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

Comparing libev/ev.pod (file contents):
Revision 1.32 by root, Fri Nov 23 08:36:35 2007 UTC vs.
Revision 1.34 by root, Fri Nov 23 16:17:12 2007 UTC

 Libev represents time as a single floating point number, representing the
 (fractional) number of seconds since the (POSIX) epoch (somewhere near
 the beginning of 1970, details are complicated, don't ask). This type is
 called C<ev_tstamp>, which is what you should use too. It usually aliases
-to the double type in C.
+to the C<double> type in C, and when you need to do any calculations on
+it, you should treat it as such.
 =head1 GLOBAL FUNCTIONS
 These functions can be called anytime, even before initialising the
 library in any way.
 Usually, it's a good idea to terminate if the major versions mismatch,
 as this indicates an incompatible change.  Minor versions are usually
 compatible to older versions, so a larger minor version alone is usually
 not a problem.
+Example: make sure we haven't accidentally been linked against the wrong
+version:
+  assert (("libev version mismatch",
+           ev_version_major () == EV_VERSION_MAJOR
+           && ev_version_minor () >= EV_VERSION_MINOR));
 =item unsigned int ev_supported_backends ()
 Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
 value) compiled into this binary of libev (independent of their
 availability on the system you are running on). See C<ev_default_loop> for
 a description of the set values.
+Example: make sure we have the epoll method, because yeah this is cool and
+a must have and can we have a torrent of it please!!!11
+  assert (("sorry, no epoll, no sex",
+           ev_supported_backends () & EVBACKEND_EPOLL));
 =item unsigned int ev_recommended_backends ()
 Return the set of all backends compiled into this binary of libev and also
 recommended for this platform. This set is often smaller than the one
 returned by C<ev_supported_backends>, as for example kqueue is broken on
 most BSDs and will not be autodetected unless you explicitly request it
 (assuming you know what you are doing). This is the set of backends that
-C<EVFLAG_AUTO> will probe for.
+libev will probe for if you specify no backends explicitly.
 =item ev_set_allocator (void *(*cb)(void *ptr, long size))
 Sets the allocation function to use (the prototype is similar to the
 realloc C function, the semantics are identical). It is used to allocate
 destructive action. The default is your system realloc function.
 You could override this function in high-availability programs to, say,
 free some memory if it cannot allocate memory, to use a special allocator,
 or even to sleep a while and retry until some memory is available.
+Example: replace the libev allocator with one that waits a bit and then
+retries: better than mine).
+   static void *
+   persistent_realloc (void *ptr, long size)
+   {
+     for (;;)
+       {
+         void *newptr = realloc (ptr, size);
+         if (newptr)
+           return newptr;
+         sleep (60);
+       }
+   }
+   ...
+   ev_set_allocator (persistent_realloc);
 =item ev_set_syserr_cb (void (*cb)(const char *msg));
 Set the callback function to call on a retryable syscall error (such
 as failed select, poll, epoll_wait). The message is a printable string
 callback is set, then libev will expect it to remedy the sitution, no
 matter what, when it returns. That is, libev will generally retry the
 requested operation, or, if the condition doesn't go away, do bad stuff
 (such as abort).
+Example: do the same thing as libev does internally:
+   static void
+   fatal_error (const char *msg)
+   {
+     perror (msg);
+     abort ();
+   }
+   ...
+   ev_set_syserr_cb (fatal_error);
 =back
 =head1 FUNCTIONS CONTROLLING THE EVENT LOOP
 An event loop is described by a C<struct ev_loop *>. The library knows two
 If you don't know what event loop to use, use the one returned from this
 function.
 The flags argument can be used to specify special behaviour or specific
-backends to use, and is usually specified as C<0> (or EVFLAG_AUTO).
+backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
-It supports the following flags:
+The following flags are supported:
 =over 4
 =item C<EVFLAG_AUTO>
 =item C<EVBACKEND_KQUEUE>  (value 8, most BSD clones)
 Kqueue deserves special mention, as at the time of this writing, it
 was broken on all BSDs except NetBSD (usually it doesn't work with
 anything but sockets and pipes, except on Darwin, where of course its
-completely useless). For this reason its not being "autodetected" unless
+completely useless). For this reason its not being "autodetected"
-you explicitly specify the flags (i.e. you don't use EVFLAG_AUTO).
+unless you explicitly specify it explicitly in the flags (i.e. using
+C<EVBACKEND_KQUEUE>).
