TreiberStacks

Treiber stack is a simple lock-free stack data structure designed for concurrent programming. It uses a singly linked list of nodes, where each node holds a value and a pointer to the next node, and a top pointer that always refers to the current top node. The implementation relies on atomic compare-and-swap (CAS) operations to modify the top pointer without using locks.

Push operation: allocate a new node with the given value, set its next pointer to the current top, and perform CAS to replace the top with the new node if the top has not changed. If the CAS fails, retry from the beginning. Pop operation: read the current top; read the next pointer; perform CAS to change the top from the current top to the next node; if successful, detach and return the value; if the CAS fails, retry. The algorithm is linearizable, meaning each operation appears atomic with respect to other threads.

The design is simple and free of locks, but it has memory-management challenges. The ABA problem can cause a pop to fail erroneously if the top node is removed and then reinserted. Solutions include hazard pointers or epoch-based reclamation to ensure safe memory reclamation. In practice, Treiber stacks are often used as teaching examples or baseline lock-free structures; many production systems use more robust memory management schemes.

Variants exist to reduce ABA risk or to support specialized memory reclamation strategies; performance depends on contention level, but the structure remains a foundational example of lock-free synchronization.