kotlin coroutines 协程教程(四) Suspend function 挂起函数
Suspend function 挂起函数，的分析，基于 Coroutine 1.3 版本的源码。
简单用法
一个简单的例子如下：
fun test1() {
GlobalScope.launch {
val arg1 = sunpendF1()
var arg2 = sunpendF2()
doLog("suspend finish arg1:$arg1 arg2:$arg2 result:${arg1 + arg2}")
}
}
private suspend fun sunpendF1(): Int {
delay(1000)
doLog("suspend fun 1")
return 2
}
private suspend fun sunpendF2(): Int {
delay(1000)
doLog("suspend fun 2")
return 4
}
最终控制台的输入结果如下：
01-07 19:21:49.626 9616-10074/com.yy.yylite.kotlinshare I/suspend: suspend fun 1
01-07 19:21:50.633 9616-10074/com.yy.yylite.kotlinshare I/suspend: suspend fun 2
suspend finish arg1:2 arg2:4 result:6
也就是说，最后的输出依赖，sunpendF1() sunpendF2，只有等两个函数都做完了，才会输出，但是挂起并不是阻塞。
Suspend 挂起函数原理
挂起函数，并不会阻塞线程，这里的实现原理背后是 kotlin 进行了巧妙的编译层次的设计，通常来说一个挂起函数如下：
suspend fun test1() {
KLog.i("test1") { "test1" }
val homeItemInfo = HomeItemInfo()
homeItemInfo.adId = "89"
delay(100)
KLog.i("test1") { "test1-end" }
}
我们使用 tools->show kotlin bytecode->decompile 查看 转化为 java 实现代码如下：
public final Object test1(@NotNull Continuation var1) {
Object $continuation;
label28: {
if (var1 instanceof <undefinedtype>) {
$continuation = (<undefinedtype>)var1;
if ((((<undefinedtype>)$continuation).getLabel() & Integer.MIN_VALUE) != 0) {
((<undefinedtype>)$continuation).setLabel(((<undefinedtype>)$continuation).getLabel() - Integer.MIN_VALUE);
break label28;
}
}
$continuation = new CoroutineImpl(var1) {
// $FF: synthetic field
Object data;
// $FF: synthetic field
Throwable exception;
Object L$0;
Object L$1;
@Nullable
public final Object doResume(@Nullable Object data, @Nullable Throwable throwable) {
this.data = data;
this.exception = throwable;
super.label |= Integer.MIN_VALUE;
return SuspendTest.this.test1(this);
}
// $FF: synthetic method
final int getLabel() {
return super.label;
}
// $FF: synthetic method
final void setLabel(int var1) {
super.label = var1;
}
};
}
Object var3 = ((<undefinedtype>)$continuation).data;
Throwable var4 = ((<undefinedtype>)$continuation).exception;
Object var6 = IntrinsicsKt.getCOROUTINE_SUSPENDED();
HomeItemInfo homeItemInfo;
switch(((<undefinedtype>)$continuation).getLabel()) {
case 0:
if (var4 != null) {
throw var4;
}
KLog.INSTANCE.i("test1", (Function0)null.INSTANCE);
homeItemInfo = new HomeItemInfo();
homeItemInfo.adId = "89";
((<undefinedtype>)$continuation).L$0 = this;
((<undefinedtype>)$continuation).L$1 = homeItemInfo;
((<undefinedtype>)$continuation).setLabel(1);
if (DelayKt.delay(100, (Continuation)$continuation) == var6) {
return var6;
}
break;
case 1:
homeItemInfo = (HomeItemInfo)((<undefinedtype>)$continuation).L$1;
SuspendTest var7 = (SuspendTest)((<undefinedtype>)$continuation).L$0;
if (var4 != null) {
throw var4;
}
break;
default:
throw new IllegalStateException("call to 'resume' before 'invoke' with coroutine");
}
KLog.INSTANCE.i("test1", (Function0)null.INSTANCE);
return Unit.INSTANCE;
}
首先来看函数签名，这里会变成传入一个参数 Continuation，这个是 kotlin 中实现挂起的接口，其源码定义如下，也就是最终挂起函数的逻辑，是通过这个 resumeWith() 分发的。
public interface Continuation<in T> {
/**
* Context of the coroutine that corresponds to this continuation.
*/
// todo: shall we provide default impl with EmptyCoroutineContext?
public val context: CoroutineContext
/**
* Resumes the execution of the corresponding coroutine passing successful or failed [result] as the
* return value of the last suspension point.
*/
public fun resumeWith(result: Result<T>)
}
所以实际上 挂起函数在编译器的封装下，变成了一个 Continuation。通过字节码工具，我们可以看到：
kotlinx/coroutines/Deferred.delay (Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
实际上这是一个 Continuation 对象。
所以实际上其流程等于：
image
