1.GlobalScope.launch
2.runBlocking 启动协程
3.async启动协程
启动协程的基本方式
1.GlobalScope.launch代码示例：
fun testGlobalScope() {
GlobalScope.launch {
println("Coroutinue started!")
delay(1000L)
println("Hello World!")
}
println("After launch!")
Thread.sleep(2000L)
println("Process end!")
}
/**
* After launch!
* Coroutinue started!
* Hello World!
* Process end!
*/
@DelicateCoroutinesApi
public object GlobalScope : CoroutineScope {
/**
* Returns [EmptyCoroutineContext].
*/
override val coroutineContext: CoroutineContext
get() = EmptyCoroutineContext
}
public fun CoroutineScope.launch(
context: CoroutineContext = EmptyCoroutineContext,
start: CoroutineStart = CoroutineStart.DEFAULT,
block: suspend CoroutineScope.() -> Unit
): Job {
val newContext = newCoroutineContext(context)
val coroutine = if (start.isLazy)
LazyStandaloneCoroutine(newContext, block) else
StandaloneCoroutine(newContext, active = true)
coroutine.start(start, coroutine, block)
return coroutine
}
launch函数是CoroutineScope的扩展函数，它有三个参数：
context: CoroutineContext = EmptyCoroutineContext, 第一个参数是协程上下文，它的默认值是 EmptyCoroutineContext，如果不传这个参数，默认就会使用 EmptyCoroutineContext。也可以传入 Kotlin 官方为我们提供的 Dispatchers，来指定协程运行的线程池。（Dispatchers.IO、Dispatchers.Unconfined、Dispatchers.Main）
start: CoroutineStart = CoroutineStart.DEFAULT，第二个参数是协程的启动模式，默认值是CoroutineStart.DEFAULT，CoroutineStart 是一个枚举类，一共有：DEFAULT、LAZY、ATOMIC、UNDISPATCHED。
block: suspend CoroutineScope.() -> Unit，第三个参数是函数类型block，它的类型是suspend CoroutineScope.() -> Unit。本质是一个挂起函数。
函数的返回值是一个 Job，它其实代表的是协程的句柄，并不能返回协程的执行结果。
2.runBlocking 启动协程代码示例
fun testRunBlocking2() {
runBlocking {
println("Coroutinue started!")
delay(1000L)
println("Hello World!")
}
println("After Launch")
Thread.sleep(2000L)
println("Process end")
}
/**
* Coroutinue started!
* Hello World!
* After Launch
* Process end
*/
@Throws(InterruptedException::class)
public actual fun <T> runBlocking(context: CoroutineContext, block: suspend CoroutineScope.() -> T): T {
contract {
callsInPlace(block, InvocationKind.EXACTLY_ONCE)
}
val currentThread = Thread.currentThread()
val contextInterceptor = context[ContinuationInterceptor]
val eventLoop: EventLoop?
val newContext: CoroutineContext
if (contextInterceptor == null) {
// create or use private event loop if no dispatcher is specified
eventLoop = ThreadLocalEventLoop.eventLoop
newContext = GlobalScope.newCoroutineContext(context + eventLoop)
} else {
// See if context's interceptor is an event loop that we shall use (to support TestContext)
// or take an existing thread-local event loop if present to avoid blocking it (but don't create one)
eventLoop = (contextInterceptor as? EventLoop)?.takeIf { it.shouldBeProcessedFromContext() }
?: ThreadLocalEventLoop.currentOrNull()
newContext = GlobalScope.newCoroutineContext(context)
}
val coroutine = BlockingCoroutine<T>(newContext, currentThread, eventLoop)
coroutine.start(CoroutineStart.DEFAULT, coroutine, block)
return coroutine.joinBlocking()
}
runBlocking是普通函数，第一个参数：context: CoroutineContext,协程上下文。第二个参数是函数类型，block: suspend CoroutineScope.() -> T,函数类型是有返回值类型 T 的，与 runBlocking 的返回值类型是一样的，runBlocking 其实是可以从协程当中返回执行结果的。
fun testRunBlocking() {
val runBlockingResult = runBlocking {
delay(500L)
return@runBlocking "HaHa"
}
println("result:$runBlockingResult")
}
result:HaHa
runBlocking特点：
runBlocking 启动的协程会阻塞当前线程的执行。
3.async启动协程使用 async{} 创建协程，可以通过它返回的Deferred拿到协程的执行结果。
代码示例
fun testAsync() {
runBlocking {
val deferred = async {
println("do async:${Thread.currentThread().name}")
delay(1000L)
return@async "do completed"
}
println("After async:${Thread.currentThread().name}")
val result = deferred.await()
println("Result is: $result")
}
}
After async:main @coroutine#1
do async:main @coroutine#2
Result is: do completed
public fun <T> CoroutineScope.async(
context: CoroutineContext = EmptyCoroutineContext,
start: CoroutineStart = CoroutineStart.DEFAULT,
block: suspend CoroutineScope.() -> T
): Deferred<T> {
val newContext = newCoroutineContext(context)
val coroutine = if (start.isLazy)
LazyDeferredCoroutine(newContext, block) else
DeferredCoroutine<T>(newContext, active = true)
coroutine.start(start, coroutine, block)
return coroutine
}
async注意点
async 启动协程以后，不会阻塞当前程序的执行流程。
async{}的返回值，是一个 Deferred 对象，它的 await() 方法，就可以拿到协程的执行结果。
await只是等待执行完，并不是触发执行。
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