Advanced Programming in the UNIX Environment: Second Edition [Electronic resources] نسخه متنی

10.13. sigpending Function

The sigpending function returns the set of signals that are blocked from delivery and currently pending for the calling process. The set of signals is returned through the

set argument.

Example

Section 10.18.

If we generate the quit signal during this sleep period, the signal is now pending and unblocked, so it is delivered before sigprocmask returns. We'll see this occur because the printf in the signal handler is output before the printf that follows the call to sigprocmask.

The process then goes to sleep for another 5 seconds. If we generate the quit signal during this sleep period, the signal should terminate the process, since we reset the handling of the signal to its default when we caught it. In the following output, the terminal prints ^\ when we input Control-backslash, the terminal quit character:

$

./a.out

^\

generate signal once (before 5 seconds are up)
SIGQUIT pending

after return from sleep
caught SIGQUIT

in signal handler
SIGQUIT unblocked

after return from sigprocmask

^\ Quit(coredump)

generate signal again
$

./a.out

^\^\^\^\^\^\^\^\^\^\

generate signal 10 times (before 5 seconds are up)
SIGQUIT pending
caught SIGQUIT

signal is generated only once
SIGQUIT unblocked

^\ Quit(coredump)

generate signal again

The message Quit(coredump) is printed by the shell when it sees that its child terminated abnormally. Note that when we run the program the second time, we generate the quit signal ten times while the process is asleep, yet the signal is delivered only once to the process when it's unblocked. This demonstrates that signals are not queued on this system.

Figure 10.15. Example of signal sets and sigprocmask