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authorroot <root>2008-10-23 06:30:48 +0000
committerroot <root>2008-10-23 06:30:48 +0000
commit88e938e5a108492683ea847bc9233c9f054f4cc0 (patch)
treecf247bb867019f48fee164cf524561880697b3d7 /ev.pod
parentc20fc675dcb3570f5da597115ced5a2a82c71029 (diff)
*** empty log message ***
Diffstat (limited to 'ev.pod')
-rw-r--r--ev.pod239
1 files changed, 170 insertions, 69 deletions
diff --git a/ev.pod b/ev.pod
index 958a8c2..aeb3a19 100644
--- a/ev.pod
+++ b/ev.pod
@@ -19,7 +19,7 @@ libev - a high performance full-featured event loop written in C
// all watcher callbacks have a similar signature
// this callback is called when data is readable on stdin
static void
- stdin_cb (EV_P_ struct ev_io *w, int revents)
+ stdin_cb (EV_P_ ev_io *w, int revents)
{
puts ("stdin ready");
// for one-shot events, one must manually stop the watcher
@@ -32,7 +32,7 @@ libev - a high performance full-featured event loop written in C
// another callback, this time for a time-out
static void
- timeout_cb (EV_P_ struct ev_timer *w, int revents)
+ timeout_cb (EV_P_ ev_timer *w, int revents)
{
puts ("timeout");
// this causes the innermost ev_loop to stop iterating
@@ -43,7 +43,7 @@ libev - a high performance full-featured event loop written in C
main (void)
{
// use the default event loop unless you have special needs
- struct ev_loop *loop = ev_default_loop (0);
+ ev_loop *loop = ev_default_loop (0);
// initialise an io watcher, then start it
// this one will watch for stdin to become readable
@@ -105,7 +105,7 @@ configuration will be described, which supports multiple event loops. For
more info about various configuration options please have a look at
B<EMBED> section in this manual. If libev was configured without 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
+name C<loop> (which is always of type C<ev_loop *>) will not have
this argument.
=head2 TIME REPRESENTATION
@@ -278,7 +278,7 @@ Example: This is basically the same thing that libev does internally, too.
=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
-An event loop is described by a C<struct ev_loop *>. The library knows two
+An event loop is described by a C<ev_loop *>. The library knows two
types of such loops, the I<default> loop, which supports signals and child
events, and dynamically created loops which do not.
@@ -712,7 +712,7 @@ respectively).
Example: Create a signal watcher, but keep it from keeping C<ev_loop>
running when nothing else is active.
- struct ev_signal exitsig;
+ ev_signal exitsig;
ev_signal_init (&exitsig, sig_cb, SIGINT);
ev_signal_start (loop, &exitsig);
evf_unref (loop);
@@ -788,14 +788,14 @@ A watcher is a structure that you create and register to record your
interest in some event. For instance, if you want to wait for STDIN to
become readable, you would create an C<ev_io> watcher for that:
- static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
+ static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
{
ev_io_stop (w);
ev_unloop (loop, EVUNLOOP_ALL);
}
struct ev_loop *loop = ev_default_loop (0);
- struct ev_io stdin_watcher;
+ ev_io stdin_watcher;
ev_init (&stdin_watcher, my_cb);
ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
ev_io_start (loop, &stdin_watcher);
@@ -931,7 +931,7 @@ which rolls both calls into one.
You can reinitialise a watcher at any time as long as it has been stopped
(or never started) and there are no pending events outstanding.
-The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
+The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
int revents)>.
Example: Initialise an C<ev_io> watcher in two steps.
@@ -1066,7 +1066,7 @@ data:
struct my_io
{
- struct ev_io io;
+ ev_io io;
int otherfd;
void *somedata;
struct whatever *mostinteresting;
@@ -1079,7 +1079,7 @@ data:
And since your callback will be called with a pointer to the watcher, you
can cast it back to your own type:
- static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
+ static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
{
struct my_io *w = (struct my_io *)w_;
...
