请教lock(obj)和Application.Lock有什么区别

请问lock(obj)和Application.Lock有什么区别？

C# code

                int a = 0;                lock (Application["delDatetime"])                {                    a += 1;                    Application["delDatetime"] = System.DateTime.Now;                }

C# code

                int a = 0;                Application.Lock();                a += 1;                Application["delDatetime"] = System.DateTime.Now;                Application.UnLock();

C# code

internal virtual void AcquireWrite(){    lock (this)    {        while (this._lock != 0)        {            try            {                Monitor.Wait(this);                continue;            }            catch (ThreadInterruptedException)            {                continue;            }        }        this._lock = -1;    }}