[ViewVC] Diff of: cvs/libev/ev.pod

Comparing libev/ev.pod (file contents):
Revision 1.243 by root, Sat Jun 20 20:22:35 2009 UTC vs.
Revision 1.253 by root, Tue Jul 14 18:33:48 2009 UTC

 happily wraps around with enough iterations.
 This value can sometimes be useful as a generation counter of sorts (it
 "ticks" the number of loop iterations), as it roughly corresponds with
 C<ev_prepare> and C<ev_check> calls.
+=item unsigned int ev_loop_depth (loop)
+Returns the number of times C<ev_loop> was entered minus the number of
+times C<ev_loop> was exited, in other words, the recursion depth.
+Outside C<ev_loop>, this number is zero. In a callback, this number is
+C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
+in which case it is higher.
+Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
+etc.), doesn't count as exit.
 =item unsigned int ev_backend (loop)
 Returns one of the C<EVBACKEND_*> flags indicating the event backend in
 use.
 By setting a higher I<io collect interval> you allow libev to spend more
 time collecting I/O events, so you can handle more events per iteration,
 at the cost of increasing latency. Timeouts (both C<ev_periodic> and
 C<ev_timer>) will be not affected. Setting this to a non-null value will
-introduce an additional C<ev_sleep ()> call into most loop iterations.
+introduce an additional C<ev_sleep ()> call into most loop iterations. The
+sleep time ensures that libev will not poll for I/O events more often then
+once per this interval, on average.
 Likewise, by setting a higher I<timeout collect interval> you allow libev
 to spend more time collecting timeouts, at the expense of increased
 latency/jitter/inexactness (the watcher callback will be called
 later). C<ev_io> watchers will not be affected. Setting this to a non-null
 Many (busy) programs can usually benefit by setting the I/O collect
 interval to a value near C<0.1> or so, which is often enough for
 interactive servers (of course not for games), likewise for timeouts. It
 usually doesn't make much sense to set it to a lower value than C<0.01>,
-as this approaches the timing granularity of most systems.
+as this approaches the timing granularity of most systems. Note that if
+you do transactions with the outside world and you can't increase the
+parallelity, then this setting will limit your transaction rate (if you
+need to poll once per transaction and the I/O collect interval is 0.01,
+then you can't do more than 100 transations per second).
 Setting the I<timeout collect interval> can improve the opportunity for
 saving power, as the program will "bundle" timer callback invocations that
 are "near" in time together, by delaying some, thus reducing the number of
 times the process sleeps and wakes up again. Another useful technique to
 reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
 they fire on, say, one-second boundaries only.
+Example: we only need 0.1s timeout granularity, and we wish not to poll
+more often than 100 times per second:
+   ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
+   ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
+=item ev_invoke_pending (loop)
+This call will simply invoke all pending watchers while resetting their
+pending state. Normally, C<ev_loop> does this automatically when required,
+but when overriding the invoke callback this call comes handy.
+=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
+This overrides the invoke pending functionality of the loop: Instead of
+invoking all pending watchers when there are any, C<ev_loop> will call
+this callback instead. This is useful, for example, when you want to
+invoke the actual watchers inside another context (another thread etc.).
+If you want to reset the callback, use C<ev_invoke_pending> as new
+callback.
+=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
+Sometimes you want to share the same loop between multiple threads. This
+can be done relatively simply by putting mutex_lock/unlock calls around
+each call to a libev function.
+However, C<ev_loop> can run an indefinite time, so it is not feasible to
+wait for it to return. One way around this is to wake up the loop via
+C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
+and I<acquire> callbacks on the loop.
+When set, then C<release> will be called just before the thread is
+suspended waiting for new events, and C<acquire> is called just
+afterwards.
+Ideally, C<release> will just call your mutex_unlock function, and
+C<acquire> will just call the mutex_lock function again.
+=item ev_set_userdata (loop, void *data)
+=item ev_userdata (loop)
+Set and retrieve a single C<void *> associated with a loop. When
