renamed METHODs to BACKENDs

[software/libev.git] / ev.pod

diff --git a/ev.pod b/ev.pod
index 82febdd73f767243bf51688414cbfcc647f6ebe2..487ff56e9606c31361abfd9afcb024833d259d08 100644 (file)
--- a/ev.pod
+++ b/ev.pod
@@ -58,7 +58,9 @@ library in any way.
 
 =item ev_tstamp ev_time ()
 
 
 =item ev_tstamp ev_time ()
 

-Returns the current time as libev would use it.
+Returns the current time as libev would use it. Please note that the
+C<ev_now> function is usually faster and also often returns the timestamp
+you actually want to know.

 
 =item int ev_version_major ()
 
 
 =item int ev_version_major ()
 


@@ -75,6 +77,22 @@ 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.
 
 compatible to older versions, so a larger minor version alone is usually
 not a problem.
 

+=item unsigned int ev_supported_backends ()
+
+Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
+value) compiled into this binary of libev (independent of their
+availability on the system you are running on). See C<ev_default_loop> for
+a description of the set values.
+
+=item unsigned int ev_recommended_backends ()
+
+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 C<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
+C<EVFLAG_AUTO> will probe for.
+

 =item ev_set_allocator (void *(*cb)(void *ptr, long size))
 
 Sets the allocation function to use (the prototype is similar to the
 =item ev_set_allocator (void *(*cb)(void *ptr, long size))
 
 Sets the allocation function to use (the prototype is similar to the


@@ -119,13 +137,13 @@ done correctly, because it's hideous and inefficient).
 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
 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, check C<ev_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
 
 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 C<0> (or EVFLAG_AUTO).

 
 It supports the following flags:
 
 
 It supports the following flags:
 


@@ -145,24 +163,70 @@ 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.
 
 useful to try out specific backends to test their performance, or to work
 around bugs.
 

-=item C<EVMETHOD_SELECT>  (portable select backend)
+=item C<EVBACKEND_SELECT>  (value 1, portable select backend)

 
 

-=item C<EVMETHOD_POLL>    (poll backend, available everywhere except on windows)
+This is your standard select(2) backend. Not I<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.

 
 

-=item C<EVMETHOD_EPOLL>   (linux only)
+=item C<EVBACKEND_POLL>    (value 2, poll backend, available everywhere except on windows)

 
 

-=item C<EVMETHOD_KQUEUE>  (some bsds only)
+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).

 
 

-=item C<EVMETHOD_DEVPOLL> (solaris 8 only)
+=item C<EVBACKEND_EPOLL>   (value 4, Linux)

 
 

-=item C<EVMETHOD_PORT>    (solaris 10 only)
+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).

 
 

-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.
+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.
+
+=item C<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.
+
+=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
+
+This is not implemented yet (and might never be).
+
+=item C<EVBACKEND_PORT>    (value 32, Solaris 10)
+
+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)).
+
+=item C<EVBACKEND_ALL>
+
+Try all backends (even potentially broken ones that wouldn't be tried
+with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
+C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.

 
 =back
 
 
 =back
 

+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 :)
+

 =item struct ev_loop *ev_loop_new (unsigned int flags)
 
 Similar to C<ev_default_loop>, but always creates a new event loop that is
 =item struct ev_loop *ev_loop_new (unsigned int flags)
 
 Similar to C<ev_default_loop>, but always creates a new event loop that is


@@ -188,9 +252,9 @@ 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).
 
 after forking, in either the parent or child process (or both, but that
 again makes little sense).
 

-You I<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 I<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
 
 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


@@ -198,15 +262,19 @@ quite nicely into a call to C<pthread_atfork>:
 
     pthread_atfork (0, 0, ev_default_fork);
 
 
     pthread_atfork (0, 0, ev_default_fork);
 

+At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
+without calling this function, so if you force one of those backends you
+do not need to care.
+

 =item ev_loop_fork (loop)
 
 Like C<ev_default_fork>, but acts on an event loop created by
 C<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.
 
 =item ev_loop_fork (loop)
 
 Like C<ev_default_fork>, but acts on an event loop created by
 C<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.
 

-=item unsigned int ev_method (loop)
+=item unsigned int ev_backend (loop)

 
 

-Returns one of the C<EVMETHOD_*> flags indicating the event backend in
+Returns one of the C<EVBACKEND_*> flags indicating the event backend in

 use.
 
 =item ev_tstamp ev_now (loop)
 use.
 
 =item ev_tstamp ev_now (loop)


@@ -239,11 +307,29 @@ This flags value could be used to implement alternative looping
 constructs, but the C<prepare> and C<check> watchers provide a better and
 more generic mechanism.
 
 constructs, but the C<prepare> and C<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.
+

 =item ev_unloop (loop, how)
 
 Can be used to make a call to C<ev_loop> return early (but only after it
 has processed all outstanding events). The C<how> argument must be either
 =item ev_unloop (loop, how)
 
 Can be used to make a call to C<ev_loop> return early (but only after it
 has processed all outstanding events). The C<how> argument must be either

-C<EVUNLOOP_ONCE>, which will make the innermost C<ev_loop> call return, or
+C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or

 C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
 
 =item ev_ref (loop)
 C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
 
 =item ev_ref (loop)


@@ -304,7 +390,7 @@ corresponding stop function (C<< 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
 
 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 C<ev_is_active
 (watcher *)> macro. To see whether an event is outstanding (but the
 
 You can check whether an event is active by calling the C<ev_is_active
 (watcher *)> macro. To see whether an event is outstanding (but the


@@ -419,7 +505,7 @@ 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).
 
