ev_io - is my file descriptor readable or writableev_io - is this file descriptor readable or writableev_timer - relative and optionally recurring timeoutsev_periodic - to cron or not to cron itev_periodic - to cron or not to cronev_signal - signal me when a signal gets signalledev_child - wait for pid status changesev_idle - when you've got nothing better to doev_prepare and ev_check - customise your event looploop (which is always of type struct ev_loop
will not have this argument.
-TIME AND OTHER GLOBAL FUNCTIONS
-
+TIME REPRESENTATION
+
Libev represents time as a single floating point number, representing the
(fractional) number of seconds since the (POSIX) epoch (somewhere near
the beginning of 1970, details are complicated, don't ask). This type is
called ev_tstamp, which is what you should use too. It usually aliases
to the double type in C.
+
+
+GLOBAL FUNCTIONS
+
- ev_tstamp ev_time ()
-
@@ -144,7 +149,7 @@ requested operation, or, if the condition doesn't go away, do bad stuff
types of such loops, the 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
-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
@@ -324,14 +329,14 @@ 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.
-You cna check whether an event is active by calling the ev_is_active
+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 cna use the ev_is_pending
+callback for it has not been called yet) you can use the ev_is_pending
(watcher *) macro.
Each and every callback receives the event loop pointer as first, the
registered watcher structure as second, and a bitset of received events as
third argument.
-The rceeived events usually include a single bit per event type received
+
The received events usually include a single bit per event type received
(you can receive multiple events at the same time). The possible bit masks
are:
@@ -391,7 +396,7 @@ programs, though, so beware.
ASSOCIATING CUSTOM DATA WITH A WATCHER
Each watcher has, by default, a member void *data that you can change
-and read at any time, libev will completely ignore it. This cna be used
+and read at any time, libev will completely ignore it. This can be used
to associate arbitrary data with your watcher. If you need more data and
don't want to allocate memory and store a pointer to it in that data
member, you can also "subclass" the watcher type and provide your own
@@ -428,12 +433,12 @@ have been omitted....
information given in the last section.
-ev_io - is my file descriptor readable or writable
-
+ev_io - is this file descriptor readable or writable
+
I/O watchers check whether a file descriptor is readable or writable
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 cna stop the watcher if you don't want to
+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
fd as you want (as long as you don't confuse yourself). Setting all file
@@ -507,7 +512,7 @@ the timer, and again will automatically restart it if need be.
-ev_periodic - to cron or not to cron it
+ev_periodic - to cron or not to cron
Periodic watchers are also timers of a kind, but they are very versatile
(and unfortunately a bit complex).
@@ -552,7 +557,7 @@ time:
This doesn't mean there will always be 3600 seconds in between triggers,
but only that the the callback will be called when the system time shows a
-full hour (UTC), or more correct, when the system time is evenly divisible
+full hour (UTC), or more correctly, when the system time is evenly divisible
by 3600.
Another way to think about it (for the mathematically inclined) is that
ev_periodic will try to run the callback in this mode at the next possible
@@ -565,10 +570,12 @@ 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: This callback MUST NOT stop or destroy the periodic or any other
-periodic watcher, ever, or make any event loop modificstions. If you need
-to stop it, return 1e30 (or so, fudge fudge) and stop it afterwards.
- Its prototype is c<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
-ev_tstamp now)>, e.g.:
+periodic watcher, ever, or make any event loop modifications. If you need
+to stop it, return now + 1e30 (or so, fudge fudge) and stop it afterwards.
+ Also, this callback must always return a time that is later than the
+passed now value. Not even now itself will be ok.
+ Its prototype is ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
+ev_tstamp now), e.g.:
static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
{
return now + 60.;
@@ -603,7 +610,7 @@ program when the crontabs have changed).
signal one or more times. Even though signals are very asynchronous, libev
will try it's best to deliver signals synchronously, i.e. as part of the
normal event processing, like any other event.
-You cna configure as many watchers as you like per signal. Only when the
+
You can configure as many watchers as you like per signal. Only when the
first watcher gets started will libev actually register a signal watcher
with the kernel (thus it coexists with your own signal handlers as long
as you don't register any with libev). Similarly, when the last signal
@@ -630,19 +637,22 @@ some child status changes (most typically when a child of yours dies).
