CODEWITHSUNDEEP
iosswiftalamofire
Andrey M.
Andrey M.

Reputation: 3079

How to synchronize multiple Alamofire requests

I have multiple requests:

var data1: MyData?
var data2: MyData?
var data3: MyData?

func makeRequest(url: String, completion: (result: ResponseResult, data: MyData?) -> Void){
    Alamofire.request(.GET, url).responseJSON { response in
        switch response.result {
        case .Success(let JSON):
        completion(result: .Success, MyData(JSON))
        case. Failure(let error):
        completion(result: .Failure, nil)
        }
    }
}

makeRequest(url1){ result, data in
    data1 = data
}
makeRequest(url2){ result, data in
    data2 = data
}
makeRequest(url3){ result, data in
    data3 = data
}

And after all data was received i must call the following function:

workWithData(data1, data2: data2, data3: data3)

How to make barrier for that three requests in that situation?

Upvotes: 3

Views: 5305

Answers (3)

Andrey Ezhov
Andrey Ezhov

Reputation: 116

You have to use DispatchGroup, and don't forget about deadlocks.

var data1: MyData?
var data2: MyData?
var data3: MyData?

func makeRequest(url: String, completion: (result: ResponseResult, data: MyData?) -> Void){
    Alamofire.request(.GET, url).responseJSON { response in
        switch response.result {
        case .Success(let JSON):
            completion(result: .Success, MyData(JSON))
        case. Failure(let error):
            completion(result: .Failure, nil)
        }
    }
}

let downloadGroup = DispatchGroup()

downloadGroup.enter()
downloadGroup.enter()
downloadGroup.enter()

makeRequest(url1){ result, data in
    data1 = data
    downloadGroup.leave()
}
makeRequest(url2){ result, data in
    data2 = data
    downloadGroup.leave()
}
makeRequest(url3){ result, data in
    data3 = data
    downloadGroup.leave()
}

DispatchQueue.global(qos: .background).async {
    downloadGroup.wait()
    DispatchQueue.main.async {
        workWithData(data1, data2: data2, data3: data3)
    }
}

Upvotes: 9

Igor B.
Igor B.

Reputation: 2229

Semaphore should work for you. Consider this:

var data1: NSData?
var data2: NSData?
var data3: NSData?

func makeRequest(url: String, completion: (data: NSData?) -> Void){

    let request = Alamofire.request(.GET, "https://google.com").responseJSON(queue: dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)) { closureResponse in

        completion(data: NSData())
    }
}

let sem = dispatch_semaphore_create(0)

makeRequest("1"){ data in
    data1 = data
    dispatch_semaphore_signal(sem)
}
makeRequest("2"){ data in
    data2 = data
    dispatch_semaphore_signal(sem)
}
makeRequest("2"){ data in
    data3 = data
    dispatch_semaphore_signal(sem)
}

dispatch_semaphore_wait(sem, DISPATCH_TIME_FOREVER)
dispatch_semaphore_wait(sem, DISPATCH_TIME_FOREVER)
dispatch_semaphore_wait(sem, DISPATCH_TIME_FOREVER)

print("123")

Per @James comment, I have spent some time playing with Alamofire. What I figured out is by default it delivers callbacks on the main queue. That's not good from my perspective, I prefere to minimise main thread load. I would recommend to use concurrent queue for callback delivery.

Upvotes: 1

BallpointBen
BallpointBen

Reputation: 13934

I think you should check whether to continue at end of Alamofire.request:

func makeRequest(url: String, completion: (result: ResponseResult, data: MyData?) -> Void){
    Alamofire.request(.GET, url).responseJSON { response in
        switch response.result {
        case .Success(let JSON):
            completion(result: .Success, MyData(JSON))
        case. Failure(let error):
            completion(result: .Failure, nil)
        }

        if data1 != nil && data2 != nil && data3 != nil {
            workWithData(data1, data2: data2, data3: data3)
        }
    }
}

Upvotes: 0

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