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

Comparing libev/ev.pod (file contents):
Revision 1.49 by root, Tue Nov 27 08:20:42 2007 UTC vs.
Revision 1.59 by root, Wed Nov 28 17:32:24 2007 UTC

 libev - a high performance full-featured event loop written in C
 =head1 SYNOPSIS
   #include <ev.h>
+=head1 EXAMPLE PROGRAM
+  #include <ev.h>
+  ev_io stdin_watcher;
+  ev_timer timeout_watcher;
+  /* called when data readable on stdin */
+  static void
+  stdin_cb (EV_P_ struct ev_io *w, int revents)
+  {
+    /* puts ("stdin ready"); */
+    ev_io_stop (EV_A_ w); /* just a syntax example */
+    ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */
+  }
+  static void
+  timeout_cb (EV_P_ struct ev_timer *w, int revents)
+  {
+    /* puts ("timeout"); */
+    ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */
+  }
+  int
+  main (void)
+  {
+    struct ev_loop *loop = ev_default_loop (0);
+    /* initialise an io watcher, then start it */
+    ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
+    ev_io_start (loop, &stdin_watcher);
+    /* simple non-repeating 5.5 second timeout */
+    ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
+    ev_timer_start (loop, &timeout_watcher);
+    /* loop till timeout or data ready */
+    ev_loop (loop, 0);
+    return 0;
+  }
 =head1 DESCRIPTION
 Libev is an event loop: you register interest in certain events (such as a
 file descriptor being readable or a timeout occuring), and it will manage
 details of the event, and then hand it over to libev by I<starting> the
 watcher.
 =head1 FEATURES
-Libev supports select, poll, the linux-specific epoll and the bsd-specific
+Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
-kqueue mechanisms for file descriptor events, relative timers, absolute
+BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
-timers with customised rescheduling, signal events, process status change
+for file descriptor events (C<ev_io>), the Linux C<inotify> interface
-events (related to SIGCHLD), and event watchers dealing with the event
+(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
-loop mechanism itself (idle, prepare and check watchers). It also is quite
+with customised rescheduling (C<ev_periodic>), synchronous signals
+(C<ev_signal>), process status change events (C<ev_child>), and event
+watchers dealing with the event loop mechanism itself (C<ev_idle>,
+C<ev_embed>, C<ev_prepare> and 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
-fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing
+L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
-it to libevent for example).
+for example).
 =head1 CONVENTIONS
-Libev is very configurable. In this manual the default configuration
+Libev is very configurable. In this manual the default configuration will
-will be described, which supports multiple event loops. For more info
+be described, which supports multiple event loops. For more info about
-about various configuration options please have a look at the file
+various configuration options please have a look at B<EMBED> section in
-F<README.embed> in the libev distribution. If libev was configured without
+this manual. If libev was configured without support for multiple event
-support for multiple event loops, then all functions taking an initial
+loops, then all functions taking an initial argument of name C<loop>
-argument of name C<loop> (which is always of type C<struct ev_loop *>)
+(which is always of type C<struct ev_loop *>) will not have this argument.
-will not have this argument.
 =head1 TIME REPRESENTATION
 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 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
+Example: Make sure we haven't accidentally been linked against the wrong
-version:
+version.
   assert (("libev version mismatch",
            ev_version_major () == EV_VERSION_MAJOR
            && ev_version_minor () >= EV_VERSION_MINOR));
 See the description of C<ev_embed> watchers for more info.
 =item ev_set_allocator (void *(*cb)(void *ptr, long size))
-Sets the allocation function to use (the prototype is similar to the
+Sets the allocation function to use (the prototype is similar - the
-realloc C function, the semantics are identical). It is used to allocate
+semantics is identical - to the realloc C function). It is used to
-and free memory (no surprises here). If it returns zero when memory
+allocate and free memory (no surprises here). If it returns zero when
-needs to be allocated, the library might abort or take some potentially
+memory needs to be allocated, the library might abort or take some
-destructive action. The default is your system realloc function.
+potentially 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
+Example: Replace the libev allocator with one that waits a bit and then
-retries: better than mine).
+retries).
    static void *
-   persistent_realloc (void *ptr, long size)
+   persistent_realloc (void *ptr, size_t size)
    {
      for (;;)
        {
          void *newptr = realloc (ptr, size);
 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:
+Example: This is basically the same thing that libev does internally, too.
    static void
    fatal_error (const char *msg)
    {
      perror (msg);
 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.
+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");
      Signals and child watchers are implemented as I/O watchers, and will
      be handled here by queueing them when their watcher gets executed.
    - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
      were used, return, otherwise continue with step *.
-Example: queue some jobs and then loop until no events are outsanding
+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);
 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>
+Example: Create a signal watcher, but keep it from keeping C<ev_loop>
 running when nothing else is active.