Configures the watcher to wait for status changes of process pid (or
any process if pid is specified as 0). The callback can look
at the rstatus member of the ev_child watcher structure to see
-the status word (use the macros from sys/wait.h). The rpid member
-contains the pid of the process causing the status change.
+the status word (use the macros from sys/wait.h and see your systems
+waitpid documentation). The rpid member contains the pid of the
+process causing the status change.
ev_idle - when you've got nothing better to do
-Idle watchers trigger events when there are no other I/O or timer (or
-periodic) events pending. That is, as long as your process is busy
-handling sockets or timeouts it will not be called. But when your process
-is idle all idle watchers are being called again and again - until
-stopped, that is, or your process receives more events.
+Idle watchers trigger events when there are no other events are pending
+(prepare, check and other idle watchers do not count). That is, as long
+as your process is busy handling sockets or timeouts (or even signals,
+imagine) it will not be triggered. But when your process is idle all idle
+watchers are being called again and again, once per event loop iteration -
+until stopped, that is, or your process receives more events and becomes
+busy.
The most noteworthy effect is that as long as any idle watchers are
active, the process will not block when waiting for new events.
Apart from keeping your process non-blocking (which is a useful
@@ -659,38 +669,44 @@ believe me.
-prepare and check - your hooks into the event loop
-
-Prepare and check watchers usually (but not always) are used in
-tandom. Prepare watchers get invoked before the process blocks and check
-watchers afterwards.
+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
+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
watchers, integrate net-snmp or a coroutine library and lots more.
This is done by examining in each prepare call which file descriptors need
-to be watched by the other library, registering ev_io watchers for them
-and starting an 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 making your callbacks set soem flags for example)
-and call back into the library.
-As another example, the perl Coro module uses these hooks to integrate
+to be watched by the other library, registering ev_io watchers for
+them and starting an 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
+callbacks will never actually be called (but must be valid neverthelles,
+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.
+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).
- ev_prepare_init (ev_prepare *, callback)
- ev_check_init (ev_check *, callback)
-
Initialises and configures the prepare or check watcher - they have no
parameters of any kind. There are ev_prepare_set and ev_check_set
-macros, but using them is utterly, utterly pointless.
+macros, but using them is utterly, utterly and completely pointless.
OTHER FUNCTIONS
-There are some other fucntions of possible interest. Described. Here. Now.
+There are some other functions of possible interest. Described. Here. Now.
- ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
-
@@ -699,36 +715,39 @@ 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
more watchers yourself.
-
If fd is less than 0, then no I/O watcher will be started and events is
-ignored. Otherwise, an ev_io watcher for the given fd and events set
-will be craeted and started.
+ 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
+events set will be craeted and started.
If timeout is less than 0, then no timeout watcher will be
-started. Otherwise an ev_timer watcher with after = timeout (and repeat
-= 0) will be started.
- The callback has the type void (*cb)(int revents, void *arg) and
-gets passed an events set (normally a combination of EV_ERROR, EV_READ,
-EV_WRITE or EV_TIMEOUT) and the arg value passed to ev_once:
+started. Otherwise an ev_timer watcher with after = timeout (and
+repeat = 0) will be started. While 0 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
+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)
{
if (revents & EV_TIMEOUT)
- /* doh, nothing entered */
+ /* doh, nothing entered */;
else if (revents & EV_READ)
- /* stdin might have data for us, joy! */
+ /* stdin might have data for us, joy! */;
}
- ev_once (STDIN_FILENO, EV_READm 10., stdin_ready, 0);
+ ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
- ev_feed_event (loop, watcher, int events)
-
Feeds the given event set into the event loop, as if the specified event
-has happened for the specified watcher (which must be a pointer to an
-initialised but not necessarily active event watcher).
+had happened for the specified watcher (which must be a pointer to an
+initialised but not necessarily started event watcher).
- ev_feed_fd_event (loop, int fd, int revents)
-
-
Feed an event on the given fd, as if a file descriptor backend detected it.
+ Feed an event on the given fd, as if a file descriptor backend detected
+the given events it.
- ev_feed_signal_event (loop, int signum)
-