HP-UX Reference (11i v1 00/12) - 2 System Calls (vol 5)
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STANDARD Printed by: Nora Chuang [nchuang] STANDARD
/build/1111/BRICK/man2/!!!intro.2
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s
signal(2) signal(2)
sig can be any one of the signals described under signal(5) except SIGKILL or SIGSTOP.
func is assigned one of four values: SIG_DFL, SIG_IGN, SIG_HOLD, or a function address. The
actions prescribed by SIG_DFL and SIG_IGN are described under signal(5). The action
prescribed by SIG_HOLD and function address are described below:
SIG_HOLD Hold signal. The signal sig is held upon receipt. Any pending sig-
nal of this signal type remains held. Only one signal of each type
is held. Note: the signals SIGKILL, SIGCONT, and SIGSTOP
cannot be held.
function address Catch signal. func must be a pointer to a function, the signal-
catching handler, that is called when signal sig occurs. sig-
set()
specifies that the process calls this function upon receipt
of signal sig. Any pending signal of this type is released. This
handler address is retained across calls to the other signal
management functions listed here. Upon receipt of signal sig,
the receiving process executes the signal-catching function
pointed to by func as described under signal(5) with the follow-
ing differences:
Before calling the signal-catching handler, the system signal
action of sig is set to SIG_HOLD. During a normal return from
the signal-catching handler, the system signal action is restored
to func and any held signal of this type is released. If a non-local
goto (longjmp(3C)) is taken, sigrelse() must be called to
restore the system signal action to func and release any held sig-
nal of this type.
sighold() holds the signal sig. sigrelse() restores the system signal action of sig to that specified
previously by
sigset(). sighold() and sigrelse() are used to establish critical regions of code.
sighold() is analogous to raising the priority level and deferring or holding a signal until the priority is
lowered by sigrelse() .
sigignore() sets the action for signal sig to SIG_IGN (see signal(5)).
sigpause() suspends the calling process until it receives an unblocked signal. If the signal sig is held, it
is released before the process pauses.
sigpause() is useful for testing variables that are changed when
a signal occurs. For example, sighold() should be used to block the signal first, then test the variables.
If they have not changed, call sigpause() to wait for the signal.
These functions can be linked into a program by giving the -lV3 option to the ld
command (see ld(1)).
ERRORS
sigset() fails and the system signal action for sig is not changed if any of the following occur:
[EFAULT] The func argument points to memory that is not a valid part of the process
address space. Reliable detection of this error is implementation-dependent.
sigset(), sighold(), sigrelse() , sigignore() , and sigpause() fail and the system signal
action for sig is not changed if any of the following occur:
[EINVAL] An attempt is made to ignore, hold, or supply a handler for a signal that
cannot be ignored, held, or caught; see signal(5).
sigpause returns when the following occurs:
[EINTR] A signal was caught.
EXAMPLES
The following call to signal() sets up a signal-catching function for the SIGINT signal:
void myhandler();
(void) signal(SIGINT, myhandler);
WARNINGS
signal() should not be used in conjunction with the facilities described under bsdproc(3C), sigaction(2),
sigset(3C), or sigvector(2).
HP-UX Release 11i: December 2000 − 2 − Section 2−−351
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