-  struct dv_signal exitsig;
+  struct ev_signal exitsig;
   ev_signal_init (&exitsig, sig_cb, SIGINT);
-  ev_signal_start (myloop, &exitsig);
+  ev_signal_start (loop, &exitsig);
-  evf_unref (myloop);
+  evf_unref (loop);
-Example: for some weird reason, unregister the above signal handler again.
+Example: For some weird reason, unregister the above signal handler again.
-  ev_ref (myloop);
+  ev_ref (loop);
-  ev_signal_stop (myloop, &exitsig);
+  ev_signal_stop (loop, &exitsig);
 =back
 =head1 ANATOMY OF A WATCHER
 received events. Callbacks of both watcher types can start and stop as
 many watchers as they want, and all of them will be taken into account
 (for example, a C<ev_prepare> watcher might start an idle watcher to keep
 C<ev_loop> from blocking).
+=item C<EV_EMBED>
+The embedded event loop specified in the C<ev_embed> watcher needs attention.
+=item C<EV_FORK>
+The event loop has been resumed in the child process after fork (see
+C<ev_fork>).
 =item C<EV_ERROR>
 An unspecified error has occured, the watcher has been stopped. This might
 happen because the watcher could not be properly started because libev
 ran out of memory, a file descriptor was found to be closed or any other
 events but its callback has not yet been invoked). As long as a watcher
 is pending (but not active) you must not call an init function on it (but
 C<ev_TYPE_set> is safe) and you must make sure the watcher is available to
 libev (e.g. you cnanot C<free ()> it).
-=item callback = ev_cb (ev_TYPE *watcher)
+=item callback ev_cb (ev_TYPE *watcher)
 Returns the callback currently set on the watcher.
 =item ev_cb_set (ev_TYPE *watcher, callback)
   {
     struct my_io *w = (struct my_io *)w_;
     ...
   }
-More interesting and less C-conformant ways of catsing your callback type
+More interesting and less C-conformant ways of casting your callback type
-have been omitted....
+instead have been omitted.
+Another common scenario is having some data structure with multiple
+watchers:
+  struct my_biggy
+  {
+    int some_data;
+    ev_timer t1;
+    ev_timer t2;
+  }
+In this case getting the pointer to C<my_biggy> is a bit more complicated,
+you need to use C<offsetof>:
+  #include <stddef.h>
+  static void
+  t1_cb (EV_P_ struct ev_timer *w, int revents)
+  {
+    struct my_biggy big = (struct my_biggy *
+      (((char *)w) - offsetof (struct my_biggy, t1));
+  }
+  static void
+  t2_cb (EV_P_ struct ev_timer *w, int revents)
+  {
+    struct my_biggy big = (struct my_biggy *
+      (((char *)w) - offsetof (struct my_biggy, t2));
+  }
 =head1 WATCHER TYPES
 This section describes each watcher in detail, but will not repeat
 The events being watched.
 =back
-Example: call C<stdin_readable_cb> when STDIN_FILENO has become, well
+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:
+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);
 or C<ev_timer_again> is called and determines the next timeout (if any),
 which is also when any modifications are taken into account.
 =back
-Example: create a timer that fires after 60 seconds.
+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
+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)
   {
 switched off. Can be changed any time, but changes only take effect when
 the periodic timer fires or C<ev_periodic_again> is being called.
 =back
-Example: call a callback every hour, or, more precisely, whenever the
+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)
   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:
+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:
+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);
 The process exit/trace status caused by C<rpid> (see your systems
 C<waitpid> and C<sys/wait.h> documentation for details).
 =back
-Example: try to exit cleanly on SIGINT and SIGTERM.
+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);
 not exist" is signified by the C<st_nlink> field being zero (which is
 otherwise always forced to be at least one) and all the other fields of
 the stat buffer having unspecified contents.
 Since there is no standard to do this, the portable implementation simply
-calls C<stat (2)> regulalry on the path to see if it changed somehow. You
+calls C<stat (2)> regularly on the path to see if it changed somehow. You
 can specify a recommended polling interval for this case. If you specify
 a polling interval of C<0> (highly recommended!) then a I<suitable,
 unspecified default> value will be used (which you can expect to be around
 five seconds, although this might change dynamically). Libev will also
 impose a minimum interval which is currently around C<0.1>, but thats
 This watcher type is not meant for massive numbers of stat watchers,
 as even with OS-supported change notifications, this can be
 resource-intensive.
-At the time of this writing, no specific OS backends are implemented, but
+At the time of this writing, only the Linux inotify interface is
-if demand increases, at least a kqueue and inotify backend will be added.
+implemented (implementing kqueue support is left as an exercise for the
+reader). Inotify will be used to give hints only and should not change the
+semantics of C<ev_stat> watchers, which means that libev sometimes needs
+to fall back to regular polling again even with inotify, but changes are
+usually detected immediately, and if the file exists there will be no
+polling.
 =over 4
 =item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
 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
+Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
-callback, free it. Alos, use no error checking, as usual.
