feat: Add new identify method with time out support

A callback provided to the `identify` method may not be executed for a
long time under the right circumstances (e.g. the network is slow or
unavailable).

Customers can now ensure their callbacks will fire within a specified
time interval by calling the new
`LDClient.identify(context:timeout:completion:)` method.

LaunchDarkly/LaunchDarkly/LDClient.swift

@@ -327,6 +327,36 @@ public class LDClient {
         identifyQueue.enqueue(request: identifyTask)
     }
 
+    /**
+     Sets the LDContext into the LDClient inline with the behavior detailed on `LDClient.identify(context: completion:)`. Additionally,
+     this method will ensure the `completion` parameter will be called within the specified time interval.
+
+     Note that the `completion` method being invoked does not mean that the identify request has been cancelled. The identify request will
+     continue attempting to complete as it would with `LDClient.identify(context: completion:)`. Subsequent identify requests queued behind
+     a timed out request will remain blocked (or shed) until the in flight request completes.
+
+     - parameter context: The LDContext set with the desired context.
+     - parameter timeout: The upper time limit before the `completion` callback will be invoked.
+     - parameter completion: Closure called when the embedded `setOnlineIdentify` call completes, subject to throttling delays.
+     */
+    public func identify(context: LDContext, timeout: TimeInterval, completion: @escaping ((_ result: IdentifyResult) -> Void)) {
+        var cancel = false
+
+        DispatchQueue.global().asyncAfter(deadline: .now() + timeout) {
+            guard !cancel else { return }
+
+            cancel = true
+            completion(.timeout)
+        }
+
+        identify(context: context) { result in
+            guard !cancel else { return }
+
+            cancel = true
+            completion(result)
+        }
+    }
+
     func internalIdentify(newContext: LDContext, completion: (() -> Void)? = nil) {
         var updatedContext = newContext
         if config.autoEnvAttributes {

LaunchDarkly/LaunchDarkly/Models/IdentifyResult.swift

@@ -13,9 +13,13 @@ public enum IdentifyResult {
      */
     case error
     /**
-     The identify request has been replaced with a subsequent request. See `LDClient.identify(context: completion:)` for more details.
+     The identify request has been replaced with a subsequent request. Read `LDClient.identify(context: completion:)` for more details.
      */
     case shed
+    /**
+     The identify request exceeded some time out parameter. Read `LDClient.identify(context: timeout: completion)` for more details.
+     */
+    case timeout
 
     init(from: TaskResult) {
         switch from {