*** empty log message ***

[software/libev.git] / ev.pod

diff --git a/ev.pod b/ev.pod
index 0f9e80f8ce0adba085b5baf9b00386d0da9a5c52..411fbb5f1a38cb0af2e56a0c39d6dc180df832bf 100644 (file)
--- a/ev.pod
+++ b/ev.pod
@@ -41,7 +41,7 @@ support for multiple event loops, then all functions taking an initial
 argument of name C<loop> (which is always of type C<struct ev_loop *>)
 will not have this argument.
 
 argument of name C<loop> (which is always of type C<struct ev_loop *>)
 will not have this argument.
 

-=head1 TIME AND OTHER GLOBAL FUNCTIONS
+=head1 TIME REPRESENTATION

 
 Libev represents time as a single floating point number, representing the
 (fractional) number of seconds since the (POSIX) epoch (somewhere near
 
 Libev represents time as a single floating point number, representing the
 (fractional) number of seconds since the (POSIX) epoch (somewhere near


@@ -49,11 +49,18 @@ the beginning of 1970, details are complicated, don't ask). This type is
 called C<ev_tstamp>, which is what you should use too. It usually aliases
 to the double type in C.
 
 called C<ev_tstamp>, which is what you should use too. It usually aliases
 to the double type in C.
 

+=head1 GLOBAL FUNCTIONS
+
+These functions can be called anytime, even before initialising the
+library in any way.
+

 =over 4
 
 =item ev_tstamp ev_time ()
 
 =over 4
 
 =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 ()
 


@@ -101,7 +108,7 @@ types of such loops, the I<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
 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
+in your main thread (or in a separate thread) and for each thread you

 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
 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


@@ -234,11 +241,29 @@ 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)


@@ -414,7 +439,7 @@ 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).


@@ -422,7 +447,8 @@ 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
 (at the time of this writing, this includes only EVMETHOD_SELECT and
 
 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


@@ -446,19 +472,23 @@ 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)


@@ -473,7 +503,7 @@ 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)


@@ -514,6 +544,10 @@ 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)


@@ -523,7 +557,6 @@ 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)


@@ -560,12 +593,10 @@ 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.
 
 reschedule callback will be called with the watcher as first, and the
 current time as second argument.
 

-NOTE: I<This callback MUST NOT stop or destroy the periodic or any other
-periodic watcher, ever, or make any event loop modifications>. If you need
-to stop it, return C<now + 1e30> (or so, fudge fudge) and stop it afterwards.
-
-Also, I<< this callback must always return a time that is later than the
-passed C<now> value >>. Not even C<now> itself will be ok.
+NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
+ever, or make any event loop modifications>. If you need to stop it,
+return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
+starting a prepare watcher).

 
 Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
 ev_tstamp now)>, e.g.:
 
 Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
 ev_tstamp now)>, e.g.:


@@ -580,10 +611,14 @@ It must return the next time to trigger, based on the passed time value
 will usually be called just before the callback will be triggered, but
 might be called at other times, too.
 
 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
+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
 


@@ -669,10 +704,10 @@ believe me.
 
 =back
 
 
 =back
 

-=head2 prepare and check - your hooks into the event loop
+=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 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


@@ -685,17 +720,17 @@ 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
 


@@ -720,7 +755,7 @@ 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


@@ -733,7 +768,7 @@ 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>:
 


@@ -764,6 +799,37 @@ 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>.