diff options
Diffstat (limited to 'ev.pod')
| -rw-r--r-- | ev.pod | 30 |
1 files changed, 19 insertions, 11 deletions
@@ -372,13 +372,16 @@ I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and testing, this flag can be useful to conserve inotify file descriptors, as otherwise each loop using C<ev_stat> watchers consumes one inotify handle. -=item C<EVFLAG_NOSIGFD> +=item C<EVFLAG_SIGNALFD> -When this flag is specified, then libev will not attempt to use the -I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This is -probably only useful to work around any bugs in libev. Consequently, this -flag might go away once the signalfd functionality is considered stable, -so it's useful mostly in environment variables and not in program code. +When this flag is specified, then libev will attempt to use the +I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API +delivers signals synchronously, which makes is both faster and might make +it possible to get the queued signal data. + +Signalfd will not be used by default as this changes your signal mask, and +there are a lot of shoddy libraries and programs (glib's threadpool for +example) that can't properly initialise their signal masks. =item C<EVBACKEND_SELECT> (value 1, portable select backend) @@ -2134,7 +2137,7 @@ not be unduly interrupted. If you have a problem with system calls getting interrupted by signals you can block all signals in an C<ev_check> watcher and unblock them in an C<ev_prepare> watcher. -=head3 The special problem of inheritance over execve +=head3 The special problem of inheritance over fork/execve/pthread_create Both the signal mask (C<sigprocmask>) and the signal disposition (C<sigaction>) are unspecified after starting a signal watcher (and after @@ -2154,10 +2157,15 @@ The simplest way to ensure that the signal mask is reset in the child is to install a fork handler with C<pthread_atfork> that resets it. That will catch fork calls done by libraries (such as the libc) as well. -In current versions of libev, you can also ensure that the signal mask is -not blocking any signals (except temporarily, so thread users watch out) -by specifying the C<EVFLAG_NOSIGFD> when creating the event loop. This -is not guaranteed for future versions, however. +In current versions of libev, the signal will not be blocked indefinitely +unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces +the window of opportunity for problems, it will not go away, as libev +I<has> to modify the signal mask, at least temporarily. + +So I can't stress this enough I<if you do not reset your signal mask +when you expect it to be empty, you have a race condition in your +program>. This is not a libev-specific thing, this is true for most event +libraries. =head3 Watcher-Specific Functions and Data Members |