Multi-Threading Concept in c#(Questions and answers)

Multi-Threading Concept in c# (Questions and answers)

Multithreading is the ability of an operating system to concurrently run programs that have been divided into threads.

Multithreading offers better utilization of processors and other system resources.

Example:

A program can spell check and save the data to disk while sending data to be printed. 

Advantages and disadvantages of using multithreading

Advantages:

Simultaneous access to multiple applications

Reduced number of required servers

Improved performance and concurrency

Simplified coding of remote procedure calls and conversations

Disadvantages:

Code writing, debugging, managing concurrency, testing, porting existing code is difficult in multithreading and multicontexting.

Programmers need to remove static variables and replace any code that is not thread-safe to introduce threading into a previously non threaded application. 

Benefits of using the Thread Pool.

The benefits of using a Thread Pool are:

Thread creation and destruction overhead is negated,

Better performance and better system stability.
It is better to use a thread pool in cases where the number of threads is very large. 

Explain how to create and manage threads using Thread class in the System.Threading namespace in .NET.

using System.Threading;

private void ThreadTask()

{

         int x;

         int val;

         Random r=new Random();

         while(true)

         {

             x=this.progressBar1.Step*r.Next(-1,2);

            val = this.progressBar1.Value + x;

            if (val > this.progressBar1.Maximum)

                  val = this.progressBar1.Maximum;

            else if (val < this.progressBar1.Minimum)

                  val = this.progressBar1.Minimum;

            this.progressBar1.Value = val;

            Thread.Sleep(100);

         }

}

You need to write these lines first:

    Thread t1 = new Thread(new ThreadStart(this.ThreadTask));

    t1.IsBackground = true;

    t1.Start(); 

Explain the purpose of Mutex class in .NET.

System uses synchronization mechanism to make sure that a resource is used by only one thread at a time when more than one thread needs to access a shared resource at the same time.

Mutex grants exclusive access to the shared resource to a single thread.

A second thread that needs to acquire a particular mutex is suspended until the first thread releases the mutex. 

Describe the concepts of Monitor class, the interlocked class and the ReaderWriterLock class.

Access to objects by is controlled by the Monitor class. It grants a lock for an object to a single thread.

Critical sections can be access restricted by using object locks.

While a thread owns the lock for an object, no other thread can acquire that lock.

Interlocked class provides atomic operations for variables that are shared by multiple threads.

When two threads are executing concurrently on separate processors error protection is done.

The methods of this class help protect against errors that can occur when the scheduler switches contexts while a thread is updating a variable that can be accessed by other threads.

ReaderWriterLock synchronizes access to a resource. It allows either concurrent read access for multiple threads, or write access for a single thread.

A ReaderWriterLock provides better throughput than a simple one lock a time like Monitor.

Explain about Serialization in .NET. Explain binary serialization and XML serialization

System.Runtime.Serialization namespace provides Serialization in .NET.

The IFormatter interface in the namespace contains Serialize and De-serialize methods that save and load data of a stream.

So we need stream as a container for the serialized object(s) and a formatter that serializes these objects onto the stream to implement serialization in .net.

Binary serialization is a mechanism that creates exact binary copy of the object onto the storage media by writing the data to the output stream such that it can be used to re-construct the object automatically.

XML serialization results in strongly typed classes with public properties and fields that are converted to a serial format for storage or transport. This XML stream conforms to a specific XML Schema definition language (XSD) document.

Explain why Serialization.

An object is stored in a file, a database or even in the memory. However, data to be transferred over a network needs to be in a linear form for which serialization and deserialization are used.

Advantage of serialization is the ability of an object to be serialized into a persistent or a non-persistent storage media and then reconstructing the same object later by de-serializing the object.

Remoting and Web Services depend heavily on Serialization and De-serialization.

Explain the components that comprise the binary serialization architecture.

To binary serialize an object we need a FileStream object,

Constructor: FileStream(file_name, FileMode.Create);

And

BinaryFormatter

Constructor: binaryFormatter.Serialize(fileStreamObject, object1);

What is Formatters? Explain the binary formatter and the SOAP formatter.