 It scales in the same way as the epoll backend, but the interface to the
 kernel is more efficient (which says nothing about its actual speed, of
 course). While starting and stopping an I/O watcher does not cause an
 extra syscall as with epoll, it still adds up to four event changes per
 If one or more of these are ored into the flags value, then only these
 backends will be tried (in the reverse order as given here). If none are
 specified, most compiled-in backend will be tried, usually in reverse
 order of their flag values :)
+The most typical usage is like this:
+  if (!ev_default_loop (0))
+    fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
+Restrict libev to the select and poll backends, and do not allow
+environment settings to be taken into account:
+  ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
+Use whatever libev has to offer, but make sure that kqueue is used if
+available (warning, breaks stuff, best use only with your own private
+event loop and only if you know the OS supports your types of fds):
+  ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
 =item struct ev_loop *ev_loop_new (unsigned int flags)
 Similar to C<ev_default_loop>, but always creates a new event loop that is
 always distinct from the default loop. Unlike the default loop, it cannot
 handle signal and child watchers, and attempts to do so will be greeted by
 undefined behaviour (or a failed assertion if assertions are enabled).
+Example: try to create a event loop that uses epoll and nothing else.
+  struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
+  if (!epoller)
+    fatal ("no epoll found here, maybe it hides under your chair");
 =item ev_default_destroy ()
 Destroys the default loop again (frees all memory and kernel state
 etc.). This stops all registered event watchers (by not touching them in
 any way whatsoever, although you cannot rely on this :).
 use.
 =item ev_tstamp ev_now (loop)
 Returns the current "event loop time", which is the time the event loop
-got events and started processing them. This timestamp does not change
+received events and started processing them. This timestamp does not
-as long as callbacks are being processed, and this is also the base time
+change as long as callbacks are being processed, and this is also the base
-used for relative timers. You can treat it as the timestamp of the event
+time used for relative timers. You can treat it as the timestamp of the
-occuring (or more correctly, the mainloop finding out about it).
+event occuring (or more correctly, libev finding out about it).
 =item ev_loop (loop, int flags)
 Finally, this is it, the event handler. This function usually is called
 after you initialised all your watchers and you want to start handling
 events.
-If the flags argument is specified as 0, it will not return until either
+If the flags argument is specified as C<0>, it will not return until
-no event watchers are active anymore or C<ev_unloop> was called.
+either no event watchers are active anymore or C<ev_unloop> was called.
+Please note that an explicit C<ev_unloop> is usually better than
+relying on all watchers to be stopped when deciding when a program has
+finished (especially in interactive programs), but having a program that
+automatically loops as long as it has to and no longer by virtue of
+relying on its watchers stopping correctly is a thing of beauty.
 A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
 those events and any outstanding ones, but will not block your process in
 case there are no events and will return after one iteration of the loop.
 A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
 neccessary) and will handle those and any outstanding ones. It will block
 your process until at least one new event arrives, and will return after
-one iteration of the loop.
+one iteration of the loop. This is useful if you are waiting for some
+external event in conjunction with something not expressible using other
+libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is
+usually a better approach for this kind of thing.
-This flags value could be used to implement alternative looping
-constructs, but the C<prepare> and C<check> watchers provide a better and
-more generic mechanism.
-Here are the gory details of what ev_loop does:
+Here are the gory details of what C<ev_loop> does:
-   1. If there are no active watchers (reference count is zero), return.
+   * If there are no active watchers (reference count is zero), return.
-   2. Queue and immediately call all prepare watchers.
+   - Queue prepare watchers and then call all outstanding watchers.
-   3. If we have been forked, recreate the kernel state.
+   - If we have been forked, recreate the kernel state.
-   4. Update the kernel state with all outstanding changes.
+   - Update the kernel state with all outstanding changes.
-   5. Update the "event loop time".
+   - Update the "event loop time".
-   6. Calculate for how long to block.
+   - Calculate for how long to block.
-   7. Block the process, waiting for events.
+   - Block the process, waiting for any events.
+   - Queue all outstanding I/O (fd) events.
-   8. Update the "event loop time" and do time jump handling.
+   - Update the "event loop time" and do time jump handling.
-   9. Queue all outstanding timers.
+   - Queue all outstanding timers.
-  10. Queue all outstanding periodics.
+   - Queue all outstanding periodics.
-  11. If no events are pending now, queue all idle watchers.
+   - If no events are pending now, queue all idle watchers.
-  12. Queue all check watchers.
+   - Queue all check watchers.
-  13. Call all queued watchers in reverse order (i.e. check watchers first).
+   - Call all queued watchers in reverse order (i.e. check watchers first).
+     Signals and child watchers are implemented as I/O watchers, and will
+     be handled here by queueing them when their watcher gets executed.
-  14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
+   - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
-      was used, return, otherwise continue with step #1.
+     were used, return, otherwise continue with step *.
+Example: queue some jobs and then loop until no events are outsanding
+anymore.
