基于资源稀缺性的背压可观察

Question

在RxJava 1 / RxScala中，如何在以下情况下对源可观察量进行节流/反压？

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() }
}

可能的解决方案就是阻止直到。哪个有效，但这非常不优雅，可以防止同时发出多个请求：

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。如果您使用此flatMap为您处理背压。

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