alongrunning

Alongrunning is a scheduling pattern in concurrent computing and data processing that describes a model in which multiple workers progress through a shared linear sequence of processing stages in a coordinated fashion. Unlike independent parallel execution, alongrunning emphasizes alignment of progress across components, so that all workers advance to the next stage together, typically using barriers or synchronization points. This approach aims to maintain a predictable sequence of outcomes and can simplify reasoning about correctness in complex pipelines.

The term arises in theoretical discussions and practical guides as a contrast to fully asynchronous or purely parallel models. It is not bound to a single technology and may be applied in diverse contexts such as workflow engines, streaming pipelines, or simulation frameworks. In practice, alongrunning often operates with a fixed sequence of stages, where each stage has a defined duration or a set of completion criteria, and where workers periodically synchronize to ensure stage alignment.

Key concepts associated with alongrunning include stages, synchronization barriers, and the management of drift and reconciliation when minor timing differences occur. Fault tolerance and checkpointing are commonly incorporated to recover from stage failures without breaking the overall progression order. Implementations must balance the benefits of deterministic ordering and easier debugging against potential idle time and increased latency due to synchronization.

Common variants include synchronous alongrunning, which enforces strict, stage-by-stage progression, and optimistic alongrunning, which tolerates small drifts with subsequent reconciliation. Applications appear in real-time streaming, scientific simulations with timestep constraints, and structured batch processing where stage integrity is essential.