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

Comparing libev/ev.pod (file contents):
Revision 1.110 by root, Tue Dec 25 07:05:45 2007 UTC vs.
Revision 1.123 by root, Thu Jan 31 13:25:10 2008 UTC

 flags. If that is troubling you, check C<ev_backend ()> afterwards).
 If you don't know what event loop to use, use the one returned from this
 function.
+The default loop is the only loop that can handle C<ev_signal> and
+C<ev_child> watchers, and to do this, it always registers a handler
+for C<SIGCHLD>. If this is a problem for your app you can either
+create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
+can simply overwrite the C<SIGCHLD> signal handler I<after> calling
+C<ev_default_init>.
 The flags argument can be used to specify special behaviour or specific
 backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
 The following flags are supported:
 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, ignoring the spurious readyness notifications, this
+backend actually performed to specification in all tests and is fully
+embeddable, which is a rare feat among the OS-specific backends.
 =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.
 =back
 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
+backends will be tried (in the reverse order as listed here). If none are
-specified, most compiled-in backend will be tried, usually in reverse
+specified, all backends in C<ev_recommended_backends ()> will be tried.
-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?");
 Like C<ev_default_destroy>, but destroys an event loop created by an
 earlier call to C<ev_loop_new>.
 =item ev_default_fork ()
+This function sets a flag that causes subsequent C<ev_loop> iterations
-This function reinitialises the kernel state for backends that have
+to reinitialise the kernel state for backends that have one. Despite the
-one. Despite the name, you can call it anytime, but it makes most sense
+name, you can call it anytime, but it makes most sense after forking, in
-after forking, in either the parent or child process (or both, but that
+the child process (or both child and parent, but that again makes little
-again makes little sense).
+sense). You I<must> call it in the child before using any of the libev
+functions, and it will only take effect at the next C<ev_loop> iteration.
-You I<must> call this function in the child process after forking if and
+On the other hand, you only need to call this function in the child
-only if you want to use the event library in both processes. If you just
+process if and only if you want to use the event library in the child. If
-fork+exec, you don't have to call it.
+you just fork+exec, you don't have to call it at all.
 The function itself is quite fast and it's usually not a problem to call
 it just in case after a fork. To make this easy, the function will fit in
 quite nicely into a call to C<pthread_atfork>:
     pthread_atfork (0, 0, ev_default_fork);
-At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
-without calling this function, so if you force one of those backends you
-do not need to care.
 =item ev_loop_fork (loop)
 Like C<ev_default_fork>, but acts on an event loop created by
 C<ev_loop_new>. Yes, you have to call this on every allocated event loop
 usually a better approach for this kind of thing.
 Here are the gory details of what C<ev_loop> does:
    - Before the first iteration, call any pending watchers.
-   * If there are no active watchers (reference count is zero), return.
+   * If EVFLAG_FORKCHECK was used, check for a fork.
-   - Queue all prepare watchers and then call all outstanding watchers.
+   - If a fork was detected, queue and call all fork watchers.
+   - Queue and call all prepare watchers.
    - If we have been forked, recreate the kernel state.
    - Update the kernel state with all outstanding changes.
    - Update the "event loop time".
-   - Calculate for how long to block.
+   - Calculate for how long to sleep or block, if at all
+     (active idle watchers, EVLOOP_NONBLOCK or not having
+     any active watchers at all will result in not sleeping).
+   - Sleep if the I/O and timer collect interval say so.
    - Block the process, waiting for any events.
    - Queue all outstanding I/O (fd) events.
    - Update the "event loop time" and do time jump handling.
    - Queue all outstanding timers.
    - Queue all outstanding periodics.
    - If no events are pending now, queue all idle watchers.
    - Queue all check watchers.
    - 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.
-   - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
+   - If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
-     were used, return, otherwise continue with step *.
+     were used, or there are no active watchers, 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 outstanding
 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);
 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
 C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
 C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
+This "unloop state" will be cleared when entering C<ev_loop> again.
