Memcache::connect()

(PECL memcache >= 0.2.0)

打开一个memcached服务端连接

说明

Memcache::connect(string $host[,int $port[,int $timeout]]): bool

Memcache::connect()建立一个到memcached服务端的连接。使用方法Memcache::connect()打开的连接在脚本执行结束后会自动关闭。当然，你也可以使用方法Memcache::close()来主动关闭。同时你也可以使用memcache_connect()函数来获取一个连接。

参数

$host

memcached服务端监听主机地址。这个参数也可以指定为其他传输方式比如unix:///path/to/memcached.sock来使用Unix域socket，在这种方式下，$port参数必须设置为0。

$port

memcached服务端监听端口。当使用Unix域socket的时候要设置此参数为0。

$timeout

连接持续（超时）时间，单位秒。默认值1秒，修改此值之前请三思，过长的连接持续时间可能会导致失去所有的缓存优势。

返回值

成功时返回TRUE，或者在失败时返回FALSE。

范例

Example #1 Memcache::connect() example

<?php
/* procedural API */
$memcache_obj = memcache_connect('memcache_host', 11211);
/* OO API */
$memcache = new Memcache;
$memcache->connect('memcache_host', 11211);
?>

参见

• Memcache::pconnect() 打开一个到服务器的持久化连接
• Memcache::close() 关闭memcache连接

If memcached is working, calling memcache_connect( ) returns an Object instance, not a boolean. If memcached is not working, calling memcache_connect( ) throws a notice AND a warning (and returns false as expected). 
<?php
/* memcache is running */
$test1 = memcache_connect('127.0.0.1',11211);
echo gettype($test1);
// object
echo get_class($test1);
// Memcache
/* memcached is stopped */
$test2 = memcache_connect('127.0.0.1',11211);
/*
Notice: memcache_connect(): Server 127.0.0.1 (tcp 11211) failed with: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.
 (10060) in C:\Program Files\Support Tools\- on line 1
Warning: memcache_connect(): Can't connect to 127.0.0.1:11211, A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.
 (10060) in C:\Program Files\Support Tools\- on line 1
*/
echo gettype($test2);
// boolean
echo $test2===false;
// 1
?>
There appears to be no way to check whether memcached is actually running without resorting to error suppression:
<?php
$test3 = @memcache_connect('127.0.0.1',11211);
if( $test3===false ){
  // memcached is _probably_ not running
}
?>

In describing the timeout there is a statement that is not completely correct, increase the timeout does not necessarily preclude or unfeasible memcache, only allows the system to wait for more concurrent connections, which is a large minority of the number of connections, this causes several problems and could simply be corrected if the timeout was increased and perform some tests. 
To prove the concept and show that the connection does not wait if the server goes down:
<?PHP
while ( ++$loop < 10000 ) {
  try {
    $memcache = new Memcache;
    @$memcache->pconnect( "127.0.0.1" , 11211 , 30 );
    $loopset = 0;
    $loopget = 0;
    
    while ( ++$loopset < 50 ) {
      if ( @$memcache->set( "foo" , "bar" ) === false ) {
        echo "Fail!" . PHP_EOL;
      }
    }
    
    while ( ++$loopget < 500 ) {
      if ( @$memcache->get( "foo" ) === false ) {
        echo "Fail!" . PHP_EOL;
      }
    }
    
    if ( $loop % 100 == 0 ) {
      echo "Try: " . $loop . PHP_EOL;
    }
  } catch ( Exception $e ) {
    echo "Fail: " . $e->getMessage() . PHP_EOL;
  }
}
?>
Replace with an invalid host and test the timeout will not make a difference! It serves only for connections to the socket that are occupied.
More detail about troubleshooting timeouts in memcached google code.

To suppress (or handle) the warning and notice thrown by a failed attempt to connect, you can use a custom error handler function, like this:
<?php
function myErrorHandler($errno, $errstr, $errfile, $errline)
{
  if (E_WARNING === $errno)
  {
    Log("PHP Warning: $errstr, $errfile, $errline", Logging::WARN); 
    return true;
  }
  
  if (E_NOTICE === $errno)
  {
    Log("PHP Notic: $errstr, $errfile, $errline", Logging::NOTICE); 
    return true;
  }  
  
  return false;
}
set_error_handler('myErrorHandler');
?>

The behavior of Memcache::connect() is to always reinitialize the pool from scratch regardless of any previous calls to addServer().
E.g.
<?php
$mmc = new Memcache()
$mmc->addServer('node1', 11211);
$mmc->addServer('node2', 11211);
$mmc->addServer('node3', 11211);
$mmc->connect('node1', 11211);
?>
The last connect() call clears out the pool and then add and connect node1:11211 making it the only server.
If you want a pool of memcache servers, do not use the connect() function.
If you only want a single memcache server then there is no need to use the addServer() function.

There is a not-so-obvious way to check whether or not a MemCache-Server is available.
Using ($memCache->connect() == false) will wait for a timeout if it can't connect. If you got a high-traffic site this may not be an option. So when the server is down, you may want to avoid waiting for this timeout on every request and instead try to reconnect only once every X seconds.
If so, this code may help:
<?php
$memCache = new \Memcache();
$memCache->addServer($host, $port);
$stats = @$memCache->getExtendedStats();
$available = (bool) $stats["$host:$port"];
if ($available && @$memCache->connect($host, $port))
  // MemCache is there
else
  // go on without MemCache
?>
The result of getExtendedStats() is an array. The information is cached and maintained by MemCache itself. If the server is not available, the result will be FALSE.
Even if the result is not false, the server may still not be available. Thus you need to check for connect() != false too, but only if the first check returns TRUE, thus avoiding the 1 second timeout in most cases.
Both getExtendedStats() and connect() issue notices/warnings if the server is not there. Thus you have to mute both calls.
Do NOT use getServerStatus() for this purpose: the result is cached on server-start and will not recognize when the connection to the server is lost (or reestablished) in between.