+ +

SUMMARY OF GENERIC WATCHER FUNCTIONS

In the following description, TYPE stands for the watcher type, +e.g. timer for ev_timer watchers and io for ev_io watchers.

ev_init (ev_TYPE *watcher, callback)

This macro initialises the generic portion of a watcher. The contents +of the watcher object can be arbitrary (so malloc will do). Only +the generic parts of the watcher are initialised, you need to call +the type-specific ev_TYPE_set macro afterwards to initialise the +type-specific parts. For each type there is also a ev_TYPE_init macro +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 void (*)(ev_loop *loop, ev_TYPE *watcher, +int revents).

ev_TYPE_set (ev_TYPE *, [args])

This macro initialises the type-specific parts of a watcher. You need to +call ev_init at least once before you call this macro, but you can +call ev_TYPE_set any number of times. You must not, however, call this +macro on a watcher that is active (it can be pending, however, which is a +difference to the ev_init macro).

Although some watcher types do not have type-specific arguments +(e.g. ev_prepare) you still need to call its set macro.

ev_TYPE_init (ev_TYPE *watcher, callback, [args])

This convinience macro rolls both ev_init and ev_TYPE_set macro +calls into a single call. This is the most convinient method to initialise +a watcher. The same limitations apply, of course.

ev_TYPE_start (loop *, ev_TYPE *watcher)

Starts (activates) the given watcher. Only active watchers will receive +events. If the watcher is already active nothing will happen.

ev_TYPE_stop (loop *, ev_TYPE *watcher)

Stops the given watcher again (if active) and clears the pending +status. It is possible that stopped watchers are pending (for example, +non-repeating timers are being stopped when they become pending), but +ev_TYPE_stop ensures that the watcher is neither active nor pending. If +you want to free or reuse the memory used by the watcher it is therefore a +good idea to always call its ev_TYPE_stop function.

bool ev_is_active (ev_TYPE *watcher)

Returns a true value iff the watcher is active (i.e. it has been started +and not yet been stopped). As long as a watcher is active you must not modify +it.

bool ev_is_pending (ev_TYPE *watcher)

Returns a true value iff the watcher is pending, (i.e. it has outstanding +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 +ev_TYPE_set is safe) and you must make sure the watcher is available to +libev (e.g. you cnanot free () it).

callback = ev_cb (ev_TYPE *watcher)

Returns the callback currently set on the watcher.

ev_cb_set (ev_TYPE *watcher, callback)

Change the callback. You can change the callback at virtually any time +(modulo threads).

+ + + + +

ASSOCIATING CUSTOM DATA WITH A WATCHER

@@ -790,8 +879,8 @@ inactivity.

Unlike ev_timer's, they are not based on real time (or relative time) but on wallclock time (absolute time). You can tell a periodic watcher to trigger "at" some specific point in time. For example, if you tell a -periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now () -+ 10.>) and then reset your system clock to the last year, then it will +periodic watcher to trigger in 10 seconds (by specifiying e.g. ev_now () ++ 10.) and then reset your system clock to the last year, then it will take a year to trigger the event (unlike an ev_timer, which would trigger roughly 10 seconds later and of course not if you reset your system time again).

@@ -933,6 +1022,10 @@ of the SIGxxx constants).

+ + + +

`ev_child` - wait for pid status changes

@@ -1015,9 +1108,10 @@ callback, free it. Alos, use no error checking, as usual.

Prepare and check watchers are usually (but not always) used in tandem: prepare watchers get invoked before the process blocks and check watchers afterwards.

Their main purpose is to integrate other event mechanisms into libev. This -could be used, for example, to track variable changes, implement your own -watchers, integrate net-snmp or a coroutine library and lots more.

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.

This is done by examining in each prepare call which file descriptors need to be watched by the other library, registering ev_io watchers for them and starting an ev_timer watcher for any timeouts (many libraries @@ -1049,6 +1143,91 @@ macros, but using them is utterly, utterly and completely pointless.

`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 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).

There are primarily two reasons you would want that: work around bugs and +prioritise I/O.

As an example for a bug workaround, the kqueue backend might only support +sockets on some platform, so it is unusable as generic backend, but you +still want to make use of it because you have many sockets and it scales +so nicely. In this case, you would create a kqueue-based loop and embed it +into your default loop (which might use e.g. poll). Overall operation will +be a bit slower because first libev has to poll and then call kevent, but +at least you can use both at what they are best.

As for prioritising I/O: rarely you have the case where some fds have +to be watched and handled very quickly (with low latency), and even +priorities and idle watchers might have too much overhead. In this case +you would put all the high priority stuff in one loop and all the rest in +a second one, and embed the second one in the first.

