SIGRTMINSIGRTMAX

SIGRTMIN and SIGRTMAX are macros defined in the POSIX signal interface, typically declared in <signal.h>, that specify the inclusive range of real-time signals on a given system. Real-time signals are a distinct class from the standard signals (such as SIGINT or SIGTERM) and are intended for reliable, asynchronous inter-process communication and timer notifications.

The exact numeric values of SIGRTMIN and SIGRTMAX are implementation-defined and can vary between operating systems and architectures. On many Linux systems, SIGRTMIN is 34 and SIGRTMAX is 64, but the important property is their role as bounds rather than their absolute numbers. The number of real-time signals available is SIGRTMAX - SIGRTMIN + 1. Programs should not assume fixed values and may instead use these constants to determine the valid range at runtime if needed.

Real-time signals have some advantages over standard signals. They are queued, meaning multiple signals in the realtime range can be delivered without loss when the receiver is capable of handling them. They can also carry additional data with each signal through mechanisms such as sigqueue and the siginfo_t structure when using a signal action established with SA_SIGINFO.

Usage typically involves selecting a specific signal within the range (for example, SIGRTMIN + n) to represent a particular event or notification. Real-time signals are commonly used for asynchronous notifications from timers, inter-process communications, and other low-latency signaling scenarios, where the ability to queue signals and attach data is beneficial.