Respond to CR.

SignalServiceKit/src/Devices/OWSDevice.m

@@ -19,7 +19,9 @@ NSString *const kTSStorageManager_MayHaveLinkedDevices = @"kTSStorageManager_May
 
 @interface OWSDeviceManager ()
 
+// This property should only be accessed while synchronized on self.
 @property (atomic, nullable) NSNumber *mayHaveLinkedDevicesCached;
+
 @property (atomic) NSDate *lastReceivedSyncMessage;
 
 @end
@@ -47,6 +49,8 @@ NSString *const kTSStorageManager_MayHaveLinkedDevices = @"kTSStorageManager_May
 {
     OWSAssert(dbConnection);
 
+    @synchronized(self)
+    {
         // We don't bother synchronizing around
         if (!self.mayHaveLinkedDevicesCached) {
             self.mayHaveLinkedDevicesCached = @([dbConnection boolForKey:kTSStorageManager_MayHaveLinkedDevices
@@ -55,16 +59,20 @@ NSString *const kTSStorageManager_MayHaveLinkedDevices = @"kTSStorageManager_May
         }
 
         return [self.mayHaveLinkedDevicesCached boolValue];
+    }
 }
 
 - (void)setMayHaveLinkedDevices
 {
+    @synchronized(self)
+    {
         if (self.mayHaveLinkedDevicesCached != nil && self.mayHaveLinkedDevicesCached.boolValue) {
             // Skip redundant writes.
             return;
         }
 
         self.mayHaveLinkedDevicesCached = @(YES);
+    }
 
     // Note that we write async to avoid opening transactions within transactions.
     [TSStorageManager.sharedManager.newDatabaseConnection