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