限制可以在示波器中运行的协程最大数量 [英] Limiting the maximum number of coroutines that can run in a scope

问题描述

我正在将当前的应用程序从Java转换为Kotlin，然后遇到了这个问题。

I am translating our current application from Java to Kotlin and I came upon this problem.

该Java实现用于使用线程从服务器传输数据。

The java implementation used to use threads to transfer data from the server.

这将创建大约100个不同的线程来请求数据，但是根据我的观察，一次最多运行4个线程，其他线程将等待一个线程

It would create about 100 different threads that would request data, but from what I have seen no more than 4 would run at a time, the others would wait for a thread to finish before starting.

将其翻译为Kotlin时，我使用了协程（Coroutines）

When translating it to Kotlin I used Coroutines

这会造成问题，因为显然是服务器无法处理实际发送的100个请求。

This creates a problem because apparently the server can't handle 100 requests actually being sent.

所有协程都在同一范围内启动，所以就像这样：

All coroutines are launched in the same scope , so it's something like this:

//this is a custom scope that launches on Dispatchers.IO + a job that I can use to cancel everything
transferScope.launch {
     //loadData is a suspending function that returns true/false 
     val futures = mDownloadJobs.map{ async { it.loadData() } }
     val responses = futures.awaitAll()
     //check that everything in responses is true etc....
}

是否有一种方法可以使特定的transferScope一次只允许多达5个协程，然后当一个完成时让另一个运行？ （我不在乎顺序）

Is there a way to make the specific transferScope to allow only up to 5 coroutines at a time and then when one finishes let a different one run? (I do not care about the order)

如果无法通过示波器完成操作，是否可以通过其他方式实现？

If it can't be done through the scope, is there a different way this can be achieved?

推荐答案

要求每个协程获得科特林 Semaphore 许可，共计5项

Require each coroutine to acquire a Kotlin Semaphore permit from a total of 5 permits before making a request.

类似这样的东西：

    import kotlinx.coroutines.sync.Semaphore

    val requestSemaphore = Semaphore(5)

    val futures = mDownloadJobs.map {
        async {
            // Will limit number of concurrent requests to 5
            requestSemaphore.withPermit {
                it.loadData()
            }
        }
    }

    val responses = futures.awaitAll()

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