The pthread_sigmask() function shall examine or change (or both) the
calling thread's signal mask, regardless of the number of threads in the
process. The function shall be equivalent to sigprocmask(), without the
restriction that the call be made in a single-threaded process.
In a single-threaded process, the sigprocmask() function shall examine or
change (or both) the signal mask of the calling thread.
If the argument set is not a null pointer, it points to a set of signals
to be used to change the currently blocked set.
The argument how indicates the way in which the set is changed, and the
application shall ensure it consists of one of the following values:
The resulting set shall be the union of the current set and
the signal set pointed to by set.
The resulting set shall be the signal set pointed to by
The resulting set shall be the intersection of the current
set and the complement of the signal set pointed to by set.
If the argument oset is not a null pointer, the previous mask shall be
stored in the location pointed to by oset. If set is a null
pointer, the value of the argument how is not significant and the
process' signal mask shall be unchanged; thus the call can be used to enquire
about currently blocked signals.
If there are any pending unblocked signals after the call to
sigprocmask(), at least one of those signals shall be delivered before
the call to sigprocmask() returns.
It is not possible to block those signals which cannot be ignored. This shall be
enforced by the system without causing an error to be indicated.
If any of the SIGFPE, SIGILL, SIGSEGV, or SIGBUS signals are generated while
they are blocked, the result is undefined, unless the signal was generated by
the kill() function, the sigqueue() function, or the
If sigprocmask() fails, the thread's signal mask shall not be changed.
The use of the sigprocmask() function is unspecified in a multi-threaded
Upon successful completion pthread_sigmask() shall return 0; otherwise,
it shall return the corresponding error number.
Upon successful completion, sigprocmask() shall return 0; otherwise, -1
shall be returned, errno shall be set to indicate the error, and the
process' signal mask shall be unchanged.
When a process' signal mask is changed in a signal-catching function that is
installed by sigaction(), the restoration of the signal mask on return
from the signal-catching function overrides that change (see
sigaction()). If the signal-catching function was installed with
signal(), it is unspecified whether this occurs.
See kill() for a discussion of the requirement on delivery of signals.
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html