Add utility function for waiting for a promise to complete

Sources/Pwomise/Extensions/Promise+Wait.swift

@@ -0,0 +1,38 @@
+//
+// File.swift
+// 
+//
+// Created by Eric Rabil on 7/25/22.
+//
+
+import Foundation
+
+public extension Promise {
+ enum TimeoutError: Error { case timedOut }
+
+ func wait(upTo time: DispatchTime) throws -> Output {
+ var completion: Completion!
+ let semaphore = DispatchSemaphore(value: 0)
+ var semaphoreLocked: Bool {
+ if semaphore.wait(timeout: .now()) == .success {
+ semaphore.signal()
+ return false
+ }
+ return true
+ }
+ always {
+ completion = $0
+ if semaphoreLocked {
+ semaphore.signal()
+ }
+ }.resolving(on: DispatchQueue.global())
+ if semaphore.wait(timeout: time) == .success {
+ // finished in time, signal and return
+ semaphore.signal()
+ } else {
+ // did not finish in time, throw
+ throw TimeoutError.timedOut
+ }
+ return try completion.get()
+ }
+}