#include <signal.h>
struct sigvec {
};
sigvec(sig, vec, ovec)
int sig;
struct sigvec *vec, *ovec;
All signals have the same priority. Signal routines execute with the signal that caused their invocation blocked, but other signals may yet occur. A global signal mask defines the set of signals currently blocked from delivery to a process. The signal mask for a process is initialized from that of its parent (normally 0). It may be changed with a sigblock(2) or sigsetmask(2) call, or when a signal is delivered to the process.
When a signal condition arises for a process, the signal is added to a set of signals pending for the process. If the signal is not currently blocked by the process then it is delivered to the process. When a signal is delivered, the current state of the process is saved, a new signal mask is calculated (as described below), and the signal handler is invoked. The call to the handler is arranged so that if the signal handling routine returns normally the process will resume execution in the context from before the signal's delivery. If the process wishes to resume in a different context, then it must arrange to restore the previous context itself.
When a signal is delivered to a process a new signal mask is installed for the duration of the process' signal handler (or until a sigblock or sigsetmask call is made). This mask is formed by taking the current signal mask, adding the signal to be delivered, and or'ing in the signal mask associated with the handler to be invoked.
Sigvec assigns a handler for a specific signal. If vec is non-zero, it specifies a handler routine and mask to be used when delivering the specified signal. Further, if the SV_ONSTACK bit is set in sv_flags, the system will deliver the signal to the process on a signal stack, specified with sigstack(2). If ovec is non-zero, the previous handling information for the signal is returned to the user.
The following is a list of all signals with names as in the include file <signal.h>:
SIGHUP 1 hangup SIGINT 2 interrupt SIGDEBUG 3* force process into debuggable state SIGILL 4* illegal instruction SIGTRAP 5* trace trap SIGIOT 6* IOT instruction SIGEMT 7* EMT instruction SIGFPE 8* floating point exception SIGKILL 9 kill (cannot be caught, blocked, or ignored) SIGMIG 10 migrate process (cannot be caught, blocked, or ignored) SIGSEGV 11* segmentation violation SIGSYS 12* bad argument to system call SIGPIPE 13 write on a pipe with no one to read it SIGALRM 14 alarm clock SIGTERM 15 software termination signal SIGURG 16@ urgent condition present on socket SIGSTOP 17|+'stop (cannot be caught, blocked, or ignored) SIGTSTP 18|+'stop signal generated from keyboard SIGCONT 19@ continue after stop (cannot be blocked) SIGCHLD 20@ child status has changed SIGTTIN 21|+'background read attempted from control terminal SIGTTOU 22|+'background write attempted to control terminal SIGIO 23@ i/o is possible on a descriptor (see fcntl(2)) SIGXCPU 24 cpu time limit exceeded (see setrlimit(2)) SIGXFSZ 25 file size limit exceeded (see setrlimit(2)) SIGVTALRM 26 virtual time alarm (see setitimer(2)) SIGPROF 27 profiling timer alarm (see setitimer(2)) SIGWINCH 28@ window size change SIGMIGHOME 29 migrate back to home node (cannot be caught, blocked, or ignored) SIGUSR1 30 user defined signal 1 SIGUSR2 31 user defined signal 2
The starred signals in the list above cause the process to enter DEBUG state if not caught or ignored.
Once a signal handler is installed, it remains installed until another sigvec call is made, or an execve(2) is performed. The default action for a signal may be reinstated by setting sv_handler to SIG_DFL; this default is termination (with a core image for starred signals) except for signals marked with @ or |+'. Signals marked with @ are discarded if the action is SIG_DFL; signals marked with |+' cause the process to stop. If sv_handler is SIG_IGN the signal is subsequently ignored, and pending instances of the signal are discarded.
If a caught signal occurs during certain system calls, the call is normally restarted. The call can be forced to terminate prematurely with an EINTR error return by setting the SV_INTERRUPT bit in sv_flags. The affected system calls are read(2) or write(2) on a slow device (such as a terminal; but not a file) and during a wait(2).
After a fork(2) or vfork(2) the child inherits all signals, the signal mask, the signal stack, and the restart/interrupt flags.
Execve(2) resets all caught signals to default action and resets all signals to be caught on the user stack. Ignored signals remain ignored; the signal mask remains the same; signals that interrupt system calls continue to do so.
The SV_INTERRUPT flag is not available in 4.2BSD, hence it should not be used if backward compatibility is needed.