X-Git-Url: https://git.llucax.com/software/libev.git/blobdiff_plain/62d055cdbaae2c64101729124774d983bfcbddd4..a04347e5cbe92a5f99231dcdb3d7d0f474bad401:/ev.pod diff --git a/ev.pod b/ev.pod index 0f9e80f..c162b21 100644 --- 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 (which is always of type C) 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 @@ -49,6 +49,11 @@ the beginning of 1970, details are complicated, don't ask). This type is called C, 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 () @@ -101,7 +106,7 @@ types of such loops, the I 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 +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 @@ -422,7 +427,8 @@ 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 -to the same file/socket etc. description. +to the same 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 @@ -446,7 +452,7 @@ 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 monotonic clock option helps a lot here). @@ -455,7 +461,7 @@ The relative timeouts are calculated relative to the C 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: +on the current time, use something like this to adjust for this: ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); @@ -473,7 +479,7 @@ 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 (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) @@ -560,12 +566,10 @@ 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. -NOTE: I. If you need -to stop it, return C (or so, fudge fudge) and stop it afterwards. - -Also, I<< this callback must always return a time that is later than the -passed C value >>. Not even C itself will be ok. +NOTE: I. If you need to stop it, +return C (or so, fudge fudge) and stop it afterwards (e.g. by +starting a prepare watcher). Its prototype is C, e.g.: @@ -580,10 +584,14 @@ 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. +NOTE: I<< This callback must always return a time that is later than the +passed C value >>. Not even C itself will do, it I 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 C 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 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 @@ -669,10 +677,10 @@ believe me. =back -=head2 prepare and check - your hooks into the event loop +=head2 C and C - 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 @@ -685,17 +693,17 @@ them and starting an C 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, +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). =over 4 @@ -720,7 +728,7 @@ 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 -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 is less than 0, then no I/O watcher will be started and events @@ -733,7 +741,7 @@ repeat = 0) will be started. While C<0> is a valid timeout, it is of dubious value. The callback has the type C and gets -passed an events set like normal event callbacks (with a combination of +passed an C set like normal event callbacks (a combination of C, C, C or C) and the C value passed to C: @@ -764,6 +772,14 @@ Feed an event as if the given signal occured (loop must be the default loop!). =back +=head1 LIBEVENT EMULATION + +TBD. + +=head1 C++ SUPPORT + +TBD. + =head1 AUTHOR Marc Lehmann .