+callback, free it. Also, use no error checking, as usual.
   static void
   idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
   {
     free (w);
 The embedded event loop.
 =back
+=head2 C<ev_fork> - the audacity to resume the event loop after a fork
+Fork watchers are called when a C<fork ()> was detected (usually because
+whoever is a good citizen cared to tell libev about it by calling
+C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
+event loop blocks next and before C<ev_check> watchers are being called,
+and only in the child after the fork. If whoever good citizen calling
+C<ev_default_fork> cheats and calls it in the wrong process, the fork
+handlers will be invoked, too, of course.
+=over 4
+=item ev_fork_init (ev_signal *, callback)
+Initialises and configures the fork watcher - it has no parameters of any
+kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
+believe me.
+=back
 =head1 OTHER FUNCTIONS
 There are some other functions of possible interest. Described. Here. Now.
 =over 4
   : io   (this, &myclass::io_cb),
     idle (this, &myclass::idle_cb)
   {
     io.start (fd, ev::READ);
   }
+=head1 MACRO MAGIC
+Libev can be compiled with a variety of options, the most fundemantal is
+C<EV_MULTIPLICITY>. This option determines wether (most) functions and
+callbacks have an initial C<struct ev_loop *> argument.
+To make it easier to write programs that cope with either variant, the
+following macros are defined:
+=over 4
+=item C<EV_A>, C<EV_A_>
+This provides the loop I<argument> for functions, if one is required ("ev
+loop argument"). The C<EV_A> form is used when this is the sole argument,
+C<EV_A_> is used when other arguments are following. Example:
+  ev_unref (EV_A);
+  ev_timer_add (EV_A_ watcher);
+  ev_loop (EV_A_ 0);
+It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
+which is often provided by the following macro.
+=item C<EV_P>, C<EV_P_>
+This provides the loop I<parameter> for functions, if one is required ("ev
+loop parameter"). The C<EV_P> form is used when this is the sole parameter,
+C<EV_P_> is used when other parameters are following. Example:
+  // this is how ev_unref is being declared
+  static void ev_unref (EV_P);
+  // this is how you can declare your typical callback
+  static void cb (EV_P_ ev_timer *w, int revents)
+It declares a parameter C<loop> of type C<struct ev_loop *>, quite
+suitable for use with C<EV_A>.
+=item C<EV_DEFAULT>, C<EV_DEFAULT_>
+Similar to the other two macros, this gives you the value of the default
+loop, if multiple loops are supported ("ev loop default").
+=back
+Example: Declare and initialise a check watcher, working regardless of
+wether multiple loops are supported or not.
+  static void
+  check_cb (EV_P_ ev_timer *w, int revents)
+  {
+    ev_check_stop (EV_A_ w);
+  }
+  ev_check check;
+  ev_check_init (&check, check_cb);
+  ev_check_start (EV_DEFAULT_ &check);
+  ev_loop (EV_DEFAULT_ 0);
 =head1 EMBEDDING
 Libev can (and often is) directly embedded into host
 applications. Examples of applications that embed it include the Deliantra
 =item EV_USE_DEVPOLL
 reserved for future expansion, works like the USE symbols above.
+=item EV_USE_INOTIFY
+If defined to be C<1>, libev will compile in support for the Linux inotify
+interface to speed up C<ev_stat> watchers. Its actual availability will
+be detected at runtime.
 =item EV_H
 The name of the F<ev.h> header file used to include it. The default if
 undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This
 can be used to virtually rename the F<ev.h> header file in case of conflicts.
 =item EV_STAT_ENABLE
 If undefined or defined to be C<1>, then stat watchers are supported. If
 defined to be C<0>, then they are not.
+=item EV_FORK_ENABLE
+If undefined or defined to be C<1>, then fork watchers are supported. If
+defined to be C<0>, then they are not.
 =item EV_MINIMAL
 If you need to shave off some kilobytes of code at the expense of some
 speed, define this symbol to C<1>. Currently only used for gcc to override
 some inlining decisions, saves roughly 30% codesize of amd64.
+=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
+increase this value (I<must> be a power of two).
+=item EV_INOTIFY_HASHSIZE
+C<ev_staz> watchers use a small hash table to distribute workload by
+inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
+usually more than enough. If you need to manage thousands of C<ev_stat>
+watchers you might want to increase this value (I<must> be a power of
+two).
 =item EV_COMMON
 By default, all watchers have a C<void *data> member. By redefining
 this macro to a something else you can include more and other types of
 =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 Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
 =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)

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Comparing libev/ev.pod (file contents): Revision 1.49 by root, Tue Nov 27 08:20:42 2007 UTC vs. Revision 1.59 by root, Wed Nov 28 17:32:24 2007 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.49 by root, Tue Nov 27 08:20:42 2007 UTC vs.
Revision 1.59 by root, Wed Nov 28 17:32:24 2007 UTC