How to solve the problem that PHP cannot implement multi-threading_php tips

Is there a way to implement multi-threading in PHP? Suppose you are writing a PHP application based on multiple servers. Ideally, you would send requests to multiple servers at the same time, rather than one after another. Is it possible? When someone wants to implement concurrency functions, they usually think of using fork or spawn threads, but when they find that PHP does not support multi-threading, they may change their minds and use some not good enough languages, such as Perl.
Suppose you want to build a service that checks n running servers to make sure they are still functioning properly. You might write code like this:

$hosts = array("host1.sample.com", "host2.sample.com", "host3.sample.com"); 
$timeout = 15; 
$status = array(); 
foreach ($hosts as $host) {  
    $errno = 0;  
    $errstr = "";  
    $s = fsockopen($host, 80, $errno, $errstr, $timeout);  
    if ($s) {  
       $status[$host] = "Connectedn";  
       fwrite($s, "HEAD / HTTP/1.0rnHost: $hostrnrn");  
      do {   
        $data = fread($s, 8192);   
        if (strlen($data) == 0) {   
        break;   
        }   
       $status[$host] .= $data;  
     }  
     while (true);  
      fclose($s);  
     }  
     else {  
       $status[$host] = "Connection failed: $errno $errstrn";  
     } 
} 
print_r($status); 
?>

It works fine, but scaling this code to manage a large number of servers would take a long time until fsockopen() has parsed the hostname and established a successful connection (or delayed $timeout seconds).

So we have to abandon this code; we can establish an asynchronous connection - no need to wait for fsockopen to return connection status. PHP still needs to resolve the hostname (so it's more sensible to use the ip directly), but it will return immediately after opening a connection, and then we can connect to the next server.

There are two ways to achieve this; in PHP5, you can use the new stream_socket_client() function to directly replace fsocketopen(). For versions before PHP5, you need to do it yourself and use sockets extension to solve the problem. Here is the solution in PHP5:

$hosts = array("host1.sample.com", "host2.sample.com", "host3.sample.com"); 
$timeout = 15; 
$status = array(); 
$sockets = array(); 
/* Initiate connections to all the hosts simultaneously */ 
foreach ($hosts as $id => $host) {  
    $s = stream_socket_client("$host:80", $errno, $errstr, $timeout,  
       STREAM_CLIENT_ASYNC_CONNECT|STREAM_CLIENT_CONNECT);  
    if ($s) {  
      $sockets[$id] = $s;  
      $status[$id] = "in progress";  
    }  
    else { $status[$id] = "failed, $errno $errstr";  
    } 
} 
/* Now, wait for the results to come back in */ 
 
while (count($sockets)) {  
   $read = $write = $sockets;  
/* This is the magic function - explained below */  
   $n = stream_select($read, $write, $e = null, $timeout);  
   if ($n > 0) {  
   /* readable sockets either have data for us, or are failed  * connection attempts */  
     foreach ($read as $r) {    
          $id = array_search($r, $sockets);    
          $data = fread($r, 8192);    
     if (strlen($data) == 0) {   
          if ($status[$id] == "in progress") {   
            $status[$id] = "failed to connect";   
          }   
     fclose($r);   
     unset($sockets[$id]);    
      }  
      else {   
         $status[$id] .= $data;    
      }  
    }  
/* writeable sockets can accept an HTTP request */  
foreach ($write as $w) {   
     $id = array_search($w, $sockets);   
     fwrite($w, "HEAD / HTTP/1.0rnHost: "   
     . $hosts[$id] . "rnrn");   
     $status[$id] = "waiting for response";  
     }  
}  
else {  
/* timed out waiting; assume that all hosts associated  * with $sockets are faulty */  
foreach ($sockets as $id => $s) {   
     $status[$id] = "timed out "  
     . $status[$id];  
     }  
break;  
 } 
} 
foreach ($hosts as $id => $host) {  
   echo "Host: $hostn"; echo "Status: "  
   . $status[$id] . "nn"; 
}  
?> 

We use stream_select() to wait for the connection event of sockets opening. stream_select() calls the system's select(2) function to work: the first three parameters are the arrays of streams you want to use; you can read, write and get exceptions from them (for the three parameters respectively). stream_select() can wait for an event to occur by setting the $timeout (seconds) parameter - when the event occurs, the corresponding socket data will be written to the parameters you passed in.

The following is the implementation of PHP 4.1.0 and later. If you have included sockets (ext/sockets) support when compiling PHP, you can use similar code as above, but you need to add the functions of the streams/filesystem function above. Implemented using ext/sockets function. The main difference is that instead of stream_socket_client() we use the following function to establish the connection:

// This value is correct for Linux, other systems have other values 
define('EINPROGRESS', 115); 
function non_blocking_connect($host, $port, &$errno, &$errstr, $timeout) {  
    $ip = gethostbyname($host);  
    $s = socket_create(AF_INET, SOCK_STREAM, 0);  
    if (socket_set_nonblock($s)) {  
      $r = @socket_connect($s, $ip, $port);  
      if ($r || socket_last_error() == EINPROGRESS) {   
         $errno = EINPROGRESS;   
         return $s;  
        }  
     }  
    $errno = socket_last_error($s);  
    $errstr = socket_strerror($errno);  
    socket_close($s);  
    return false; 
} 
?> 

Now replace stream_select() with socket_select(), fread() with socket_read(), fwrite() with socket_write(), and fclose() with socket_close() to execute the script!
The advancement of PHP5 is that you can use stream_select() to process almost any stream. For example, you can use it to receive keyboard input and save it into an array by including STDIN. You can also receive data from a pipe opened by proc_open().

I hope that through this article, everyone can cleverly solve the problem that PHP cannot implement multi-threading.