Tuesday, March 7, 2017

ConcurrentCounter - Reduce code with Functional programming

The fashion of functional programming

Now a days functional programming already made its come back and every language, companies and developers want to embrace functional programming. When we look at their works we can see it needs to travel more to reach the functional programming world. It was same for object oriented world as well. People used C++ but the code looked like C.

That is not the concern with this post. One of the reasons we here when people adopt FP is that it helps us to achieve things with less code. This is just a scenario where FP can reduce some amount of code.

Scenario - Thread safe manipulation of resources

We are in the world of threads. Knowingly or unknowingly we had to deal with threads. Some languages / technologies already has better ways to deal threading without developer write any explicit line. NodeJS can be an example. But for C# guys like me, has to write programs properly to make sure it works with threads. If all the tasks are ready to run in parallel,  there are no issues. But the reality is not that way. There will be so many critical sections we had to handle to achieve a good working software. We rely heavily on thread synchronization mechanisms to achieve the same. Whenever we deal with those, it is nightmare and there are so many chances to produce duplicate code. That is the place functional programming can help us.

Taking one situation. We have a counter inside a web service.That counter can be considered as a resource just like file or other resources. Counter variable is accessed by multiple service methods, some reads some writes. So the first way comes to our mind would be C# lock (VB.Net SyncLock) keyword. When we implement it there are chances that we may write lock statement in multiple places. Below is a mechanism to avoid that by using functional techniques of C#.
Please note that in real world no one should use this mechanism for integers as far as Interlocked class is there in .Net framework. This is just a sample for understanding purpose.

Wrap the lock statement in fuction and pass the actions into it

The technique here is simple as anyone might have guessed. Just have a wrapper around the lock and inside the locked section execute the real manipulation code which is passed into it as Action<T>. Lets see the code snippet below.
internal class ThreadSafeCounter
{
    private int internalValue;
    private object lockObject = new object();
    public int Value
    {
        get
        {
            return ExecuteWithLock(() => { return internalValue; });
        }
    }
    public ThreadSafeCounter(int initialValue)
    {
        this.internalValue = initialValue;
    }
    public void Increment()
    {
        ExecuteWithLock(() => { internalValue++; });
    }
    public void Decrement()
    {
        ExecuteWithLock(() => { internalValue--; });
    }
    public void Reset()
    {
        ExecuteWithLock(() => { internalValue=0; });
    }
    #region Helpers
    private void ExecuteWithLock(Action action)
    {
        lock (lockObject)
        {
            action();
        }
    }
    private int ExecuteWithLock(Func<int> fun)
    {
        int result = 0;
        ExecuteWithLock(() => result = fun());
        return result;
    }
    #endregion
}
The main functions to notice here are as below.

ExecuteWithLock(Action a)
ExecuteWithLock(Func)

The lock(){} is there only in one function named ExecuteWithLock() and all other functions those wants to execute critical section of code has to call ExecuteWithLock and pass the code as parameter. That code passing as parameter is obtained by the well known Action<T>. Hope there is no need of further explanation. 

2 comments:

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Stepherd said...

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