您好,提前感谢您的宝贵时间。
在我的代码中,我向 AWSSQS 发出各种请求,这些请求都返回 AWSTask。我发现使用这些 AWSTask 对象非常困难,同时还试图将特定于 AWS 的所有逻辑保留在单个类中,以便我可以在需要时轻松切换到不同的云服务。
理想情况下,我想做的是以串行方式异步执行一系列 AWS 任务。通常我只会将任务添加到自定义串行调度队列中,但由于 AWSTask 对象本身就是异步任务,因此我无法这样做。
这是一个简单的例子,说明了我遇到的问题。它没有任何现实世界的目的,但它很好地说明了问题。下面,我有代码来创建 SQS 队列、向 SQS 队列发送消息、从 SQS 队列接收消息以及删除 SQS 队列。假设我想以串行、异步的方式完成这四件事。换句话说,我想在尝试下一个任务之前确保上一个任务成功。
视图控制器
DispatchQueue.global(qos: DispatchQoS.QoSClass.userInitiated).async {
awsClass.runTest()
DispatchQueue.main.async {
print("Test Finished")
}
}
AWSClass
public func createQueue(){
guard let createQueueRequest = AWSSQSCreateQueueRequest() else{fatalError()}
createQueueRequest.queueName = "TestQueue"
sqs.createQueue(createQueueRequest).continueWith(block: {(task) -> AnyObject? in
if task.error != nil {
print(task.error!)
}
else if task.result != nil {
self.queueUrl = task.result!.queueUrl!
print("created queue at: \(self.queueUrl!)")
}
return nil
})
}
public func deleteQueue(){
if queueUrl != nil {
guard let deleteQueueRequest = AWSSQSDeleteQueueRequest() else{fatalError()}
deleteQueueRequest.queueUrl = queueUrl
sqs.deleteQueue(deleteQueueRequest).continueWith(block: {(task) -> AnyObject? in
if task.error != nil {
print(task.error!)
}
else if task.result != nil {
print("queue sucessfully deleted from \(self.queueUrl!)")
self.queueUrl = nil
}
return nil
})
}
else{
print("Queue has already been deleted")
}
}
public func sendMessage(messageData: String, toConnectId: String) {
guard let sendMessageRequest = AWSSQSSendMessageRequest() else{fatalError()}
sendMessageRequest.queueUrl = toConnectId
sendMessageRequest.delaySeconds = 0
sendMessageRequest.messageBody = messageData
sqs.sendMessage(sendMessageRequest).continueWith(block: {(task) -> AnyObject? in
if task.error != nil {
print(task.error!)
}
else if task.result != nil {
print("successfully sent message to \(toConnectId)")
}
return nil
})
}
public func receiveMessage(){
guard let receiveMessageRequest = AWSSQSReceiveMessageRequest() else{fatalError()}
receiveMessageRequest.queueUrl = self.queueUrl
receiveMessageRequest.maxNumberOfMessages = 1
sqs.receiveMessage(receiveMessageRequest).continueWith(block: {(task) -> AnyObject? in
if task.error != nil {
print(task.error!)
}
else if task.result != nil {
let message = (task.result?.messages?.first)!
print("successfully received message with body: \(message.body ?? "failed")")
}
return nil
})
}
public func runTest(){
let mySerialQueue = DispatchQueue(label: "mySerialQueue")
mySerialQueue.sync {
self.createQueue()
}
mySerialQueue.sync {
self.sendMessage(messageData: "test", toConnectId: "https://someUrl")
}
mySerialQueue.sync {
self.receiveMessage()
}
mySerialQueue.sync {
self.deleteQueue()
}
}
由于 AWSTasks 与完成函数异步,因此代码会快速进行所有四个调用,然后在这些任务完成时调用完成函数。相反,我希望第一个任务的完成功能在下一个任务开始之前完成。
AWSTask 对象旨在“链接”在一起。 文档可以在这里找到:http://docs.aws.amazon.com/mobile/sdkforios/developerguide/awstask.html
这里有一个小例子:
sqs.createQueue(/* parameters */).continueWithSuccess(block: {(task) -> Void in
// Success
return sqs.sendMessage(/* parameters */)
}).continueWithSuccess(block: {(task) -> Void in
// Success
return sqs.receiveMessage(/* parameters */)
}).continueWithSuccess(block: {(task) -> Void in
// Success
return sqs.deleteQueue(/* parameters */)
})
好吧,我找到了解决问题的方法。它完全按照预期工作,但它是在这个令人讨厌的完成函数链中实现的。如果有人知道更优雅的解决方案,我洗耳恭听!
