crossthread

Crossthread is a term used in two distinct domains to describe misalignment or unsafe interaction across a thread or axis. The word combines cross, implying an incorrect crossing or alignment, with thread, referring to a helical ridge or to a sequence of execution in software. In common usage, the term most often appears in mechanical contexts, but it is also employed in software development to describe cross-thread interactions.

In mechanical engineering, cross-threading refers to the improper engagement of a threaded fastener, such as a bolt and nut. It occurs when the male and female threads do not align along the axis, often due to misalignment, starting at an angle, dirty or damaged threads, or applying excessive force. The result is damaged threads, reduced clamping force, and potential fastener failure. Symptoms include binding, binding sounds, or a rough turn. Repairs typically involve backing out and rethreading with careful alignment, cleaning threads, or using a thread repair method such as a helicoil insert. Prevention relies on proper alignment, manual starting of threads by feel, adequate lubrication, and avoiding forced advancement.

In computing, cross-threading (often described as unsafe cross-thread access) denotes code that manipulates data or resources from a thread different from the one that owns or created them without proper synchronization. This can lead to data races, corruption, or crashes. Common scenarios include updating a user interface from a background thread. Prevention strategies include synchronization primitives (mutexes, locks), thread confinement, mutex-protected data structures, and frameworks that marshal calls to the appropriate thread. By ensuring correct thread alignment in both mechanical and software contexts, crossthread issues are mitigated.