Signal (IPC)

Signals

Exception handling, if provided, is facilitated by specialized programming language constructs, hardware mechanisms like interrupts, or operating system (OS) inter-process communication (IPC) facilities like signals.

On Unix-like operating systems this involves sending a signal such as SIGSEGV, SIGBUS, SIGILL or SIGFPE, which may either call a signal handler or execute a default action (terminating the program).

In computing, is a command that is used in several popular operating systems to send signals to running processes.

The kernel program should provide a communication channel between executing processes. For a large software system, it may be desirable to engineer the system into smaller processes. Processes may communicate with one another by sending and receiving signals.

An alternative to polling is the use of interrupts, which are signals generated by devices or processes to indicate that they need attention, want to communicate, etc. Although polling can be very simple, in many situations (e.g., multitasking operating systems) it is more efficient to use interrupts because it can reduce processor usage and/or bandwidth consumption.

Signals are received in signal handlers, small, limited pieces of code that run while the rest of the task is suspended; if a signal is received and handled while the task is blocking in, select will return early with EINTR; if a signal is received while the task is CPU bound, the task will be suspended between instructions until the signal handler returns.

This sends the "interrupt" signal (SIGINT), which defaults to terminating the process, though it can be overridden.

The SIGCHLD signal is sent to the parent of a child process when it exits, is interrupted, or resumes after being interrupted.

In POSIX systems, the sequence causes the active program to receive SIGINT, the interruption signal.