[ViewVC] Diff of: cvs/libev/ev.pod

Comparing libev/ev.pod (file contents):
Revision 1.347 by sf-exg, Wed Nov 10 19:50:09 2010 UTC vs.
Revision 1.351 by root, Mon Jan 10 14:24:26 2011 UTC

    }
    ...
    ev_set_syserr_cb (fatal_error);
+=item ev_feed_signal (int signum)
+This function can be used to "simulate" a signal receive. It is completely
+safe to call this function at any time, from any context, including signal
+handlers or random threads.
+Its main use is to customise signal handling in your process, especially
+in the presence of threads. For example, you could block signals
+by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
+creating any loops), and in one thread, use C<sigwait> or any other
+mechanism to wait for signals, then "deliver" them to libev by calling
+C<ev_feed_signal>.
 =back
 =head1 FUNCTIONS CONTROLLING EVENT LOOPS
 An event loop is described by a C<struct ev_loop *> (the C<struct> is
 threads that are not interested in handling them.
 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<EVFLAG_NOSIGMASK>
+When this flag is specified, then libev will avoid to modify the signal
+mask. Specifically, this means you ahve to make sure signals are unblocked
+when you want to receive them.
+This behaviour is useful when you want to do your own signal handling, or
+want to handle signals only in specific threads and want to avoid libev
+unblocking the signals.
+This flag's behaviour will become the default in future versions of libev.
 =item C<EVBACKEND_SELECT>  (value 1, portable select backend)
 This is your standard select(2) backend. Not I<completely> standard, as
 libev tries to roll its own fd_set with no limits on the number of fds,
 =item C<EVBACKEND_PORT>    (value 32, Solaris 10)
 This uses the Solaris 10 event port mechanism. As with everything on Solaris,
 it's really slow, but it still scales very well (O(active_fds)).
-Please note that Solaris event ports can deliver a lot of spurious
-notifications, so you need to use non-blocking I/O or other means to avoid
-blocking when no data (or space) is available.
 While this backend scales well, it requires one system call per active
 file descriptor per loop iteration. For small and medium numbers of file
 descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
 might perform better.
-On the positive side, with the exception of the spurious readiness
+On the positive side, this backend actually performed fully to
-notifications, this backend actually performed fully to specification
-in all tests and is fully embeddable, which is a rare feat among the
+specification in all tests and is fully embeddable, which is a rare feat
-OS-specific backends (I vastly prefer correctness over speed hacks).
+among the OS-specific backends (I vastly prefer correctness over speed
+hacks).
+On the negative side, the interface is I<bizarre>, with the event polling
+function sometimes returning events to the caller even though an error
+occured, but with no indication whether it has done so or not (yes, it's
+even documented that way) - deadly for edge-triggered interfaces, but
+fortunately libev seems to be able to work around it.
 This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
 C<EVBACKEND_POLL>.
 =item C<EVBACKEND_ALL>
 Try all backends (even potentially broken ones that wouldn't be tried
 with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
 C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
-It is definitely not recommended to use this flag.
+It is definitely not recommended to use this flag, use whatever
+C<ev_recommended_backends ()> returns, or simply do not specify a backend
+at all.
+=item C<EVBACKEND_MASK>
+Not a backend at all, but a mask to select all backend bits from a
+C<flags> value, in case you want to mask out any backends from a flags
+value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
 =back
 If one or more of the backend flags are or'ed into the flags value,
 then only these backends will be tried (in the reverse order as listed
 running when nothing else is active.
    ev_signal exitsig;
    ev_signal_init (&exitsig, sig_cb, SIGINT);
    ev_signal_start (loop, &exitsig);
-   evf_unref (loop);
+   ev_unref (loop);
 Example: For some weird reason, unregister the above signal handler again.
    ev_ref (loop);
    ev_signal_stop (loop, &exitsig);
 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 code>. This
 is not a libev-specific thing, this is true for most event libraries.
+=head3 The special problem of threads signal handling
+POSIX threads has problematic signal handling semantics, specifically,
+a lot of functionality (sigfd, sigwait etc.) only really works if all
+threads in a process block signals, which is hard to achieve.
+When you want to use sigwait (or mix libev signal handling with your own
+for the same signals), you can tackle this problem by globally blocking
+all signals before creating any threads (or creating them with a fully set
+sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
+loops. Then designate one thread as "signal receiver thread" which handles
+these signals. You can pass on any signals that libev might be interested
+in by calling C<ev_feed_signal>.
 =head3 Watcher-Specific Functions and Data Members
 =over 4
 it by calling C<ev_async_send>, which is thread- and signal safe.
 This functionality is very similar to C<ev_signal> watchers, as signals,
 too, are asynchronous in nature, and signals, too, will be compressed
 (i.e. the number of callback invocations may be less than the number of
-C<ev_async_sent> calls).
+C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
+of "global async watchers" by using a watcher on an otherwise unused
+signal, and C<ev_feed_signal> to signal this watcher from another thread,
+even without knowing which loop owns the signal.
 Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
 just the default loop.
 =head3 Queueing
 Feed an event on the given fd, as if a file descriptor backend detected
 the given events it.
 =item ev_feed_signal_event (loop, int signum)
-Feed an event as if the given signal occurred (C<loop> must be the default
+Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
-loop!).
+which is async-safe.
 =back
 =head1 COMMON OR USEFUL IDIOMS (OR BOTH)

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Comparing libev/ev.pod (file contents): Revision 1.347 by sf-exg, Wed Nov 10 19:50:09 2010 UTC vs. Revision 1.351 by root, Mon Jan 10 14:24:26 2011 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.347 by sf-exg, Wed Nov 10 19:50:09 2010 UTC vs.
Revision 1.351 by root, Mon Jan 10 14:24:26 2011 UTC