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

Comparing libev/ev.pod (file contents):
Revision 1.255 by root, Tue Jul 14 19:11:31 2009 UTC vs.
Revision 1.265 by root, Wed Aug 26 17:11:42 2009 UTC

 =head2 FEATURES
 Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
 BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
 for file descriptor events (C<ev_io>), the Linux C<inotify> interface
-(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
+(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
-with customised rescheduling (C<ev_periodic>), synchronous signals
+inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
-(C<ev_signal>), process status change events (C<ev_child>), and event
+timers (C<ev_timer>), absolute timers with customised rescheduling
-watchers dealing with the event loop mechanism itself (C<ev_idle>,
+(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
-C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
+change events (C<ev_child>), and event watchers dealing with the event
-file watchers (C<ev_stat>) and even limited support for fork events
+loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
-(C<ev_fork>).
+C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
+limited support for fork events (C<ev_fork>).
 It also is quite fast (see this
 L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
 for example).
 forget about forgetting to tell libev about forking) when you use this
 flag.
 This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
 environment variable.
+=item C<EVFLAG_NOINOTIFY>
+When this flag is specified, then libev will not attempt to use the
+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_NOSIGNALFD>
+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.
 =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,
 It is definitely not recommended to use this flag.
 =back
-If one or more of these are or'ed into the flags value, then only these
+If one or more of the backend flags are or'ed into the flags value,
-backends will be tried (in the reverse order as listed here). If none are
+then only these backends will be tried (in the reverse order as listed
-specified, all backends in C<ev_recommended_backends ()> will be tried.
+here). If none are specified, all backends in C<ev_recommended_backends
+()> will be tried.
 Example: This is the most typical usage.
    if (!ev_default_loop (0))
      fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
 This call will simply invoke all pending watchers while resetting their
 pending state. Normally, C<ev_loop> does this automatically when required,
 but when overriding the invoke callback this call comes handy.
+=item int ev_pending_count (loop)
+Returns the number of pending watchers - zero indicates that no watchers
+are pending.
 =item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
 This overrides the invoke pending functionality of the loop: Instead of
 invoking all pending watchers when there are any, C<ev_loop> will call
 this callback instead. This is useful, for example, when you want to
 If the event loop is suspended for a long time, you can also force an
 update of the time returned by C<ev_now ()> by calling C<ev_now_update
 ()>.
+=head3 The special problems of suspended animation
+When you leave the server world it is quite customary to hit machines that
+can suspend/hibernate - what happens to the clocks during such a suspend?
+Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
+all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
+to run until the system is suspended, but they will not advance while the
+system is suspended. That means, on resume, it will be as if the program
+was frozen for a few seconds, but the suspend time will not be counted
+towards C<ev_timer> when a monotonic clock source is used. The real time
+clock advanced as expected, but if it is used as sole clocksource, then a
+long suspend would be detected as a time jump by libev, and timers would
+be adjusted accordingly.
+I would not be surprised to see different behaviour in different between
+operating systems, OS versions or even different hardware.
+The other form of suspend (job control, or sending a SIGSTOP) will see a
+time jump in the monotonic clocks and the realtime clock. If the program
+is suspended for a very long time, and monotonic clock sources are in use,
+then you can expect C<ev_timer>s to expire as the full suspension time
+will be counted towards the timers. When no monotonic clock source is in
+use, then libev will again assume a timejump and adjust accordingly.
+It might be beneficial for this latter case to call C<ev_suspend>
+and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
+deterministic behaviour in this case (you can do nothing against
+C<SIGSTOP>).
 =head3 Watcher-Specific Functions and Data Members
 =over 4
 =item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
 If the timer is repeating, either start it if necessary (with the
 C<repeat> value), or reset the running timer to the C<repeat> value.
 This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
 usage example.
+=item ev_timer_remaining (loop, ev_timer *)
+Returns the remaining time until a timer fires. If the timer is active,
+then this time is relative to the current event loop time, otherwise it's
+the timeout value currently configured.
