提供是否使协程关闭或取消？

Question

我正在查看 Android 开发者网站上的流程文档，但我有一个问题。

https://developer.android.com/kotlin/flow#callback

如果你看上面的 link，你会看到这样的代码。

class FirestoreUserEventsDataSource(
    private val firestore: FirebaseFirestore
) {
    // Method to get user events from the Firestore database
    fun getUserEvents(): Flow<UserEvents> = callbackFlow {

        // Reference to use in Firestore
        var eventsCollection: CollectionReference? = null
        try {
            eventsCollection = FirebaseFirestore.getInstance()
                .collection("collection")
                .document("app")
        } catch (e: Throwable) {
            // If Firebase cannot be initialized, close the stream of data
            // flow consumers will stop collecting and the coroutine will resume
            close(e)
        }

        // Registers callback to firestore, which will be called on new events
        val subscription = eventsCollection?.addSnapshotListener { snapshot, _ ->
            if (snapshot == null) { return@addSnapshotListener }
            // Sends events to the flow! Consumers will get the new events
            try {
                offer(snapshot.getEvents())
            } catch (e: Throwable) {
                // Event couldn't be sent to the flow
            }
        }

        // The callback inside awaitClose will be executed when the flow is
        // either closed or cancelled.
        // In this case, remove the callback from Firestore
        awaitClose { subscription?.remove() }
    }
}

上面代码中解释了awaitClose是在协程关闭或取消时执行

但是，除了初始化 eventsCollection.

的 try-catch 语句外，代码中没有 close()

此外，在 Android 开发者页面底部说 offer does not add the element to the channel and **returns false** immediately。

我的问题是，在上面的代码中，执行offer(snapshot.getEvents())时，协程是否与return false取消，所以执行awaitClose？

Answer 1

期望：

如文档所述：

When you try to add a new element to a full channel, send suspends the producer until there's space for the new element, whereas offer does not add the element to the channel and returns false immediately.

因此：

如果不违反其容量限制，它会立即将指定的元素添加到此通道，并且 returns 是成功的结果。否则，returns 失败或关闭结果。这是 send 的同步变体，在发送挂起或抛出时退出。

所以当 trySend 调用 return 一个不成功的结果时，它保证该元素没有交付给消费者，它不会调用 onUndeliveredElement 为这个频道。有关处理未交付元素的详细信息，请参阅频道文档中的“Undelivered elements”部分。

结论：

onDeliveredElement 的典型用法是关闭正在通过通道传输的资源。以下代码模式保证即使生产者、消费者、and/or 通道被取消，打开的资源也会关闭。 资源永不丢失。所以不，它没有 return false.

提供是否使协程关闭或取消？

Does offer make the coroutines close or cancelled?

android

coroutine

kotlin