From b767996dba0bc4c82e2b79280b13a6c46074e539 Mon Sep 17 00:00:00 2001
From: Matthew Chen <matthew@signal.org>
Date: Fri, 4 May 2018 10:39:42 -0400
Subject: [PATCH 1/3] oOnly one system contacts fetch at a time.

---
 .../contacts/SystemContactsFetcher.swift       | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/SignalMessaging/contacts/SystemContactsFetcher.swift b/SignalMessaging/contacts/SystemContactsFetcher.swift
index b4c750fca..db835e064 100644
--- a/SignalMessaging/contacts/SystemContactsFetcher.swift
+++ b/SignalMessaging/contacts/SystemContactsFetcher.swift
@@ -146,6 +146,9 @@ public class SystemContactsFetcher: NSObject {
     public private(set) var systemContactsHaveBeenRequestedAtLeastOnce = false
     private var hasSetupObservation = false
 
+    private var isFetching = false
+    private var hasQueuedFetch = false
+
     override init() {
         self.contactStoreAdapter = ContactsFrameworkContactStoreAdaptee()
 
@@ -232,6 +235,7 @@ public class SystemContactsFetcher: NSObject {
     @objc
     public func fetchOnceIfAlreadyAuthorized() {
         SwiftAssertIsOnMainThread(#function)
+
         guard authorizationStatus == .authorized else {
             return
         }
@@ -269,11 +273,25 @@ public class SystemContactsFetcher: NSObject {
             Logger.error("background task time ran out contacts fetch completed.")
         })
 
+        guard !isFetching else {
+            Logger.info("\(self.TAG) queuing contact fetch; contact fetch already in flight.")
+            hasQueuedFetch = true
+            return
+        }
+        isFetching = true
+
         // Ensure completion is invoked on main thread.
         let completion: (Error?) -> Void = { error in
             DispatchMainThreadSafe({
+                self.isFetching = false
+
                 completionParam?(error)
                 backgroundTask = nil
+
+                if self.hasQueuedFetch {
+                    self.hasQueuedFetch = false
+                    self.fetchOnceIfAlreadyAuthorized()
+                }
             })
         }
 

From bec5a9f428057476bedc46a75dd45ed207417bb6 Mon Sep 17 00:00:00 2001
From: Matthew Chen <matthew@signal.org>
Date: Fri, 4 May 2018 12:08:11 -0400
Subject: [PATCH 2/3] Revert "oOnly one system contacts fetch at a time."

This reverts commit d84e27f5a5f953fd68dbdf1086a75ffe6aee6720.
---
 .../contacts/SystemContactsFetcher.swift       | 18 ------------------
 1 file changed, 18 deletions(-)

diff --git a/SignalMessaging/contacts/SystemContactsFetcher.swift b/SignalMessaging/contacts/SystemContactsFetcher.swift
index db835e064..b4c750fca 100644
--- a/SignalMessaging/contacts/SystemContactsFetcher.swift
+++ b/SignalMessaging/contacts/SystemContactsFetcher.swift
@@ -146,9 +146,6 @@ public class SystemContactsFetcher: NSObject {
     public private(set) var systemContactsHaveBeenRequestedAtLeastOnce = false
     private var hasSetupObservation = false
 
-    private var isFetching = false
-    private var hasQueuedFetch = false
-
     override init() {
         self.contactStoreAdapter = ContactsFrameworkContactStoreAdaptee()
 
@@ -235,7 +232,6 @@ public class SystemContactsFetcher: NSObject {
     @objc
     public func fetchOnceIfAlreadyAuthorized() {
         SwiftAssertIsOnMainThread(#function)
-
         guard authorizationStatus == .authorized else {
             return
         }
@@ -273,25 +269,11 @@ public class SystemContactsFetcher: NSObject {
             Logger.error("background task time ran out contacts fetch completed.")
         })
 
-        guard !isFetching else {
-            Logger.info("\(self.TAG) queuing contact fetch; contact fetch already in flight.")
-            hasQueuedFetch = true
-            return
-        }
-        isFetching = true
-
         // Ensure completion is invoked on main thread.
         let completion: (Error?) -> Void = { error in
             DispatchMainThreadSafe({
-                self.isFetching = false
-
                 completionParam?(error)
                 backgroundTask = nil
-
-                if self.hasQueuedFetch {
-                    self.hasQueuedFetch = false
-                    self.fetchOnceIfAlreadyAuthorized()
-                }
             })
         }
 

From f9d5421edc0f04e3804f41ff908075bddbcd7be9 Mon Sep 17 00:00:00 2001
From: Matthew Chen <matthew@signal.org>
Date: Fri, 4 May 2018 12:10:03 -0400
Subject: [PATCH 3/3] Modify system contacts fetch to use serial queue.

---
 SignalMessaging/contacts/SystemContactsFetcher.swift | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/SignalMessaging/contacts/SystemContactsFetcher.swift b/SignalMessaging/contacts/SystemContactsFetcher.swift
index b4c750fca..d11be0f6a 100644
--- a/SignalMessaging/contacts/SystemContactsFetcher.swift
+++ b/SignalMessaging/contacts/SystemContactsFetcher.swift
@@ -121,6 +121,9 @@ public enum ContactStoreAuthorizationStatus {
 public class SystemContactsFetcher: NSObject {
 
     private let TAG = "[SystemContactsFetcher]"
+
+    private let serialQueue = DispatchQueue(label: "SystemContactsFetcherQueue")
+
     var lastContactUpdateHash: Int?
     var lastDelegateNotificationDate: Date?
     let contactStoreAdapter: ContactsFrameworkContactStoreAdaptee
@@ -280,7 +283,7 @@ public class SystemContactsFetcher: NSObject {
         systemContactsHaveBeenRequestedAtLeastOnce = true
         setupObservationIfNecessary()
 
-        DispatchQueue.global().async {
+        serialQueue.async {
 
             Logger.info("\(self.TAG) fetching contacts")