+That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
+C<5>. When the timer is started and one second passes, C<ev_timer_remain>
+will return C<4>. When the timer expires and is restarted, it will return
+roughly C<7> (likely slightly less as callback invocation takes some time,
+too), and so on.
 =item ev_tstamp repeat [read-write]
 The current C<repeat> value. Will be used each time the watcher times out
 or C<ev_timer_again> is called, and determines the next timeout (if any),
 Signal watchers will trigger an event when the process receives a specific
 signal one or more times. Even though signals are very asynchronous, libev
 will try it's best to deliver signals synchronously, i.e. as part of the
 normal event processing, like any other event.
-If you want signals asynchronously, just use C<sigaction> as you would
+If you want signals to be delivered truly asynchronously, just use
-do without libev and forget about sharing the signal. You can even use
+C<sigaction> as you would do without libev and forget about sharing
-C<ev_async> from a signal handler to synchronously wake up an event loop.
+the signal. You can even use C<ev_async> from a signal handler to
+synchronously wake up an event loop.
-You can configure as many watchers as you like per signal. Only when the
+You can configure as many watchers as you like for the same signal, but
+only within the same loop, i.e. you can watch for C<SIGINT> in your
+default loop and for C<SIGIO> in another loop, but you cannot watch for
+C<SIGINT> in both the default loop and another loop at the same time. At
+the moment, C<SIGCHLD> is permanently tied to the default loop.
-first watcher gets started will libev actually register a signal handler
+When the first watcher gets started will libev actually register something
 with the kernel (thus it coexists with your own signal handlers as long as
-you don't register any with libev for the same signal). Similarly, when
+you don't register any with libev for the same signal).
-the last signal watcher for a signal is stopped, libev will reset the
-signal handler to SIG_DFL (regardless of what it was set to before).
 If possible and supported, libev will install its handlers with
-C<SA_RESTART> behaviour enabled, so system calls should not be unduly
+C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
-interrupted. If you have a problem with system calls getting interrupted by
+not be unduly interrupted. If you have a problem with system calls getting
-signals you can block all signals in an C<ev_check> watcher and unblock
+interrupted by signals you can block all signals in an C<ev_check> watcher
-them in an C<ev_prepare> watcher.
+and unblock them in an C<ev_prepare> watcher.
+=head3 The special problem of inheritance over execve
+Both the signal mask (C<sigprocmask>) and the signal disposition
+(C<sigaction>) are unspecified after starting a signal watcher (and after
+stopping it again), that is, libev might or might not block the signal,
+and might or might not set or restore the installed signal handler.
+While this does not matter for the signal disposition (libev never
+sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
+C<execve>), this matters for the signal mask: many programs do not expect
+many signals to be blocked.
+This means that before calling C<exec> (from the child) you should reset
+the signal mask to whatever "default" you expect (all clear is a good
+choice usually).
 =head3 Watcher-Specific Functions and Data Members
 =over 4
 libev)
 =head3 Process Interaction
 Libev grabs C<SIGCHLD> as soon as the default event loop is
-initialised. This is necessary to guarantee proper behaviour even if
+initialised. This is necessary to guarantee proper behaviour even if the
-the first child watcher is started after the child exits. The occurrence
+first child watcher is started after the child exits. The occurrence
 of C<SIGCHLD> is recorded asynchronously, but child reaping is done
 synchronously as part of the event loop processing. Libev always reaps all
 children, even ones not watched.
 =head3 Overriding the Built-In Processing
 =head3 Stopping the Child Watcher
 Currently, the child watcher never gets stopped, even when the
 child terminates, so normally one needs to stop the watcher in the
 callback. Future versions of libev might stop the watcher automatically
-when a child exit is detected.
+when a child exit is detected (calling C<ev_child_stop> twice is not a
+problem).
