scala - 基于资源稀缺性的背压可观测

Question

在 RxJava 1 / RxScala 中，如何在以下情况下限制/背压可观察的源？

def fast: Observable[Foo] // Supports backpressure

def afterExpensiveOp: Observable[Bar] = 
    fast.flatMap(foo => Observable.from(expensiveOp(foo))

// Signature and behavior is out of my control
def expensiveOp(foo: Foo)(implicit ec: ExecutionContext): Future[Bar] = {
   if(noResources()) Future.failed(new OutOfResourcesException())
   else Future { Bar() }
}

一个可能的解决方案就是阻塞直到。哪个有效，但这非常不雅，并且会阻止多个同时请求：

def afterExpensiveOp: Observable[Bar] = fast.flatMap(foo => 
   Observable.just(Observable.from(expensiveOp(foo)).toBlocking.head)
)

Answer 1

flatMap 有一个参数来限制并发订阅者的数量。如果你使用这个 flatMap 会为你处理背压。

def afterExpensiveOp = fast.flatMap(safeNumberOfConccurrentExpensiveOps, x => Observable.from(expensiveOp(x)))