 =item ev_ref (loop)
 =item ev_unref (loop)
 returning, ev_unref() after starting, and ev_ref() before stopping it. For
 example, libev itself uses this for its internal signal pipe: It is not
 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>.
+libraries. Just remember to I<unref after start> and I<ref before stop>
+(but only if the watcher wasn't active before, or was active before,
+respectively).
 Example: Create a signal watcher, but keep it from keeping C<ev_loop>
 running when nothing else is active.
   struct ev_signal exitsig;
 =item C<EV_FORK>
 The event loop has been resumed in the child process after fork (see
 C<ev_fork>).
+=item C<EV_ASYNC>
+The given async watcher has been asynchronously notified (see C<ev_async>).
 =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
 =item int events [read-only]
 The events being watched.
 =back
+=head3 Examples
 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.
 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
+=head3 Examples
 Example: Create a timer that fires after 60 seconds.
   static void
   one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
   {
 When active, contains the absolute time that the watcher is supposed to
 trigger next.
 =back
+=head3 Examples
 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
 =head3 Watcher-Specific Functions and Data Members
 =over 4
-=item ev_child_init (ev_child *, callback, int pid)
+=item ev_child_init (ev_child *, callback, int pid, int trace)
-=item ev_child_set (ev_child *, int pid)
+=item ev_child_set (ev_child *, int pid, int trace)
 Configures the watcher to wait for status changes of process C<pid> (or
 I<any> process if C<pid> is specified as C<0>). The callback can look
 at the C<rstatus> member of the C<ev_child> watcher structure to see
 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.
+process causing the status change. C<trace> must be either C<0> (only
+activate the watcher when the process terminates) or C<1> (additionally
+activate the watcher when the process is stopped or continued).
 =item int pid [read-only]
 The process id this watcher watches out for, or C<0>, meaning any process id.
 The process exit/trace status caused by C<rpid> (see your systems
 C<waitpid> and C<sys/wait.h> documentation for details).
 =back
+=head3 Examples
 Example: Try to exit cleanly on SIGINT and SIGTERM.
   static void
   sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
 kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
 believe me.
 =back
+=head3 Examples
 Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
 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);
     // now do something you wanted to do when the program has
-    // no longer asnything immediate to do.
+    // no longer anything 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);
 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
+=head3 Examples
 There are a number of principal ways to embed other event loops or modules
 into libev. Here are some ideas on how to include libadns into libev
 (there is a Perl module named C<EV::ADNS> that does this, which you could
 use for an actually working example. Another Perl module named C<EV::Glib>
 embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV
 portable one.
 So when you want to use this feature you will always have to be prepared
 that you cannot get an embeddable loop. The recommended way to get around
 this is to have a separate variables for your embeddable loop, try to
-create it, and if that fails, use the normal loop for everything:
+create it, and if that fails, use the normal loop for everything.
+=head3 Watcher-Specific Functions and Data Members
+=over 4
+=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
+=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
+Configures the watcher to embed the given loop, which must be
+embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
+invoked automatically, otherwise it is the responsibility of the callback
+to invoke it (it will continue to be called until the sweep has been done,
+if you do not want thta, you need to temporarily stop the embed watcher).
+=item ev_embed_sweep (loop, ev_embed *)
+Make a single, non-blocking sweep over the embedded loop. This works
+similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
+apropriate way for embedded loops.
+=item struct ev_loop *other [read-only]
+The embedded event loop.
