Singlerunners

A singlerunner is a term used in software development and systems administration to describe an application or process that is designed to run only one instance of itself at any given time on a particular system. This is often a requirement for applications where multiple concurrent instances would lead to data corruption, race conditions, or other undesirable behavior. Examples include database servers, certain configuration management tools, or applications that manage a unique hardware resource.

Implementing a singlerunner mechanism typically involves a locking mechanism. This can be achieved through various methods such as creating a lock file in a specific directory, using operating system-level mutexes or semaphores, or employing database-level locking. When a singlerunner process starts, it attempts to acquire the lock. If the lock is already held by another instance, the new instance will typically exit or wait for the lock to be released. Upon successful acquisition, the process proceeds with its operation. When the process terminates gracefully, it releases the lock, allowing another instance to start. Error handling is crucial, as a crashed process might leave the lock file in place, preventing any future instances from running. Mechanisms for detecting and cleaning up stale locks are often incorporated into singlerunner implementations. This ensures system stability and prevents unintended service disruptions.