Don't cache CNContact.

SignalMessaging/contacts/OWSContactsManager.m

@@ -36,7 +36,7 @@ NSString *const OWSContactsManagerSignalAccountsDidChangeNotification
 @property (nonatomic, readonly) SystemContactsFetcher *systemContactsFetcher;
 @property (nonatomic, readonly) YapDatabaseConnection *dbReadConnection;
 @property (nonatomic, readonly) YapDatabaseConnection *dbWriteConnection;
-@property (nonatomic, readonly) NSCache<NSString *, CNContact *> *cnContactCache;
+@property (nonatomic, readonly) AnyLRUCache *cnContactCache;
 
 @end
 
@@ -61,8 +61,7 @@ NSString *const OWSContactsManagerSignalAccountsDidChangeNotification
     _signalAccounts = @[];
     _systemContactsFetcher = [SystemContactsFetcher new];
     _systemContactsFetcher.delegate = self;
-    _cnContactCache = [NSCache new];
-    _cnContactCache.countLimit = 50;
+    _cnContactCache = [[AnyLRUCache alloc] initWithMaxSize:50];
 
     OWSSingletonAssert();
 
@@ -145,11 +144,14 @@ NSString *const OWSContactsManagerSignalAccountsDidChangeNotification
         return nil;
     }
 
-    CNContact *_Nullable cnContact = [self.cnContactCache objectForKey:contactId];
-    if (!cnContact) {
-        cnContact = [self.systemContactsFetcher fetchCNContactWithContactId:contactId];
-        if (cnContact) {
-            [self.cnContactCache setObject:cnContact forKey:contactId];
+    CNContact *_Nullable cnContact;
+    @synchronized(self.cnContactCache) {
+        cnContact = (CNContact * _Nullable)[self.cnContactCache getWithKey:contactId];
+        if (!cnContact) {
+            cnContact = [self.systemContactsFetcher fetchCNContactWithContactId:contactId];
+            if (cnContact) {
+                [self.cnContactCache setWithKey:contactId value:cnContact];
+            }
         }
     }
 

SignalMessaging/utils/LRUCache.swift

@@ -24,26 +24,46 @@ public class AnyLRUCache: NSObject {
 }
 
 // A simple LRU cache bounded by the number of entries.
-//
-// TODO: We might want to observe memory pressure notifications.
 public class LRUCache<KeyType: Hashable & Equatable, ValueType> {
 
     private var cacheMap: [KeyType: ValueType] = [:]
     private var cacheOrder: [KeyType] = []
     private let maxSize: Int
 
+    @objc
     public init(maxSize: Int) {
         self.maxSize = maxSize
+
+        NotificationCenter.default.addObserver(self,
+                                               selector: #selector(didReceiveMemoryWarning),
+                                               name: NSNotification.Name.UIApplicationDidReceiveMemoryWarning,
+                                               object: nil)
+    }
+
+    deinit {
+        NotificationCenter.default.removeObserver(self)
+    }
+
+    @objc func didReceiveMemoryWarning() {
+        SwiftAssertIsOnMainThread(#function)
+
+        cacheMap.removeAll()
+        cacheOrder.removeAll()
+    }
+
+    private func updateCacheOrder(key: KeyType) {
+        cacheOrder = cacheOrder.filter { $0 != key }
+        cacheOrder.append(key)
     }
 
     public func get(key: KeyType) -> ValueType? {
         guard let value = cacheMap[key] else {
+            // Miss
             return nil
         }
 
-        // Update cache order.
-        cacheOrder = cacheOrder.filter { $0 != key }
-        cacheOrder.append(key)
+        // Hit
+        updateCacheOrder(key: key)
 
         return value
     }
@@ -51,9 +71,7 @@ public class LRUCache<KeyType: Hashable & Equatable, ValueType> {
     public func set(key: KeyType, value: ValueType) {
         cacheMap[key] = value
 
-        // Update cache order.
-        cacheOrder = cacheOrder.filter { $0 != key }
-        cacheOrder.append(key)
+        updateCacheOrder(key: key)
 
         while cacheOrder.count > maxSize {
             guard let staleKey = cacheOrder.first else {