Onblocked

Onblocked is a term used in software development to refer to the naming of a callback or event handler that is invoked when an operation becomes blocked and cannot proceed immediately. The phrase is not tied to a single standardized API; its exact meaning and usage vary across languages and libraries. In practice, onblocked represents a hook that signals that a resource, constraint, or policy is temporarily preventing progress.

Common usage patterns place onblocked within asynchronous, event-driven, or streaming contexts. In concurrency and I/O frameworks, an onblocked handler may be invoked when a task must wait for a resource, such as a locked mutex, a full buffer, or a network backchannel. The handler often implements backpressure strategies, such as delaying further work, retrying later, or switching to alternative routes. In data streaming or message-processing systems, onblocked may fire when input or output channels are unable to accept data, prompting flow-control responses. In user interface or policy-driven contexts, the term can be used to indicate that an action is temporarily prevented by a modal dialog, permission requirement, or other blocking condition.

Variants and related terms include onBlock, onBlocked, and BlockedEvent, reflecting stylistic differences across libraries. Implementations typically involve logging, scheduling retries, or notifying users or systems of the blockage. When encountering onblocked in a codebase, developers should consult the specific framework’s documentation to understand the exact semantics and recommended handling patterns.

See also: blocking, backpressure, event-driven programming, flow control.