Question

I came across this definition of Object constructor (metadata from mscorlib.dll)

[ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]
public Object();

I didn’t understood what ConstrainedExecution (Cer.MayFail) mean can someone tell me with an example in this case.

I came across this code, also tell me if it is correct to write like this,

public class MyClass
{
    private static object instanceLock = new object();

    private void Func()
    {
        bool instanceLockTaken = false;

        Monitor.TryEnter(instanceLock, ref instanceLockTaken);
        //...
        Monitor.Exit(instanceLock);
    }
}

Answer 1

Constrained Execution is what you’re trying to achieve by locking the thread.

From: http://msdn.microsoft.com/en-us/magazine/cc163716.aspx

A Cer value of MayFail is used to signal that when faced with
asynchronous exceptions, the code may not complete in an expected
fashion. Since thread aborts are being delayed over constrained
execution regions, this really means that your code is doing something
that may cause memory to be allocated or that might result in a stack
overflow. More importantly, it means that you must take the possible
failures into consideration when calling this method.

In your case, because the object is static and only created once, this will not be a problem.

Monitor.TryEnter returns immediately even if a lock was not acquired. It has a boolean value, which you’re not checking, something like this would work:

Monitor.TryEnter(instanceLock, ref instanceLockTaken);

  if (instanceLockTaken) 
  {
    // Do stuff here

    Monitor.Exit(instanceLock);
  }

However, this code would mean that the if {} block would not be executed every time, if you want to acquire a lock on every thread, you’ll need to do something like this:

lock(instanceLock)
{
  // Do stuff here
}

This means that only a single thread can run the contents of the lock {} statement at a time, and the contents of the lock statement will be executed every time.

On a side note, you can also make the object you’re locking readonly:

private static readonly object instanceLock = new object();