ev_idle - when you've got nothing better to do...ev_prepare and ev_check - customise your event loop!ev_embed - when one backend isn't enough...ev_fork - the audacity to resume the event loop after a forklibev - 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 @@ -85,29 +133,33 @@ 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
@@ -116,12 +168,8 @@
to the double type in C, and when you need to do any calculations on
it, you should treat it as such.
These functions can be called anytime, even before initialising the library in any way.
@@ -144,8 +192,8 @@ 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));
@@ -183,20 +231,20 @@
recommended ones.
See the description of ev_embed watchers for more info.
- Sets the allocation function to use (the prototype is similar to the -realloc C function, the semantics are identical). It is used to allocate -and free memory (no surprises here). If it returns zero when memory -needs to be allocated, the library might abort or take some potentially -destructive action. The default is your system realloc function.
+Sets the allocation function to use (the prototype and semantics are +identical to the realloc C function). It is used to allocate and free +memory (no surprises here). If it returns zero when memory needs to be +allocated, the library might abort or take some 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 -retries: better than mine).
+Example: Replace the libev allocator with one that waits a bit and then +retries).
static void *
- persistent_realloc (void *ptr, long size)
+ persistent_realloc (void *ptr, size_t size)
{
for (;;)
{
@@ -223,7 +271,7 @@
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)
{
@@ -239,7 +287,7 @@
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
@@ -369,7 +417,7 @@
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");
@@ -472,7 +520,7 @@
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..)
@@ -501,17 +549,17 @@
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);
@@ -522,7 +570,7 @@
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
@@ -608,6 +656,15 @@
(for example, a ev_prepare watcher might start an idle watcher to keep
ev_loop from blocking).
EV_EMBEDThe embedded event loop specified in the ev_embed watcher needs attention.
EV_FORKThe event loop has been resumed in the child process after fork (see
+ev_fork).
EV_ERRORAn unspecified error has occured, the watcher has been stopped. This might @@ -736,7 +793,7 @@
This section describes each watcher in detail, but will not repeat information given in the last section. Any initialisation/set macros, @@ -806,9 +863,9 @@
The 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)
{
@@ -901,7 +958,7 @@
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)
{
@@ -913,7 +970,7 @@
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)
@@ -1039,7 +1096,7 @@
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
@@ -1053,7 +1110,7 @@
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
@@ -1065,7 +1122,7 @@
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);
@@ -1136,7 +1193,7 @@
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)
{
@@ -1269,8 +1326,8 @@
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)
{
@@ -1482,7 +1539,30 @@
ev_fork - the audacity to resume the event loop after a forkFork watchers are called when a fork () was detected (usually because
+whoever is a good citizen cared to tell libev about it by calling
+ev_default_fork or ev_loop_fork). The invocation is done before the
+event loop blocks next and before ev_check watchers are being called,
+and only in the child after the fork. If whoever good citizen calling
+ev_default_fork cheats and calls it in the wrong process, the fork
+handlers will be invoked, too, of course.
Initialises and configures the fork watcher - it has no parameters of any
+kind. There is a ev_fork_set macro, but using it is utterly pointless,
+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:
@@ -1559,7 +1639,7 @@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 @@ -1633,6 +1713,10 @@
Invokes ev_embed_sweep.
ev::stat onlyInvokes ev_stat_stat.
Libev can be compiled with a variety of options, the most fundemantal is
+EV_MULTIPLICITY. This option determines wether (most) functions and
+callbacks have an initial struct ev_loop * argument.
To make it easier to write programs that cope with either variant, the +following macros are defined:
+EV_A, EV_A_This provides the loop argument for functions, if one is required ("ev
+loop argument"). The EV_A form is used when this is the sole argument,
+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 loop of type struct ev_loop * is in scope,
+which is often provided by the following macro.
EV_P, EV_P_This provides the loop parameter for functions, if one is required ("ev
+loop parameter"). The EV_P form is used when this is the sole parameter,
+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 loop of type struct ev_loop *, quite
+suitable for use with EV_A.
EV_DEFAULT, 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").
+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);
+
+
+
+
+
+
+Libev can (and often is) directly embedded into host applications. Examples of applications that embed it include the Deliantra @@ -1889,12 +2037,24 @@
If undefined or defined to be 1, then stat watchers are supported. If
defined to be 0, then they are not.
If undefined or defined to be 1, then fork watchers are supported. If
+defined to be 0, then they are not.
If you need to shave off some kilobytes of code at the expense of some
speed, define this symbol to 1. Currently only used for gcc to override
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.
By default, all watchers have a void *data member. By redefining
@@ -1949,7 +2109,7 @@
In this section the complexities of (many of) the algorithms used inside libev will be explained. For complexity discussions about backends see the @@ -1972,7 +2132,7 @@
Marc Lehmann <libev@schmorp.de>.