视图控制器
print("Starting Test")
DispatchQueue.global(qos: DispatchQoS.QoSClass.userInitiated).async {
atomConnector.runTest(completion: {
print("test finshed")
})
}
AWSClass
public func createQueue(completion: @escaping () -> Void){
guard let createQueueRequest = AWSSQSCreateQueueRequest() else{fatalError()}
createQueueRequest.queueName = "TestQueue"
sqs.createQueue(createQueueRequest).continueWith(block: {(task) -> Void in
if task.error != nil {
print(task.error!)
}
else if task.result != nil {
self.queueUrl = task.result!.queueUrl!
print("created queue at: \(self.queueUrl!)")
completion()
}
})
}
public func deleteQueue(completion: @escaping () -> Void){
if queueUrl != nil {
guard let deleteQueueRequest = AWSSQSDeleteQueueRequest() else{fatalError()}
deleteQueueRequest.queueUrl = queueUrl
sqs.deleteQueue(deleteQueueRequest).continueWith(block: {(task) -> Void in
if task.error != nil {
print(task.error!)
}
else if task.result != nil {
print("queue sucessfully deleted from \(self.queueUrl!)")
self.queueUrl = nil
completion()
}
})
}
else{
print("Queue has already been deleted")
}
}
public func sendMessage(messageData: String, toConnectId: String, completion: @escaping () -> Void) {
guard let sendMessageRequest = AWSSQSSendMessageRequest() else{fatalError()}
sendMessageRequest.queueUrl = toConnectId
sendMessageRequest.delaySeconds = 0
sendMessageRequest.messageBody = messageData
sqs.sendMessage(sendMessageRequest).continueWith(block: {(task) -> Void in
if task.error != nil {
print(task.error!)
}
else if task.result != nil {
print("successfully sent message to \(toConnectId)")
completion()
}
})
}
public func receiveMessage(completion: @escaping () -> Void){
guard let receiveMessageRequest = AWSSQSReceiveMessageRequest() else{fatalError()}
receiveMessageRequest.queueUrl = self.queueUrl
receiveMessageRequest.maxNumberOfMessages = 1
sqs.receiveMessage(receiveMessageRequest).continueWith(block: {(task) -> Void in
if task.error != nil {
print(task.error!)
}
else if task.result != nil {
let message = (task.result?.messages?.first)!
print("successfully received message with body: \(message.body ?? "failed")")
self.deleteMessage(receiptHandle: message.receiptHandle, completion: completion)
}
})
}
public func deleteMessage(receiptHandle: String?, completion: @escaping () -> Void){
guard let deleteMessageRequest = AWSSQSDeleteMessageRequest() else{fatalError()}
deleteMessageRequest.queueUrl = self.queueUrl
deleteMessageRequest.receiptHandle = receiptHandle
sqs.deleteMessage(deleteMessageRequest).continueWith(block: {(task) -> Void in
if task.error != nil {
print(task.error!)
}
else if task.result != nil {
print("successfully deleted message with receiptHandle: \(receiptHandle)")
completion()
}
})
}
public func runTest(completion: @escaping () -> Void){
self.createQueue(completion: {
self.sendMessage(messageData: "test", toConnectId: "https://someUrl", completion: {
self.receiveMessage(completion: {
self.deleteQueue(completion: {
completion()
})
})
})
})
}
我正在使用 Swift Concurrency 来使用 AWS SDK。我发现使用
await withCheckedContinuation
是使用 AWSTask
的正确方法。我觉得这是一个更优雅的解决方案。
这是一个如何调整 Alec 的
func createQueue
以使用 Swift Concurrency 的示例
public func createQueue() async {
guard let createQueueRequest = AWSSQSCreateQueueRequest() else{fatalError()}
createQueueRequest.queueName = "TestQueue"
let task = sqs.createQueue(createQueueRequest)
await withCheckedContinuation { continuation in
task.continueWith { _ in
if task.error != nil {
print(task.error!)
}
else if task.result != nil {
self.queueUrl = task.result!.queueUrl!
print("created queue at: \(self.queueUrl!)")
}
continuation.resume()
return true
}
}
}
AWSTask.continueWith
进入 await withCheckedContinuation
块内。设计您的 AWSTask.continueWith
块,使得 continuation.resume()
在块内仅被调用一次。
一旦使用上述模型将所有方法转换为 Swift Concurrency,那么
func runTest
就更加优雅了
public func runTest() async {
await self.createQueue()
await self.sendMessage(messageData: "test", toConnectId: "https://someUrl")
await self.receiveMessage()
await self.deleteQueue()
}