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, +

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), the Linux inotify interface +(for ev_stat), 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).

@@ -231,13 +235,14 @@ might be supported on the current system, you would need to look at recommended ones.

See the description of ev_embed watchers for more info.

ev_set_allocator (void *(*cb)(void *ptr, size_t size))

ev_set_allocator (void *(*cb)(void *ptr, long size))

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.

Sets the allocation function to use (the prototype is similar - the +semantics is 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.

@@ -325,6 +330,23 @@ or setgid) then libev will not look at the environment variable override the flags completely if it is found in the environment. This is useful to try out specific backends to test their performance, or to work around bugs.

EVFLAG_FORKCHECK

Instead of calling ev_default_fork or ev_loop_fork manually after +a fork, you can also make libev check for a fork in each iteration by +enabling this flag.

This works by calling getpid () on every iteration of the loop, +and thus this might slow down your event loop if you do a lot of loop +iterations and little real work, but is usually not noticeable (on my +Linux system for example, getpid is actually a simple 5-insn sequence +without a syscall and thus very fast, but my Linux system also has +pthread_atfork which is even faster).

The big advantage of this flag is that you can forget about fork (and +forget about forgetting to tell libev about forking) when you use this +flag.

This flag setting cannot be overriden or specified in the LIBEV_FLAGS +environment variable.

EVBACKEND_SELECT (value 1, portable select backend)

@@ -463,6 +485,15 @@ do not need to care.

Like ev_default_fork, but acts on an event loop created by ev_loop_new. Yes, you have to call this on every allocated event loop after fork, and how you do this is entirely your own problem.

unsigned int ev_loop_count (loop)

Returns the count of loop iterations for the loop, which is identical to +the number of times libev did poll for new events. It starts at 0 and +happily wraps around with enough iterations.

This value can sometimes be useful as a generation counter of sorts (it +"ticks" the number of loop iterations), as it roughly corresponds with +ev_prepare and ev_check calls.

unsigned int ev_backend (loop)

@@ -740,10 +771,11 @@ it.

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).

+ev_TYPE_set is safe), you must not change its priority, and you must +make sure the watcher is available to libev (e.g. you cannot free () +it).

callback = ev_cb (ev_TYPE *watcher)

callback ev_cb (ev_TYPE *watcher)

Returns the callback currently set on the watcher.

@@ -752,6 +784,40 @@ libev (e.g. you cnanot free () it).

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

ev_set_priority (ev_TYPE *watcher, priority)

int ev_priority (ev_TYPE *watcher)

Set and query the priority of the watcher. The priority is a small +integer between EV_MAXPRI (default: 2) and EV_MINPRI +(default: -2). Pending watchers with higher priority will be invoked +before watchers with lower priority, but priority will not keep watchers +from being executed (except for ev_idle watchers).

This means that priorities are only used for ordering callback +invocation after new events have been received. This is useful, for +example, to reduce latency after idling, or more often, to bind two +watchers on the same event and make sure one is called first.

If you need to suppress invocation when higher priority events are pending +you need to look at ev_idle watchers, which provide this functionality.

You must not change the priority of a watcher as long as it is active or +pending.

The default priority used by watchers when no priority has been set is +always 0, which is supposed to not be too high and not be too low :).

Setting a priority outside the range of EV_MINPRI to EV_MAXPRI is +fine, as long as you do not mind that the priority value you query might +or might not have been adjusted to be within valid range.

ev_invoke (loop, ev_TYPE *watcher, int revents)

Invoke the watcher with the given loop and revents. Neither +loop nor revents need to be valid as long as the watcher callback +can deal with that fact.

int ev_clear_pending (loop, ev_TYPE *watcher)

If the watcher is pending, this function returns clears its pending status +and returns its revents bitset (as if its callback was invoked). If the +watcher isn't pending it does nothing and returns 0.

@@ -785,13 +851,41 @@ can cast it back to your own type:

} -

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));
+  }
 
 
 
 
+

WATCHER TYPES

@@ -843,7 +937,7 @@ it is best to always use non-blocking I/O: An extra read(2) returni EAGAIN is far preferable to a program hanging until some data arrives.

If you cannot run the fd in non-blocking mode (for example you should not play around with an Xlib connection), then you have to seperately re-test -wether a file descriptor is really ready with a known-to-be good interface +whether a file descriptor is really ready with a known-to-be good interface such as poll (fortunately in our Xlib example, Xlib already does this on its own, so its quite safe to use).

