Returns the current time as libev would use it.
+Returns the current time as libev would use it. Please note that the
+ev_now function is usually faster and also often returns the timestamp
+you actually want to know.
Return the set of all backends (i.e. their corresponding EV_BACKEND_*
+value) compiled into this binary of libev (independent of their
+availability on the system you are running on). See ev_default_loop for
+a description of the set values.
Return the set of all backends compiled into this binary of libev and also
+recommended for this platform. This set is often smaller than the one
+returned by ev_supported_backends, as for example kqueue is broken on
+most BSDs and will not be autodetected unless you explicitly request it
+(assuming you know what you are doing). This is the set of backends that
+EVFLAG_AUTO will probe for.
This will initialise the default event loop if it hasn't been initialised yet and return it. If the default loop could not be initialised, returns false. If it already was initialised it simply returns it (and ignores the -flags).
+flags. If that is troubling you, checkev_backend () afterwards).
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 as0 (or EVFLAG_AUTO).
It supports the following flags:
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)EVBACKEND_SELECT (value 1, portable select backend)This is your standard select(2) backend. Not completely standard, as +libev tries to roll its own fd_set with no limits on the number of fds, +but if that fails, expect a fairly low limit on the number of fds when +using this backend. It doesn't scale too well (O(highest_fd)), but its usually +the fastest backend for a low number of fds.
+EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)And this is your standard poll(2) backend. It's more complicated than +select, but handles sparse fds better and has no artificial limit on the +number of fds you can use (except it will slow down considerably with a +lot of inactive fds). It scales similarly to select, i.e. O(total_fds).
+EVBACKEND_EPOLL (value 4, Linux)For few fds, this backend is a bit little slower than poll and select, +but it scales phenomenally better. While poll and select usually scale like +O(total_fds) where n is the total number of fds (or the highest fd), epoll scales +either O(1) or O(active_fds).
+While stopping and starting an I/O watcher in the same iteration will +result in some caching, there is still a syscall per such incident +(because the fd could point to a different file description now), so its +best to avoid that. Also, dup()ed file descriptors might not work very +well if you register events for both fds.
+Please note that epoll sometimes generates spurious notifications, so you +need to use non-blocking I/O or other means to avoid blocking when no data +(or space) is available.
+EVBACKEND_KQUEUE (value 8, most BSD clones)Kqueue deserves special mention, as at the time of this writing, it +was broken on all BSDs except NetBSD (usually it doesn't work with +anything but sockets and pipes, except on Darwin, where of course its +completely useless). For this reason its not being "autodetected" unless +you explicitly specify the flags (i.e. you don't use EVFLAG_AUTO).
+It scales in the same way as the epoll backend, but the interface to the +kernel is more efficient (which says nothing about its actual speed, of +course). While starting and stopping an I/O watcher does not cause an +extra syscall as with epoll, it still adds up to four event changes per +incident, so its best to avoid that.
+EVBACKEND_DEVPOLL (value 16, Solaris 8)This is not implemented yet (and might never be).
+EVBACKEND_PORT (value 32, Solaris 10)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 -specified, any backend will do.
+This uses the Solaris 10 port mechanism. As with everything on Solaris, +it's really slow, but it still scales very well (O(active_fds)).
+Please note that solaris ports can result in a lot of spurious +notifications, so you need to use non-blocking I/O or other means to avoid +blocking when no data (or space) is available.
+EVBACKEND_ALLTry all backends (even potentially broken ones that wouldn't be tried
+with EVFLAG_AUTO). Since this is a mask, you can do stuff such as
+EVBACKEND_ALL & ~EVBACKEND_KQUEUE.
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 none are +specified, most compiled-in backend will be tried, usually in reverse +order of their flag values :)
ev_loop_new.
one. Despite the name, you can call it anytime, but it makes most sense
after forking, in either the parent or child process (or both, but that
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.
+You must call this function in the child process 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 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);+
At the moment, EVBACKEND_SELECT and EVBACKEND_POLL are safe to use
+without calling this function, so if you force one of those backends you
+do not need to care.
pthread_atfork:
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.
Returns one of the EVMETHOD_* flags indicating the event backend in
+
Returns one of the EVBACKEND_* flags indicating the event backend in
use.
This flags value could be used to implement alternative looping
constructs, but the prepare and check watchers provide a better and
more generic mechanism.
