C# 程式設計/關鍵字/lock

在多執行緒應用程式中，lock 關鍵字允許一段程式碼獨佔使用資源。如果當一段程式碼嘗試鎖定某個物件時，該物件的鎖已被其他程式碼佔用，則這段程式碼所在的執行緒將被阻塞，直到該物件可用。

using System;
using System.Threading;

class LockDemo
{
    private static int number = 0;
    private static object lockObject = new object();
    
    private static void DoSomething()
    {
        while (true)
        {
            lock (lockObject)
            {
                int originalNumber = number;
                
                number += 1;
                Thread.Sleep((new Random()).Next(1000)); // sleep for a random amount of time
                number += 1;
                Thread.Sleep((new Random()).Next(1000)); // sleep again
                
                Console.Write("Expecting number to be " + (originalNumber + 2).ToString());
                Console.WriteLine(", and it is: " + number.ToString());
                // without the lock statement, the above would produce unexpected results, 
                // since the other thread may have added 2 to the number while we were sleeping.
            }
        }
    }
    
    public static void Main()
    {
        Thread t = new Thread(new ThreadStart(DoSomething));
        
        t.Start();
        DoSomething(); // at this point, two instances of DoSomething are running at the same time.
    }
}

lock 語句的引數必須是物件引用，而不是值型別。

class LockDemo2
{
    private int number;
    private object obj = new object();
    
    public void DoSomething()
    {
        lock (this) // ok
        {
            ...
        }
        
        lock (number) // not ok, number is not a reference
        {
            ...
        }
        
        lock (obj) // ok, obj is a reference
        {
            ...
        }
    }
}

C# 關鍵字
abstract as base bool break byte case catch char checked class const continue decimal default delegate do double else enum event explicit extern false finally fixed float for foreach goto if implicit in int interface internal is lock long namespace new null object operator out override params private protected public readonly ref return sbyte sealed short sizeof stackalloc static string struct switch this throw true try typeof uint ulong unchecked unsafe ushort using var virtual void volatile while
特殊的 C# 識別符號（上下文關鍵字）
add alias async await dynamic get global nameof partial remove set value when where yield
上下文關鍵字（用於查詢）
ascending by descending equals from group in into join let on orderby select where