libev - a high performance full-featured event loop written in C
#include <ev.h>
#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;
+ }
+
+
+
+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 @@ -87,29 +133,33 @@ details of the event, and then hand it over to libev by starting the watcher.
Libev supports select, poll, the linux-specific epoll and the bsd-specific -kqueue mechanisms for file descriptor events, relative timers, absolute -timers with customised rescheduling, signal events, process status change -events (related to SIGCHLD), and event watchers dealing with the event -loop mechanism itself (idle, prepare and check watchers). It also is quite -fast (see this benchmark comparing -it to libevent for example).
+Libev supports select, poll, the linux-specific epoll, the
+bsd-specific kqueue and the solaris-specific event port mechanisms
+for file descriptor events (ev_io), relative timers (ev_timer),
+absolute timers with customised rescheduling (ev_periodic), synchronous
+signals (ev_signal), process status change events (ev_child), and
+event watchers dealing with the event loop mechanism itself (ev_idle,
+ev_embed, ev_prepare and ev_check watchers) as well as
+file watchers (ev_stat) and even limited support for fork events
+(ev_fork).
It also is quite fast (see this +benchmark comparing it to libevent +for example).
Libev is very configurable. In this manual the default configuration
-will be described, which supports multiple event loops. For more info
-about various configuration options please have a look at the file
-README.embed in the libev distribution. If libev was configured without
-support for multiple event loops, then all functions taking an initial
-argument of name loop (which is always of type struct ev_loop *)
-will not have this argument.
Libev is very configurable. In this manual the default configuration will
+be described, which supports multiple event loops. For more info about
+various configuration options please have a look at EMBED section in
+this manual. If libev was configured without support for multiple event
+loops, then all functions taking an initial argument of name loop
+(which is always of type struct ev_loop *) will not have this argument.
Libev represents time as a single floating point number, representing the
(fractional) number of seconds since the (POSIX) epoch (somewhere near
@@ -119,7 +169,7 @@ to the double type in C, and when you need to do any calculations o
it, you should treat it as such.
These functions can be called anytime, even before initialising the library in any way.
@@ -142,8 +192,8 @@ version of the library your program was compiled against. 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:
+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));
@@ -191,8 +241,8 @@ 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).
+ Example: Replace the libev allocator with one that waits a bit and then
+retries).
static void *
persistent_realloc (void *ptr, size_t size)
{
@@ -221,7 +271,7 @@ 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)
{
@@ -237,7 +287,7 @@ requested operation, or, if the condition doesn't go away, do bad stuff
An event loop is described by a struct ev_loop *. The library knows two
types of such loops, the default loop, which supports signals and child
@@ -367,7 +417,7 @@ event loop and only if you know the OS supports your types of fds):
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");
@@ -470,7 +520,7 @@ usually a better approach for this kind of thing.
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..)
@@ -499,17 +549,17 @@ visible to the libev user and should not keep ev_loop from exiting
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 unref after start and ref before stop.
- Example: create a signal watcher, but keep it from keeping ev_loop
+
Example: Create a signal watcher, but keep it from keeping 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);
- evf_unref (myloop);
+ ev_signal_start (loop, &exitsig);
+ evf_unref (loop);
- Example: for some weird reason, unregister the above signal handler again.
- ev_ref (myloop);
- ev_signal_stop (myloop, &exitsig);
+ Example: For some weird reason, unregister the above signal handler again.
+ ev_ref (loop);
+ ev_signal_stop (loop, &exitsig);
@@ -520,7 +570,7 @@ running when nothing else is active.
A watcher is a structure that you create and register to record your
interest in some event. For instance, if you want to wait for STDIN to
@@ -693,7 +743,7 @@ 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).
Returns the callback currently set on the watcher.
More interesting and less C-conformant ways of catsing your callback type -have been omitted....
+More interesting and less C-conformant ways of casting your callback type +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 my_biggy is a bit more complicated,
+you need to use 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));
+ }
+
+
This section describes each watcher in detail, but will not repeat
information given in the last section. Any initialisation/set macros,
@@ -813,9 +891,9 @@ rceeive events for and events is either EV_READ, EV_WRITEThe events being watched.
Example: call stdin_readable_cb when STDIN_FILENO has become, well
+
Example: Call 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)
{
@@ -908,7 +986,7 @@ or ev_timer_again is called and determines the next timeout (if any
which is also when any modifications are taken into account.
-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)
{
@@ -920,7 +998,7 @@ which is also when any modifications are taken into account.
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)
@@ -1046,7 +1124,7 @@ switched off. Can be changed any time, but changes only take effect when
the periodic timer fires or ev_periodic_again is being called.
-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
@@ -1060,7 +1138,7 @@ potentially a lot of jittering, but good long-term stability.
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
@@ -1072,7 +1150,7 @@ potentially a lot of jittering, but good long-term stability.
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);
@@ -1143,7 +1221,7 @@ process causing the status change.
waitpid and sys/wait.h documentation for details).
-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)
{
@@ -1171,7 +1249,7 @@ not exist" is signified by the st_nlink field being zero (whic
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 stat (2) regulalry on the path to see if it changed somehow. You
+calls 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 0 (highly recommended!) then a suitable,
unspecified default value will be used (which you can expect to be around
@@ -1181,8 +1259,13 @@ usually overkill.
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
-if demand increases, at least a kqueue and inotify backend will be added.
+At the time of this writing, only the Linux inotify interface is
+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 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.
ev_idle_set macro, but using it is utterly pointle
believe me.
Example: dynamically allocate an ev_idle, start it, and in the
-callback, free it. Alos, use no error checking, as usual.
Example: Dynamically allocate an 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)
{
@@ -1512,7 +1595,7 @@ believe me.
There are some other functions of possible interest. Described. Here. Now.
Libev offers a compatibility emulation layer for libevent. It cannot emulate the internals of libevent, so here are some usage hints:
@@ -1589,7 +1672,7 @@ to use the libev header file and library.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 @@ -1694,7 +1777,7 @@ the constructor.
Libev can be compiled with a variety of options, the most fundemantal is
EV_MULTIPLICITY. This option determines wether (most) functions and
@@ -1755,7 +1838,7 @@ wether multiple loops are supported or not.
Libev can (and often is) directly embedded into host applications. Examples of applications that embed it include the Deliantra @@ -1939,6 +2022,12 @@ backend for Solaris 10 systems.
reserved for future expansion, works like the USE symbols above.
If defined to be 1, libev will compile in support for the Linux inotify
+interface to speed up ev_stat watchers. Its actual availability will
+be detected at runtime.
The name of the ev.h header file used to include it. The default if @@ -2003,7 +2092,15 @@ some inlining decisions, saves roughly 30% codesize of amd64.
ev_child watchers use a small hash table to distribute workload by
pid. The default size is 16 (or 1 with EV_MINIMAL), usually more
than enough. If you need to manage thousands of children you might want to
-increase this value.
ev_staz watchers use a small hash table to distribute workload by
+inotify watch id. The default size is 16 (or 1 with EV_MINIMAL),
+usually more than enough. If you need to manage thousands of ev_stat
+watchers you might want to increase this value (must be a power of
+two).
In this section the complexities of (many of) the algorithms used inside
libev will be explained. For complexity discussions about backends see the
@@ -2070,7 +2167,7 @@ documentation for ev_default_init.
ev_default_init.
Marc Lehmann <libev@schmorp.de>.