In computing, sigaction is a function API defined by POSIX

POSIX

POSIX , an acronym for "Portable Operating System Interface", is a family of standards specified by the IEEE for maintaining compatibility between operating systems...

 to give the programmer access to what should be a program's behavior when receiving specific OS signals

Signal (computing)

A signal is a limited form of inter-process communication used in Unix, Unix-like, and other POSIX-compliant operating systems. Essentially it is an asynchronous notification sent to a process in order to notify it of an event that occurred. When a signal is sent to a process, the operating system...

.

General

In Unix-like

Unix-like

A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification....

 operating systems, one means of inter-process communication

Inter-process communication

In computing, Inter-process communication is a set of methods for the exchange of data among multiple threads in one or more processes. Processes may be running on one or more computers connected by a network. IPC methods are divided into methods for message passing, synchronization, shared...

 is through signals. When an executing unit (process

Process (computing)

In computing, a process is an instance of a computer program that is being executed. It contains the program code and its current activity. Depending on the operating system , a process may be made up of multiple threads of execution that execute instructions concurrently.A computer program is a...

 or thread

Thread (computer science)

In computer science, a thread of execution is the smallest unit of processing that can be scheduled by an operating system. The implementation of threads and processes differs from one operating system to another, but in most cases, a thread is contained inside a process...

) receives a signal from the OS, it should react in some way defined by the datasheet and the conventional meaning of this signal (ie. by dumping its data, stopping execution, synchronizing something...).

The sigaction system call is used to declare the behavior of the program should it receive one particular non-system-reserved signal. This is done by giving along with the system call a structure containing, among others, a function pointer to the signal handling routine. Some predefined signals (such as SIGKILL) have locked behavior that is handled by the system and cannot be overridden by such system calls.

Replacement of deprecated signal

The sigaction function provides an interface for reliable signals in replacement of the unreliable and deprecated signal function. Signal handlers installed by the signal interface will be uninstalled immediately prior to execution of the handler. Permanent handlers must therefore be reinstalled by a call to signal during the handler's execution, causing unreliability in the event a signal of the same type is received during the handler's execution but before the reinstall. Handlers installed by the sigaction interface can be installed permanently and a custom set of signals can be blocked during the execution of the handler. These signals will be unblocked immediately following the normal termination of the handler (but not in the event of an abnormal termination such as a C++ exception throw.)

Use in C++

In C++, the try {/* ... */} catch {/* ... */} programming structure may be (depending on host platforms) based on signalling. To catch signals translated into C++ exceptions, special compiler switches may be necessary on some platforms such as -fnon-call-exceptions for GCC

GNU Compiler Collection

The GNU Compiler Collection is a compiler system produced by the GNU Project supporting various programming languages. GCC is a key component of the GNU toolchain...

and the Intel C Compiler.