NSURLSession extension to add synchronous data task request.

NSURLSession+sendSynchronousRequest.swift

import Foundation

/** 
 NSURLSession extension to add synchronous data task request, throwing on
 timeout. 
 
 Using a GCD semaphore internally.

Deeper wisdom from Quinn the Eskimo on why you may not want this:
<https://forums.developer.apple.com/thread/11519>

*/

enum SynchronousRequest : ErrorType { case Timeout }

extension NSURLSession {
  func sendSynchronousRequest(request:NSURLRequest) -> (NSData?,NSURLResponse?,NSError?)
  {
    let sem = dispatch_semaphore_create(0)
    var result:(NSData?,NSURLResponse?,NSError?)
    let task = self.dataTaskWithRequest(request) { (theData, theResponse, theError) in
      result = (theData,theResponse,theError)
      dispatch_semaphore_signal(sem)
    }
    task.resume()
    dispatch_semaphore_wait(sem, DISPATCH_TIME_FOREVER)
    return result
  }

  func sendSynchronousRequest(request:NSURLRequest,timeout:NSTimeInterval) throws -> (NSData?,NSURLResponse?,NSError?)
  {
    let sem = dispatch_semaphore_create(0)
    var result:(NSData?,NSURLResponse?,NSError?)
    let task = self.dataTaskWithRequest(request) { (theData, theResponse, theError) in
      result = (theData,theResponse,theError)
      dispatch_semaphore_signal(sem)
    }
    task.resume()
    let t = dispatch_time(DISPATCH_TIME_NOW, Int64(NSEC_PER_SEC) * Int64(timeout))
    let noTimeout = dispatch_semaphore_wait(sem, t)
    if noTimeout != 0 {
      throw SynchronousRequest.Timeout
    }
    return result
  }
}