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   1  <?php
   2  /**
   3  *
   4  * This file is part of the phpBB Forum Software package.
   5  *
   6  * @copyright (c) phpBB Limited <https://www.phpbb.com>
   7  * @license GNU General Public License, version 2 (GPL-2.0)
   8  *
   9  * For full copyright and license information, please see
  10  * the docs/CREDITS.txt file.
  11  *
  12  */
  13  
  14  namespace phpbb\lock;
  15  
  16  /**
  17  * Database locking class
  18  */
  19  class db
  20  {
  21      /**
  22      * Name of the config variable this lock uses
  23      * @var string
  24      */
  25      private $config_name;
  26  
  27      /**
  28      * Unique identifier for this lock.
  29      *
  30      * @var string
  31      */
  32      private $unique_id;
  33  
  34      /**
  35      * Stores the state of this lock
  36      * @var bool
  37      */
  38      private $locked;
  39  
  40      /**
  41      * The phpBB configuration
  42      * @var \phpbb\config\config
  43      */
  44      private $config;
  45  
  46      /**
  47      * A database connection
  48      * @var \phpbb\db\driver\driver_interface
  49      */
  50      private $db;
  51  
  52      /**
  53      * Creates a named released instance of the lock.
  54      *
  55      * You have to call acquire() to actually create the lock.
  56      *
  57      * @param    string                                $config_name    A config variable to be used for locking
  58      * @param    \phpbb\config\config                $config            The phpBB configuration
  59      * @param    \phpbb\db\driver\driver_interface    $db                A database connection
  60      */
  61  	public function __construct($config_name, \phpbb\config\config $config, \phpbb\db\driver\driver_interface $db)
  62      {
  63          $this->config_name = $config_name;
  64          $this->config = $config;
  65          $this->db = $db;
  66      }
  67  
  68      /**
  69      * Tries to acquire the lock by updating
  70      * the configuration variable in the database.
  71      *
  72      * As a lock may only be held by one process at a time, lock
  73      * acquisition may fail if another process is holding the lock
  74      * or if another process obtained the lock but never released it.
  75      * Locks are forcibly released after a timeout of 1 hour.
  76      *
  77      * @return    bool            true if lock was acquired
  78      *                            false otherwise
  79      */
  80  	public function acquire()
  81      {
  82          if ($this->locked)
  83          {
  84              return false;
  85          }
  86  
  87          if (!isset($this->config[$this->config_name]))
  88          {
  89              $this->config->set($this->config_name, '0', false);
  90          }
  91          $lock_value = $this->config[$this->config_name];
  92  
  93          // make sure lock cannot be acquired by multiple processes
  94          if ($lock_value)
  95          {
  96              // if the other process is running more than an hour already we have to assume it
  97              // aborted without cleaning the lock
  98              $time = explode(' ', $lock_value);
  99              $time = $time[0];
 100  
 101              if ($time + 3600 >= time())
 102              {
 103                  return false;
 104              }
 105          }
 106  
 107          $this->unique_id = time() . ' ' . unique_id();
 108  
 109          // try to update the config value, if it was already modified by another
 110          // process we failed to acquire the lock.
 111          $this->locked = $this->config->set_atomic($this->config_name, $lock_value, $this->unique_id, false);
 112  
 113          return $this->locked;
 114      }
 115  
 116      /**
 117      * Does this process own the lock?
 118      *
 119      * @return    bool            true if lock is owned
 120      *                            false otherwise
 121      */
 122  	public function owns_lock()
 123      {
 124          return (bool) $this->locked;
 125      }
 126  
 127      /**
 128      * Releases the lock.
 129      *
 130      * The lock must have been previously obtained, that is, acquire() call
 131      * was issued and returned true.
 132      *
 133      * Note: Attempting to release a lock that is already released,
 134      * that is, calling release() multiple times, is harmless.
 135      *
 136      * @return null
 137      */
 138  	public function release()
 139      {
 140          if ($this->locked)
 141          {
 142              $this->config->set_atomic($this->config_name, $this->unique_id, '0', false);
 143              $this->locked = false;
 144          }
 145      }
 146  }