带有Promise的Rx.js并发

Question

我想通过一系列异步/网络操作（远程HTTP请求）将它们移动来处理对象数组。

在其中某些操作中，我想确保同时处理的项目不超过X个。

我该如何实现？

示例代码：

function someAsyncOp(item) {...} // returns a promise

var source = Rx.Observable.from([{item1},{item2},...])
source
  .flatMap((item) => {

    // I WANT THE FOLLOWING OPERATION TO BE EXECUTING  
    // ON AT MAX 10 ITEMS AT A TIME, NEXT ITEM SHOULD
    // BE SUBMITTED ONLY WHEN A SLOT GETS FREED AS A 
    // RESULT OF THE PROMISE SUCCEEDING OR FAILING

    return Rx.Observable.fromPromise(someAsyncOp(item))

  })
  .subscribe(
    console.log, 
    console.error, 
    () => console.log('completed')
  )

Answer 1

flatMap一个同胞称为flatMapWithMaxConcurrent ，它带有一个并发参数。 它在功能上类似于本杰明的答案所建议的map(fn).merge(n) 。

function someAsyncOp(item) {...} // returns a promise

var source = Rx.Observable.from([{item1},{item2},...])
source
   //Only allow a max of 10 items to be subscribed to at once
  .flatMapWithMaxConcurrent(10, (item) => {

    //Since a promise is eager you need to defer execution of the function
    //that produces it until subscription. Defer will implicitly accept a promise
    return Rx.Observable.defer(() => someAsyncOp(item))

    //If you want the whole thing to continue regardless of exceptions you should also
    //catch errors from the individual processes
                        .catch(Rx.Observable.empty())
  })
  .subscribe(
    console.log, 
    console.error, 
    () => console.log('completed')
  )

Answer 2

您可以使用map而不是flatMap merge ：

var concurrency = 10;
source.map(someAsyncOp).merge(concurrency).subscribe(x => console.log(x));

请注意，由于Promise迫切需要Promise，而Observable则是懒惰的，因此Promise不会削减它（Rx可以在没有Promise的情况下吸收Promise）。 我建议将其包装在create 。

 var delay = function(ms){ return new Promise(function(r){ setTimeout(r, 2000, ms) }); } var log = function(msg){ document.body.innerHTML += msg + "<br />"; } Rx.Observable.range(1000, 10).map(delay).merge(2).subscribe(log) 

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