Improve threading

SignalServiceKit/src/Loki/API/Onion Requests/OnionRequestAPI+Encryption.swift

@@ -7,10 +7,6 @@ extension OnionRequestAPI {
 
     internal typealias EncryptionResult = (ciphertext: Data, symmetricKey: Data, ephemeralPublicKey: Data)
 
-    private static func getQueue() -> DispatchQueue {
-        return DispatchQueue(label: UUID().uuidString, qos: .userInitiated)
-    }
-
     /// Returns `size` bytes of random data generated using the default secure random number generator. See
     /// [SecRandomCopyBytes](https://developer.apple.com/documentation/security/1399291-secrandomcopybytes) for more information.
     private static func getSecureRandomData(ofSize size: UInt) throws -> Data {
@@ -46,7 +42,7 @@ extension OnionRequestAPI {
     /// Encrypts `payload` for `snode` and returns the result. Use this to build the core of an onion request.
     internal static func encrypt(_ payload: JSON, forTargetSnode snode: LokiAPITarget) -> Promise<EncryptionResult> {
         let (promise, seal) = Promise<EncryptionResult>.pending()
-        getQueue().async {
+        DispatchQueue.global().async {
             do {
                 guard JSONSerialization.isValidJSONObject(payload) else { return seal.reject(HTTP.Error.invalidJSON) }
                 let payloadAsData = try JSONSerialization.data(withJSONObject: payload, options: [])
@@ -66,7 +62,7 @@ extension OnionRequestAPI {
     /// Encrypts the previous encryption result (i.e. that of the hop after this one) for this hop. Use this to build the layers of an onion request.
     internal static func encryptHop(from lhs: LokiAPITarget, to rhs: LokiAPITarget, using previousEncryptionResult: EncryptionResult) -> Promise<EncryptionResult> {
         let (promise, seal) = Promise<EncryptionResult>.pending()
-        getQueue().async {
+        DispatchQueue.global().async {
             let parameters: JSON = [
                 "ciphertext" : previousEncryptionResult.ciphertext.base64EncodedString(),
                 "ephemeral_key" : previousEncryptionResult.ephemeralPublicKey.toHexString(),

SignalServiceKit/src/Loki/API/Onion Requests/OnionRequestAPI.swift

@@ -53,7 +53,7 @@ internal enum OnionRequestAPI {
     /// Tests the given snode. The returned promise errors out if the snode is faulty; the promise is fulfilled otherwise.
     private static func testSnode(_ snode: LokiAPITarget) -> Promise<Void> {
         let (promise, seal) = Promise<Void>.pending()
-        let queue = DispatchQueue(label: UUID().uuidString, qos: .userInitiated) // No need to block the work queue for this
+        let queue = DispatchQueue.global() // No need to block the work queue for this
         queue.async {
             let url = "\(snode.address):\(snode.port)/get_stats/v1"
             let timeout: TimeInterval = 6 // Use a shorter timeout for testing