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.

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).

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).

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.

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.

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).

ev_prepare and 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 could be used, for example, to track variable changes, implement your own @@ -686,16 +690,16 @@ 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).

ev_prepare_init (ev_prepare *, callback)
ev_check_init (ev_check *, callback)

`ev_prepare` and `ev_check` - customise your event loop

LIBEVENT EMULATION

C++ SUPPORT

AUTHOR

ev_prepare and ev_check - customise your event loop

LIBEVENT EMULATION

C++ SUPPORT

AUTHOR

`ev_prepare` and `ev_check` - customise your event loop