As long as the watcher is active, the callback will be invoked every time +there might be events pending in the embedded loop. The callback must then +call ev_embed_sweep (mainloop, watcher) to make a single sweep and invoke +their callbacks (you could also start an idle watcher to give the embedded +loop strictly lower priority for example). You can also set the callback +to 0, in which case the embed watcher will automatically execute the +embedded loop sweep.

As long as the watcher is started it will automatically handle events. The +callback will be invoked whenever some events have been handled. You can +set the callback to 0 to avoid having to specify one if you are not +interested in that.

Also, there have not currently been made special provisions for forking: +when you fork, you not only have to call ev_loop_fork on both loops, +but you will also have to stop and restart any ev_embed watchers +yourself.

Unfortunately, not all backends are embeddable, only the ones returned by +ev_embeddable_backends are, which, unfortunately, does not include any +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:

  struct ev_loop *loop_hi = ev_default_init (0);
+  struct ev_loop *loop_lo = 0;
+  struct ev_embed embed;
+
+  // see if there is a chance of getting one that works
+  // (remember that a flags value of 0 means autodetection)
+  loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
+    ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
+    : 0;
+
+  // if we got one, then embed it, otherwise default to loop_hi
+  if (loop_lo)
+    {
+      ev_embed_init (&embed, 0, loop_lo);
+      ev_embed_start (loop_hi, &embed);
+    }
+  else
+    loop_lo = loop_hi;
+
+

ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
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 0, then 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).
+
ev_embed_sweep (loop, ev_embed *): +
Make a single, non-blocking sweep over the embedded loop. This works +similarly to ev_loop (embedded_loop, EVLOOP_NONBLOCK), but in the most +apropriate way for embedded loops.
+

+ + + + +

OTHER FUNCTIONS

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@@ -1084,20 +1263,21 @@ value passed to ev_once:

ev_feed_event (loop, watcher, int events)

ev_feed_event (ev_loop *, watcher *, int revents)

Feeds the given event set into the event loop, as if the specified event had happened for the specified watcher (which must be a pointer to an initialised but not necessarily started event watcher).

ev_feed_fd_event (loop, int fd, int revents)

ev_feed_fd_event (ev_loop *, int fd, int revents)

Feed an event on the given fd, as if a file descriptor backend detected the given events it.

ev_feed_signal_event (loop, int signum)

ev_feed_signal_event (ev_loop *loop, int signum)

Feed an event as if the given signal occured (loop must be the default loop!).

Feed an event as if the given signal occured (loop must be the default +loop!).

@@ -1128,7 +1308,100 @@ to use the libev header file and library.

C++ SUPPORT

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TBD.

Libev comes with some simplistic wrapper classes for C++ that mainly allow +you to use some convinience methods to start/stop watchers and also change +the callback model to a model using method callbacks on objects.

To use it,

  #include <ev++.h>
+
+

(it is not installed by default). This automatically includes ev.h +and puts all of its definitions (many of them macros) into the global +namespace. All C++ specific things are put into the ev namespace.

It should support all the same embedding options as ev.h, most notably +EV_MULTIPLICITY.

Here is a list of things available in the ev namespace:

ev::READ, ev::WRITE etc.

These are just enum values with the same values as the EV_READ etc. +macros from ev.h.

ev::tstamp, ev::now

Aliases to the same types/functions as with the ev_ prefix.

ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc.

For each ev_TYPE watcher in ev.h there is a corresponding class of +the same name in the ev namespace, with the exception of ev_signal +which is called ev::sig to avoid clashes with the signal macro +defines by many implementations.

All of those classes have these methods:

ev::TYPE::TYPE (object *, object::method *)

ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)

ev::TYPE::~TYPE

The constructor takes a pointer to an object and a method pointer to +the event handler callback to call in this class. The constructor calls +ev_init for you, which means you have to call the set method +before starting it. If you do not specify a loop then the constructor +automatically associates the default loop with this watcher.

The destructor automatically stops the watcher if it is active.

w->set (struct ev_loop *)

Associates a different struct ev_loop with this watcher. You can only +do this when the watcher is inactive (and not pending either).

w->set ([args])

Basically the same as ev_TYPE_set, with the same args. Must be +called at least once. Unlike the C counterpart, an active watcher gets +automatically stopped and restarted.

w->start ()

Starts the watcher. Note that there is no loop argument as the +constructor already takes the loop.

w->stop ()

Stops the watcher if it is active. Again, no loop argument.

w->again () ev::timer, ev::periodic only

For ev::timer and ev::periodic, this invokes the corresponding +ev_TYPE_again function.

w->sweep () ev::embed only

Invokes ev_embed_sweep.

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_idle idle  void idle_cb (ev::idle &w, int revents);
+
+    myclass ();
+  }
+
+  myclass::myclass (int fd)
+  : io   (this, &myclass::io_cb),
+    idle (this, &myclass::idle_cb)
+  {
+    io.start (fd, ev::READ);
+  }
+
+

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