Libev is very configurable. In this manual the default configuration will be described, which supports multiple event loops. For more info -about various configuraiton options please have a look at the file +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 *) @@ -107,7 +109,7 @@ you linked against by calling the functions ev_version_major and ev_version_minor. If you want, you can compare against the global symbols EV_VERSION_MAJOR and EV_VERSION_MINOR, which specify the version of the library your program was compiled against.

Usually, its a good idea to terminate if the major versions mismatch, +

Usually, it's a good idea to terminate if the major versions mismatch, 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.

@@ -115,10 +117,10 @@ not a problem.

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

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

+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.

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.

@@ -129,7 +131,7 @@ or even to sleep a while and retry until some memory is available.

as failed select, poll, epoll_wait). The message is a printable string indicating the system call or subsystem causing the problem. If this callback is set, then libev will expect it to remedy the sitution, no -matter what, when it returns. That is, libev will geenrally retry the +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).

@@ -143,9 +145,10 @@ types of such loops, the default loop, which supports signals and child events, and dynamically created loops which do not.

If you use threads, a common model is to run the default event loop in your main thread (or in a separate thrad) and for each thread you -create, you also create another event loop. Libev itself does no lockign -whatsoever, so if you mix calls to different event loops, make sure you -lock (this is usually a bad idea, though, even if done right).

+create, you also create another event loop. Libev itself does no locking +whatsoever, so if you mix calls to the same event loop in different +threads, make sure you lock (this is usually a bad idea, though, even if +done correctly, because it's hideous and inefficient).

struct ev_loop *ev_default_loop (unsigned int flags)

@@ -156,29 +159,30 @@ flags).

If you don't know what event loop to use, use the one returned from this function.

The flags argument can be used to specify special behaviour or specific -backends to use, and is usually specified as 0 (or EVFLAG_AUTO)

+backends to use, and is usually specified as 0 (or EVFLAG_AUTO).

It supports the following flags:

EVFLAG_AUTO

EVFLAG_AUTO

The default flags value. Use this if you have no clue (its the right +

The default flags value. Use this if you have no clue (it's the right thing, believe me).

EVFLAG_NOENV

EVFLAG_NOENV

If this flag bit is ored into the flag value then libev will not look -at the environment variable LIBEV_FLAGS. Otherwise (the default), this -environment variable will override the flags completely. This is useful -to try out specific backends to tets their performance, or to work around -bugs.

If this flag bit is ored into the flag value (or the program runs setuid +or setgid) then libev will not look at the environment variable +LIBEV_FLAGS. Otherwise (the default), this environment variable will +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.

EVMETHOD_SELECT portable select backend

EVMETHOD_POLL poll backend (everywhere except windows)

EVMETHOD_EPOLL linux only

EVMETHOD_KQUEUE some bsds only

EVMETHOD_DEVPOLL solaris 8 only

EVMETHOD_PORT solaris 10 only

EVMETHOD_SELECT (portable select backend)

EVMETHOD_POLL (poll backend, available everywhere except on windows)

EVMETHOD_EPOLL (linux only)

EVMETHOD_KQUEUE (some bsds only)

EVMETHOD_DEVPOLL (solaris 8 only)

EVMETHOD_PORT (solaris 10 only)

If one or more of these are ored into the flags value, then only these backends will be tried (in the reverse order as given here). If one are @@ -198,7 +202,7 @@ undefined behaviour (or a failed assertion if assertions are enabled).

Destroys the default loop again (frees all memory and kernel state etc.). This stops all registered event watchers (by not touching them in -any way whatsoever, although you cnanot rely on this :).

+any way whatsoever, although you cannot rely on this :).

ev_loop_destroy (loop)

@@ -214,7 +218,7 @@ again makes little sense).

You must call this function after forking if and only if you want to use the event library in both processes. If you just fork+exec, you don't have to call it.

