fun foo(){}
//类型为 () -> Unit
fun foo(p: Int){}
//类型为 (Int) -> String
class Foo{
fun bar(p0: String,p1: Long):Any{}
}
//那么 bar 的类型为：Foo.(String,Long) -> Any
//Foo就是bar的 receiver。也可以写成 (Foo,String,Long) ->Any
函数引用
fun foo(){}
//引用是 ::foo
fun foo(p0: Int): String
//引用也是 ::foo
咋都一样？没办法，就这样规定的。使用的时候 只能靠编译器推断
val f: () -> Unit = ::foo //编译器会推断出是fun foo(){}
val g: (Int) -> String = ::foo //推断为fun foo(p0: Int): String
带Receiver的写法
class Foo{
fun bar(p0: String,p1: Long):Any{}
}
val h: (Foo,String,Long) -> Any = Foo:bar
绑定receiver的函数引用：
val foo: Foo = Foo()
val m: (String,Long) -> Any = foo:bar
额外知识点
val x: (Foo,String,Long) -> Any = Foo:bar
val y: Function3<Foo,String,Long,Any> = x
Foo.(String,Long) -> Any = (Foo,String,Long) ->Any = Function3<Foo,String,Long,Any>
函数作为参数传递
fun yy(p: (Foo,String,Long)->Any){
p(Foo(),"Hello",3L)//直接p()就能调用
//p.invoke(Foo(),"Hello",3L) 也可以用invoke形式
}
Lambda 就是匿名函数，它跟普通函数比是没有名字的，听起来好像是废话
//普通函数
fun func(){
println("hello");
}
//去掉函数名 func,就成了匿名函数
fun(){
println("hello");
}
//可以赋值给一个变量
val func = fun(){
println("hello");
}
//匿名函数的类型
val func :()->Unit = fun(){
println("hello");
}
//Lambda表达式
val func={
print("Hello");
}
//Lambda类型
val func :()->String = {
print("Hello");
"Hello" //如果是Lambda中，最后一行被当作返回值，能省掉return。普通函数则不行
}
//带参数Lambda
val f1: (Int)->Unit = {p:Int ->
print(p);
}
//可进一步简化为
val f1 = {p:Int ->
print(p);
}
//当只有一个参数的时候，还可以写成
val f1: (Int)->Unit = {
print(it);
}
internal abstract class BaseContinuationImpl{
fun resumeWith(result: Result<Any?>) {
// This loop unrolls recursion in current.resumeWith(param) to make saner and shorter stack traces on resume
var current = this
var param = result
while (true) {
with(current) {
val completion = completion!! // fail fast when trying to resume continuation without completion
val outcome: Result<Any?> =
try {
val outcome = invokeSuspend(param)//调用状态机
if (outcome === COROUTINE_SUSPENDED) return
Result.success(outcome)
} catch (exception: Throwable) {
Result.failure(exception)
}
releaseIntercepted() // this state machine instance is terminating
if (completion is BaseContinuationImpl) {
// unrolling recursion via loop
current = completion
param = outcome
} else {
//最终走到这里，这个completion就是被塞的第一颗球。
completion.resumeWith(outcome)
return
}
}
}
}
}
状态机代码截取
public final Object invokeSuspend(@NotNull Object $result) {
Object var3 = IntrinsicsKt.getCOROUTINE_SUSPENDED();
Object var10000;
switch(this.label) {
case 0://第一次进来 label = 0
ResultKt.throwOnFailure($result);
// label改成1了，意味着下一次被恢复的时候会走case 1，这就是所谓的【状态流转】
this.label = 1;
//全体目光向我看齐，我宣布个事：this is 协程体对象。
var10000 = TestSampleKt.hello2(this);
if (var10000 == var3) {
return var3;
}
break;
case 1:
ResultKt.throwOnFailure($result);
var10000 = $result;
break;
default:
throw new IllegalStateException("call to 'resume' before 'invoke' with coroutine");
}
int a = ((Number)var10000).intValue();
return Boxing.boxInt(a);
}
public suspend inline fun <T> suspendCoroutine(crossinline block: (Continuation<T>) -> Unit): T =
suspendCoroutineUninterceptedOrReturn { c: Continuation<T> ->
//封装一个代理Continuation对象
val safe = SafeContinuation(c.intercepted())
block(safe)
//根据block返回结果判断要不要返回COROUTINE_SUSPENDED
safe.getOrThrow()
}
SafeContinuation的奥秘
//调用单参数的这个构造方法
internal actual constructor(delegate: Continuation<T>) : this(delegate, UNDECIDED)
@Volatile
private var result: Any? = initialResult //UNDECIDED赋值给 result
//java原子属性更新器那一套东西
private companion object {
@Suppress("UNCHECKED_CAST")
@JvmStatic
private val RESULT = AtomicReferenceFieldUpdater.newUpdater<SafeContinuation<*>, Any?>(
SafeContinuation::class.java, Any::class.java as Class<Any?>, "result"
)
}
internal actual fun getOrThrow(): Any? {
var result = this.result // atomic read
if (result === UNDECIDED) { //如果UNDECIDED，那么就把result设置为COROUTINE_SUSPENDED
if (RESULT.compareAndSet(this, UNDECIDED, COROUTINE_SUSPENDED)) returnCOROUTINE_SUSPENDED
result = this.result // reread volatile var
}
return when {
result === RESUMED -> COROUTINE_SUSPENDED // already called continuation, indicate COROUTINE_SUSPENDED upstream
result is Result.Failure -> throw result.exception
else -> result // either COROUTINE_SUSPENDED or data <-这里返回白板
}
}
public actual override fun resumeWith(result: Result<T>) {
while (true) { // lock-free loop
val cur = this.result // atomic read。不理解这里的官方注释为啥叫做原子读。我觉得 Volatile只能保证可见性。
when {
//这里如果是UNDECIDED 就把 结果附上去。
cur === UNDECIDED -> if (RESULT.compareAndSet(this, UNDECIDED, result.value)) return
//如果是挂起状态，就通过resumeWith回调状态机
cur === COROUTINE_SUSPENDED -> if (RESULT.compareAndSet(this, COROUTINE_SUSPENDED, RESUMED)){
delegate.resumeWith(result)
return
}
else -> throw IllegalStateException("Already resumed")
}
}
}
val safe = SafeContinuation(c.intercepted())
block(safe)
safe.getOrThrow()
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发布于：2022-03-29 15:55
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