@@ -1107,14 +1107,14 @@ programmers):
#include <stddef.h>
static void
- t1_cb (EV_P_ struct ev_timer *w, int revents)
+ t1_cb (EV_P_ ev_timer *w, int revents)
{
struct my_biggy big = (struct my_biggy *
(((char *)w) - offsetof (struct my_biggy, t1));
}
static void
- t2_cb (EV_P_ struct ev_timer *w, int revents)
+ t2_cb (EV_P_ ev_timer *w, int revents)
{
struct my_biggy big = (struct my_biggy *
(((char *)w) - offsetof (struct my_biggy, t2));
@@ -1259,7 +1259,7 @@ readable, but only once. Since it is likely line-buffered, you could
attempt to read a whole line in the callback.
static void
- stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
+ stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
{
ev_io_stop (loop, w);
.. read from stdin here (or from w->fd) and handle any I/O errors
@@ -1267,7 +1267,7 @@ attempt to read a whole line in the callback.
...
struct ev_loop *loop = ev_default_init (0);
- struct ev_io stdin_readable;
+ ev_io stdin_readable;
ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
ev_io_start (loop, &stdin_readable);
ev_loop (loop, 0);
@@ -1288,6 +1288,134 @@ The callback is guaranteed to be invoked only I<after> its timeout has
passed, but if multiple timers become ready during the same loop iteration
then order of execution is undefined.
+=head3 Be smart about timeouts
+
+Many real-world problems invole some kind of time-out, usually for error
+recovery. A typical example is an HTTP request - if the other side hangs,
+you want to raise some error after a while.
+
+Here are some ways on how to handle this problem, from simple and
+inefficient to very efficient.
+
+In the following examples a 60 second activity timeout is assumed - a
+timeout that gets reset to 60 seconds each time some data ("a lifesign")
+was received.
+
+=over 4
+
+=item 1. Use a timer and stop, reinitialise, start it on activity.
+
+This is the most obvious, but not the most simple way: In the beginning,
+start the watcher:
+
+ ev_timer_init (timer, callback, 60., 0.);
+ ev_timer_start (loop, timer);
+
+Then, each time there is some activity, C<ev_timer_stop> the timer,
+initialise it again, and start it:
+
+ ev_timer_stop (loop, timer);
+ ev_timer_set (timer, 60., 0.);
+ ev_timer_start (loop, timer);
+
+This is relatively simple to implement, but means that each time there
+is some activity, libev will first have to remove the timer from it's
+internal data strcuture and then add it again.
+
+=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
+
+This is the easiest way, and involves using C<ev_timer_again> instead of
+C<ev_timer_start>.
+
+For this, configure an C<ev_timer> with a C<repeat> value of C<60> and
+then call C<ev_timer_again> at start and each time you successfully read
+or write some data. If you go into an idle state where you do not expect
+data to travel on the socket, you can C<ev_timer_stop> the timer, and
+C<ev_timer_again> will automatically restart it if need be.
+
+That means you can ignore the C<after> value and C<ev_timer_start>
+altogether and only ever use the C<repeat> value and C<ev_timer_again>.
+
+At start:
+
+ ev_timer_init (timer, callback, 0., 60.);
+ ev_timer_again (loop, timer);
+
+Each time you receive some data:
+
+ ev_timer_again (loop, timer);
+
+It is even possible to change the time-out on the fly:
+
+ timer->repeat = 30.;
+ ev_timer_again (loop, timer);
+
+This is slightly more efficient then stopping/starting the timer each time
+you want to modify its timeout value, as libev does not have to completely
+remove and re-insert the timer from/into it's internal data structure.
+
+=item 3. Let the timer time out, but then re-arm it as required.
+
+This method is more tricky, but usually most efficient: Most timeouts are
+relatively long compared to the loop iteration time - in our example,
+within 60 seconds, there are usually many I/O events with associated
+activity resets.
+
+In this case, it would be more efficient to leave the C<ev_timer> alone,
+but remember the time of last activity, and check for a real timeout only
+within the callback:
+
+ ev_tstamp last_activity; // time of last activity
+
+ static void
+ callback (EV_P_ ev_timer *w, int revents)
+ {
+ ev_tstamp now = ev_now (EV_A);
+ ev_tstamp timeout = last_activity + 60.;
+
+ // if last_activity is older than now - timeout, we did time out
+ if (timeout < now)
+ {
+ // timeout occured, take action
+ }
+ else
+ {
+ // callback was invoked, but there was some activity, re-arm
+ // to fire in last_activity + 60.
