Signal (IPC)

In the realm of inter-process communication (IPC), a signal is a mechanism used to notify a process of an event. It’s a limited form of communication, primarily used for asynchronous notification rather than transferring large amounts of data. Signals can be triggered by various events, including hardware exceptions (like division by zero), software conditions (like the termination of a child process), or explicit requests from other processes.

When a signal is delivered to a process, the operating system interrupts the process's normal execution. The process then either executes a pre-defined signal handler (a function specifically designed to respond to that signal), performs a default action as determined by the operating system (which might be termination, ignoring the signal, or pausing the process), or simply ignores the signal altogether.

Signals provide a fundamental way for processes to react to system events and other asynchronous occurrences. The set of signals available, their default actions, and the mechanism for handling them are generally standardized by the operating system, although some operating systems may offer extensions or variations. Typical uses of signals include terminating a process cleanly, handling errors, or coordinating actions between processes.

Because signal handling is asynchronous and can interrupt normal program flow, it is crucial to design signal handlers carefully to avoid race conditions, deadlocks, and other concurrency issues. Signal handling can become complex, especially in multithreaded programs.