Today I was digging with TPL and found a new class Task.Now I just wanted to know that what is diffrence between task and Thread,and which one is better?
C# Multithreading – Difference Between Task and Thread in .NET 4.0
.net-4.0c++multithreading
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In computer science terms, a Task is a future or a promise. (Some people use those two terms synonymously, some use them differently, nobody can agree on a precise definition.) Basically, a Task<T> "promises" to return you a T, but not right now honey, I'm kinda busy, why don't you come back later?
A Thread is a way of fulfilling that promise. But not every Task needs a brand-new Thread. (In fact, creating a thread is often undesirable, because doing so is much more expensive than re-using an existing thread from the thread pool. More on that in a moment.) If the value you are waiting for comes from the filesystem or a database or the network, then there is no need for a thread to sit around and wait for the data when it can be servicing other requests. Instead, the Task might register a callback to receive the value(s) when they're ready.
In particular, the Task does not say why it is that it takes such a long time to return the value. It might be that it takes a long time to compute, or it might be that it takes a long time to fetch. Only in the former case would you use a Thread to run a Task. (In .NET, threads are freaking expensive, so you generally want to avoid them as much as possible and really only use them if you want to run multiple heavy computations on multiple CPUs. For example, in Windows, a thread weighs 12 KiByte (I think), in Linux, a thread weighs as little as 4 KiByte, in Erlang/BEAM even just 400 Byte. In .NET, it's 1 MiByte!)
Task is an order to program to do something in asynchronous way. The Thread is actually OS kernel object which executes what was requested. Think about Task like a clever thread aggregator/organizer that "knows" how much task is better to run contemporary on your CPU. It's just cleverer then common implementations of multi-threading (that's why it's suggested choice from Microsoft). It's a feature that helps you managing Threads in easier way.
Look also on this Should i use ThreadPools or Task Parallel Library for IO-bound operations that may give you some hints on performance issues you may be interested in.
Best Answer
Suppose you are running a book delivery company. You have four cars and four drivers. A car is a thread, a driver is a processor, and a book delivery is a task. The problem you face is how to efficiently schedule the drivers and cars so that the tasks get done as quickly as possible.
Where things get weird is when there are more cars (threads) than drivers (processors). What happens then is halfway through a trip the driver parks one car (suspends the thread) and gets into a different car (switches context), drives that one around for a while performing tasks, and then eventually comes back to the first car. Obviously that is not as efficient as one driver staying in one car.
The idea of task-based parallism is to break up the work into small tasks that can produce results in the future, and then efficiently allocate exactly as many threads as there are processors so that you don't waste time context switching. In practice, it usually does not work out that nicely, but that's the idea.
The question cannot be answered because it doesn't make any sense. Which is better, a book to deliver to a customer, or a car to deliver it in? A car is a device that can be used to deliver a book; those two things are not things you can sensibly describe as "better" or "worse" than the other. It's like asking "which is better, a hole or a drill?"