C# Programming/Keywords/lock

The lock keyword allows a section of code to exclusively use a resource, a feature useful in multi-threaded applications. If a lock to the specified object is already held when a piece of code tries to lock the object, the code's thread is blocked until the object is available.

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.
    }
}

The parameter to the lock statement must be an object reference, not a value type:

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# Keywords
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
Special C# Identifiers (Contextual Keywords)
add alias async await dynamic get global nameof partial remove set value when where yield
Contextual Keywords (Used in Queries)
ascending by descending equals from group in into join let on orderby select where