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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  * File locking class
  18  */
  19  class flock
  20  {
  21      /**
  22      * Path to the file to which access is controlled
  23      *
  24      * @var string
  25      */
  26      private $path;
  27  
  28      /**
  29      * File pointer for the lock file
  30      * @var string
  31      */
  32      private $lock_fp;
  33  
  34      /**
  35      * Constructor.
  36      *
  37      * You have to call acquire() to actually acquire the lock.
  38      *
  39      * @param    string    $path    Path to the file to which access is controlled
  40      */
  41  	public function __construct($path)
  42      {
  43          $this->path = $path;
  44          $this->lock_fp = null;
  45      }
  46  
  47      /**
  48      * Tries to acquire the lock.
  49      *
  50      * If the lock is already held by another process, this call will block
  51      * until the other process releases the lock. If a lock is acquired and
  52      * is not released before script finishes but the process continues to
  53      * live (apache/fastcgi) then subsequent processes trying to acquire
  54      * the same lock will be blocked forever.
  55      *
  56      * If the lock is already held by the same process via another instance
  57      * of this class, this call will block forever.
  58      *
  59      * If flock function is disabled in php or fails to work, lock
  60      * acquisition will fail and false will be returned.
  61      *
  62      * @return    bool            true if lock was acquired
  63      *                            false otherwise
  64      */
  65  	public function acquire()
  66      {
  67          if ($this->lock_fp)
  68          {
  69              return false;
  70          }
  71  
  72          // For systems that can't have two processes opening
  73          // one file for writing simultaneously
  74          if (file_exists($this->path . '.lock'))
  75          {
  76              $mode = 'rb+';
  77          }
  78          else
  79          {
  80              $mode = 'wb';
  81          }
  82  
  83          $this->lock_fp = @fopen($this->path . '.lock', $mode);
  84  
  85          if ($mode == 'wb')
  86          {
  87              if (!$this->lock_fp)
  88              {
  89                  // Two processes may attempt to create lock file at the same time.
  90                  // Have the losing process try opening the lock file again for reading
  91                  // on the assumption that the winning process created it
  92                  $mode = 'rb+';
  93                  $this->lock_fp = @fopen($this->path . '.lock', $mode);
  94              }
  95              else
  96              {
  97                  // Only need to set mode when the lock file is written
  98                  @chmod($this->path . '.lock', 0666);
  99              }
 100          }
 101  
 102          if ($this->lock_fp)
 103          {
 104              if (!@flock($this->lock_fp, LOCK_EX))
 105              {
 106                  throw new \phpbb\exception\http_exception(500, 'Failure while aqcuiring locks.');
 107              }
 108          }
 109  
 110          return (bool) $this->lock_fp;
 111      }
 112  
 113      /**
 114      * Does this process own the lock?
 115      *
 116      * @return    bool            true if lock is owned
 117      *                            false otherwise
 118      */
 119  	public function owns_lock()
 120      {
 121          return (bool) $this->lock_fp;
 122      }
 123  
 124      /**
 125      * Releases the lock.
 126      *
 127      * The lock must have been previously obtained, that is, acquire() call
 128      * was issued and returned true.
 129      *
 130      * Note: Attempting to release a lock that is already released,
 131      * that is, calling release() multiple times, is harmless.
 132      *
 133      * @return null
 134      */
 135  	public function release()
 136      {
 137          if ($this->lock_fp)
 138          {
 139              @flock($this->lock_fp, LOCK_UN);
 140              fclose($this->lock_fp);
 141              $this->lock_fp = null;
 142          }
 143      }
 144  }