Is a Task lightweight compared to a Thread?

Question

I overheard a coworker saying that a Task is basically a lightweight thread. Coming from a C++ background (where threads where the lightest weight processing unit), this seems counter-intuitive to me.

Aren't Tasks just as heavy as Threads?

Answer 1

You need to distinguish between a unit of work (Tasks) from the underlying process used to host/execute them. It isn't even necessary for Tasks to run on other threads. For example, Tasks can be executed in a single threaded application that periodically yields control to the task pool.

Even when Tasks are executed on separate threads, there is usually not a 1 to 1 relationship between Task and Thread. The threads are preallocated as part of a pool, and then tasks are scheduled to run on these threads as available. Creating a new task does not require the overhead of creating a thread, it only requires the cost of an enque in a task queue.

This makes tasks inherently more scalable. I can have millions of tasks throughout the lifetime of my application, but only ever actually use some constant number of threads.