Roman Elizarov在有关Kotlin中的结构化并发的文章(https://medium.com/@elizarov/structured-concurrency-722d765aa952)中,通过以下示例解释了并行分解:
coroutineScope {
val deferred1 = async { loadImage(name1) }
val deferred2 = async { loadImage(name2) }
combineImages(deferred1.await(), deferred2.await())
}
显然,此代码是不言自明的。但是,如果我们改写这个,我们会得到相同的结果
coroutineScope {
val result1 = async { loadImage(name1) }.await()
val result2 = async { loadImage(name2) }.await()
combineImages(result1, result2)
}
意思是,两个异步都会仍然并行运行,还是第二个异步调用永远不会运行,直到result1可用?
范例1:
fun main(args: Array<String>) = runBlocking<Unit> {
val time = measureTimeMillis {
val one = async {
delay(1000)
return@async 1
}
val two = async {
delay(3000)
return@async 2
}
println("The answer is ${one.await() + two.await()}")
}
println("Completed in $time ms")
}
结果1:
The answer is 3
Completed in 3041 ms
范例2:
fun main(args: Array<String>) = runBlocking<Unit> {
val time = measureTimeMillis {
val one = async {
delay(1000)
return@async 1
}.await()
val two = async {
delay(3000)
return@async 2
}.await()
println("The answer is ${one + two}")
}
println("Completed in $time ms")
}
结果2:
The answer is 3
Completed in 4043 ms
查阅此链接以获取有关使用异步并发的官方文档
结论
async-await-async-await将产生纯顺序代码
async-async-await-await将并行运行
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