+=back
+=head3 Examples
+Example: Try to get an embeddable event loop and embed it into the default
+event loop. If that is not possible, use the default loop. The default
+loop is stored in C<loop_hi>, while the mebeddable loop is stored in
+C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be
+used).
   struct ev_loop *loop_hi = ev_default_init (0);
   struct ev_loop *loop_lo = 0;
   struct ev_embed embed;
       ev_embed_start (loop_hi, &embed);
     }
   else
     loop_lo = loop_hi;
-=head3 Watcher-Specific Functions and Data Members
+Example: Check if kqueue is available but not recommended and create
+a kqueue backend for use with sockets (which usually work with any
+kqueue implementation). Store the kqueue/socket-only event loop in
+C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
-=over 4
+  struct ev_loop *loop = ev_default_init (0);
+  struct ev_loop *loop_socket = 0;
+  struct ev_embed embed;
+  if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
+    if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
+      {
+        ev_embed_init (&embed, 0, loop_socket);
+        ev_embed_start (loop, &embed);
+      }
-=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
+  if (!loop_socket)
+    loop_socket = loop;
-=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
+  // now use loop_socket for all sockets, and loop for everything else
-Configures the watcher to embed the given loop, which must be
-embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
-invoked automatically, otherwise it is the responsibility of the callback
-to invoke it (it will continue to be called until the sweep has been done,
-if you do not want thta, you need to temporarily stop the embed watcher).
-=item ev_embed_sweep (loop, ev_embed *)
-Make a single, non-blocking sweep over the embedded loop. This works
-similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
-apropriate way for embedded loops.
-=item struct ev_loop *other [read-only]
-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
 believe me.
 =back
+=head2 C<ev_async> - how to wake up another event loop
+In general, you cannot use an C<ev_loop> from multiple threads or other
+asynchronous sources such as signal handlers (as opposed to multiple event
+loops - those are of course safe to use in different threads).
+Sometimes, however, you need to wake up another event loop you do not
+control, for example because it belongs to another thread. This is what
+C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
+can signal 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).
+Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
+just the default loop.
+=head3 Watcher-Specific Functions and Data Members
+=over 4
+=item ev_async_init (ev_async *, callback)
+Initialises and configures the async watcher - it has no parameters of any
+kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,
+believe me.
+=item ev_async_send (loop, ev_async *)
+Sends/signals/activates the given C<ev_async> watcher, that is, feeds
+an C<EV_ASYNC> event on the watcher into the event loop. Unlike
+C<ev_feed_event>, this call is safe to do in other threads, signal or
+similar contexts (see the dicusssion of C<EV_ATOMIC_T> in the embedding
+section below on what exactly this means).
+This call incurs the overhead of a syscall only once per loop iteration,
+so while the overhead might be noticable, it doesn't apply to repeated
+calls to C<ev_async_send>.
+=back
 =head1 OTHER FUNCTIONS
 There are some other functions of possible interest. Described. Here. Now.
 =over 4
 Example: Define a class with an IO and idle watcher, start one of them in
 the constructor.
   class myclass
   {
-    ev_io   io;   void io_cb   (ev::io   &w, int revents);
+    ev::io   io;  void io_cb   (ev::io   &w, int revents);
-    ev_idle idle  void idle_cb (ev::idle &w, int revents);
+    ev:idle idle  void idle_cb (ev::idle &w, int revents);
-    myclass ();
+    myclass (int fd)
-  }
-  myclass::myclass (int fd)
-  {
+    {
-    io  .set <myclass, &myclass::io_cb  > (this);
+      io  .set <myclass, &myclass::io_cb  > (this);
-    idle.set <myclass, &myclass::idle_cb> (this);
+      idle.set <myclass, &myclass::idle_cb> (this);
-    io.start (fd, ev::READ);
+      io.start (fd, ev::READ);
+    }
-  }
+  };
 =head1 MACRO MAGIC
 Libev can be compiled with a variety of options, the most fundamantal
 wants osf handles on win32 (this is the case when the select to
 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
+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_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
 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_ATOMIC_T
+Libev requires an integer type (suitable for storing C<0> or C<1>) whose
+access is atomic with respect to other threads or signal contexts. No such type
+is easily found using, so you cna provide your own type that you know is safe.
+In the absense of this define, libev will use C<sig_atomic_t volatile>
+from F<signal.h>, which is usually good enough on most platforms.
