spring-mvc - 除非使用GobalScope调用，否则将依次调用kotlin异步调用

Question

好的，所以我有一个 Controller 方法，该方法需要对外部服务进行大量肥皂调用，每个调用都非常繁重。我试图并行执行这些操作以节省一些时间，但是除非我从GlobalScope构建async调用，否则将按顺序解决延迟的操作。让我给你演示。

执行以下代码

@ResponseBody
@GetMapping(path = ["/buildSoapCall"])
fun searchStations(): String = runBlocking {

    var travels: List<Travel> = service.getTravels().take(500)
    val deferred = travels
            .map {
                async() {
                    print("START")
                    val result = service.executeSoapCall(it)
                    print("END")
                    result
                }
            }
    println("Finished deferred")
    val callResults = deferred.awaitAll()
    println("Finished Awaiting")

    ""
}

得到以下控制台消息:

Finished deferred
START-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-END.....

-由 executeSoapCall打印

如您所见，延期被依次调用。

但是，如果我使用 GlobalScope，像这样:

@ResponseBody
@GetMapping(path = ["/buildSoapCall"])
fun searchStations(): String = runBlocking {

    var travels: List<Travel> = service.getTravels().take(500)
    val deferred = travels
            .map {
                GlobalScope.async() {
                    print("START")
                    val result = service.executeSoapCall(it)
                    print("END")
                    result
                }
            }
    println("Finished deferred")
    val callResults = deferred.awaitAll()
    println("Finished Awaiting")

    ""
}

我收到以下控制台消息:

Finished Treating 
STARTSTARTSTARTSTARTSTARTSTARTSTARTSTARTSTARTSTARTSTARTFinished deferred
START-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART--ENDENDSTARTSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-ENDSTART-END...START-END-END-END-END-END-END-END-END-END-END-END-ENDFinished Awaiting

表示“延期”都是并行开始的。另外，治疗时间相当短。

我真的不明白为什么我会有这种行为。

Answer 1

您对service.executeSoapCall的调用会阻止正在运行runBlocking协程的线程。您需要每次在不同的线程上启动async协程以获得并发行为。您可以使用线程池来实现这一点，例如Dispatchers.IO:

...
async(Dispatchers.IO) {
    print("START")
    val result = service.executeSoapCall(it)
    print("END")
    result
}
...

或在每次调用时创建一个新线程:

...
async(newSingleThreadContext("MyThread")) {
    print("START")
    val result = service.executeSoapCall(it)
    print("END")
    result
}
...

GlobalScope之所以有效，是因为它默认情况下使用ThreadPool，但您应避免使用它。您可以通过 this article阅读有关该主题的 Roman Elizarov。