diff options
| -rw-r--r-- | ev.pod | 47 |
1 files changed, 46 insertions, 1 deletions
@@ -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... |