+   ... queue jobs here, make sure they register event watchers as long
+   ... as they still have work to do (even an idle watcher will do..)
+   ev_loop (my_loop, 0);
+   ... jobs done. yeah!
 =item ev_unloop (loop, how)
 Can be used to make a call to C<ev_loop> return early (but only after it
 has processed all outstanding events). The C<how> argument must be either
 visible to the libev user and should not keep C<ev_loop> from exiting if
 no event watchers registered by it are active. It is also an excellent
 way to do this for generic recurring timers or from within third-party
 libraries. Just remember to I<unref after start> and I<ref before stop>.
+Example: create a signal watcher, but keep it from keeping C<ev_loop>
+running when nothing else is active.
+  struct dv_signal exitsig;
+  ev_signal_init (&exitsig, sig_cb, SIGINT);
+  ev_signal_start (myloop, &exitsig);
+  evf_unref (myloop);
+Example: for some weird reason, unregister the above signal handler again.
+  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
 =head1 WATCHER TYPES
 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
 I/O watchers check whether a file descriptor is readable or writable
 in each iteration of the event loop (This behaviour is called
 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
+attempt to read a whole line in the callback:
+  static void
+  stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
+  {
+     ev_io_stop (loop, w);
+    .. read from stdin here (or from w->fd) and haqndle any I/O errors
+  }
+  ...
+  struct ev_loop *loop = ev_default_init (0);
+  struct ev_io stdin_readable;
+  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
 Timer watchers are simple relative timers that generate an event after a
 given time, and optionally repeating in regular intervals after that.
 state where you do not expect data to travel on the socket, you can stop
 the timer, and again will automatically restart it if need be.
 =back
+Example: create a timer that fires after 60 seconds.
+  static void
+  one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
+  {
+    .. one minute over, w is actually stopped right here
+  }
+  struct ev_timer mytimer;
+  ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
+  ev_timer_start (loop, &mytimer);
+Example: create a timeout timer that times out after 10 seconds of
+inactivity.
+  static void
+  timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
+  {
+    .. ten seconds without any activity
+  }
+  struct ev_timer mytimer;
+  ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
+  ev_timer_again (&mytimer); /* start timer */
+  ev_loop (loop, 0);
+  // 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
 Periodic watchers are also timers of a kind, but they are very versatile
 (and unfortunately a bit complex).
 a different time than the last time it was called (e.g. in a crond like
 program when the crontabs have changed).
 =back
+Example: call a callback every hour, or, more precisely, whenever the
+system clock is divisible by 3600. The callback invocation times have
+potentially a lot of jittering, but good long-term stability.
+  static void
+  clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
+  {
+    ... its now a full hour (UTC, or TAI or whatever your clock follows)
+  }
+  struct ev_periodic hourly_tick;
+  ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
+  ev_periodic_start (loop, &hourly_tick);
+Example: the same as above, but use a reschedule callback to do it:
+  #include <math.h>
+  static ev_tstamp
+  my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
+  {
+    return fmod (now, 3600.) + 3600.;
+  }
+  ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
+Example: call a callback every hour, starting now:
+  struct ev_periodic hourly_tick;
+  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
 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
 the status word (use the macros from C<sys/wait.h> and see your systems
 C<waitpid> documentation). The C<rpid> member contains the pid of the
 process causing the status change.
 =back
+Example: try to exit cleanly on SIGINT and SIGTERM.
+  static void
+  sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
+  {
+    ev_unloop (loop, EVUNLOOP_ALL);
+  }
+  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
 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
 Initialises and configures the idle watcher - it has no parameters of any
 kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
 believe me.
 =back
+Example: dynamically allocate an C<ev_idle>, start it, and in the
+callback, free it. Alos, use no error checking, as usual.
+  static void
+  idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
+  {
+    free (w);
+    // now do something you wanted to do when the program has
+    // no longer asnything immediate to do.
+  }
+  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
 Prepare and check watchers are usually (but not always) used in tandem:
 prepare watchers get invoked before the process blocks and check watchers
 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*.
 =head1 OTHER FUNCTIONS
 There are some other functions of possible interest. Described. Here. Now.
 =over 4
 Feed an event as if the given signal occured (loop must be the default loop!).
 =back
 =head1 LIBEVENT EMULATION
 Libev offers a compatibility emulation layer for libevent. It cannot
 emulate the internals of libevent, so here are some usage hints:

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Comparing libev/ev.pod (file contents): Revision 1.32 by root, Fri Nov 23 08:36:35 2007 UTC vs. Revision 1.34 by root, Fri Nov 23 16:17:12 2007 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.32 by root, Fri Nov 23 08:36:35 2007 UTC vs.
Revision 1.34 by root, Fri Nov 23 16:17:12 2007 UTC