lock statement in c#

Question

1.00/5 (1 vote)

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Ex, i've a class like this:

public class myclass
{
      private Object x;
      public void method1()
      {
          lock(x)
          {
                //access to x from thread1
          }
      }
      
      public void method2()
      {
             //access to x from thread2
      }
}

Now, if method1() is called from a thread(but not completed yet). And method2() is called from an another thread(method1() hasn't completed yet from thread thread1). Will thread2 have to wait until method1() completed?

Posted 17-May-11 3:06am

thanhvinh0906

Updated 17-May-11 3:11am

ambarishtv

v3

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Sergey Alexandrovich Kryukov 17-May-11 19:01pm

Don't re-post. Yes, I understand the question is a bit different; but you should have improved your previous question as it's too close.
--SA

2 solutions

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Manfred Rudolf Bihy · Accepted Answer · 2011-05-17T03:10:00

Solution 1

No, the locking will have to be in both methods. Locking on an object keeps other threads from entering on a lock section on that object. The method doesn't have to finish as a whole, unless the lock spans the whole of the method body. As soon as one lock section is exited any other thread trying to enter a lock on the same object get a chance to enter their lock.

C#

public class myclass
{
      private Object x;
      public void method1()
      {
          lock(x)
          {
                //access to x from thread1
          }
      }

      public void method2()
      {
          lock(x)
          {
                //access to x from thread2
          }
      }
}

Regards,

-MRB

Posted 17-May-11 3:10am

Manfred Rudolf Bihy

Updated 17-May-11 3:12am

v3

Comments

Olivier Levrey 17-May-11 9:13am

Great answer. You were faster than me. Have a 5.

Manfred Rudolf Bihy 17-May-11 9:23am

Thank you!

ambarishtv 17-May-11 9:13am

i agreed :) 5

Manfred Rudolf Bihy 17-May-11 9:23am

Thanks!

thanhvinh0906 17-May-11 9:24am

But, my question is that if method2() hasn't got a lock statement, will it have to wait?

Manfred Rudolf Bihy 17-May-11 10:10am

That is what I wrote in my solution. No lock, no wait!
Please clarify your doubts as I thought I had put it quite clearly.
The lock statment does a check if a lock on the object in the parameter has already been acquired by another thread and if that turns out to be true the current thread that wants to enter that lock will have to wait.
Cheers!

Sergey Alexandrovich Kryukov 17-May-11 19:02pm

Correct, my 5.
--SA

Olivier Levrey · Accepted Answer · 2011-05-17T03:12:00

No, the lock is only about x. The wait will occure if a thread is inside the lock block, and another thread is trying to enter the lock at the same time.

To make method2 block, you should write something like this:

C#

public void method1()
{
    lock(x)
    {
          //access to x from thread1
    }
}

public void method2()
{
    lock(x)
    {
        ...
    }
}

-------------------------------

But, my question is that if method2() hasn't got a lock statement, will it have to wait?

If there is no lock in method2, it will not wait.
Now about puting a lock or not, it depends what you do in method1 and method2.
If you put the lock in method1 to protect a few members, and you access the same members in method2, then you will probably have to use a lock in method2 too.
If you do something very different, then you don't need to lock in method2.