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@groz
Created February 15, 2018 22:29
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Synchronous http request in Swift
import Foundation
func query(address: String) -> String {
let url = URL(string: address)
let semaphore = DispatchSemaphore(value: 0)
var result: String = ""
let task = URLSession.shared.dataTask(with: url!) {(data, response, error) in
result = String(data: data!, encoding: String.Encoding.utf8)!
semaphore.signal()
}
task.resume()
semaphore.wait()
return result
}
let preference = query(address: "http://the-rock-paper-scissors.herokuapp.com/newgame")
print("Computer preference: \(preference)")
@impul
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impul commented Sep 26, 2019

NSLock will be better here

@eonil
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eonil commented Oct 15, 2019

NSLock will be better here

How? @impul

@impul
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impul commented Oct 16, 2019

@eonil ,

import Foundation

func query(address: String) -> String {
    let url = URL(string: address)
    let lock = NSLock()
    
    var result: String = ""
    
    let task = URLSession.shared.dataTask(with: url!) {(data, response, error) in
        result = String(data: data!, encoding: String.Encoding.utf8)!
        lock.unlock()
    }
    
    task.resume()
    lock.lock()
    return result
}

let preference = query(address: "http://the-rock-paper-scissors.herokuapp.com/newgame")
print("Computer preference: \(preference)")

@eonil
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eonil commented Oct 16, 2019

@impul Are you sure that code work? It seems query function exits before result getting set.

@mehdico
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mehdico commented Jun 25, 2020

NSLock is better because we have only one thread.

@brett-eugenelabs
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Can only be better if it actually worked.
Original works, NSLock version exits straightaway as pointed out by @eonil

@ppave
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ppave commented Nov 13, 2020

The NSLock class uses POSIX threads to implement its locking behavior. When sending an unlock message to an NSLock object, you must be sure that message is sent from the same thread that sent the initial lock message. Unlocking a lock from a different thread can result in undefined behavior. https://developer.apple.com/documentation/foundation/nslock

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