ID: 39809
User updated by: e at osterman dot com
Reported By: e at osterman dot com
-Status: Feedback
+Status: Open
Bug Type: CGI related
Operating System: FC6
PHP Version: 5.2.0
Assigned To: dmitry
New Comment:
By changing the example code to use PHP's sockets (e.g.
socket_create/connect/read/write) allows one to use the socket_shutdown
as you suggested. But calling shutdown after the request defeats the
purpose of persistent connections, since that just negates the effect
of passing FCGI_KEEP_CONN. Connections cannot be reused to send
requests once they're shutdown after a request.
So, it sounds like PHP's design decision is to support PHP_KEEP_CONN,
but when PHP_FCGI_CHILDREN is reached, all new connections are
queued/blocked. When a client releases its connection to a php-cgi
child process, then the next connection in the queue is handed over to
the next available child. While this makes a lot of sense when you're
dealing with only non-persistent connections or only a single php-cgi
server, it's not desireable when you have lots of persistent
connections or lots of fcgi servers. For example, in HTTP/1.1, servers
respond "503 Server too busy". If the client were notified in some way,
either by way of a closed connection, refused connection, or
FCGI_OVERLOADED packet, then the client could try another FCGI server.
But since that doesn't happen, the client must just sit and wait.
Perhaps, indefinitely or just timeout =(
What is your take on this?
Best Regards,
Erik Osterman
Previous Comments:
------------------------------------------------------------------------
[2006-12-18 18:53:58] [EMAIL PROTECTED]
> <?
> $socket1 = FCGI_Connect('localhost', 1234);
> FCGI_Test($socket1);
> FCGI_Response($socket1);
> sleep(30);
> fclose($socket1);
> ?>
this code is not perferct, and this is the reason of bad behavior. You
should call shutdown() "man 2 shutdown" after writing request into
socket, but PHP doesn't implement such function.
<?
$socket1 = FCGI_Connect('localhost', 1234);
FCGI_Test($socket1);
shutdown($socket1, SHUT_WR); //we don't have this function
FCGI_Response($socket1);
sleep(30);
fclose($socket1);
?>
I cannot repeat your behavior with telnet. I always get "Connection
closed" after a timeout.
BTW you can insert debug output into fastcgi.c right after accept() and
try it.
------------------------------------------------------------------------
[2006-12-18 18:29:13] e at osterman dot com
For what it's worth, this shows some conflicting data. Perhaps I'm just
interpretting it wrong.
Start theh FCGI server in single process mode
# php-cgi -b 1234
Modify the test script as follows:
<?
$socket1 = FCGI_Connect('localhost', 1234);
FCGI_Test($socket1);
FCGI_Response($socket1);
sleep(30);
fclose($socket1);
?>
Now, the single process php-cgi server should not be accept()ing any
more connections for 30 seconds.
# telnet localhost 1234
Trying 127.0.0.1...
Connected to localhost.localdomain.
Escape character is '^]'.
Per my previous post, when a stream_socket_server server does not call
accept(), the 'telnet' session gets "connection refused". In this
example, it's not getting refused by the php-cgi server, which leads me
to believe that php-cgi might actually be calling accept. This could be
a implementation difference.. but I don't know.
Regards,
Erik Osterman
------------------------------------------------------------------------
[2006-12-18 18:20:11] e at osterman dot com
Dimitry,
You're example shocked me. I tried something similar making a simple
stream_socket_server, but didn't make the client in PHP.
<?
$server = stream_socket_server('tcp://127.0.0.1:1234');
if (!$server) {
die('Unable to create AF_INET socket');
}
sleep(10);
?>
# telnet localhost 1234
Trying 127.0.0.1...
telnet: Unable to connect to remote host: Connection refused
I had expected the same behavior in PHP's fsockopen, but indeed, as you
said fsocketopen returns a valid resource even though the connection has
not yet been accept()'d by the server. More over, feof returns false and
fwrite to the socket returns the correct number of bytes "written".
stream_get_metadata returns nothing interesting either.
How is a PHP fsockopen/stream_socket_client client to know when a
connection truely has been accept()'d?
The reason why this is all so important to us, is that we have a
cluster of frontend servers that use a pool of FCGI backend servers. We
need the busier frontend servers to dynamically open up more persistent
connections (FCGI_KEEP_CONN) to FCGI servers (and release them as
demand subsides). When a particular FCGI server is at capacity
(PHP_FCGI_CHILDREN), we need the client to try (in a round robin
fashion) another FCGI server. The current problem, as you understand by
now, is that the client get's stuck when connecting to an FCGI server at
capacity and timeout.
As you've now suggested, it's apparently b/c they getting stuck waiting
for the accept(), but never get it.
What recourse does the client have?
Regards,
Erik Osterman
------------------------------------------------------------------------
[2006-12-18 13:15:46] [EMAIL PROTECTED]
No you are :)
But you made a great job writting test script, and I think this
discussion may lead us to some good result.
The fact that connect() returns file descriptor doesn't mean that
accept() was really called. See the folllowing script. You can even
write to socket befor it is really accepted.
<?php
$server = stream_socket_server('tcp://127.0.0.1:1234');
if (!$server) {
die('Unable to create AF_INET socket [server]');
}
$socket1 = fsockopen('127.0.0.1', 1234, $errno, $errstr, 5);
if (!$socket1)
die("Failed to connect to 127.0.0.1:1234\n");
fwrite($socket1, "Hello\n");
$socket2 = fsockopen('127.0.0.1', 1234, $errno, $errstr, 5);
if (!$socket2)
die("Failed to connect to 127.0.0.1:1234\n");
fwrite($socket2, "World\n");
$socket = stream_socket_accept($server);
$data = fgets($socket, 1024);
echo($data);
fclose($socket);
$socket = stream_socket_accept($server);
$data = fgets($socket, 1024);
echo($data);
fclose($socket);
fclose($socket2);
fclose($socket1);
fclose($server);
?>
------------------------------------------------------------------------
[2006-12-15 21:35:04] e at osterman dot com
> PHP process DOESN'T accept() new connections
> if it already has persistent connection opened.
> Note that php/fastcgi is one-process-one-connection
> server that doesn't implement multiplexion
If this were actually the case, I'd be satisfied. That would mean the
FCGI clients would get "connection refused" when there are no more
sockets/children available. But what actually happens is that the
connection is established, meaning accept() does get called.
To test this, modify the example like this
// Open up the first connection
$socket1 = FCGI_Connect('localhost', 1234);
// Send a request with FCGI_KEEP_CONN
FCGI_Test($socket1);
// Open up the second connection (should be refused)
$socket2 = FCGI_Connect('localhost', 1234);
printf("socket1:%d socket2:%d\n", feof($socket1), feof($socket2));
Expected output:
socket1:0 socket2:1
Actual output:
socket1:0 socket2:0
In otherwords, both connections are established => accept() was
called.
Am I making sense?
Regards,
Erik Osterman
------------------------------------------------------------------------
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http://bugs.php.net/39809
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