The function itself is quite fast and its usually not a problem to call +

The function itself is quite fast and it's usually not a problem to call it just in case after a fork. To make this easy, the function will fit in quite nicely into a call to pthread_atfork:

    pthread_atfork (0, 0, ev_default_fork);
@@ -232,7 +236,7 @@ after fork, and how you do this is entirely your own problem.
 		Returns one of the EVMETHOD_* flags indicating the event backend in
 use.

ev_tstamp = ev_now (loop)

ev_tstamp ev_now (loop)

Returns the current "event loop time", which is the time the event loop got events and started processing them. This timestamp does not change @@ -249,33 +253,35 @@ events.

no event watchers are active anymore or ev_unloop was called.

A flags value of EVLOOP_NONBLOCK will look for new events, will handle those events and any outstanding ones, but will not block your process in -case there are no events.

+case there are no events and will return after one iteration of the loop.

A flags value of EVLOOP_ONESHOT will look for new events (waiting if neccessary) and will handle those and any outstanding ones. It will block -your process until at least one new event arrives.

+your process until at least one new event arrives, and will return after +one iteration of the loop.

This flags value could be used to implement alternative looping constructs, but the prepare and check watchers provide a better and more generic mechanism.

ev_unloop (loop, how)

Can be used to make a call to ev_loop return early. The how argument -must be either EVUNLOOP_ONCE, which will make the innermost ev_loop -call return, or EVUNLOOP_ALL, which will make all nested ev_loop -calls return.

Can be used to make a call to ev_loop return early (but only after it +has processed all outstanding events). The how argument must be either +EVUNLOOP_ONCE, which will make the innermost ev_loop call return, or +EVUNLOOP_ALL, which will make all nested ev_loop calls return.

ev_ref (loop)

ev_unref (loop)

Ref/unref can be used to add or remove a refcount on the event loop: Every -watcher keeps one reference. If you have a long-runing watcher you never -unregister that should not keep ev_loop from running, ev_unref() after -starting, and ev_ref() before stopping it. Libev itself uses this for -example for its internal signal pipe: It is not visible to you as a user -and should not keep ev_loop from exiting if the work is done. 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.

Ref/unref can be used to add or remove a reference count on the event +loop: Every watcher keeps one reference, and as long as the reference +count is nonzero, ev_loop will not return on its own. If you have +a watcher you never unregister that should not keep ev_loop from +returning, ev_unref() after starting, and ev_ref() before stopping it. For +example, libev itself uses this for its internal signal pipe: It is not +visible to the libev user and should not keep ev_loop from exiting if +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.

@@ -284,7 +290,7 @@ before stop.

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 -become readable, you would create an ev_io watcher for that:

+become readable, you would create an ev_io watcher for that:

  static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
   {
     ev_io_stop (w);
@@ -318,55 +324,55 @@ corresponding stop function (ev_<type>_stop (loop, watcher *)
 As long as your watcher is active (has been started but not stopped) you
 must not touch the values stored in it. Most specifically you must never
 reinitialise it or call its set method.
-You cna check wether an event is active by calling the ev_is_active
-(watcher *) macro. To see wether an event is outstanding (but the
-callback for it has not been called yet) you cna use the ev_is_pending
+
You can check whether an event is active by calling the ev_is_active
+(watcher *) macro. To see whether an event is outstanding (but the
+callback for it has not been called yet) you can use the ev_is_pending
 (watcher *) macro.

 Each and every callback receives the event loop pointer as first, the
 registered watcher structure as second, and a bitset of received events as
 third argument.
-The rceeived events usually include a single bit per event type received
+
The received events usually include a single bit per event type received
 (you can receive multiple events at the same time). The possible bit masks
 are:
 
-	EV_READ
-	EV_WRITE
+	EV_READ
+	EV_WRITE
 	
-		The file descriptor in the ev_io watcher has become readable and/or
+		
The file descriptor in the ev_io watcher has become readable and/or
 writable.
 	
-	EV_TIMEOUT
+	EV_TIMEOUT
 	
-		The ev_timer watcher has timed out.
+		The ev_timer watcher has timed out.
 	
-	EV_PERIODIC
+	EV_PERIODIC
 	
-		The ev_periodic watcher has timed out.
+		The ev_periodic watcher has timed out.
 	
