Examine pending signals
int sigpending(sigset_t *set);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
sigpending(): _POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _POSIX_SOURCE
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 set.
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).
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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