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

Comparing libev/ev.pod (file contents):
Revision 1.40 by root, Sat Nov 24 10:15:16 2007 UTC vs.
Revision 1.46 by root, Mon Nov 26 10:20:43 2007 UTC

   ev_ref (myloop);
   ev_signal_stop (myloop, &exitsig);
 =back
 =head1 ANATOMY OF A WATCHER
 A watcher is a structure that you create and register to record your
 interest in some event. For instance, if you want to wait for STDIN to
 become readable, you would create an C<ev_io> watcher for that:
 with the error from read() or write(). This will not work in multithreaded
 programs, though, so beware.
 =back
-=head2 SUMMARY OF GENERIC WATCHER FUNCTIONS
+=head2 GENERIC WATCHER FUNCTIONS
 In the following description, C<TYPE> stands for the watcher type,
 e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
 =over 4
 which rolls both calls into one.
 You can reinitialise a watcher at any time as long as it has been stopped
 (or never started) and there are no pending events outstanding.
-The callbakc is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
+The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
 int revents)>.
 =item C<ev_TYPE_set> (ev_TYPE *, [args])
 This macro initialises the type-specific parts of a watcher. You need to
 This section describes each watcher in detail, but will not repeat
 information given in the last section.
-=head2 C<ev_io> - is this file descriptor readable or writable
+=head2 C<ev_io> - is this file descriptor readable or writable?
 I/O watchers check whether a file descriptor is readable or writable
-in each iteration of the event loop (This behaviour is called
+in each iteration of the event loop, or, more precisely, when reading
-level-triggering because you keep receiving events as long as the
+would not block the process and writing would at least be able to write
-condition persists. Remember you can stop the watcher if you don't want to
+some data. This behaviour is called level-triggering because you keep
-act on the event and neither want to receive future events).
+receiving events as long as the condition persists. Remember you can stop
+the watcher if you don't want to act on the event and neither want to
+receive future events.
 In general you can register as many read and/or write event watchers per
 fd as you want (as long as you don't confuse yourself). Setting all file
 descriptors to non-blocking mode is also usually a good idea (but not
 required if you know what you are doing).
 You have to be careful with dup'ed file descriptors, though. Some backends
 (the linux epoll backend is a notable example) cannot handle dup'ed file
 descriptors correctly if you register interest in two or more fds pointing
-to the same underlying file/socket etc. description (that is, they share
+to the same underlying file/socket/etc. description (that is, they share
 the same underlying "file open").
 If you must do this, then force the use of a known-to-be-good backend
 (at the time of this writing, this includes only C<EVBACKEND_SELECT> and
 C<EVBACKEND_POLL>).
+Another thing you have to watch out for is that it is quite easy to
+receive "spurious" readyness notifications, that is your callback might
+be called with C<EV_READ> but a subsequent C<read>(2) will actually block
+because there is no data. Not only are some backends known to create a
+lot of those (for example solaris ports), it is very easy to get into
+this situation even with a relatively standard program structure. Thus
+it is best to always use non-blocking I/O: An extra C<read>(2) returning
+C<EAGAIN> is far preferable to a program hanging until some data arrives.
+If you cannot run the fd in non-blocking mode (for example you should not
+play around with an Xlib connection), then you have to seperately re-test
+wether a file descriptor is really ready with a known-to-be good interface
+such as poll (fortunately in our Xlib example, Xlib already does this on
+its own, so its quite safe to use).
 =over 4
 =item ev_io_init (ev_io *, callback, int fd, int events)
 =item ev_io_set (ev_io *, int fd, int events)
-Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive
+Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
-events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |
+rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or
-EV_WRITE> to receive the given events.
+C<EV_READ | EV_WRITE> to receive the given events.
-Please note that most of the more scalable backend mechanisms (for example
-epoll and solaris ports) can result in spurious readyness notifications
-for file descriptors, so you practically need to use non-blocking I/O (and
-treat callback invocation as hint only), or retest separately with a safe
-interface before doing I/O (XLib can do this), or force the use of either
-C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>, which don't suffer from this
-problem. Also note that it is quite easy to have your callback invoked
-when the readyness condition is no longer valid even when employing
-typical ways of handling events, so its a good idea to use non-blocking
-I/O unconditionally.