This will act as if the timer timed out and restart it again if it is repeating. The exact semantics are:

If the timer is started but nonrepeating, stop it.

If the timer is repeating, either start it if necessary (with the repeat -value), or reset the running timer to the repeat value.

If the timer is pending, its pending status is cleared.

If the timer is started but nonrepeating, stop it (as if it timed out).

If the timer is repeating, either start it if necessary (with the +repeat value), or reset the running timer to the repeat value.

This sounds a bit complicated, but here is a useful and typical -example: Imagine you have a tcp connection and you want a so-called -idle timeout, that is, you want to be called when there have been, -say, 60 seconds of inactivity on the socket. The easiest way to do -this is to configure an ev_timer with after=repeat=60 and calling +example: Imagine you have a tcp connection and you want a so-called idle +timeout, that is, you want to be called when there have been, say, 60 +seconds of inactivity on the socket. The easiest way to do this is to +configure an ev_timer with a repeat value of 60 and then call ev_timer_again each time you successfully read or write some data. If you go into an idle state where you do not expect data to travel on the -socket, you can stop the timer, and again will automatically restart it if -need be.

You can also ignore the after value and ev_timer_start altogether -and only ever use the repeat value:

+socket, you can ev_timer_stop the timer, and ev_timer_again will +automatically restart it if need be.

That means you can ignore the after value and ev_timer_start +altogether and only ever use the repeat value and ev_timer_again:

   ev_timer_init (timer, callback, 0., 5.);
    ev_timer_again (loop, timer);
    ...
@@ -948,8 +1043,8 @@ and only ever use the repeat value:
    ev_timer_again (loop, timer);

This is more efficient then stopping/starting the timer eahc time you want -to modify its timeout value.

This is more slightly efficient then stopping/starting the timer each time +you want to modify its timeout value.

ev_tstamp repeat [read-write]

@@ -1220,8 +1315,10 @@ not exist" is a status change like any other. The condition "path does not exist" is signified by the st_nlink field being zero (which is otherwise always forced to be at least one) and all the other fields of the stat buffer having unspecified contents.

The path should be absolute and must not end in a slash. If it is +relative and your working directory changes, the behaviour is undefined.

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 @@ -1231,8 +1328,13 @@ 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_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)

ev_idle - when you've got nothing better to do...

Idle watchers trigger events when there are no other events are pending -(prepare, check and other idle watchers do not count). That is, as long -as your process is busy handling sockets or timeouts (or even signals, -imagine) it will not be triggered. But when your process is idle all idle -watchers are being called again and again, once per event loop iteration - -until stopped, that is, or your process receives more events and becomes -busy.

Idle watchers trigger events when no other events of the same or higher +priority are pending (prepare, check and other idle watchers do not +count).

That is, as long as your process is busy handling sockets or timeouts +(or even signals, imagine) of the same or higher priority it will not be +triggered. But when your process is idle (or only lower-priority watchers +are pending), the idle watchers are being called once per event loop +iteration - until stopped, that is, or your process receives more events +and becomes busy again with higher priority stuff.

The most noteworthy effect is that as long as any idle watchers are active, the process will not block when waiting for new events.

Apart from keeping your process non-blocking (which is a useful @@ -1411,7 +1515,8 @@ pseudo-code only of course:

static void adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents) { - int timeout = 3600000;truct pollfd fds [nfd]; + int timeout = 3600000; + struct pollfd fds [nfd]; // actual code will need to loop here and realloc etc. adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ())); @@ -1648,11 +1753,19 @@ the callback model to a model using method callbacks on objects.

  #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.

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.

Care has been taken to keep the overhead low. The only data member the C++ +classes add (compared to plain C-style watchers) is the event loop pointer +that the watcher is associated with (or no additional members at all if +you disable EV_MULTIPLICITY when embedding libev).

Currently, functions, and static and non-static member functions can be +used as callbacks. Other types should be easy to add as long as they only +need one additional pointer for context. If you need support for other +types of functors please contact the author (preferably after implementing +it).

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

ev::READ, ev::WRITE etc.

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.

DESCRIPTION

FEATURES

WATCHER TYPES

`ev_idle` - when you've got nothing better to do...

MACRO MAGIC

DESCRIPTION

FEATURES

WATCHER TYPES

ev_idle - when you've got nothing better to do...

MACRO MAGIC

`ev_idle` - when you've got nothing better to do...