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fix and update ev_stat docs

master
Marc Alexander Lehmann 14 years ago
parent
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3891cec873
  1. 47
      ev.pod

47
ev.pod

@ -1498,6 +1498,23 @@ to fall back to regular polling again even with inotify, but changes are
usually detected immediately, and if the file exists there will be no
polling.
=head3 The special problem of stat time resolution
The C<stat ()> syscall only supports full-second resolution portably, and
even on systems where the resolution is higher, many filesystems still
only support whole seconds.
That means that, if the time is the only thing that changes, you might
miss updates: on the first update, C<ev_stat> detects a change and calls
your callback, which does something. When there is another update within
the same second, C<ev_stat> will be unable to detect it.
The solution to this is to delay acting on a change for a second (or till
the next second boundary), using a roughly one-second delay C<ev_timer>
(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>
is added to work around small timing inconsistencies of some operating
systems.
=head3 Watcher-Specific Functions and Data Members
=over 4
@ -1566,8 +1583,36 @@ Example: Watch C</etc/passwd> for attribute changes.
...
ev_stat passwd;
ev_stat_init (&passwd, passwd_cb, "/etc/passwd");
ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
ev_stat_start (loop, &passwd);
Example: Like above, but additionally use a one-second delay so we do not
miss updates (however, frequent updates will delay processing, too, so
one might do the work both on C<ev_stat> callback invocation I<and> on
C<ev_timer> callback invocation).
static ev_stat passwd;
static ev_timer timer;
static void
timer_cb (EV_P_ ev_timer *w, int revents)
{
ev_timer_stop (EV_A_ w);
/* now it's one second after the most recent passwd change */
}
static void
stat_cb (EV_P_ ev_stat *w, int revents)
{
/* reset the one-second timer */
ev_timer_again (EV_A_ &timer);
}
...
ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
ev_stat_start (loop, &passwd);
ev_timer_init (&timer, timer_cb, 0., 1.01);
=head2 C<ev_idle> - when you've got nothing better to do...

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