-	EV_SIGNAL
+	EV_SIGNAL
 	
-		The signal specified in the ev_signal watcher has been received by a thread.
+		The signal specified in the ev_signal watcher has been received by a thread.
 	
-	EV_CHILD
+	EV_CHILD
 	
-		The pid specified in the ev_child watcher has received a status change.
+		The pid specified in the ev_child watcher has received a status change.
 	
-	EV_IDLE
+	EV_IDLE
 	
-		The ev_idle watcher has determined that you have nothing better to do.
+		The ev_idle watcher has determined that you have nothing better to do.
 	
-	EV_PREPARE
-	EV_CHECK
+	EV_PREPARE
+	EV_CHECK
 	
-		All ev_prepare watchers are invoked just before ev_loop starts
-to gather new events, and all ev_check watchers are invoked just after
+		
All ev_prepare watchers are invoked just before ev_loop starts
+to gather new events, and all ev_check watchers are invoked just after
 ev_loop has gathered them, but before it invokes any callbacks for any
 received events. Callbacks of both watcher types can start and stop as
 many watchers as they want, and all of them will be taken into account
-(for example, a ev_prepare watcher might start an idle watcher to keep
+(for example, a ev_prepare watcher might start an idle watcher to keep
 ev_loop from blocking).
 	
-	EV_ERROR
+	EV_ERROR
 	
 		An unspecified error has occured, the watcher has been stopped. This might
 happen because the watcher could not be properly started because libev
@@ -385,7 +391,7 @@ programs, though, so beware.
 ASSOCIATING CUSTOM DATA WITH A WATCHER
 
 Each watcher has, by default, a member void *data that you can change
-and read at any time, libev will completely ignore it. This cna be used
+and read at any time, libev will completely ignore it. This can be used
 to associate arbitrary data with your watcher. If you need more data and
 don't want to allocate memory and store a pointer to it in that data
 member, you can also "subclass" the watcher type and provide your own
@@ -422,26 +428,37 @@ have been omitted....
 information given in the last section.
 
 
-struct ev_io - is my file descriptor readable or writable
-
-I/O watchers check wether a file descriptor is readable or writable
+
ev_io - is this file descriptor readable or writable
+
+I/O watchers check whether a file descriptor is readable or writable
 in each iteration of the event loop (This behaviour is called
 level-triggering because you keep receiving events as long as the
-condition persists. Remember you cna stop the watcher if you don't want to
+condition persists. Remember you can stop the watcher if you don't want to
 act on the event and neither want to receive future events).
+In general you can register as many read and/or write event watchers oer
+fd as you want (as long as you don't confuse yourself). Setting all file
+descriptors to non-blocking mode is also usually a good idea (but not
+required if you know what you are doing).
+You have to be careful with dup'ed file descriptors, though. Some backends
+(the linux epoll backend is a notable example) cannot handle dup'ed file
+descriptors correctly if you register interest in two or more fds pointing
+to the same file/socket etc. description.
+If you must do this, then force the use of a known-to-be-good backend
+(at the time of this writing, this includes only EVMETHOD_SELECT and
+EVMETHOD_POLL).
 
 	ev_io_init (ev_io *, callback, int fd, int events)
 	ev_io_set (ev_io *, int fd, int events)
 	
-		Configures an ev_io watcher. The fd is the file descriptor to rceeive
+		
Configures an ev_io watcher. The fd is the file descriptor to rceeive
 events for and events is either EV_READ, EV_WRITE or EV_READ |
 EV_WRITE to receive the given events.
 	
 
 
 
-struct ev_timer - relative and optionally recurring timeouts
-
+ev_timer - relative and optionally recurring timeouts
+
 Timer watchers are simple relative timers that generate an event after a
 given time, and optionally repeating in regular intervals after that.
 The timers are based on real time, that is, if you register an event that
@@ -449,6 +466,14 @@ times out after an hour and youreset your system clock to last years
 time, it will still time out after (roughly) and hour. "Roughly" because
 detecting time jumps is hard, and soem inaccuracies are unavoidable (the
 monotonic clock option helps a lot here).
+The relative timeouts are calculated relative to the ev_now ()
+time. This is usually the right thing as this timestamp refers to the time
+of the event triggering whatever timeout you are modifying/starting.  If
+you suspect event processing to be delayed and you *need* to base the timeout
+ion the current time, use something like this to adjust for this:
+   ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
+
+
 
 	ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
 	ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
@@ -474,7 +499,7 @@ value), or reset the running timer to the repeat value.
 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 ev_timer_again each
+configure an ev_timer with after=repeat=60 and calling 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.
@@ -482,16 +507,16 @@ the timer, and again will automatically restart it if need be.
 
