Lock Keyword Code Listing

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

Code Listing: Lock

// statements_lock2.cs
using System;
using System.Threading;

class Account
{
int balance;

Random r = new Random();

public Account(int initial) { balance = initial; }

int Withdraw(int amount)
{

// This condition will never be true unless the lock statement
// is commented out:

if (balance < 0)
{
throw new Exception("Negative Balance");
}
// Comment out the next line to see the effect of leaving out
// the lock keyword:
lock (this)
{
if (balance >= amount)
{
Console.WriteLine("Balance before Withdrawal : " + balance);
Console.WriteLine("Amount to Withdraw : -" + amount);
balance = balance - amount;
Console.WriteLine("Balance after Withdrawal : " + balance);
return amount;
}

else
{
return 0; // transaction rejected
}
}
}

public void DoTransactions()
{
for (int i = 0; i < 100; i++)
{
Withdraw(r.Next(1, 100));
}
}
}

class Test
{
public static void Main()
{
Thread[] threads = new Thread[10];
Account acc = new Account (1000);
for (int i = 0; i < 10; i++)
{
Thread t = new Thread(new ThreadStart(acc.DoTransactions));
threads[i] = t;
}
for (int i = 0; i < 10; i++)
{
threads[i].Start();
}
}
}