A formatter determines the serialization format for objects.

.NET framework provides Binary formatter and SOAP formatter which inherit from the IFormatter interface

The Binary Formatter

It provides binary encoding for compact serialization for storage or socket-based network streams.

It is not appropriate for data to be passed through a firewall.

The SOAP Formatter

It provides formatting that can be used to enable objects to be serialized using the SOAP protocol.

The class is used for serialization through firewalls or diverse systems. 

What are the main advantages of binary serialization?

An object is stored in a file, a database or even in the memory. However, data to be transferred over a network needs to be in a linear form for which serialization and deserialization are used.

Advantage of serialization is the ability of an object to be serialized into a persistent or a non-persistent storage media and then reconstructing the same object later by de-serializing the object.

Also Binary Serialization is faster, supports complex objects too with read only properties and even circular references. 

How do you encapsulate the binary serialization?

public static void SerializeBinary( object o, string file_name)

{

   using (FileStream fs = new FileStream(file_name, FileMode.Create)) {

  BinaryFormatter fmt = new BinaryFormatter ();

  fmt.Serialize(fs, o);

  }

} 

How do you implement a custom serialization?

CUSTOM SERIALIZATION implementation

public class A: ISerializable

{

           private int a;

           protected A(SerializationInfo si, StreamingContext sc)

           {

                   this.a = serializationInfo.GetInt32("a");

           }

           public void ISerializable.GetObjectData(SerializationInfo si, StreamingContext sc)

           {

                     si.AddValue("a", this.a);

            }

} 

What is the difference between the SoapFormatter and the XmlSerializer?

SoapFormatter

SOAP formatter will actually take the field values of an object and store all of that information in the stream passed.

SoapFormatter is better to serialize arbitrary data

XmlSerializer

XML Serialization would just serialize the public properties of an object.

The XML Serializer is used typically for serializing simple types across web services

xmlserializer is better, more flexible and faster 

How can I optimize the serialization process?

The first call to a Web Service takes long because XmlSerializer generate an assembly optimized for each type in memory.

To optimize the serialization process pregeneration of serialization assembly with Visual Studio or sgen.exe is needed.

Implementing serialization separately can also increase the performance. 

Apartments

COM objects in the process as divided into groups called apartments. A COM object lives in exactly one apartment, in the sense that its methods can legally be directly called only by a thread that belongs to that apartment. Any other thread that wants to call the object must go through a proxy.

There are two types of apartments: single-threaded apartments, and multithreaded apartments.

1.Single-threaded Apartments—Single-threaded apartments consist of exactly one thread, so all COM objects that live in a single-threaded apartment can receive method calls only from the one thread that belongs to that apartment. All method calls to a COM object in a single-threaded apartment are synchronized with the windows message queue for the single-threaded apartment's thread. A process with a single thread of execution is simply a special case of this model.

2. Multithreaded Apartments—Multithreaded apartments consist of one or more threads, so all COM objects that live in an multithreaded apartment can receive method calls directly from any of the threads that belong to the multithreaded apartment. Threads in a multithreaded apartment use a model called free-threading. Calls to COM objects in a multithreaded apartment are synchronized by the objects themselves.

Synchronizing objects

Lock

Locks are useful when only one thread at a time can be allowed to modify data or some other controlled resource.

Monitors

Monitors are Like the lock keyword, monitors prevent blocks of code from simultaneous execution by multiple threads. The Enter method allows one and only one thread to proceed into the following statements; all other threads are blocked until the executing thread calls Exit. This is just like using the lock keyword. In fact, the lock keyword is implemented with the Monitor class.

Mutex

A mutex is similar to a monitor; it prevents the simultaneous execution of a block of code by more than one thread at a time. In fact, the name "mutex" is a shortened form of the term "mutually exclusive." Unlike monitors, however, a mutex can be used to synchronize threads across processes.

Semaphore is same as Mutex but it ensures not more than a specified number of threads can access a resource, or section of code.