lock Statement (C# Reference)

The lock keyword marks a statement block as a critical section by obtaining the mutual-exclusion lock for a given object, executing a statement, and then releasing the lock. The following example includes a lock statement.

The lock keyword ensures that one thread does not enter a critical section of code while another thread is in the critical section. If another thread tries to enter a locked code, it will wait, block, until the object is released.

As long as the lock statement is present, the statement block is a critical section and balance will never become a negative number. See the following example.

//Account.cs

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;

          }

     }
}