 
 
-ev_periodic
-
+ev_periodic - to cron or not to cron
+
 Periodic watchers are also timers of a kind, but they are very versatile
 (and unfortunately a bit complex).
-Unlike ev_timer's, they are not based on real time (or relative time)
+
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
-take a year to trigger the event (unlike an ev_timer, which would trigger
+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).
 They can also be used to implement vastly more complex timers, such as
@@ -527,10 +552,10 @@ time:


 					This doesn't mean there will always be 3600 seconds in between triggers,
 but only that the the callback will be called when the system time shows a
-full hour (UTC), or more correct, when the system time is evenly divisible
+full hour (UTC), or more correctly, when the system time is evenly divisible
 by 3600.
 					Another way to think about it (for the mathematically inclined) is that
-ev_periodic will try to run the callback in this mode at the next possible
+ev_periodic will try to run the callback in this mode at the next possible
 time where time = at (mod interval), regardless of any time jumps.


 				* manual reschedule mode (reschedule_cb = callback)
@@ -540,10 +565,12 @@ ignored. Instead, each time the periodic watcher gets scheduled, the
 reschedule callback will be called with the watcher as first, and the
 current time as second argument.
 					NOTE: This callback MUST NOT stop or destroy the periodic or any other
-periodic watcher, ever, or make any event loop modificstions. If you need
-to stop it, return 1e30 (or so, fudge fudge) and stop it afterwards.
-					Its prototype is c<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
-ev_tstamp now)>, e.g.:
+periodic watcher, ever, or make any event loop modifications. If you need
+to stop it, return now + 1e30 (or so, fudge fudge) and stop it afterwards.
+					Also, this callback must always return a time that is later than the
+passed now value. Not even now itself will be ok.
+					Its prototype is ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
+ev_tstamp now), e.g.:
    static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
    {
      return now + 60.;
@@ -572,13 +599,13 @@ program when the crontabs have changed).

`ev_signal` - signal me when a signal gets signalled

Signal watchers will trigger an event when the process receives a specific signal one or more times. Even though signals are very asynchronous, libev -will try its best to deliver signals synchronously, i.e. as part of the +will try it's best to deliver signals synchronously, i.e. as part of the normal event processing, like any other event.

You cna configure as many watchers as you like per signal. Only when the +

You can configure as many watchers as you like per signal. Only when the first watcher gets started will libev actually register a signal watcher with the kernel (thus it coexists with your own signal handlers as long as you don't register any with libev). Similarly, when the last signal @@ -594,8 +621,8 @@ of the SIGxxx constants).

ev_child - wait for pid status changes

`ev_child` - wait for pid status changes

Child watchers trigger when your process receives a SIGCHLD in response to some child status changes (most typically when a child of yours dies).

@@ -605,19 +632,22 @@ some child status changes (most typically when a child of yours dies).

Configures the watcher to wait for status changes of process pid (or any process if pid is specified as 0). The callback can look at the rstatus member of the ev_child watcher structure to see -the status word (use the macros from sys/wait.h). The rpid member -contains the pid of the process causing the status change.

+the status word (use the macros from sys/wait.h and see your systems +waitpid documentation). The rpid member contains the pid of the +process causing the status change.

ev_idle - when you've got nothing better to do

Idle watchers trigger events when there are no other I/O or timer (or -periodic) events pending. That is, as long as your process is busy -handling sockets or timeouts it will not be called. But when your process -is idle all idle watchers are being called again and again - until -stopped, that is, or your process receives more events.

`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.

