I have 12 years of experience and working as a Principal Engineer @Atlassian and I have seen concurrency scaring the hell out of a lot of junior engineers.

It’s one of the most feared topics in system design & backend interviews — race conditions, deadlocks, thread pools… you name it.

But once you internalize these 20 must-know concepts, everything clicks.

Save this thread. Read till the end.
Your future interviews and production systems will thank you. 1) Concurrency

Multiple tasks make progress by taking turns on one CPU (or across cores).

It’s about dealing with many things at once, even if not truly simultaneous.

Why it matters: Almost every modern backend, mobile, or distributed system is concurrent.

How to learn it: Take any single-threaded program and refactor it to handle multiple requests using threads or async. Visualize the timeline of execution.