 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).
 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).


@@ -427,11 +513,12 @@ 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
 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
 
 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 C<EVBACKEND_SELECT> and
+C<EVBACKEND_POLL>).

 
 =over 4
 
 
 =over 4
 


@@ -451,19 +538,23 @@ 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
 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
 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 C<ev_now ()>
 time. This is usually the right thing as this timestamp refers to the time
 monotonic clock option helps a lot here).
 
 The relative timeouts are calculated relative to the C<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:
+of the event triggering whatever timeout you are modifying/starting. If
+you suspect event processing to be delayed and you I<need> to base the timeout
+on the current time, use something like this to adjust for this:

 
    ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
 
 
    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.
+

 =over 4
 
 =item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
 =over 4
 
 =item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)


@@ -478,7 +569,7 @@ later, again, and again, until stopped manually.
 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 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.
 
 =item ev_timer_again (loop)
 timer will not fire more than once per event loop iteration.
 
 =item ev_timer_again (loop)


@@ -519,6 +610,10 @@ again).
 They can also be used to implement vastly more complex timers, such as
 triggering an event on eahc midnight, local time.
 
 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 (C<at>) has been passed, but if multiple periodic timers become ready
+during the same loop iteration then order of execution is undefined.
+

 =over 4
 
 =item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
 =over 4
 
 =item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)


@@ -528,7 +623,6 @@ triggering an event on eahc midnight, local time.
 Lots of arguments, lets sort it out... There are basically three modes of
 operation, and we will explain them from simplest to complex:
 
 Lots of arguments, lets sort it out... There are basically three modes of
 operation, and we will explain them from simplest to complex:
 

-

 =over 4
 
 =item * absolute timer (interval = reschedule_cb = 0)
 =over 4
 
 =item * absolute timer (interval = reschedule_cb = 0)


@@ -584,12 +678,13 @@ will usually be called just before the callback will be triggered, but
 might be called at other times, too.
 
 NOTE: I<< This callback must always return a time that is later than the
 might be called at other times, too.
 
 NOTE: I<< This callback must always return a time that is later than the

-passed C<now> value >>. Not even C<now> itself will do, it must be larger.
+passed C<now> value >>. Not even C<now> itself will do, it I<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
 
 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 C<now> and return the timestamp value for this. How you do this
-is, again, up to you (but it is not trivial).
+next midnight after C<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).

 
 =back
 
 
 =back
 


@@ -678,7 +773,7 @@ believe me.
 =head2 C<ev_prepare> and C<ev_check> - customise your event loop
 
 Prepare and check watchers are usually (but not always) used in tandem:
 =head2 C<ev_prepare> and C<ev_check> - customise your event loop
 
 Prepare 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
 afterwards.
 
 Their main purpose is to integrate other event mechanisms into libev. This


@@ -691,17 +786,17 @@ them and starting an C<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
 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
 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).

 
 =over 4
 
 
 =over 4
 


@@ -726,7 +821,7 @@ There are some other functions of possible interest. Described. Here. Now.
 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
 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 C<fd> is less than 0, then no I/O watcher will be started and events
 more watchers yourself.
 
 If C<fd> is less than 0, then no I/O watcher will be started and events


@@ -739,7 +834,7 @@ repeat = 0) will be started. While C<0> is a valid timeout, it is of
 dubious value.
 
 The callback has the type C<void (*cb)(int revents, void *arg)> and gets
 dubious value.
 
 The callback has the type C<void (*cb)(int revents, void *arg)> and gets

-passed an events set like normal event callbacks (with a combination of
+passed an C<revents> set like normal event callbacks (a combination of

 C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
 value passed to C<ev_once>:
 
 C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
 value passed to C<ev_once>:
 


@@ -770,6 +865,37 @@ Feed an event as if the given signal occured (loop must be the default loop!).
 
 =back
 
 
 =back
 

+=head1 LIBEVENT EMULATION
+
+Libev offers a compatibility emulation layer for libevent. It cannot
+emulate the internals of libevent, so here are some usage hints:
+
+=over 4
+
+=item * Use it by including <event.h>, as usual.
+
+=item * The following members are fully supported: ev_base, ev_callback,
+ev_arg, ev_fd, ev_res, ev_events.
+
+=item * Avoid using ev_flags and the EVLIST_*-macros, while it is
+maintained by libev, it does not work exactly the same way as in libevent (consider
+it a private API).
+
+=item * Priorities are not currently supported. Initialising priorities
+will fail and all watchers will have the same priority, even though there
+is an ev_pri field.
+
+=item * Other members are not supported.
+
+=item * The libev emulation is I<not> ABI compatible to libevent, you need
+to use the libev header file and library.
+
+=back
+
+=head1 C++ SUPPORT
+
+TBD.
+

 =head1 AUTHOR
 
 Marc Lehmann <libev@schmorp.de>.
 =head1 AUTHOR
 
 Marc Lehmann <libev@schmorp.de>.