 =back
 Example: call C<stdin_readable_cb> when STDIN_FILENO has become, well
 readable, but only once. Since it is likely line-buffered, you could
   ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
   ev_io_start (loop, &stdin_readable);
   ev_loop (loop, 0);
-=head2 C<ev_timer> - relative and optionally recurring timeouts
+=head2 C<ev_timer> - relative and optionally repeating timeouts
 Timer watchers are simple relative timers that generate an event after a
 given time, and optionally repeating in regular intervals after that.
 The timers are based on real time, that is, if you register an event that
   // and in some piece of code that gets executed on any "activity":
   // reset the timeout to start ticking again at 10 seconds
   ev_timer_again (&mytimer);
-=head2 C<ev_periodic> - to cron or not to cron
+=head2 C<ev_periodic> - to cron or not to cron?
 Periodic watchers are also timers of a kind, but they are very versatile
 (and unfortunately a bit complex).
 Unlike C<ev_timer>'s, they are not based on real time (or relative time)
   ev_periodic_init (&hourly_tick, clock_cb,
                     fmod (ev_now (loop), 3600.), 3600., 0);
   ev_periodic_start (loop, &hourly_tick);
-=head2 C<ev_signal> - signal me when a signal gets signalled
+=head2 C<ev_signal> - signal me when a signal gets signalled!
 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.
 of the C<SIGxxx> constants).
 =back
-=head2 C<ev_child> - wait for pid status changes
+=head2 C<ev_child> - watch out for process status changes
 Child watchers trigger when your process receives a SIGCHLD in response to
 some child status changes (most typically when a child of yours dies).
 =over 4
   struct ev_signal signal_watcher;
   ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
   ev_signal_start (loop, &sigint_cb);
-=head2 C<ev_idle> - when you've got nothing better to do
+=head2 C<ev_idle> - when you've got nothing better to do...
 Idle watchers trigger events when there are no other events are pending
 (prepare, check and other idle watchers do not count). That is, as long
 as your process is busy handling sockets or timeouts (or even signals,
 imagine) it will not be triggered. But when your process is idle all idle
   struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
   ev_idle_init (idle_watcher, idle_cb);
   ev_idle_start (loop, idle_cb);
-=head2 C<ev_prepare> and C<ev_check> - customise your event loop
+=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
 Prepare and check watchers are usually (but not always) used in tandem:
 prepare watchers get invoked before the process blocks and check watchers
 afterwards.
+You I<must not> call C<ev_loop> or similar functions that enter
+the current event loop from either C<ev_prepare> or C<ev_check>
+watchers. Other loops than the current one are fine, however. The
+rationale behind this is that you do not need to check for recursion in
+those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
+C<ev_check> so if you have one watcher of each kind they will always be
+called in pairs bracketing the blocking call.
 Their main purpose is to integrate other event mechanisms into libev and
 their use is somewhat advanced. This could be used, for example, to track
 variable changes, implement your own watchers, integrate net-snmp or a
-coroutine library and lots more.
+coroutine library and lots more. They are also occasionally useful if
+you cache some data and want to flush it before blocking (for example,
+in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
+watcher).
 This is done by examining in each prepare call which file descriptors need
 to be watched by the other library, registering C<ev_io> watchers for
 them and starting an C<ev_timer> watcher for any timeouts (many libraries
 provide just this functionality). Then, in the check watcher you check for
 parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
 macros, but using them is utterly, utterly and completely pointless.
 =back
-Example: *TODO*.
+Example: To include a library such as adns, you would add IO watchers
+and a timeout watcher in a prepare handler, as required by libadns, and
+in a check watcher, destroy them and call into libadns. What follows is
+pseudo-code only of course:
+  static ev_io iow [nfd];
+  static ev_timer tw;
+  static void
+  io_cb (ev_loop *loop, ev_io *w, int revents)
+  {
+    // set the relevant poll flags
+    // could also call adns_processreadable etc. here
+    struct pollfd *fd = (struct pollfd *)w->data;
+    if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
+    if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
+  }
+  // create io watchers for each fd and a timer before blocking
+  static void
+  adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
+  {
+    int timeout = 3600000;truct pollfd fds [nfd];
+    // actual code will need to loop here and realloc etc.
