Lock-Free Queue

A lock-free queue is a concurrent data structure that allows multiple threads to enqueue and dequeue elements without blocking. It is typically implemented using atomic operations — particularly compare-and-swap — to link nodes through a singly-linked list while maintaining consistency under all thread interleavings. The Michael-Scott queue is the canonical algorithm, using separate head and tail pointers with careful null handling to ensure that at least one thread makes progress on every operation.

The lock-free queue is a litmus test for concurrent programming expertise: if you can implement one correctly, you understand memory ordering, the ABA problem, and the difference between obstruction-freedom and true lock-freedom. If you cannot, you are writing race conditions with extra steps.