Serialize renewing the access token

Frameworks/Account/FeedProvider/Reddit/RedditFeedProvider.swift

@@ -48,6 +48,7 @@ public final class RedditFeedProvider: FeedProvider {
 		return oauthSwift?.client
 	}
 
+	private var renewingAccessToken = false
 	private var rateLimitRemaining: Int?
 	private var rateLimitReset: Date?
 	
@@ -324,25 +325,37 @@ private extension RedditFeedProvider {
 		if case .tokenExpired = error {
 			os_log(.debug, log: self.log, "Access token expired, attempting to renew...")
 
+			if renewingAccessToken {
+				DispatchQueue.main.asyncAfter(deadline: .now() + 3) {
+					completion(nil)
+				}
+			}
+			
+			renewingAccessToken = true
+			
 			oauthSwift?.renewAccessToken(withRefreshToken: oauthRefreshToken) { [weak self] result in
-				guard let self = self, let username = self.username else {
+				guard let strongSelf = self, let username = strongSelf.username else {
+					self?.renewingAccessToken = false
 					completion(nil)
 					return
 				}
 				
 				switch result {
 				case .success(let tokenSuccess):
-					self.oauthToken = tokenSuccess.credential.oauthToken
-					self.oauthRefreshToken = tokenSuccess.credential.oauthRefreshToken
+					strongSelf.oauthToken = tokenSuccess.credential.oauthToken
+					strongSelf.oauthRefreshToken = tokenSuccess.credential.oauthRefreshToken
 					do {
-						try Self.storeCredentials(username: username, oauthToken: self.oauthToken, oauthRefreshToken: self.oauthRefreshToken)
-						os_log(.debug, log: self.log, "Access token renewed.")
+						try Self.storeCredentials(username: username, oauthToken: strongSelf.oauthToken, oauthRefreshToken: strongSelf.oauthRefreshToken)
+						os_log(.debug, log: strongSelf.log, "Access token renewed.")
 					} catch {
+						strongSelf.renewingAccessToken = false
 						completion(error)
 						return
 					}
+					strongSelf.renewingAccessToken = false
 					completion(nil)
 				case .failure(let oathError):
+					strongSelf.renewingAccessToken = false
 					completion(oathError)
 				}
 			}