+ +

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 +890,8 @@ 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 +1033,10 @@ of the SIGxxx constants).

+ + + +

`ev_child` - wait for pid status changes

@@ -1015,9 +1119,10 @@ 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 +1154,91 @@ 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

Top

@@ -1084,20 +1274,21 @@ 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!).

@@ -1128,12 +1319,384 @@ to use the libev header file and library.

C++ SUPPORT

Top

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);
+  }
+
+

+ +

EMBEDDING

Top

Libev can (and often is) directly embedded into host +applications. Examples of applications that embed it include the Deliantra +Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe) +and rxvt-unicode.

The goal is to enable you to just copy the neecssary files into your +source directory without having to change even a single line in them, so +you can easily upgrade by simply copying (or having a checked-out copy of +libev somewhere in your source tree).

+ +

FILESETS

Depending on what features you need you need to include one or more sets of files +in your app.

+ +

CORE EVENT LOOP

To include only the libev core (all the ev_* functions), with manual +configuration (no autoconf):

  #define EV_STANDALONE 1
+  #include "ev.c"
+
+

This will automatically include ev.h, too, and should be done in a +single C source file only to provide the function implementations. To use +it, do the same for ev.h in all files wishing to use this API (best +done by writing a wrapper around ev.h that you can include instead and +where you can put other configuration options):

  #define EV_STANDALONE 1
+  #include "ev.h"
+
+

Both header files and implementation files can be compiled with a C++ +compiler (at least, thats a stated goal, and breakage will be treated +as a bug).

You need the following files in your source tree, or in a directory +in your include path (e.g. in libev/ when using -Ilibev):

  ev.h
+  ev.c
+  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_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)
+
+

ev.c includes the backend files directly when enabled, so you only need +to compile a single file.

+ +

LIBEVENT COMPATIBILITY API

To include the libevent compatibility API, also include:

  #include "event.c"
+
+

in the file including ev.c, and:

  #include "event.h"
+
+

in the files that want to use the libevent API. This also includes ev.h.

You need the following additional files for this:

  event.h
+  event.c
+
+

+ +

AUTOCONF SUPPORT

Instead of using EV_STANDALONE=1 and providing your config in +whatever way you want, you can also m4_include([libev.m4]) in your +configure.ac and leave EV_STANDALONE off. ev.c will then include +config.h and configure itself accordingly.

For this of course you need the m4 file:

  libev.m4
+
+

+ +

PREPROCESSOR SYMBOLS/MACROS

Libev can be configured via a variety of preprocessor symbols you have to define +before including any of its files. The default is not to build for multiplicity +and only include the select backend.

EV_STANDALONE

Must always be 1 if you do not use autoconf configuration, which +keeps libev from including config.h, and it also defines dummy +implementations for some libevent functions (such as logging, which is not +supported). It will also not define any of the structs usually found in +event.h that are not directly supported by the libev core alone.

EV_USE_MONOTONIC

If defined to be 1, libev will try to detect the availability of the +monotonic clock option at both compiletime and runtime. Otherwise no use +of the monotonic clock option will be attempted. If you enable this, you +usually have to link against librt or something similar. Enabling it when +the functionality isn't available is safe, though, althoguh you have +to make sure you link against any libraries where the clock_gettime +function is hiding in (often -lrt).

EV_USE_REALTIME

If defined to be 1, libev will try to detect the availability of the +realtime clock option at compiletime (and assume its availability at +runtime if successful). Otherwise no use of the realtime clock option will +be attempted. This effectively replaces gettimeofday by clock_get +(CLOCK_REALTIME, ...) and will not normally affect correctness. See tzhe note about libraries +in the description of EV_USE_MONOTONIC, though.

EV_USE_SELECT

If undefined or defined to be 1, libev will compile in support for the +select(2) backend. No attempt at autodetection will be done: if no +other method takes over, select will be it. Otherwise the select backend +will not be compiled in.