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 @@ -636,36 +666,42 @@ believe me.

prepare and check - your hooks into the event loop

Prepare and check watchers usually (but not always) are used in -tandom. Prepare watchers get invoked before the process blocks and check -watchers afterwards.

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.

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 provide -just this functionality). Then, in the check watcher you check for any -events that occured (by making your callbacks set soem flags for example) -and call back into the library.

As another example, the perl Coro module uses these hooks to integrate +to be watched by the other library, registering ev_io watchers for +them and starting an ev_timer watcher for any timeouts (many libraries +provide just this functionality). Then, in the check watcher you check for +any events that occured (by checking the pending status of all watchers +and stopping them) and call back into the library. The I/O and timer +callbacks will never actually be called (but must be valid neverthelles, +because you never know, you know?).

As another example, the Perl Coro module uses these hooks to integrate coroutines into libev programs, by yielding to other active coroutines during each prepare and only letting the process block if no coroutines -are ready to run.

+are ready to run (its actually more complicated, it only runs coroutines +with priority higher than the event loop and one lower priority once, +using idle watchers to keep the event loop from blocking if lower-priority +coroutines exist, thus mapping low-priority coroutines to idle/background +tasks).

ev_prepare_init (ev_prepare *, callback)

ev_check_init (ev_check *, callback)

Initialises and configures the prepare or check watcher - they have no parameters of any kind. There are ev_prepare_set and ev_check_set -macros, but using them is utterly, utterly pointless.

+macros, but using them is utterly, utterly and completely pointless.

OTHER FUNCTIONS

Top

There are some other fucntions of possible interest. Described. Here. Now.

There are some other functions of possible interest. Described. Here. Now.

ev_once (loop, int fd, int events, ev_tstamp timeout, callback)

@@ -674,36 +710,39 @@ callback on whichever event happens first and automatically stop both watchers. This is useful if you want to wait for a single event on an fd or timeout without havign to allocate/configure/start/stop/free one or more watchers yourself.

If fd is less than 0, then no I/O watcher will be started and events is -ignored. Otherwise, an ev_io watcher for the given fd and events set -will be craeted and started.

If fd is less than 0, then no I/O watcher will be started and events +is being ignored. Otherwise, an ev_io watcher for the given fd and +events set will be craeted and started.

If timeout is less than 0, then no timeout watcher will be -started. Otherwise an ev_timer watcher with after = timeout (and repeat -= 0) will be started.

The callback has the type void (*cb)(int revents, void *arg) and -gets passed an events set (normally a combination of EV_ERROR, EV_READ, -EV_WRITE or EV_TIMEOUT) and the arg value passed to ev_once:

+started. Otherwise an ev_timer watcher with after = timeout (and +repeat = 0) will be started. While 0 is a valid timeout, it is of +dubious value.

The callback has the type void (*cb)(int revents, void *arg) and gets +passed an events set like normal event callbacks (with a combination of +EV_ERROR, EV_READ, EV_WRITE or EV_TIMEOUT) and the arg +value passed to ev_once:

  static void stdin_ready (int revents, void *arg)
   {
     if (revents & EV_TIMEOUT)
-      /* doh, nothing entered */
+      /* doh, nothing entered */;
     else if (revents & EV_READ)
-      /* stdin might have data for us, joy! */
+      /* stdin might have data for us, joy! */;
   }
 
-  ev_once (STDIN_FILENO, EV_READm 10., stdin_ready, 0);
+  ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);

ev_feed_event (loop, watcher, int events)

Feeds the given event set into the event loop, as if the specified event -has happened for the specified watcher (which must be a pointer to an -initialised but not necessarily active event watcher).

+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)

Feed an event on the given fd, as if a file descriptor backend detected it.

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)

CONVENTIONS

ASSOCIATING CUSTOM DATA WITH A WATCHER

struct ev_io - is my file descriptor readable or writable

`ev_io` - is this file descriptor readable or writable

struct ev_timer - relative and optionally recurring timeouts

`ev_timer` - relative and optionally recurring timeouts

ev_periodic

`ev_periodic` - to cron or not to cron