sahandler

Sahandler refers to the signal handler designated by the sa_handler member of the POSIX sigaction structure. It is the function that the operating system will call in response to a specified signal when the action is installed as a handler rather than ignored or used with a default action. The handler function typically has the prototype void handler(int signum).

When a signal is delivered and sa_handler is in use, the kernel invokes the function pointed to by sa_handler with the signal number as its sole argument. If the SA_SIGINFO flag is set, a different member, sa_sigaction, is used, and the handler can receive additional information about the signal via a three-argument function. The sa_mask member specifies a set of signals that should be blocked during execution of the handler, and sa_flags controls behavior such as whether system calls are automatically restarted after the handler returns (SA_RESTART), whether the handler is automatically blocked during its execution (SA_NODEFER), and other options.

Usage typically involves defining a handler function, initializing a sigaction structure, assigning sa_handler, initializing sa_mask with sigemptyset(&act.sa_mask), setting appropriate sa_flags, and calling sigaction for the desired signal. Example:

void sahandler(int sig) { /* handle signal */ }

struct sigaction act;

act.sa_handler = sahandler;

sigemptyset(&act.sa_mask);

act.sa_flags = 0;

sigaction(SIGINT, &act, NULL);

Sahandler is preferred in modern Unix-like systems over the older signal() interface because sigaction provides more precise control over masking, information delivery, and restart behavior. It is a core concept in interrupt-driven and asynchronous programming in C on POSIX platforms.