Understanding socket_select routine

[mydejamail]

I have begun dabbling in php socket programming, and I have been trying
to get the hang of the socket_select command based on the example here
- http://www.zend.com/pecl/tutorials/sockets.php.

From examining the code it seems that if socket_select returns a value

of >= 2 and $sock is find in the $read array will the code flow on to
the reading portion. What is the significance of having a value of >=2
in the $ready variable.

I know that this may be due to some lack of familiarity with sockets
and PHPs approach to them, but can anyone enlighten me on the value in
$ready variable and how the $read array passed to the socket_select
variable is modified?

while (true) {
// Setup clients listen socket for reading
$read[0] = $sock;
for ($i = 0; $i < $max_clients; $i++)
{
if ($client[$i]['sock'] != null)
$read[$i + 1] = $client[$i]['sock'] ;
}
// Set up a blocking call to socket_select()
$ready = socket_select($read,null,null,null);
/* if a new connection is being made add it to the client array */
if (in_array($sock, $read)) {
for ($i = 0; $i < $max_clients; $i++)
{
if ($client[$i]['sock'] == null) {
$client[$i]['sock'] = socket_accept($sock);
break;
}
elseif ($i == $max_clients - 1)
print ("too many clients")
}
if (--$ready <= 0)
continue;
} // end if in_array

[Sjoerd]

my********@yahoo.co.uk schreef:

From examining the code it seems that if socket_select returns a value of >= 2 and $sock is find in the $read array will the code flow on to
the reading portion. What is the significance of having a value of >=2
in the $ready variable.

$ready contains the number of sockets on which the state has changed.
The code which you posted goes through the loop $ready times, accepting
$sock and putting the result in an empty $client[$i]['sock'].

This is a hard example. It is probably best to try out socket_select
with just one socket. Try what it does and what its return value is.
$ready = socket_select($read,null,null,null);
/* if a new connection is being made add it to the client array */
if (in_array($sock, $read)) {
for ($i = 0; $i < $max_clients; $i++)
{
if ($client[$i]['sock'] == null) {
$client[$i]['sock'] = socket_accept($sock);
break;
}
elseif ($i == $max_clients - 1)
print ("too many clients")
}
if (--$ready <= 0)
continue;
} // end if in_array

[Chung Leong]

my********@yahoo.co.uk wrote:

I have begun dabbling in php socket programming, and I have been trying
to get the hang of the socket_select command based on the example here
- http://www.zend.com/pecl/tutorials/sockets.php.

From examining the code it seems that if socket_select returns a value

of >= 2 and $sock is find in the $read array will the code flow on to
the reading portion. What is the significance of having a value of >=2
in the $ready variable.

In the example, socket_select() is used to watch for two types of
events: new connections and availability of data. $sock is different
from the other sockets in the array in that it's not really connected
to anything. It's sort of a placeholder for a new socket. When it
becomes readable, it means there's a new incoming connection, and you
call socket_accept() to get the actual socket for that new connection.

So $ready is the number of new connections (1 or 0) plus the number of
sockets with readable data. If it's 1 and the socket is $sock, then
there are no sockets with readable data.

[mydejamail]

This appears to imply that socket_select can only notify just 1 new
socket, and that if more than 1 new connections have been made, the
additional connections can only be detected on the next pass - is it
so?

Concerning the $sock value, the $read[0] = $sock at the top of the loop
always makes $sock an element of the array, so I would expect
in_array($sock, $read) to always return true. So I would take it that
socket_select removes or modifies $read[0], or any instances of $read
where $read[x] = $sock if there is no new connection, right?
Chung Leong wrote:

my********@yahoo.co.uk wrote:

I have begun dabbling in php socket programming, and I have been trying
to get the hang of the socket_select command based on the example here
- http://www.zend.com/pecl/tutorials/sockets.php.

From examining the code it seems that if socket_select returns a value

of >= 2 and $sock is find in the $read array will the code flow on to
the reading portion. What is the significance of having a value of >=2
in the $ready variable.

In the example, socket_select() is used to watch for two types of
events: new connections and availability of data. $sock is different
from the other sockets in the array in that it's not really connected
to anything. It's sort of a placeholder for a new socket. When it
becomes readable, it means there's a new incoming connection, and you
call socket_accept() to get the actual socket for that new connection.

So $ready is the number of new connections (1 or 0) plus the number of
sockets with readable data. If it's 1 and the socket is $sock, then
there are no sockets with readable data.

[Chung Leong]

my********@yahoo.co.uk wrote:

This appears to imply that socket_select can only notify just 1 new
socket, and that if more than 1 new connections have been made, the
additional connections can only be detected on the next pass - is it
so?
For practical purpose you're right. You can obviously select() multiple
sockets listening on different ports, but that's not the typical
scenario.
Concerning the $sock value, the $read[0] = $sock at the top of the loop
always makes $sock an element of the array, so I would expect
in_array($sock, $read) to always return true. So I would take it that
socket_select removes or modifies $read[0], or any instances of $read
where $read[x] = $sock if there is no new connection, right?

That is correct. Hence the reference declaration for the arguments. PHP
typically doesn't do things this way. The semantic came from the socket
functions in C.