图像，你有一个Kotlin暂停功能
suspend fun foo(): String { return "" }
我需要使它基于回调而不是挂起，即

interface Cancellable {
    fun cancel()
}

internal class CancellableImpl : Cancellable {
    var cancellationCallback: (() -> Unit)? = null

    override fun cancel() {
        cancellationCallback?.invoke()
    }
}

fun foo(callback: (String) -> Unit): Cancellable

GlobalScope方法是否有效？

fun foo(callback: (String) -> Unit): Cancellable {
        val task = CancellableImpl()

        val job = GlobalScope.launch {
            val fooResult = foo()
            callback(fooResult)
        }

        task.cancellationCallback = {
            job.cancel()
        }
        return task
}

它有哪些缺点？