 =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 F<ev.c>. This can be used to
+undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
-virtually rename the F<ev.h> header file in case of conflicts.
+used to virtually rename the F<ev.h> header file in case of conflicts.
 =item EV_CONFIG_H
 If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
 F<ev.c>'s idea of where to find the F<config.h> file, similarly to
 C<EV_H>, above.
 =item EV_EVENT_H
 Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
-of how the F<event.h> header can be found, the dfeault is C<"event.h">.
+of how the F<event.h> header can be found, the default is C<"event.h">.
 =item EV_PROTOTYPES
 If defined to be C<0>, then F<ev.h> will not define any function
 prototypes, but still define all the structs and other symbols. This is
 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_ASYNC_ENABLE
+If undefined or defined to be C<1>, then async 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
 watchers becomes O(1) w.r.t. prioritiy handling.
 =back
+=head1 Win32 platform limitations and workarounds
+Win32 doesn't support any of the standards (e.g. POSIX) that libev
+requires, and its I/O model is fundamentally incompatible with the POSIX
+model. Libev still offers limited functionality on this platform in
+the form of the C<EVBACKEND_SELECT> backend, and only supports socket
+descriptors. This only applies when using Win32 natively, not when using
+e.g. cygwin.
+There is no supported compilation method available on windows except
+embedding it into other applications.
+Due to the many, low, and arbitrary limits on the win32 platform and the
+abysmal performance of winsockets, using a large number of sockets is not
+recommended (and not reasonable). If your program needs to use more than
+a hundred or so sockets, then likely it needs to use a totally different
+implementation for windows, as libev offers the POSIX model, which cannot
+be implemented efficiently on windows (microsoft monopoly games).
+=over 4
+=item The winsocket select function
+The winsocket C<select> function doesn't follow POSIX in that it requires
+socket I<handles> and not socket I<file descriptors>. This makes select
+very inefficient, and also requires a mapping from file descriptors
+to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,
+C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor
+symbols for more info.
+The configuration for a "naked" win32 using the microsoft runtime
+libraries and raw winsocket select is:
+  #define EV_USE_SELECT 1
+  #define EV_SELECT_IS_WINSOCKET 1   /* forces EV_SELECT_USE_FD_SET, too */
+Note that winsockets handling of fd sets is O(n), so you can easily get a
+complexity in the O(n²) range when using win32.
+=item Limited number of file descriptors
+Windows has numerous arbitrary (and low) limits on things. Early versions
+of winsocket's select only supported waiting for a max. of C<64> handles
+(probably owning to the fact that all windows kernels can only wait for
+C<64> things at the same time internally; microsoft recommends spawning a
+chain of threads and wait for 63 handles and the previous thread in each).
+Newer versions support more handles, but you need to define C<FD_SETSIZE>
+to some high number (e.g. C<2048>) before compiling the winsocket select
+call (which might be in libev or elsewhere, for example, perl does its own
+select emulation on windows).
+Another limit is the number of file descriptors in the microsoft runtime
+libraries, which by default is C<64> (there must be a hidden I<64> fetish
+or something like this inside microsoft). You can increase this by calling
+C<_setmaxstdio>, which can increase this limit to C<2048> (another
+arbitrary limit), but is broken in many versions of the microsoft runtime
+libraries.
+This might get you to about C<512> or C<2048> sockets (depending on
+windows version and/or the phase of the moon). To get more, you need to
+wrap all I/O functions and provide your own fd management, but the cost of
+calling select (O(n²)) will likely make this unworkable.
+=back
 =head1 AUTHOR
 Marc Lehmann <libev@schmorp.de>.

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Comparing libev/ev.pod (file contents): Revision 1.110 by root, Tue Dec 25 07:05:45 2007 UTC vs. Revision 1.123 by root, Thu Jan 31 13:25:10 2008 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.110 by root, Tue Dec 25 07:05:45 2007 UTC vs.
Revision 1.123 by root, Thu Jan 31 13:25:10 2008 UTC