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HomeBackend DevelopmentPHP TutorialPHP使用flock实现文件加锁的方法_php技巧

本文实例讲述了PHP使用flock实现文件加锁的方法。分享给大家供大家参考。具体分析如下:

flock在官方文档里的解释是:flock() 允许你执行一个简单的可以在任何平台中使用的读取/写入模型(包括大部分的 Unix 派生版和甚至是Windows)。如果锁定会堵塞的话(EWOULDBLOCK 错误码情况下),请将可选的第三个参数设置为 TRUE。锁定操作也可以被 fclose() 释放(代码执行完毕时也会自动调用)。

简单来说,就是对一个文件进行锁定操作,使得多进程访问该文件时受到限制,从而防止冲突。举个例子:

<&#63;php 
  $file = fopen("test.txt","w+"); 
  if (flock($file,LOCK_EX)) 
  { 
   fwrite($file,"Write something"); 
   flock($file,LOCK_UN); 
  } 
  else 
  { 
    echo "Error locking file!"; 
  } 
  fclose($file); 
&#63;>

说明:

1.这段代码的意思是,以读写方式打开文件test.txt,当一个用户调用该php页面时,即对test.txt文件进行操作,那么就会执行flock($file,LOCK_EX)代码,即将test.txt文件进行独占锁定(该文件只能由该用户进行读写操作),那么如果有其他新的用户想访问该文件,就会被阻塞,直到前者关闭文件(释放锁定)。

2.如果将代码改成flock($file,LOCK_EX+LOCK_NB)表示锁定时直接返回错误,那么如果有新的用户访问该文件,就会输出“Error locking file!”

3.该函数的语法是flock(file,lock,block),其中file必需。规定要锁定或释放的已打开的文件。lock 必需。规定要使用哪种锁定类型。block可选。若设置为 1 或 true,则当进行锁定时阻挡其他进程。

例如:请写一段PHP代码,确保多个进程同时写入同一个文件成功

function writeData($path, $mode,$data) 
{ 
  $fp = fopen($path, $mode);  
  $retries = 0; 
  $max_retries = 100;  
  do{ 
    if ($retries > 0)  
    { 
      usleep(rand(1, 10000)); 
    } 
    $retries += 1; 
  }while (!flock($fp, LOCK_EX) and $retries<= $max_retries);  
  if ($retries == $max_retries)  
  { 
    return false; 
  } 
  fwrite($fp, "$data\n"); 
  flock($fp, LOCK_UN); 
  fclose($fp);  
  return true;  
}

希望本文所述对大家的php程序设计有所帮助。

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