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                百度百科的解釋:具有強烈的獨占和排他特性。它指的是對數據被外界(包括本系統當前的其他事務,以及來自外部系統的事務處理)修改持保守態度,因此,在整個數據處理過程中,將數據處于鎖定狀態。悲觀鎖的實現,往往依靠數據庫提供的鎖機制(也只有數據庫層提供的鎖機制才能真正保證數據訪問的排他性,否則,即使在本系統中實現了加鎖機制,也無法保證外部系統不會修改數據)。 ```php <?php /** * redis實戰 * * 實現悲觀鎖機制 * * @author TIGERB <https://github.com/TIGERB> * @example php pessmistic-lock.php */ $timeout = 5000; $redis = new \Redis(); $redis->connect('127.0.0.1', 6379); do { $microtime = microtime(true) * 1000; $microtimeout = $microtime+$timeout+1; // 上鎖 $isLock = $redis->setnx('lock.count', $microtimeout); if (!$isLock) { $getTime = $redis->get('lock.count'); if ($getTime > $microtime) { // 睡眠 降低搶鎖頻率 緩解redis壓力 usleep(5000); // 未超時繼續等待 continue; } // 超時,搶鎖,可能有幾毫秒級時間差可忽略 $previousTime = $redis->getset('lock.count', $microtimeout); if ((int)$previousTime < $microtime) { break; } } } while (!$isLock); $count = $redis->get('count')? : 0; // file_put_contents('/var/log/count.log.1', ($count+1)); // 業務邏輯 echo "執行count加1操作~ \n\n"; $redis->set('count', $count+1); // 刪除鎖 $redis->del('lock.count'); // 打印count值 $count = $redis->get('count'); echo "count值為:$count \n"; ```
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