signalfd may behave differently to sigaction/signal, so to avoid
breaking libevent users (like [1], [2]) disable it by default.
[1]: https://github.com/tmux/tmux/pull/3621
[2]: https://github.com/tmux/tmux/pull/3626
Also signalfd is not that perfect:
- you need to SIG_BLOCK the signal before
- blocked signals are not reset on exec
- blocked signals are allowed to coalesce - so in case of multiple
signals sent you may get the signal only once (ok for most of the
signals, but may be a problem for SIGCHLD, though you may call
waitpid() in a loop or use pidfd)
- and also one implementation problem -
sigprocmask is unspecified in a multithreaded process
Refs:
- https://lwn.net/Articles/415684/
- https://ldpreload.com/blog/signalfd-is-useless
Refs: https://github.com/libevent/libevent/issues/1460
Refs: #1342 (cc @dmantipov)
Linux-specific signal handling backend based on signalfd(2)
system call, and public function event_base_get_signal_method()
to obtain an underlying kernel signal handling mechanism.
Signed-off-by: Dmitry Antipov <dantipov@cloudlinux.com>
