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int sigprocmask(int how, const sigset_t *set, sigset_t *oldset);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
sigprocmask(): _POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _POSIX_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
The behavior of the call is dependent on the value of how, as follows.
The set of blocked signals is the union of the current set and
the set argument.
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.
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
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).
The use of sigprocmask() is unspecified in a multithreaded process; see
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 allo-
cated address space.
EINVAL The value specified in how was invalid.
kill(2), pause(2), sigaction(2), signal(2), sigpending(2), sigsus-
pend(2), pthread_sigmask(3), sigqueue(3), sigsetops(3), signal(7)
Linux 2013-04-19 SIGPROCMASK(2)