The newest version of this document is also available as a html-formatted +web page you might find easier to navigate when reading it for the first +time: http://cvs.schmorp.de/libev/ev.html.

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 these event sources and provide your program with events.

@@ -232,13 +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.

@@ -326,6 +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)

@@ -464,6 +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)

@@ -753,6 +783,26 @@ 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.

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.

@@ -872,7 +922,7 @@ 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);
    ...
@@ -977,8 +1028,8 @@ 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]

@@ -1249,6 +1300,8 @@ 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) regularly on the path to see if it changed somehow. You can specify a recommended polling interval for this case. If you specify @@ -1339,13 +1392,15 @@ was some error while stating the file.

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 @@ -1445,7 +1500,8 @@ 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 ())); @@ -1781,7 +1837,7 @@ the constructor.

MACRO MAGIC

Libev can be compiled with a variety of options, the most fundemantal is -EV_MULTIPLICITY. This option determines wether (most) functions and +EV_MULTIPLICITY. This option determines whether (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:

@@ -1820,8 +1876,9 @@ suitable for use with EV_A.

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.

Example: Declare and initialise a check watcher, utilising the above +macros so it will work regardless of whether multiple loops are supported +or not.

  static void
   check_cb (EV_P_ ev_timer *w, int revents)
   {
@@ -1833,9 +1890,6 @@ wether multiple loops are supported or not.
   ev_check_start (EV_DEFAULT_ &check);
   ev_loop (EV_DEFAULT_ 0);
 
-
-
-

@@ -1886,7 +1940,7 @@ in your include path (e.g. in libev/ when using -Ilibev):

ev_win32.c required on win32 platforms only - ev_select.c only when select backend is enabled (which is by default) + ev_select.c only when select backend is enabled (which is enabled 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) @@ -2060,11 +2114,31 @@ will have the struct ev_loop * as first argument, and you can creat 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_MINPRI

EV_MAXPRI

The range of allowed priorities. EV_MINPRI must be smaller or equal to +EV_MAXPRI, but otherwise there are no non-obvious limitations. You can +provide for more priorities by overriding those symbols (usually defined +to be -2 and 2, respectively).

When doing priority-based operations, libev usually has to linearly search +all the priorities, so having many of them (hundreds) uses a lot of space +and time, so using the defaults of five priorities (-2 .. +2) is usually +fine.

If your embedding app does not need any priorities, defining these both to +0 will save some memory and cpu.

EV_PERIODIC_ENABLE

If undefined or defined to be 1, then periodic timers are supported. If defined to be 0, then they are not. Disabling them saves a few kB of +code.

EV_IDLE_ENABLE

If undefined or defined to be 1, then idle watchers are supported. If +defined to be 0, then they are not. Disabling them saves a few kB of code.

EV_EMBED_ENABLE

@@ -2138,11 +2212,16 @@ interface) and EV.xs (implementation) files. Only the EV.xs

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
+that everybody includes and which overrides some configure choices:
+  #define EV_MINIMAL 1
+  #define EV_USE_POLL 0
   #define EV_MULTIPLICITY 0
-  #define EV_PERIODICS 0
+  #define EV_PERIODIC_ENABLE 0
+  #define EV_STAT_ENABLE 0
+  #define EV_FORK_ENABLE 0
   #define EV_CONFIG_H <config.h>
+  #define EV_MINPRI 0
+  #define EV_MAXPRI 0
 
   #include "ev++.h"
 
@@ -2162,16 +2241,48 @@ that everybody includes and which overrides some autoconf choices:
 		In this section the complexities of (many of) the algorithms used inside
 libev will be explained. For complexity discussions about backends see the
 documentation for ev_default_init.
+		All of the following are about amortised time: If an array needs to be
+extended, libev needs to realloc and move the whole array, but this
+happens asymptotically never with higher number of elements, so O(1) might
+mean it might do a lengthy realloc operation in rare cases, but on average
+it is much faster and asymptotically approaches constant time.
 		
 			

 				Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
+				
+					This means that, when you have a watcher that triggers in one hour and
+there are 100 watchers that would trigger before that then inserting will
+have to skip those 100 watchers.
+				
 				Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)
+				
+					That means that for changing a timer costs less than removing/adding them
+as only the relative motion in the event queue has to be paid for.
+				
 				Starting io/check/prepare/idle/signal/child watchers: O(1)
-				Stopping check/prepare/idle watchers: O(1)
+				
+					These just add the watcher into an array or at the head of a list.
+=item Stopping check/prepare/idle watchers: O(1)
+				
 				Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
+				
+					These watchers are stored in lists then need to be walked to find the
+correct watcher to remove. The lists are usually short (you don't usually
+have many watchers waiting for the same fd or signal).
+				
 				Finding the next timer per loop iteration: O(1)
 				Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
+				
+					A change means an I/O watcher gets started or stopped, which requires
+libev to recalculate its status (and possibly tell the kernel).
+				
 				Activating one watcher: O(1)
+				Priority handling: O(number_of_priorities)
+				
+					Priorities are implemented by allocating some space for each
+priority. When doing priority-based operations, libev usually has to
+linearly search all the priorities.
+

DESCRIPTION

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

MACRO MAGIC

DESCRIPTION

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

MACRO MAGIC

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