+ w->again = timeout - now;
+ ev_timer_again (EV_A_ w);
+ }
+ }
+
+To summarise the callback: first calculate the real time-out (defined as
+"60 seconds after the last activity"), then check if that time has been
+reached, which means there was a real timeout. Otherwise the callback was
+invoked too early (timeout is in the future), so re-schedule the timer to
+fire at that future time.
+
+Note how C<ev_timer_again> is used, taking advantage of the
+C<ev_timer_again> optimisation when the timer is already running.
+
+This scheme causes more callback invocations (about one every 60 seconds),
+but virtually no calls to libev to change the timeout.
+
+To start the timer, simply intiialise the watcher and C<last_activity>,
+then call the callback:
+
+ ev_timer_init (timer, callback);
+ last_activity = ev_now (loop);
+ callback (loop, timer, EV_TIMEOUT);
+
+And when there is some activity, simply remember the time in
+C<last_activity>:
+
+ last_actiivty = ev_now (loop);
+
+This technique is slightly more complex, but in most cases where the
+time-out is unlikely to be triggered, much more efficient.
+
+=back
+
=head3 The special problem of time updates
Establishing the current time is a costly operation (it usually takes at
@@ -1340,36 +1468,8 @@ If the timer is started but non-repeating, stop it (as if it timed out).
If the timer is repeating, either start it if necessary (with the
C<repeat> value), or reset the running timer to the C<repeat> value.
-This sounds a bit complicated, but here is a useful and typical
-example: Imagine you have a TCP connection and you want a so-called idle
-timeout, that is, you want to be called when there have been, say, 60
-seconds of inactivity on the socket. The easiest way to do this is to
-configure an C<ev_timer> with a C<repeat> value of C<60> and then call
-C<ev_timer_again> each time you successfully read or write some data. If
-you go into an idle state where you do not expect data to travel on the
-socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
-automatically restart it if need be.
-
-That means you can ignore the C<after> value and C<ev_timer_start>
-altogether and only ever use the C<repeat> value and C<ev_timer_again>:
-
- ev_timer_init (timer, callback, 0., 5.);
- ev_timer_again (loop, timer);
- ...
- timer->again = 17.;
- ev_timer_again (loop, timer);
- ...
- timer->again = 10.;
- ev_timer_again (loop, timer);
-
-This is more slightly efficient then stopping/starting the timer each time
-you want to modify its timeout value.
-
-Note, however, that it is often even more efficient to remember the
-time of the last activity and let the timer time-out naturally. In the
-callback, you then check whether the time-out is real, or, if there was
-some activity, you reschedule the watcher to time-out in "last_activity +
-timeout - ev_now ()" seconds.
+This sounds a bit complicated, see "Be smart about timeouts", above, for a
+usage example.
=item ev_tstamp repeat [read-write]
@@ -1384,12 +1484,12 @@ which is also when any modifications are taken into account.
Example: Create a timer that fires after 60 seconds.
static void
- one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
+ one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
{
.. one minute over, w is actually stopped right here
}
- struct ev_timer mytimer;
+ ev_timer mytimer;
ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
ev_timer_start (loop, &mytimer);
@@ -1397,12 +1497,12 @@ Example: Create a timeout timer that times out after 10 seconds of
inactivity.
static void
- timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
+ timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
{
.. ten seconds without any activity
}
- struct ev_timer mytimer;
+ ev_timer mytimer;
ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
ev_timer_again (&mytimer); /* start timer */
ev_loop (loop, 0);
@@ -1498,10 +1598,11 @@ If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
only event loop modification you are allowed to do).
-The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic
+The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
*w, ev_tstamp now)>, e.g.:
- static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
+ static ev_tstamp
+ my_rescheduler (ev_periodic *w, ev_tstamp now)
{
return now + 60.;
}
@@ -1548,7 +1649,7 @@ The current interval value. Can be modified any time, but changes only
take effect when the periodic timer fires or C<ev_periodic_again> is being
called.
