ev_io - is my file descriptor readable or writableev_timer - relative and optionally recurring timeoutsev_periodic - to cron or not to cron itev_signal - signal me when a signal gets signalledev_child - wait for pid status changesev_idle - when you've got nothing better to doLibev 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 events.
+these event sources and provide your program with events.To do this, it must take more or less complete control over your process (or thread) by executing the event loop handler, and will then communicate events via a callback mechanism.
@@ -73,14 +73,16 @@ watcher. 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). +loop mechanism itself (idle, prepare and check watchers). 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 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.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).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).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_AUTOThe 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_NOENVIf 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, 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 :).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.
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 orev_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.
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.
This flags value could be used to implement alternative looping
constructs, but the prepare and check watchers provide a better and
more generic mechanism.
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.
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.
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 anev_io watcher for that:
static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
{
ev_io_stop (w);
@@ -318,8 +324,8 @@ 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
+
You cna 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 cna use the ev_is_pending
(watcher *) macro.
Each and every callback receives the event loop pointer as first, the
@@ -329,44 +335,44 @@ third argument.
(you can receive multiple events at the same time). The possible bit masks
are:
EV_READEV_WRITEThe 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_TIMEOUTThe ev_timer watcher has timed out.
+The ev_timer watcher has timed out.
EV_PERIODICThe ev_periodic watcher has timed out.
+The ev_periodic watcher has timed out.
EV_SIGNALThe 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_CHILDThe 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_IDLEThe 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_PREPAREEV_CHECKAll 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_ERRORAn unspecified error has occured, the watcher has been stopped. This might happen because the watcher could not be properly started because libev @@ -422,26 +428,37 @@ have been omitted....
information given in the last section.I/O watchers check wether a file descriptor is readable or writable +
ev_io - is my file descriptor readable or writableI/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 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).
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.
ev_timer - relative and optionally recurring timeoutsTimer 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 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 - to cron or not to cron itPeriodic 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 @@ -530,7 +555,7 @@ 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 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.
ev_signal - signal me when a signal gets signalledSignal 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
first watcher gets started will libev actually register a signal watcher
@@ -594,8 +619,8 @@ of the SIGxxx constants).
ev_child - wait for pid status changesChild watchers trigger when your process receives a SIGCHLD in response to some child status changes (most typically when a child of yours dies).
ev_idle - when you've got nothing better to doIdle 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 @@ -643,8 +668,8 @@ watchers afterwards.
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
+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.
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
+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
+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:
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)