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<?php
final class ITSEC_Mutex {
/** @var int */
private $id;
/** @var string */
private $name;
/** @var int */
private $expires;
/**
* ITSEC_Mutex constructor.
*
* @param int $id
* @param string $name
* @param int $expires
*/
private function __construct( $id, $name, $expires ) {
$this->id = $id;
$this->name = $name;
$this->expires = $expires;
}
/**
* Get a mutex.
*
* @param string $name Name of the mutex.
* @param int $ttl How long to hold the mutex for.
*
* @return ITSEC_Mutex|null Returns null if the mutex is already being held.
*/
public static function get( $name, $ttl = 30 ) {
global $wpdb;
$expires_at = time() + $ttl;
while ( ! $id = self::create( $name, $expires_at ) ) {
$existing = $wpdb->get_row( $wpdb->prepare(
"SELECT `mutex_id`, `mutex_expires` FROM `{$wpdb->base_prefix}itsec_mutexes` WHERE `mutex_name` = %s",
$name
), ARRAY_A );
if ( ! $existing ) {
continue;
}
if ( $existing['mutex_expires'] < time() ) {
self::delete_by_id( $existing['mutex_id'] );
continue;
}
return null;
}
return new self( $wpdb->insert_id, $name, $expires_at );
}
/**
* Release the mutex back.
*/
public function release() {
self::delete_by_id( $this->get_id() );
}
/**
* Has the mutex expired.
*
* @return bool
*/
public function is_expired() {
return $this->get_expires() < time();
}
/**
* Checks if this mutex still exists.
*
* @return bool
*/
public function exists() {
global $wpdb;
return (bool) $wpdb->get_var( $wpdb->prepare(
"SELECT `mutex_id` FROM {$wpdb->base_prefix}itsec_mutexes WHERE `mutex_id` = %d",
$this->get_id()
) );
}
/**
* Get the mutex's id.
*
* @return int
*/
public function get_id() {
return $this->id;
}
/**
* Get the name of the mutex.
*
* @return string
*/
public function get_name() {
return $this->name;
}
/**
* Get the epoch the mutex expires at.
*
* @return int
*/
public function get_expires() {
return $this->expires;
}
/**
* Delete a mutex by it's id.
*
* @param string $id
*/
private static function delete_by_id( $id ) {
global $wpdb;
$wpdb->delete( $wpdb->base_prefix . 'itsec_mutexes', [
'mutex_id' => $id,
] );
}
/**
* Create a mutex record.
*
* @param string $name
* @param int $expires_at
*
* @return int The mutex id, or 0 if it could not be acquired.
*/
private static function create( $name, $expires_at ) {
global $wpdb;
$r = $wpdb->query( $wpdb->prepare(
"INSERT IGNORE INTO `{$wpdb->base_prefix}itsec_mutexes` (`mutex_name`, `mutex_expires`) VALUES (%s, %s) /* LOCK */",
$name,
$expires_at
) );
if ( ! $r || ! $wpdb->insert_id ) {
return 0;
}
return (int) $wpdb->insert_id;
}
}
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