Why is php's fsockopen returning (Resource temporarily unavailable)?

Question

I have a very simple server php code like this

function listenForClients()
 {
      $this->serviceConnection = socket_create(AF_UNIX, SOCK_STREAM, 0);
      socket_bind($this->serviceConnection, "\tmp\mysock", 0);
      socket_listen($this->serviceConnection, 10000000);

      while($clientSocket = socket_accept($this->serviceConnection))
      {
           $clientMessage = socket_read($clientSocket, 1024);
           socket_close($clientSocket);
      }
 }

Then I have a very simple client that does this

for ( $counter = 0; $counter <= 1000; $counter ++) {    
   $fp = fsockopen("unix///tmp/mysock", 0, $errno, $errstr);

   if (!$fp){
      echo  "Error: Could not open socket connection at " . $counter . "\n";
      exit;
   }else{    
      fputs ($fp, "hello", strlen("hello"));
      fclose($fp);
   }
}

For some reason, after a random number of connections (around 300-500) fsockopen will return with a warning Resource temporarily unavailable. In the beginning I was getting the warning at around 20-30 connections. But once I increased the backlog parameter in socket_listen it got a bit better to around 300-500. How do I overcome this?

What is the way to build a php server socket to accept a lot of incoming connections per second (sustained).

Thanks!

The full error:

PHP Warning: fsockopen(): unable to connect to unix:///tmp/mysock:0 (Resource temporarily unavailable) in test.php on line 22

Answer 1

Check your ulimit. Are you overflowing your file descriptor table?

EDIT: the backlog value you have in accept() is bogus. Most OS-es have the max incoming connection queue size on the scale of dozens, not thousands.

Answer 2

I realize this might not be a particularly popular answer, but I wouldn't really recommend PHP as a great language for writing a server that accepts a heavily sustained number of client connections.

Answer 3

I've just been looking at this issue (got here through Google) and I've found that a solution to get rid of the error:

PHP Warning: fsockopen(): unable to connect to unix:///tmp/mysock:0 (Resource temporarily unavailable) in test.php on line 22

..is to not use fsockopen() in the writer thread; try something like this instead:

if (! ($cSock = socket_create(AF_UNIX, SOCK_STREAM, 0))) {
    exit("Failed to create socket");
    continue;
} else if (! socket_connect($cSock, IPC_SOCK)) {
    exit("Failed to connect socket");
} else {
    $bw = socket_write($cSock, $msg);
    if ($bw === false) {
        exit("Socket write failed, %s", array(socket_strerror(socket_last_error())));
    } else {
        exit("Wrote $bw bytes to socket");
    }
}
socket_shutdown($cSock);
socket_close($cSock);

Better late than never ? ;-)