What is the difference between task and thread?
In C# 4.0, we have Task in the System.Threading.Tasks namespace. What is the true difference between Thread and Task . I did some sample program(help taken from MSDN) for my own sake of learning with
Parallel.Invoke
Parallel.For
Parallel.ForEach
but have many doubts as the idea is not so clear.
I have initially searched in Stackoverflow for a similar type of question but may be with this question title I was not able to get the same. If anyone knows about the same type of question being posted here earlier, kindly give the reference of the link.
A task is something you want done.
A thread is one of the many possible workers which performs that task.
In .NET 4.0 terms, a Task represents an asynchronous operation. Thread(s) are used to complete that operation by breaking the work up into chunks and assigning to separate threads.
In computer science terms, a Task is a future or a promise. (Some people use those two terms synomymously, 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 threadpool. 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 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!)
When we execute things on multiple threads, it's not guaranteed that the threads are separated across multiple processors.
Task is a lightweight object for managing a parallelizable unit of work. It can be used whenever you want to execute something in parallel. Parallel means the work is spread across multiple processors to maximize computational speed. Tasks are tuned for leveraging multicores processors.
Task provides following powerful features over thread.
Wait on a set of tasks, without a signaling construct.
We can chain tasks together to execute one after the other.
Establish a parent/child relationship when one task is started from another task.
Child task exception can propagate to parent task.
Task support cancellation through the use of cancellation tokens.
Asynchronous implementation is easy in task, using' async' and 'await' keywords.
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