 =head3 Watcher-Specific Functions and Data Members
 =over 4
 =item Ocaml
 Erkki Seppala has written Ocaml bindings for libev, to be found at
 L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
+=item Lua
+Brian Maher has written a partial interface to libev
+for lua (only C<ev_io> and C<ev_timer>), to be found at
+L<http://github.com/brimworks/lua-ev>.
 =back
 =head1 MACRO MAGIC
 keeps libev from including F<config.h>, and it also defines dummy
 implementations for some libevent functions (such as logging, which is not
 supported). It will also not define any of the structs usually found in
 F<event.h> that are not directly supported by the libev core alone.
-In stanbdalone mode, libev will still try to automatically deduce the
+In standalone mode, libev will still try to automatically deduce the
 configuration, but has to be more conservative.
 =item EV_USE_MONOTONIC
 If defined to be C<1>, libev will try to detect the availability of the
 be used is the winsock select). This means that it will call
 C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
 it is assumed that all these functions actually work on fds, even
 on win32. Should not be defined on non-win32 platforms.
-=item EV_FD_TO_WIN32_HANDLE
+=item EV_FD_TO_WIN32_HANDLE(fd)
 If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
 file descriptors to socket handles. When not defining this symbol (the
 default), then libev will call C<_get_osfhandle>, which is usually
 correct. In some cases, programs use their own file descriptor management,
 in which case they can provide this function to map fds to socket handles.
+=item EV_WIN32_HANDLE_TO_FD(handle)
+If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
+using the standard C<_open_osfhandle> function. For programs implementing
+their own fd to handle mapping, overwriting this function makes it easier
+to do so. This can be done by defining this macro to an appropriate value.
+=item EV_WIN32_CLOSE_FD(fd)
+If programs implement their own fd to handle mapping on win32, then this
+macro can be used to override the C<close> function, useful to unregister
+file descriptors again. Note that the replacement function has to close
+the underlying OS handle.
 =item EV_USE_POLL
 If defined to be C<1>, libev will compile in support for the C<poll>(2)
 backend. Otherwise it will be enabled on non-win32 platforms. It
 Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
 provide a bare-bones event library. See C<ev.h> for details on what parts
 of the API are still available, and do not complain if this subset changes
 over time.
+=item EV_NSIG
+The highest supported signal number, +1 (or, the number of
+signals): Normally, libev tries to deduce the maximum number of signals
+automatically, but sometimes this fails, in which case it can be
+specified. Also, using a lower number than detected (C<32> should be
+good for about any system in existance) can save some memory, as libev
+statically allocates some 12-24 bytes per signal number.
 =item EV_PID_HASHSIZE
 C<ev_child> watchers use a small hash table to distribute workload by
 pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
 than enough. If you need to manage thousands of children you might want to
    }
 Instead of invoking all pending watchers, the C<l_invoke> callback will
 signal the main thread via some unspecified mechanism (signals? pipe
 writes? C<Async::Interrupt>?) and then waits until all pending watchers
-have been called:
+have been called (in a while loop because a) spurious wakeups are possible
+and b) skipping inter-thread-communication when there are no pending
+watchers is very beneficial):
    static void
    l_invoke (EV_P)
    {
      userdata *u = ev_userdata (EV_A);
+     while (ev_pending_count (EV_A))
+       {
-     wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
+         wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
-     pthread_cond_wait (&u->invoke_cv, &u->lock);
+         pthread_cond_wait (&u->invoke_cv, &u->lock);
+       }
    }
 Now, whenever the main thread gets told to invoke pending watchers, it
 will grab the lock, call C<ev_invoke_pending> and then signal the loop
 thread to continue:

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Comparing libev/ev.pod (file contents): Revision 1.255 by root, Tue Jul 14 19:11:31 2009 UTC vs. Revision 1.265 by root, Wed Aug 26 17:11:42 2009 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.255 by root, Tue Jul 14 19:11:31 2009 UTC vs.
Revision 1.265 by root, Wed Aug 26 17:11:42 2009 UTC