How does C# lock work?

Question:

I was looking at an MSDN article, but it wasn't quite clear why I should use this.

class Account
{
    decimal balance;
    private Object thisLock = new Object();

    public void Withdraw(decimal amount)
    {
        lock (thisLock)
        {
            if (amount > balance)
            {
                throw new Exception("Insufficient funds");
            }
            balance -= amount;
        }
    }
}

Answer:

Lock is a very useful tool when you need to grant exclusive access to a given resource, or ensure Thread safety .

This function makes use of an object as a synchronization flag (in your example, the thislock object).

In the example code, the first thread to execute the Withdraw method will get the lock from the thislock object, and will execute the code block. Any other thread that tries to execute the same method instance will go into WaitState (or wait state ) if it encounters the lock instruction and another thread has the access right.

A queue is created, and the waiting threads will receive a FIFO-style lock release ( First In, First Out ).