Concurrency primitives, race conditions, deadlocks, and the practical patterns for thread-safe code in real systems — explained without hand-waving and with the failure modes that actually bite.
7 articles · updated regularly
When building high-performance network servers with Linux epoll, Edge-Triggered (EPOLLET) mode promises fewer syscalls than Level-Triggered mode. But without careful loop management, a single greedy socket streaming large payloads can starve all other file descriptors in the event loop.
A lock-free stack built on compare-and-swap passed every load test and then corrupted itself in production, popping a node that had already been freed. The CAS never failed, and a failing CAS was the only case anyone had thought to worry about. The bug was a value swinging from A to B and back to A while a paused thread was not looking, so the compare saw the same bit pattern and happily proceeded on data that was no longer the data it started with.
We used a Redis lock with a TTL to make sure exactly one worker processed each payout. For months it worked, then a batch ran twice and double-charged a handful of accounts. The lock was doing its job perfectly. The problem was that a stop-the-world GC pause outlived the lock's expiry, so a worker that believed it still held the lock kept working while a second worker had already taken it.
The endpoint was fine in every test and fine in staging. Then traffic crossed some invisible line in production and it stopped responding entirely, not slow, fully frozen, with no errors in the logs. The pool had ten connections, and under load every request was holding one while waiting for a second that would never come.
Four strategies for safe concurrent code, from heaviest to lightest — and the one most teams should default to.
Two transactions, two rows, locked in opposite order — and your whole worker pool grinds to a halt. Here's the theory and the fixes.
Why your unit tests passed and your bank balance didn't. A practical intro to races, with Java, Go, and Postgres examples.