Signals Management

method	description
sigemptyset()	initializes an empty signal set with all signals excluded from the set.
sigfillset()	initializes a full signal set including all signals.
sigaddset()	adds a signal to a set.
sigdelset()	removes a signal from a set.
sigprocmask()	retrieves and/or changes the signal mask of the calling thread.
sigaction()	changes the action of a signal.
sigwait()	waits for a signal.
strsignal()	returns a string describing the signal.

#include <signal.h>

int sigemptyset (sigget_t *set);
int sigaddset (sigset_t *set, int signo);
int sigprocmask (int how, cont sigset_t *set, sigset_t *oldset);

int sigaction (int signo, const struct sigaction *act, struct sigaction *oldact);

struct sigaction {
  void (*sa_handler)(int);
  void (*sa_sigaction)(int, siginfo_t *, void *);
  sigset_t sa_mark;
  int sa_flags;
  void (*sa_restorer)(void);
};

sigemptyset() initializes the signal set specified by set by marking it empty (all signals are excluded from the set).

sigaddset() adds a signal to the signal set specified by set, while sigdelset() removes the signal from the signal set specified by set. Both return 0 on success, or -1 on error, in which case the error is set to error code EINVAL, which means the signal is an invalid signal identifier.

The behavior of sigprocmask() depends on the value of one of the following:

Field	Description
SIG_SETMASK	Sets the signal mask of the calling process.
SIG_BLOCK	Signals are added to the signal mask of the calling process.
SIG_UNBLOCK	Signals are removed from the signal mask of the calling process.

The sigaction structure:

Field	Description
SA_HANDLER	Address of the handler SIG_IGN or SIG_DFL
SA_MASK	Signals to block
SA_FLAGS	Additional flags, such as SA_RESETHAND
SA_RESETHAND	Allows "one-shot" mode. The behavior of the given signal returns to default after the signal handler returns.

Calling sigaction() changes the behavior of the signal identified by signo, which can be any value except those associated with SIGKILL and SIGSTOP. If act is not NULL, the system call changes the current signal behavior as specified in act. If oldact is not NULL, the system call saves the previous behavior of the given signal (or the current one if act is NULL).