sigpending, rt_sigpending - examine pending signals
sigpending() returns the set of signals that are pending for delivery to the calling thread (i.e., the signals which have been raised while blocked). The mask of pending signals is returned in
sigpending() returns 0 on success and -1 on error. In the event of an error,
errno is set to indicate the cause.
set points to memory which is not a valid part of the process address space.
See sigsetops(3) for details on manipulating signal sets.
If a signal is both blocked and has a disposition of "ignored", it is
not added to the mask of pending signals when generated.
The set of signals that is pending for a thread is the union of the set of signals that is pending for that thread and the set of signals that is pending for the process as a whole; see signal(7).
A child created via fork(2) initially has an empty pending signal set; the pending signal set is preserved across an execve(2). The original Linux system call was named sigpending(). However, with the addition of real-time signals in Linux 2.2, the fixed-size, 32-bit
sigset_t argument supported by that system call was no longer fit for purpose. Consequently, a new system call, rt_sigpending(), was added to support an enlarged
sigset_t type. The new system call takes a second argument,
size_t sigsetsize, which specifies the size in bytes of the signal set in
set. The glibc sigpending() wrapper function hides these details from us, transparently calling rt_sigpending() when the kernel provides it. In versions of glibc up to and including 2.2.1, there is a bug in the wrapper function for sigpending() which means that information about pending real-time signals is not correctly returned.
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