Using STM to atomically update fields

STM (Software Transactional Memory) is a concurrency control mechanism for managing access to shared memory. In the traditional threaded model of concurrent programming, when we share data among threads, we keep it consistent using locks. A lock is an object which signals ownership of some resource, and which has one really important property; it references at most one process, and when you want to look at it and update it, nothing can intervene between the read and write. On simple systems, reasoning in terms of threads and locks is relatively simple. But as soon as the system grows in complexity, it becomes really complicated to understand and debug hundreds of threads updating several shared variables. A typical issue is a deadlock; when two threads wait on each other to acquire a resource they are locking.

There are several methods that try to make it easier to do coordination between multiple tasks such as enforcing ordering, semaphores, and monitors...