With the introduction of Intel’s restricted hardware transactional memory (HTM) in commodity hardware, the transactional memory abstraction has finally become practical to use. Transactional memory allows a programmer to easily implement safe concurrent code by specifying that certain blocks of code should be executed atomically. However, Intel’s HTM implementation does not offer any progress guarantees. Even in a single threaded system, a transaction can repeatedly fail for complex (and often undocumented) reasons.