SIGEVTHREAD

SIGEVTHREAD, more commonly referenced as SIGEV_THREAD in POSIX documentation, is a notification method used with POSIX real-time timers and asynchronous event delivery. When an event configured with this notification fires, the implementation creates a new thread to execute a user-defined function, rather than delivering a signal to a process or placing work on a queue.

Configuration and usage: The feature is used via the sigevent structure and timer_create (or similar real-time interfaces). To use SIGEV_THREAD, set sigev_notify to SIGEV_THREAD, provide a pointer to the handler function in sigev_notify_function, and supply data through sigev_value (a sigval_t). The handler function has the signature void handler(sigval_t val) and will be invoked in the context of the newly created thread with the passed value. The timer or event source typically triggers the creation of the thread exactly at the moment of expiration or event occurrence.

Behavior and characteristics: Upon the event, a thread is spawned by the implementation to run the specified function. The newly created thread runs independently of the triggering thread and usually terminates after the handler returns. The exact threading attributes (such as stack size and detachment) are determined by the implementation; the thread is generally managed by the C library or runtime.

Considerations: SIGEV_THREAD can simplify asynchronous notification by avoiding signal handling, but it can also lead to resource pressure if events occur rapidly, as each event may spawn a thread. Developers should ensure that the handler performs only lightweight work or delegates heavier tasks to other threads or work queues. As with all POSIX real-time features, exact behavior may vary between systems; consult the platform’s documentation for specifics.