多線程環境下非安全Dictionary引起的“已添加了具有相同鍵的項”問題

2019-11-14 13:56:41

字體：大中小

來源：轉載

供稿：網友

問題:

代碼是在多線程環境下，做了簡單的Key是否存的判斷, 測試代碼如下:

public class PRogram    {        static Dictionary<string, Logger> loggreDic;        static object loggerDicLocker = new object();        public static void Main()        {            loggreDic = new Dictionary<string, Logger>();            for (int i = 0; i < 100; i++)            {                ThreadPool.QueueUserWorkItem(o =>                {                    try                    {                        var logger = GetLogger("AAA");                    }                    catch (Exception)                    {                        Console.WriteLine(string.Format("弟{0}個線程出現問題", o));                    }                }, i);            }            Console.ReadKey();        }        static Logger GetLogger(string cmdId)        {            if (!loggreDic.ContainsKey(cmdId))            {                loggreDic.Add(cmdId, LogManager.GetLogger(string.Format("ChinaPnrApi.{0}", cmdId)));            }            return loggreDic[cmdId];        }    }

可以看到在GetLogger的地方做了判斷的處理，但是在多線程的時候還是會出現在取的時候取不到的問題?？梢詤⒖枷旅娼貓D :

從錯誤異常很容易判斷，是在Dictionary中加了重復的Key造成的.

所以總體上來看這段代碼所犯的問題是不是線程安全的代碼.

解決方案 :

1. 使用Locker解決

2. 使用線程安全的

下面對兩種方式都做了實現:

public interface IGetLogger    {        Logger GetLogger(string cmdId);    }    public class ConcurrentDictionaryLogger : IGetLogger    {        ConcurrentDictionary<string, Logger> loggreDic = new ConcurrentDictionary<string, Logger>();        public Logger GetLogger(string cmdId)        {            if (!loggreDic.ContainsKey(cmdId))            {                loggreDic.TryAdd(cmdId, LogManager.GetLogger(string.Format("ChinaPnrApi.{0}", cmdId)));            }            return loggreDic[cmdId];        }    }    public class LockerDictionaryLogger : IGetLogger    {        Dictionary<string, Logger> loggreDic = new Dictionary<string, Logger>();        object locker = new object();        public Logger GetLogger(string cmdId)        {            if (!loggreDic.ContainsKey(cmdId))            {                lock (locker)                {                    if (!loggreDic.ContainsKey(cmdId))                    {                        loggreDic.Add(cmdId, LogManager.GetLogger(string.Format("ChinaPnrApi.{0}", cmdId)));                    }                }            }            return loggreDic[cmdId];        }    }

測試代碼如下:

public static void Main()        {            IGetLogger conLogger = new ConcurrentDictionaryLogger();            IGetLogger lockerLogger = new LockerDictionaryLogger();            CodeTimer.Time("使用ConcurrentDictionary", 1000000, () =>            {                ThreadPool.QueueUserWorkItem(o =>                {                    try                    {                        var logger = conLogger.GetLogger("AAA");                        if (logger == null)                        {                            Console.WriteLine(string.Format("弟{0}個線程獲取到的值是 NULL", o));                        }                    }                    catch (Exception ex)                    {                        Console.WriteLine(string.Format("弟{0}個線程出現問題, {1}", o, ex.Message));                    }                });            });            CodeTimer.Time("使用LockDictionary", 1000000, () =>            {                ThreadPool.QueueUserWorkItem(o =>                {                    try                    {                        var logger = conLogger.GetLogger("AAA");                        if (logger == null)                        {                            Console.WriteLine(string.Format("弟{0}個線程獲取到的值是 NULL", o));                        }                    }                    catch (Exception ex)                    {                        Console.WriteLine(string.Format("弟{0}個線程出現問題, {1}", o, ex.Message));                    }                });            });            Console.WriteLine("已執行完成");            Console.ReadKey();        }