sigprocmask(2)sigprocmask(2)NAME
sigprocmask, sigsetmask - Set the current signal mask
SYNOPSIS
#include <signal.h>
int sigprocmask(
int how,
const sigset_t *set,
sigset_t *o_set );
The following function declaration does not conform to current stan‐
dards and is supported only for backward compatibility: int sigsetmask(
int signal_mask );
STANDARDS
Interfaces documented on this reference page conform to industry stan‐
dards as follows:
sigprocmask(): XSH4.0, XSH4.2, XSH5.0
Refer to the standards(5) reference page for more information about
industry standards and associated tags.
PARAMETERS
Indicates the manner in which the set of masked signals is changed; it
has one of the following values: The resulting set is the union of the
current set and the signal set pointed to by the set parameter. The
resulting set is the intersection of the current set and the complement
of the signal set pointed to by the set parameter. The resulting set
is the signal set pointed to by the set parameter. Specifies the sig‐
nal set. If the value of the set parameter is not null, it points to a
set of signals to be used to change the currently blocked set. If the
value of the set parameter is null, the value of the how parameter is
not significant and the process signal mask is unchanged; thus, the
call can be used to inquire about currently blocked signals. If the
o_set parameter is not the null value, the signal mask in effect at the
time of the call is stored in the space pointed to by the o_set parame‐
ter. Specifies the new signal mask for the process.
DESCRIPTION
The sigprocmask() function is used to examine or change the signal mask
of the calling process.
Typically, you would use the sigprocmask (SIG_BLOCK) call to block sig‐
nals during a critical section of code, and then use the sigprocmask
(SIG_SETMASK) call to restore the mask to the previous value returned
by the sigprocmask (SIG_BLOCK) call.
If there are any unblocked signals pending after the call to the sig‐
procmask() function, at least one of those signals will be delivered
before the sigprocmask() function returns.
The sigprocmask() function does not allow the SIGKILL or SIGSTOP sig‐
nals to be blocked. If a program attempts to block one of these sig‐
nals, the sigprocmask() function gives no indication of the error.
The sigsetmask() function allows the process signal mask to change for
signal values 1 to 31. This same function can be accomplished for all
values with the sigprocmask(SIG_SETMASK) call. The signal of value i
will be blocked if the i-th bit of the signal_mask parameter is set.
RETURN VALUES
Upon successful completion, the sigprocmask() function returns a value
of 0 (zero). If the sigprocmask() function fails, the signal mask of
the process is unchanged, a value of -1 is returned, and errno is set
to indicate the error.
Upon successful completion, the sigsetmask() function returns the value
of the previous signal mask. If the function fails, a value of -1 is
returned.
ERRORS
The sigprocmask() function sets errno to the specified value for the
following conditions: The value of the how parameter is not equal to
one of the defined values. [Tru64 UNIX] The set or o_set parameter
points to a location outside the allocated address space of the
process.
EXAMPLES
The following example sets the signal mask to block only the SIGINT
signal from delivery:
#include <signal.h> int return_value; sigset_t newset;
... sigemptyset(&newset); sigaddset(&newset, SIGINT); return_value =
sigprocmask (SIG_SETMASK, &newset, NULL);
SEE ALSO
Functions: kill(2), sigaction(2), sigsuspend(2), sigvec(2), sigpause(3)
Standards: standards(5)sigprocmask(2)