mysql 事务锁实验

		$this->initVar('cny');
		echo "try...\n";
		$lock1 = $this->mUF->dbLock(Trade_CoinModel::LOCK_PRE . '12', 3);
		echo 'result:' . $lock1 . "\n";
		echo "sleeping...\n";
		sleep(10);
		echo "wakeup!\n";
		if ($lock1) {
			$this->mUF->dbUnlock(Trade_CoinModel::LOCK_PRE . '12');
			echo "release it!\n";
		}
		echo "sleeping...\n";
		sleep(10);
		echo "try again!\n";
		$lock1 = $this->mUF->dbLock(Trade_CoinModel::LOCK_PRE . '12', 3);
		echo 'result:' . $lock1 . "\n";
		echo "sleeping...\n";
		sleep(10);
		echo "wakeup!\n";
		if ($lock1) {
			$this->mUF->dbUnlock(Trade_CoinModel::LOCK_PRE . '12');
			echo "release it!\n";
		}
		echo "done\n";

代码如上。

经实验，mysql的get_lock事务锁第一个参数是锁名，第二个参数是指获取不锁的时候等待时间。

dbLock与dbUnlock的实现如下：

	/**
	 * mysql信号锁
	 * @param string $key 锁key
	 * @param int    $timeout 超时长（秒）
	 *
	 * @return bool
	 */
	public function dbLock($key, $timeout = 10) {
		$lockKey = $this->lockPrefix . $key;
		$sth = self::instance()->prepare("SELECT GET_LOCK(:key, :expire) AS result");
		$sth->execute(array(':key' => $lockKey, ':expire' => $timeout));
		$result = $sth->fetch();
		return ($result['result'] == 1);
	}

	/**
	 * mysql信号解锁
	 * @param string $key 锁key
	 *
	 * @return bool
	 */
	public function dbUnlock($key) {
		$lockKey = $this->lockPrefix . $key;
		$sth = self::instance()->prepare("SELECT RELEASE_LOCK(:key) AS result");
		$sth->execute(array(':key' => $lockKey));
		$result = $sth->fetch();
		return ($result['result'] == 1);
	}

此锁有版本限制，在5.7.5之前，一个会话同时只能获取一个锁，如果获取了第二个锁，会自动把前一锁给释放。

只有到了5.7.5版本之后，此锁才支持了mdl规范，一个会话可以同时获取多个锁。

具体可以参考官方文档。