Scala:ExecutionContext用于将来的理解 [英] Scala: ExecutionContext for future for-comprehension
问题描述
当我制作future
或应用onSuccess
和map
之类的方法时,我可以为其指定ExecutionContext.
When I make a future
, or apply methods like onSuccess
and map
, I can specify ExecutionContext for them.
例如,
val f = future {
// code
} executionContext
f.map(someFunction)(executionContext)
f onSuccess {
// code
} executionContext
但是,如果我对未来有所了解,如何为yield
部分指定ExecutionContext?
However, if I use a for-comprehension of future, how can I specify ExecutionContext for the yield
part?
for {
f <- future1
g <- future2
} yield {
// code to be executed after future1 onSuccess and future2 onSuccess
// What ExecutionContext runs this code?
} // (executionContext) here does not work
而且,如果未指定,什么ExecutionContext可以在yield中运行代码?
And, what ExecutionContext runs the code in yield if not specified?
编辑
好.多亏了答案,我发现了一些东西.
如果我没有定义或导入 隐式 ExecutionContext (例如Implicits.global
),
理解不能编译.这意味着,理解会使用隐式的ExecutionContext.
OK. Thanks to answers, I found something.
If I don't define or import implicit ExecutionContext (like Implicits.global
),
the for-comprehension does not compile. That means, for-comprehension uses implicit ExecutionContext.
然后,如何在没有隐式ExecutionContext的情况下使用理解功能,即如何指定?
Then, how can I use for-comprehension without implicit ExecutionContext, i.e. how to specify?
推荐答案
ExecutionContext
参数实际上是implicit
.这意味着您可以:
The ExecutionContext
parameter is actually implicit
. That means you can:
import scala.concurrent.ExecutionContext
implicit val context = ExecutionContext.fromExecutor(//etc)
for {
f <- future1
g <- future2
} yield {
// code to be executed after future1 onSuccess and future2 onSuccess
// What ExecutionContext runs this code?: the one above.
}
您也有一个默认值,即scala.concurrent.ExecutionContext.Implicits.global
.
它具有与正在运行的计算机上的处理器一样多的线程.
You also have a default, namely scala.concurrent.ExecutionContext.Implicits.global
.
This has as many threads as the processors on the running machine.
默认情况下,并不是所有期货都使用它,您仍然必须导入它.
It won't be used by all Futures by default, you still have to import it.
更新:如果您确实要指定规范,尽管不建议这样做,但是您可以展开for yield
Update: If you really want to specifiy, although it's not recommended, you can unwrap the for yield
val combined = futureA.flatMap(x => futureB)(context)
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