sigprocmask, rt_sigprocmask - examine and change blocked signals
#include <signal.h>
/* Prototype for the glibc wrapper function */
int sigprocmask(int how, const sigset_t *set, sigset_t *oldset);
/* Prototype for the underlying system call */
int rt_sigprocmask(int how, const kernel_sigset_t *set,
kernel_sigset_t *oldset, size_t sigsetsize);
/* Prototype for the legacy system call (deprecated) */
int sigprocmask(int how, const old_kernel_sigset_t *set,
old_kernel_sigset_t *oldset);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
sigprocmask(): _POSIX_C_SOURCE
sigprocmask() is used to fetch and/or change the signal mask of the
calling thread. The signal mask is the set of signals whose delivery is
currently blocked for the caller (see also
signal(7) for more details).
The behavior of the call is dependent on the value of
how, as follows.
- SIG_BLOCK
- The set of blocked signals is the union of the current set and the
set argument.
- SIG_UNBLOCK
- The signals in set are removed from the current set of blocked
signals. It is permissible to attempt to unblock a signal which is not
blocked.
- SIG_SETMASK
- The set of blocked signals is set to the argument set.
If
oldset is non-NULL, the previous value of the signal mask is stored in
oldset.
If
set is NULL, then the signal mask is unchanged (i.e.,
how is
ignored), but the current value of the signal mask is nevertheless returned in
oldset (if it is not NULL).
A set of functions for modifying and inspecting variables of type
sigset_t ("signal sets") is described in
sigsetops(3).
The use of
sigprocmask() is unspecified in a multithreaded process; see
pthread_sigmask(3).
sigprocmask() returns 0 on success and -1 on error. In the event of an
error,
errno is set to indicate the cause.
- EFAULT
- The set or oldset argument points outside the process's
allocated address space.
- EINVAL
- Either the value specified in how was invalid or the kernel does
not support the size passed in sigsetsize.
POSIX.1-2001, POSIX.1-2008.
It is not possible to block
SIGKILL or
SIGSTOP. Attempts to do so
are silently ignored.
Each of the threads in a process has its own signal mask.
A child created via
fork(2) inherits a copy of its parent's signal mask;
the signal mask is preserved across
execve(2).
If
SIGBUS,
SIGFPE,
SIGILL, or
SIGSEGV are generated
while they are blocked, the result is undefined, unless the signal was
generated by
kill(2),
sigqueue(3), or
raise(3).
See
sigsetops(3) for details on manipulating signal sets.
Note that it is permissible (although not very useful) to specify both
set and
oldset as NULL.
The kernel's definition of
sigset_t differs in size from that used by the
C library. In this manual page, the former is referred to as
kernel_sigset_t (it is nevertheless named
sigset_t in the kernel
sources).
The glibc wrapper function for
sigprocmask() silently ignores attempts to
block the two real-time signals that are used internally by the NPTL threading
implementation. See
nptl(7) for details.
The original Linux system call was named
sigprocmask(). However, with the
addition of real-time signals in Linux 2.2, the fixed-size, 32-bit
sigset_t (referred to as
old_kernel_sigset_t in this manual
page) type supported by that system call was no longer fit for purpose.
Consequently, a new system call,
rt_sigprocmask(), was added to support
an enlarged
sigset_t type (referred to as
kernel_sigset_t in
this manual page). The new system call takes a fourth argument,
size_t
sigsetsize, which specifies the size in bytes of the signal sets in
set and
oldset. This argument is currently required to have a
fixed architecture specific value (equal to
sizeof(kernel_sigset_t)).
The glibc
sigprocmask() wrapper function hides these details from us,
transparently calling
rt_sigprocmask() when the kernel provides it.
kill(2),
pause(2),
sigaction(2),
signal(2),
sigpending(2),
sigsuspend(2),
pthread_sigmask(3),
sigqueue(3),
sigsetops(3),
signal(7)