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FileMutex通过本地文件系统文件实现互斥锁“锁定”机制。
该组件依赖于PHP flock（）函数。
应用配置示例：
[
'components' => [
'mutex' => [
'class' => 'yii\mutex\FileMutex'
],
],
]注意1：此组件只能为单个Web服务器维护锁，如果您使用的是云服务器解决方案，则可能还不够。
注意2：由于flock（）函数的性质，当使用像ISAPI这样的多线程服务器API时，这个组件是不可靠的。
<?php
/**
* @link http://www.yiiframework.com/
* @copyright Copyright (c) 2008 Yii Software LLC
* @license http://www.yiiframework.com/license/
*/
namespace yii\mutex;
use Yii;
use yii\base\InvalidConfigException;
use yii\helpers\FileHelper;
/**
* FileMutex implements mutex "lock" mechanism via local file system files.
*
* This component relies on PHP `flock()` function.
*
* Application configuration example:
*
* ```php
* [
* 'components' => [
* 'mutex' => [
* 'class' => 'yii\mutex\FileMutex'
* ],
* ],
* ]
* ```
*
* > Note: this component can maintain the locks only for the single web server,
* > it probably will not suffice in case you are using cloud server solution.
*
* > Warning: due to `flock()` function nature this component is unreliable when
* > using a multithreaded server API like ISAPI.
*
* @see Mutex
*
* @author resurtm <[email protected]>
* @since 2.0
*/
class FileMutex extends Mutex
{
/**
* @var string the directory to store mutex files. You may use [path alias](guide:concept-aliases) here.
* Defaults to the "mutex" subdirectory under the application runtime path.
*/
public $mutexPath = '@runtime/mutex';//锁所在的文件目录
/**
* @var int the permission to be set for newly created mutex files.
* This value will be used by PHP chmod() function. No umask will be applied.
* If not set, the permission will be determined by the current environment.
*/
public $fileMode;//锁文件权限
/**
* @var int the permission to be set for newly created directories.
* This value will be used by PHP chmod() function. No umask will be applied.
* Defaults to 0775, meaning the directory is read-writable by owner and group,
* but read-only for other users.
*/
public $dirMode = 0775;//锁文件所在目录权限
/**
* @var bool whether file handling should assume a Windows file system.
* This value will determine how [[releaseLock()]] goes about deleting the lock file.
* If not set, it will be determined by checking the DIRECTORY_SEPARATOR constant.
* @since 2.0.16
*/
public $isWindows;//是否是windows系统
/**
* @var resource[] stores all opened lock files. Keys are lock names and values are file handles.
*/
private $_files = [];
/**
* Initializes mutex component implementation dedicated for UNIX, GNU/Linux, Mac OS X, and other UNIX-like
* operating systems.
* @throws InvalidConfigException
*/
public function init()//初始化
{
parent::init();
$this->mutexPath = Yii::getAlias($this->mutexPath);
if (!is_dir($this->mutexPath)) {//创建锁文件所在目录
FileHelper::createDirectory($this->mutexPath, $this->dirMode, true);
}
if ($this->isWindows === null) {//设置是否是windows标记
$this->isWindows = DIRECTORY_SEPARATOR === '\\';
}
}
/**
* Acquires lock by given name.
* @param string $name of the lock to be acquired.
* @param int $timeout time (in seconds) to wait for lock to become released.
* @return bool acquiring result.
*/
protected function acquireLock($name, $timeout = 0)//获取锁
{
$filePath = $this->getLockFilePath($name);
$waitTime = 0;
while (true) {
$file = fopen($filePath, 'w+');
if ($file === false) {
return false;
}
if ($this->fileMode !== null) {
@chmod($filePath, $this->fileMode);
}
if (!flock($file, LOCK_EX | LOCK_NB)) {//调用flock函数，阻塞式获取锁
fclose($file);
if (++$waitTime > $timeout) {//超时未获取到锁
return false;
}
sleep(1);//sleep计时
continue;
}
// Under unix we delete the lock file before releasing the related handle. Thus it's possible that we've acquired a lock on
// a non-existing file here (race condition). We must compare the inode of the lock file handle with the inode of the actual lock file.
// If they do not match we simply continue the loop since we can assume the inodes will be equal on the next try.
// Example of race condition without inode-comparison:
// Script A: locks file
// Script B: opens file
// Script A: unlinks and unlocks file
// Script B: locks handle of *unlinked* file
// Script C: opens and locks *new* file
// In this case we would have acquired two locks for the same file path.
if (DIRECTORY_SEPARATOR !== '\\' && fstat($file)['ino'] !== @fileinode($filePath)) {
clearstatcache(true, $filePath);
flock($file, LOCK_UN);
fclose($file);
continue;
}
$this->_files[$name] = $file;
return true;
}
// Should not be reached normally.
return false;
}
/**
* Releases lock by given name.
* @param string $name of the lock to be released.
* @return bool release result.
*/
protected function releaseLock($name)//释放锁
{
if (!isset($this->_files[$name])) {
return false;
}
if ($this->isWindows) {
// Under windows it's not possible to delete a file opened via fopen (either by own or other process).
// That's why we must first unlock and close the handle and then *try* to delete the lock file.
flock($this->_files[$name], LOCK_UN);
fclose($this->_files[$name]);
@unlink($this->getLockFilePath($name));
} else {//linux情况下，可以在未释放锁的情况下删除锁文件，这里删除再释放
// Under unix it's possible to delete a file opened via fopen (either by own or other process).
// That's why we must unlink (the currently locked) lock file first and then unlock and close the handle.
unlink($this->getLockFilePath($name));
flock($this->_files[$name], LOCK_UN);
fclose($this->_files[$name]);
}
unset($this->_files[$name]);//清除锁标记
return true;
}
/**
* Generate path for lock file.
* @param string $name
* @return string
* @since 2.0.10
*/
protected function getLockFilePath($name)
{
return $this->mutexPath . DIRECTORY_SEPARATOR . md5($name) . '.lock';
}
}