-=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]
+=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
The current reschedule callback, or C<0>, if this functionality is
switched off. Can be changed any time, but changes only take effect when
@@ -1563,12 +1664,12 @@ system time is divisible by 3600. The callback invocation times have
potentially a lot of jitter, but good long-term stability.
static void
- clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
+ clock_cb (struct ev_loop *loop, ev_io *w, int revents)
{
... its now a full hour (UTC, or TAI or whatever your clock follows)
}
- struct ev_periodic hourly_tick;
+ ev_periodic hourly_tick;
ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
ev_periodic_start (loop, &hourly_tick);
@@ -1577,7 +1678,7 @@ Example: The same as above, but use a reschedule callback to do it:
#include <math.h>
static ev_tstamp
- my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
+ my_scheduler_cb (ev_periodic *w, ev_tstamp now)
{
return now + (3600. - fmod (now, 3600.));
}
@@ -1586,7 +1687,7 @@ Example: The same as above, but use a reschedule callback to do it:
Example: Call a callback every hour, starting now:
- struct ev_periodic hourly_tick;
+ ev_periodic hourly_tick;
ev_periodic_init (&hourly_tick, clock_cb,
fmod (ev_now (loop), 3600.), 3600., 0);
ev_periodic_start (loop, &hourly_tick);
@@ -1638,12 +1739,12 @@ The signal the watcher watches out for.
Example: Try to exit cleanly on SIGINT.
static void
- sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
+ sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
{
ev_unloop (loop, EVUNLOOP_ALL);
}
- struct ev_signal signal_watcher;
+ ev_signal signal_watcher;
ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
ev_signal_start (loop, &signal_watcher);
@@ -1728,7 +1829,7 @@ its completion.
ev_child cw;
static void
- child_cb (EV_P_ struct ev_child *w, int revents)
+ child_cb (EV_P_ ev_child *w, int revents)
{
ev_child_stop (EV_A_ w);
printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
@@ -1990,14 +2091,14 @@ Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
callback, free it. Also, use no error checking, as usual.
static void
- idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
+ idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
{
free (w);
// now do something you wanted to do when the program has
// no longer anything immediate to do.
}
- struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
+ ev_idle *idle_watcher = malloc (sizeof (ev_idle));
ev_idle_init (idle_watcher, idle_cb);
ev_idle_start (loop, idle_cb);
@@ -2088,13 +2189,13 @@ the callbacks for the IO/timeout watchers might not have been called yet.
static ev_timer tw;
static void
- io_cb (ev_loop *loop, ev_io *w, int revents)
+ io_cb (struct ev_loop *loop, ev_io *w, int revents)
{
}
// create io watchers for each fd and a timer before blocking
static void
- adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
+ adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
{
int timeout = 3600000;
struct pollfd fds [nfd];
@@ -2119,7 +2220,7 @@ the callbacks for the IO/timeout watchers might not have been called yet.
// stop all watchers after blocking
static void
- adns_check_cb (ev_loop *loop, ev_check *w, int revents)
+ adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
{
ev_timer_stop (loop, &tw);
@@ -2297,7 +2398,7 @@ used).
struct ev_loop *loop_hi = ev_default_init (0);
struct ev_loop *loop_lo = 0;
- struct ev_embed embed;
+ ev_embed embed;
// see if there is a chance of getting one that works
// (remember that a flags value of 0 means autodetection)
@@ -2321,7 +2422,7 @@ C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
struct ev_loop *loop = ev_default_init (0);
struct ev_loop *loop_socket = 0;
- struct ev_embed embed;
+ ev_embed embed;
if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
@@ -2545,18 +2646,18 @@ Example: wait up to ten seconds for data to appear on STDIN_FILENO.
ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
-=item ev_feed_event (ev_loop *, watcher *, int revents)
+=item ev_feed_event (struct ev_loop *, watcher *, int revents)
Feeds the given event set into the event loop, as if the specified event
had happened for the specified watcher (which must be a pointer to an
initialised but not necessarily started event watcher).
-=item ev_feed_fd_event (ev_loop *, int fd, int revents)
+=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
Feed an event on the given fd, as if a file descriptor backend detected
the given events it.
-=item ev_feed_signal_event (ev_loop *loop, int signum)
+=item ev_feed_signal_event (struct ev_loop *loop, int signum)
Feed an event as if the given signal occurred (C<loop> must be the default
loop!).