Here are the gory details of what ev_loop does:
+1. If there are no active watchers (reference count is zero), return. + 2. Queue and immediately call all prepare watchers. + 3. If we have been forked, recreate the kernel state. + 4. Update the kernel state with all outstanding changes. + 5. Update the "event loop time". + 6. Calculate for how long to block. + 7. Block the process, waiting for events. + 8. Update the "event loop time" and do time jump handling. + 9. Queue all outstanding timers. + 10. Queue all outstanding periodics. + 11. If no events are pending now, queue all idle watchers. + 12. Queue all check watchers. + 13. Call all queued watchers in reverse order (i.e. check watchers first). + 14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK + was used, return, otherwise continue with step #1. + +
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_ONE, which will make the innermost ev_loop call return, or
EVUNLOOP_ALL, which will make all nested ev_loop calls return.
ev_<type>_start (loop, watch
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.
+reinitialise it or call its set macro.
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
@@ -442,17 +537,18 @@ 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 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
+
In general you can register as many read and/or write event watchers per
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.
+to the same underlying file/socket etc. description (that is, they share
+the same underlying "file open").
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).
+(at the time of this writing, this includes only EVBACKEND_SELECT and
+EVBACKEND_POLL).
- ev_io_init (ev_io *, callback, int fd, int events)
- ev_io_set (ev_io *, int fd, int events)
@@ -460,6 +556,16 @@ EVMETHOD_POLL).
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.
+ Please note that most of the more scalable backend mechanisms (for example
+epoll and solaris ports) can result in spurious readyness notifications
+for file descriptors, so you practically need to use non-blocking I/O (and
+treat callback invocation as hint only), or retest separately with a safe
+interface before doing I/O (XLib can do this), or force the use of either
+EVBACKEND_SELECT or EVBACKEND_POLL, which don't suffer from this
+problem. Also note that it is quite easy to have your callback invoked
+when the readyness condition is no longer valid even when employing
+typical ways of handling events, so its a good idea to use non-blocking
+I/O unconditionally.
@@ -469,18 +575,21 @@ EV_WRITE to receive the given events.
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 -times out after an hour and youreset your system clock to last years +times out after an hour and you reset 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 +detecting time jumps is hard, and some 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.);+
The callback is guarenteed to be invoked only when its timeout has passed, +but if multiple timers become ready during the same loop iteration then +order of execution is undefined.
The timer itself will do a best-effort at avoiding drift, that is, if you configure a timer to trigger every 10 seconds, then it will trigger at exactly 10 second intervals. If, however, your program cannot keep up with -the timer (ecause it takes longer than those 10 seconds to do stuff) the +the timer (because it takes longer than those 10 seconds to do stuff) the timer will not fire more than once per event loop iteration.
They can also be used to implement vastly more complex timers, such as triggering an event on eahc midnight, local time.
+As with timers, the callback is guarenteed to be invoked only when the
+time (at) has been passed, but if multiple periodic timers become ready
+during the same loop iteration then order of execution is undefined.
Lots of arguments, lets sort it out... There are basically three modes of operation, and we will explain them from simplest to complex:
- - - -
NOTE: This callback must always return a time that is later than the
-passed now value. Not even now itself will do, it must be larger.
now value. Not even now itself will do, it must be larger.
This can be used to create very complex timers, such as a timer that
triggers on each midnight, local time. To do this, you would calculate the
-next midnight after now and return the timestamp value for this. How you do this
-is, again, up to you (but it is not trivial).
now and return the timestamp value for this. How
+you do this is, again, up to you (but it is not trivial, which is the main
+reason I omitted it as an example).
ev_prepare and ev_check - customise your event loopPrepare and check watchers are usually (but not always) used in tandem: -Prepare watchers get invoked before the process blocks and check watchers +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
@@ -686,16 +795,16 @@ them and starting an ev_timer watcher for any timeouts (many librar
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,
+callbacks will never actually be called (but must be valid nevertheless,
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 (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).
+are ready to run (it's actually more complicated: it only runs coroutines +with priority higher than or equal to the event loop and one coroutine +of lower priority, but only once, using idle watchers to keep the event +loop from blocking if lower-priority coroutines are active, thus mapping +low-priority coroutines to idle/background tasks).This function combines a simple timer and an I/O watcher, calls your 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 +or timeout without having 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 being ignored. Otherwise, an ev_io watcher for the given fd and
@@ -726,7 +835,7 @@ started. Otherwise an ev_timer watcher with after = timeout0 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
+passed an revents set like normal event callbacks (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) @@ -758,6 +867,31 @@ the given events it.
Libev offers a compatibility emulation layer for libevent. It cannot +emulate the internals of libevent, so here are some usage hints:
+TBD.
+