+    adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
+    /* the callback is illegal, but won't be called as we stop during check */
+    ev_timer_init (&tw, 0, timeout * 1e-3);
+    ev_timer_start (loop, &tw);
+    // create on ev_io per pollfd
+    for (int i = 0; i < nfd; ++i)
+      {
+        ev_io_init (iow + i, io_cb, fds [i].fd,
+          ((fds [i].events & POLLIN ? EV_READ : 0)
+           | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
+        fds [i].revents = 0;
+        iow [i].data = fds + i;
+        ev_io_start (loop, iow + i);
+      }
+  }
+  // stop all watchers after blocking
+  static void
+  adns_check_cb (ev_loop *loop, ev_check *w, int revents)
+  {
+    ev_timer_stop (loop, &tw);
+    for (int i = 0; i < nfd; ++i)
+      ev_io_stop (loop, iow + i);
+    adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
+  }
-=head2 C<ev_embed> - when one backend isn't enough
+=head2 C<ev_embed> - when one backend isn't enough...
 This is a rather advanced watcher type that lets you embed one event loop
 into another (currently only C<ev_io> events are supported in the embedded
 loop, other types of watchers might be handled in a delayed or incorrect
 fashion and must not be used).
   ev_vars.h
   ev_wrap.h
   ev_win32.c      required on win32 platforms only
-  ev_select.c     only when select backend is enabled (which is is by default)
+  ev_select.c     only when select backend is enabled (which is by default)
   ev_poll.c       only when poll backend is enabled (disabled by default)
   ev_epoll.c      only when the epoll backend is enabled (disabled by default)
   ev_kqueue.c     only when the kqueue backend is enabled (disabled by default)
   ev_port.c       only when the solaris port backend is enabled (disabled by default)
 F<ev.c> includes the backend files directly when enabled, so you only need
-to compile a single file.
+to compile this single file.
 =head3 LIBEVENT COMPATIBILITY API
 To include the libevent compatibility API, also include:
 =head3 AUTOCONF SUPPORT
 Instead of using C<EV_STANDALONE=1> and providing your config in
 whatever way you want, you can also C<m4_include([libev.m4])> in your
-F<configure.ac> and leave C<EV_STANDALONE> off. F<ev.c> will then include
+F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
-F<config.h> and configure itself accordingly.
+include F<config.h> and configure itself accordingly.
 For this of course you need the m4 file:
   libev.m4
 otherwise another method will be used as fallback. This is the preferred
 backend for BSD and BSD-like systems, although on most BSDs kqueue only
 supports some types of fds correctly (the only platform we found that
 supports ptys for example was NetBSD), so kqueue might be compiled in, but
 not be used unless explicitly requested. The best way to use it is to find
-out wether kqueue supports your type of fd properly and use an embedded
+out whether kqueue supports your type of fd properly and use an embedded
 kqueue loop.
 =item EV_USE_PORT
 If defined to be C<1>, libev will compile in support for the Solaris
   #define EV_COMMON                       \
     SV *self; /* contains this struct */  \
     SV *cb_sv, *fh /* note no trailing ";" */
-=item EV_CB_DECLARE(type)
+=item EV_CB_DECLARE (type)
-=item EV_CB_INVOKE(watcher,revents)
+=item EV_CB_INVOKE (watcher, revents)
-=item ev_set_cb(ev,cb)
+=item ev_set_cb (ev, cb)
 Can be used to change the callback member declaration in each watcher,
 and the way callbacks are invoked and set. Must expand to a struct member
 definition and a statement, respectively. See the F<ev.v> header file for
 their default definitions. One possible use for overriding these is to
-avoid the ev_loop pointer as first argument in all cases, or to use method
+avoid the C<struct ev_loop *> as first argument in all cases, or to use
-calls instead of plain function calls in C++.
+method calls instead of plain function calls in C++.
 =head2 EXAMPLES
 For a real-world example of a program the includes libev
 verbatim, you can have a look at the EV perl module
 And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
   #include "ev_cpp.h"
   #include "ev.c"
+=head1 COMPLEXITIES
+In this section the complexities of (many of) the algorithms used inside
+libev will be explained. For complexity discussions about backends see the
+documentation for C<ev_default_init>.
+=over 4
+=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
+=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)
+=item Starting io/check/prepare/idle/signal/child watchers: O(1)
+=item Stopping check/prepare/idle watchers: O(1)
+=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % 16))
+=item Finding the next timer per loop iteration: O(1)
+=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
+=item Activating one watcher: O(1)
+=back
 =head1 AUTHOR
 Marc Lehmann <libev@schmorp.de>.

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Comparing libev/ev.pod (file contents): Revision 1.40 by root, Sat Nov 24 10:15:16 2007 UTC vs. Revision 1.46 by root, Mon Nov 26 10:20:43 2007 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.40 by root, Sat Nov 24 10:15:16 2007 UTC vs.
Revision 1.46 by root, Mon Nov 26 10:20:43 2007 UTC