Coroutines

Question 1

Define the relationship between Coroutines and Dispatchers (3)

Answer 1

• All Coroutines must run in a Dispatcher
• Dispatchers determine which threads are used for Coroutine execution
• Coroutines can suspend themselves, and the dispatcher is responsible for resuming them

Question 2

What are the four types of CoroutineDispatchers and their purposes?

Answer 2

Default - optimised to perform CPU-intensive work outside of the main thread
IO - offloads blocking IO tasks to a shared pool of threads
Main - confined to the Main thread operating with UI objects.
Unconfined - mandates no specific threading policy - executes coroutine immediately on the current thread and later resumes it in whatever thread called resume

Question 3

What is the purpose of a runBlocking block?

Answer 3

• Bridges synchronous and asynchronous functions.
• Blocks thread calling the async function until it returns.
• Specifically for use in main functions and tests

Question 4

What are the steps for executing work on a non-main thread?

Answer 4

1. Define a CoroutineScope
   val myScope = CoroutineScope(Dispatchers.Default)
2. Launch CoroutineScope
   myScope.launch{ }

Question 5

When within a CoroutineScope, how do you come back to do work on the main thread?

Answer 5

withContext(Dispatchers.Main){ }

Question 6

Why do we launch coroutines within a scope?

Answer 6

Any coroutine launched in a scope is automatically cancelled if the scope’s owner is cleared. (e.g. Navigating away from a ViewModel’s fragment)

Question 7

What advantages do Coroutines have over Callbacks?

Answer 7

Coroutines are written sequentially so they are easier to read and maintain.

Coroutines can safely use valuable language features such as exceptions (callbacks cannot).

Question 8

What is the difference between blocking and suspending?

Answer 8

If a thread is blocked, no other work happens.

If the thread is suspended, other work happens until the result is available.

Question 9

What 3 things are needed to use coroutines in Kotlin?

Answer 9

Job: anything that can be canceled. Every coroutine has a job, and you can use the job to cancel the coroutine.

Dispatcher: The dispatcher sends off coroutines to run on various threads.

Scope: A coroutine’s scope defines the context in which the coroutine runs. A scope combines information about a coroutine’s job and dispatchers.
eg ViewModelScope / LifecycleScope / liveData