at once by making progress on them in overlapping time periods. It's about structuring a program so tasks can run independently — even if the CPU switches between them rather than running them literally simultaneously.

Concurrency vs. Parallelism:

• Concurrency: Managing many tasks at once (dealing with lots of things)
• Parallelism: Actually running tasks at the same time on multiple cores (doing lots of things)

You can have concurrency on a single core by interleaving tasks.

How It's Achieved:

• Threads: Multiple paths of execution within a process
• Async/await: Non-blocking code that yields while waiting
• Event loops: Handle many tasks by reacting to events
• Processes: Separate programs coordinated together

Why It Matters:

• Responsiveness: Keep an app usable while work happens
• Throughput: Handle more requests at once
• Efficient waiting: Do other work while waiting on I/O

FAQ

Is concurrency the same as multithreading?

No. Multithreading is one way to achieve concurrency. You can also use async programming, event loops, or multiple processes without traditional threads.

Why is concurrency considered hard?

Because tasks share resources and timing is unpredictable, you can get race conditions, deadlocks, and subtle bugs that only appear sometimes. Careful coordination is essential.