Does locking also lock the variables which is being used inside the locked block?

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class ThreadSafe
{
  public static readonly object _locker = new object();
  public static int _val1;
  public int _val2 = 1;
  public void Go()
  {
    lock (_locker)
    {
      if (_val2 != 0) Console.WriteLine (_val1 / _val2);
      _val2 = 0;
    }
  }
}

In the above example is it possible for another thread to change the values of _val2 and _val1?

Posted 18-Aug-10 23:28pm

piushs

Updated 18-Aug-10 23:31pm

LittleYellowBird

v2

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Fredrik Bornander · Answer 1 · 2010-08-19T00:08:00

Solution 1

The lock keyword locks only access to the code section, not the data used inside of it. This means that it is possible for another thread to modify both _val1 and _val2 even when the locked section is executed.

Hope this helps,
Fredrik

Posted 19-Aug-10 0:08am

Fredrik Bornander

Comments

piushs 19-Aug-10 6:24am

Hi Fredrik
Thanks for your reply.
If such is the case, then how does locking satisfy the purpose of synchronisation? I mean, here i am trying to use "lock" on _locker object to avoid "division by zero" error, just in case, if two different threads are trying to access the code block and change the value of _val2 to zero.

Now if the _val2 can be modified by another thread and changed to zero, then i find above locking useless.
Please help me as i am a bit confused with locking.

CPallini 19-Aug-10 6:33am

You should provide syncrhonized accessors to _val1, _val2, not expose them as public variables.