php inotify blocking but with timeout

Question

I want to use the pecl extension to php and use the inotify_read() function to detect changes in a file.

As a fail safe, I would like to specify a timeout value to the inotify_read function, just so I don't wind up blocking forever, in case an event is raised and is missed.

Does anyone know how to use the stream_select function to block for a specified number of seconds, but return immediately if an event is raised on the inotify_read.

I know there is way to perform the inotify_read non-blocking, but I don't want to sit there and poll, and I don't want the lag between when the file change happens vs. when I'll be informed by it.

I was able to use pcntl_alarm to interrupt the the system call, but I was hoping for something less intense.

Wez Furlong · Accepted Answer · 2014-06-05 06:45:35Z

2

Looks like the pecl inotify_init() function returns a php_stream wrapper around the underlying file descriptor. So yes, you should be able to use stream_select() to wait for something to signal the inotify descriptor.

Something like the following should work:

$in = inotify_init();
stream_set_blocking($in, false); // probably a good idea to make it non-blocking
$r = array($in);
$timeout = 10;
$n = stream_select($r, $w = array(), $e = array(), $timeout);
if ($n == 0) {
   // Timed out, so do something else
} else {
   // We know that inotify_read will not block; use it and process
   // the results
}

answered Jun 5, 2014 at 6:45

Wez Furlong

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2 Comments

user1279887 Over a year ago

Thanks for explaining how to use the file descriptor - you should add your code to the php man page!

anonymous-one Over a year ago

Its almost 2023, so this is almost 9 years old... None the less, excellent answer!

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