Kotlin middle process understanding and Practice (I)

What is a journey

Coroutines are thread based , It is a lightweight thread

stay Android What kind of problem is the middle process used to solve

1. Processing time-consuming operations , Such tasks often block the main thread .
2. Keep the main thread safe , That is to ensure that any... Is called safely from the main thread suspend function .

Coroutines is ：

Coroutines synchronize asynchronous logic , Put an end to hell .
The core of the collaborative process is , Functions or a program can be suspended , Restore in the suspended location later .
# Suspension and recovery of collaboration
Basic operations of general functions include ：invoke（ or call) and return, The program added suspend and resume：

suspend - Also known as suspend or pause , Used to pause the execution of the current program , And save all local variables ;

resume - Used to allow a suspended process to resume execution from where it was suspended

Suspend function

1. Use suspend Keyword decorated functions are called suspended functions .
2. Suspended functions can only be called within a coroutine body or other suspended functions

Scheduler

All collaborations must run in the scheduler , Even if they run on the main thread

-Dispatchers.Main

Android Main thread on , Used for processing UI Interaction and some lightweight tasks ,
call suspend function
call UI function
to update LiveData

-Dispatchers.IO

Non main thread , Designed for disk and network IO To optimize
call suspend function
call UI function
to update LiveData

-Dispatchers.Default

Non main thread , Specially designed for CPU Intensive tasks are optimized
Array sorting
JSON Data analysis
Deal with differences and judge

Two parts of the process

Kotlind There are two levels to realize the co process

1. Infrastructure layer , Standard library collaboration API, It mainly provides the most basic conceptual and semantic support for collaborative process
2. Business framework layer , The upper framework of the collaborative process supports

Mission leaks

1. When a collaborative task is lost , Unable to track , Will cause memory 、CPU、 Disk and other resources are wasted , Even sending a useless network request , This situation is called task leakage .
2. In order to avoid the coprocess leak ,Kotlin Structured concurrency mechanism is introduced .

Structured concurrency

Using structured concurrency can ：
1. Cancel the task , Cancel a task when it is no longer needed .
2. Tracking mission , When the task is in progress , Track it .
3. Send out the wrong signal , When the coroutine fails , An error signal indicates that an error has occurred .

CoroutinScope

One . Defining a coroutine must specify its CoroutineScope. It tracks all collaborations , It can also cancel all the coroutines it started .

Two . Common related API Yes ：

1.GlobalScope, The life cycle is process Grade , Even if Activity perhaps Fragment Has been destroyed , The collaboration process is still being implemented .
2.MainScope, stay Activity Use in , Can be in onDestroy() Cancel the cooperation process .
3.viewModelScope, Only in ViewModel Use in , binding ViewModel Life cycle of .
4.lifecycleScope, Only in Activity、Fragment Use in , Will bind Activity and Fragment Life cycle of .

Start and cancel the process

1. Start the coroutines ： Start the builder , Boot mode , Scope builder ,Job Life cycle of
2. Cancel the program ： Cancellation of the agreement ,CPU Intensive tasks are cancelled , Side effects of synergetic cancellation , Overtime task