EV_SELECT_USE_FD_SET

If defined to 1, then the select backend will use the system fd_set +structure. This is useful if libev doesn't compile due to a missing +NFDBITS or fd_mask definition or it misguesses the bitset layout on +exotic systems. This usually limits the range of file descriptors to some +low limit such as 1024 or might have other limitations (winsocket only +allows 64 sockets). The FD_SETSIZE macro, set before compilation, might +influence the size of the fd_set used.

EV_SELECT_IS_WINSOCKET

When defined to 1, the select backend will assume that +select/socket/connect etc. don't understand file descriptors but +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 +_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.

EV_USE_POLL

If defined to be 1, libev will compile in support for the poll(2) +backend. Otherwise it will be enabled on non-win32 platforms. It +takes precedence over select.

EV_USE_EPOLL

If defined to be 1, libev will compile in support for the Linux +epoll(7) backend. Its availability will be detected at runtime, +otherwise another method will be used as fallback. This is the +preferred backend for GNU/Linux systems.

EV_USE_KQUEUE

If defined to be 1, libev will compile in support for the BSD style +kqueue(2) backend. Its actual availability will be detected at runtime, +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 +kqueue loop.

EV_USE_PORT

If defined to be 1, libev will compile in support for the Solaris +10 port style backend. Its availability will be detected at runtime, +otherwise another method will be used as fallback. This is the preferred +backend for Solaris 10 systems.

EV_USE_DEVPOLL

reserved for future expansion, works like the USE symbols above.

EV_H

The name of the ev.h header file used to include it. The default if +undefined is <ev.h> in event.h and "ev.h" in ev.c. This +can be used to virtually rename the ev.h header file in case of conflicts.

EV_CONFIG_H

If EV_STANDALONE isn't 1, this variable can be used to override +ev.c's idea of where to find the config.h file, similarly to +EV_H, above.

EV_EVENT_H

Similarly to EV_H, this macro can be used to override event.c's idea +of how the event.h header can be found.

EV_PROTOTYPES

If defined to be 0, then ev.h will not define any function +prototypes, but still define all the structs and other symbols. This is +occasionally useful if you want to provide your own wrapper functions +around libev functions.

EV_MULTIPLICITY

If undefined or defined to 1, then all event-loop-specific functions +will have the struct ev_loop * as first argument, and you can create +additional independent event loops. Otherwise there will be no support +for multiple event loops and there is no first event loop pointer +argument. Instead, all functions act on the single default loop.

EV_PERIODICS

If undefined or defined to be 1, then periodic timers are supported, +otherwise not. This saves a few kb of code.

EV_COMMON

By default, all watchers have a void *data member. By redefining +this macro to a something else you can include more and other types of +members. You have to define it each time you include one of the files, +though, and it must be identical each time.

For example, the perl EV module uses something like this:

  #define EV_COMMON                       \
+    SV *self; /* contains this struct */  \
+    SV *cb_sv, *fh /* note no trailing ";" */
+
+

EV_CB_DECLARE(type)

EV_CB_INVOKE(watcher,revents)

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 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 +calls instead of plain function calls in C++.

+ +

EXAMPLES

For a real-world example of a program the includes libev +verbatim, you can have a look at the EV perl module +(http://software.schmorp.de/pkg/EV.html). It has the libev files in +the libev/ subdirectory and includes them in the EV/EVAPI.h (public +interface) and EV.xs (implementation) files. Only the EV.xs file +will be compiled. It is pretty complex because it provides its own header +file.

The usage in rxvt-unicode is simpler. It has a ev_cpp.h header file +that everybody includes and which overrides some autoconf choices:

   #define EV_USE_POLL 0
+   #define EV_MULTIPLICITY 0
+   #define EV_PERIODICS 0
+   #define EV_CONFIG_H <config.h>
+
+   #include "ev++.h"
+
+

And a ev_cpp.C implementation file that contains libev proper and is compiled:

   #include "rxvttoolkit.h"
+
+   /* darwin has problems with its header files in C++, requiring this namespace juggling */
+   using namespace ev;
+
+   #include "ev.c"
+
+
+
+
+

AUTHOR

Top

Marc Lehmann <libev@schmorp.de>.