I have a wrapper function to limit concurrent calls to a ser kotlinlang #coroutines

private val concurrentRequests = Semaphore(50)

private suspend fun <T> requestWithLimit(block: suspend () -> T): T {
    try {
        withTimeout(10) {
            concurrentRequests.acquire()
        }
    } catch (e: Exception) {
        throw RuntimeException("Overloaded", e)
    }
    try {
        return block()
    } finally {
        concurrentRequests.release()
    }
}

I usually call io.ktor.client.HttpClient.request inside block(). If I want to write it as an extension function on io.ktor.client.HttpClient (just to make the call site a bit cleaner), how would I define it? It seems that the extension function cannot access the variable

concurrentRequests

wasyl

09/07/2020, 10:58 AM

Making

requestWithLimit

shouldn’t change how you access

concurrentRequests

. This does seem to work for me:

suspend fun <T> HttpClient.requestWithLimit(block: suspend HttpClient.() -> T): T

Full code:

abstract class HttpClient {

    abstract val request: Any
}

val concurrentRequests = Semaphore(50)
private suspend fun <T> HttpClient.requestWithLimit(block: suspend HttpClient.() -> T): T {
    try {
        withTimeout(10) {
            concurrentRequests.acquire()
        }
    } catch (e: Exception) {
        throw RuntimeException("Overloaded", e)
    }
    try {
        return block()
    } finally {
        concurrentRequests.release()
    }
}

suspend fun usage(httpClient: HttpClient) {
    httpClient.requestWithLimit {
        println("Doing something with $request")
    }
}

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