+C<ev_set_userdata> has never been called, then C<ev_userdata> returns
+C<0.>
+These two functions can be used to associate arbitrary data with a loop,
+and are intended solely for the C<invoke_pending_cb>, C<release> and
+C<acquire> callbacks described above, but of course can be (ab-)used for
+any other purpose as well.
 =item ev_loop_verify (loop)
 This function only does something when C<EV_VERIFY> support has been
 compiled in, which is the default for non-minimal builds. It tries to go
 The callback is guaranteed to be invoked only I<after> its timeout has
 passed (not I<at>, so on systems with very low-resolution clocks this
 might introduce a small delay). If multiple timers become ready during the
 same loop iteration then the ones with earlier time-out values are invoked
-before ones with later time-out values (but this is no longer true when a
+before ones of the same priority with later time-out values (but this is
-callback calls C<ev_loop> recursively).
+no longer true when a callback calls C<ev_loop> recursively).
 =head3 Be smart about timeouts
 Many real-world problems involve some kind of timeout, usually for error
 recovery. A typical example is an HTTP request - if the other side hangs,
 some child status changes (most typically when a child of yours dies or
 exits). It is permissible to install a child watcher I<after> the child
 has been forked (which implies it might have already exited), as long
 as the event loop isn't entered (or is continued from a watcher), i.e.,
 forking and then immediately registering a watcher for the child is fine,
-but forking and registering a watcher a few event loop iterations later is
+but forking and registering a watcher a few event loop iterations later or
-not.
+in the next callback invocation is not.
 Only the default event loop is capable of handling signals, and therefore
 you can only register child watchers in the default event loop.
+Due to some design glitches inside libev, child watchers will always be
+handled at maximum priority (their priority is set to C<EV_MAXPRI> by
+libev)
 =head3 Process Interaction
 Libev grabs C<SIGCHLD> as soon as the default event loop is
 initialised. This is necessary to guarantee proper behaviour even if
 defined to be C<0>, then they are not.
 =item EV_MINIMAL
 If you need to shave off some kilobytes of code at the expense of some
-speed, define this symbol to C<1>. Currently this is used to override some
+speed (but with the full API), define this symbol to C<1>. Currently this
-inlining decisions, saves roughly 30% code size on amd64. It also selects a
+is used to override some inlining decisions, saves roughly 30% code size
-much smaller 2-heap for timer management over the default 4-heap.
+on amd64. It also selects a much smaller 2-heap for timer management over
+the default 4-heap.
+You can save even more by disabling watcher types you do not need
+and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
+(C<-DNDEBUG>) will usually reduce code size a lot.
+Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
+provide a bare-bones event library. See C<ev.h> for details on what parts
+of the API are still available, and do not complain if this subset changes
+over time.
 =item EV_PID_HASHSIZE
 C<ev_child> watchers use a small hash table to distribute workload by
 pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
 default loop and triggering an C<ev_async> watcher from the default loop
 watcher callback into the event loop interested in the signal.
 =back
+=head4 THREAD LOCKING EXAMPLE
 =head3 COROUTINES
 Libev is very accommodating to coroutines ("cooperative threads"):
 libev fully supports nesting calls to its functions from different
 coroutines (e.g. you can call C<ev_loop> on the same loop from two
 =item C<double> must hold a time value in seconds with enough accuracy
 The type C<double> is used to represent timestamps. It is required to
 have at least 51 bits of mantissa (and 9 bits of exponent), which is good
 enough for at least into the year 4000. This requirement is fulfilled by
-implementations implementing IEEE 754 (basically all existing ones).
+implementations implementing IEEE 754, which is basically all existing
+ones. With IEEE 754 doubles, you get microsecond accuracy until at least
+2200.
 =back
 If you know of other additional requirements drop me a note.

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Comparing libev/ev.pod (file contents): Revision 1.243 by root, Sat Jun 20 20:22:35 2009 UTC vs. Revision 1.253 by root, Tue Jul 14 18:33:48 2009 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.243 by root, Sat Jun 20 20:22:35 2009 UTC vs.
Revision 1.253 by root, Tue Jul 14 18:33:48 2009 UTC