Async tasks execution in C#

Question

I am new to TAP and TPL in C#, After googling and reading some material I am not able to understand how async tasks are executed.(particularly on which thread) Please help me to understand out of following two options which one is correct:

If async tasks are executed on the same thread on which they are invoked, then what if I create 1000 tasks and they all will be executed by time slicing on same thread? if it is not so and tasks execute on different threads then how is it different from multi-threading (parallel execution)?

Answer 1

If async tasks are executed on the same thread on which they are invoked, then what if I create 1000 tasks and they all will be executed by time slicing on same thread?

Since async tasks are not executed on the same thread on which they are invoked, it is meaningless to consider whether they will all be executed in some specific manner. In any case, there is no mechanism in .NET to "time-slice" within a single thread. Time-slicing is done at the granularity of a thread; ie CPU time is granted to threads, not subsets of threads.

In some scenarios involving async methods, it is possible that a given thread may service two or more tasks. This is inherent in the nature of thread pools, which are used extensively throughout the TPL API. But the only reason that such methods would be serviced in any sense of the word "concurrently" would be if they themselves are waiting on other asynchronous operations. In those cases, they can yield the thread cooperatively, at which point some other task might make use of it.

if it is not so and tasks execute on different threads then how is it different from multi-threading (parallel execution)?

async and Task are super-sets of "parallel execution". That is, some tasks execute in parallel. But async and Task are also used for operations that don't involve execution at all per se, but rather just waiting for some asynchronous event to occur outside the CPU (eg network or file I/O).

Computational tasks will be assigned an individual thread, for that task to use for the duration of the task. Other types of asynchronous operations will not use a thread at all.

For computational tasks, these are not different from multi-threading on a fundamental level. Like many things in programming, it's more that async and Task offer useful abstractions that allow one to write code more easily to take advantage of multi-threading features in the computer, and at the same time also represent non-computational operations that are otherwise semantically similar to concurrent computational operations.

I have done my best to answer your questions as directly and concisely as possible. I would not be surprised however if the above raises as many new questions as it's answered old. Unfortunately, that's the nature of potentially broad questions. I do hope that the above has satisfied your curiosity, but if not that would mean that your original question is too broad for Stack Overflow. Please consider rewriting your question so that it focuses more specifically on an issue; include a good, minimal , complete code example for context, so that the question can be addressed in a specific manner and without ambiguity.