Assert that session mutation occurs on serial queue

// FREEBIE

src/Storage/AxolotlStore/TSStorageManager+SessionStore.m

@@ -6,12 +6,21 @@
 
 #define TSStorageManagerSessionStoreCollection @"TSStorageManagerSessionStoreCollection"
 
-@implementation TSStorageManager (SessionStore)
+void AssertIsOnSessionStoreQueue()
+{
+    if (SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(10, 0)) {
+        dispatch_assert_queue([OWSDispatch sessionStoreQueue]);
+    } // else, skip assert as it's a development convenience.
+}
 
+@implementation TSStorageManager (SessionStore)
 
 #pragma mark - SessionStore
 
-- (SessionRecord *)loadSession:(NSString *)contactIdentifier deviceId:(int)deviceId {
+- (SessionRecord *)loadSession:(NSString *)contactIdentifier deviceId:(int)deviceId
+{
+    AssertIsOnSessionStoreQueue();
+
     NSDictionary *dictionary =
         [self dictionaryForKey:contactIdentifier inCollection:TSStorageManagerSessionStoreCollection];
 
@@ -28,7 +37,10 @@
     return record;
 }
 
-- (NSArray *)subDevicesSessions:(NSString *)contactIdentifier {
+- (NSArray *)subDevicesSessions:(NSString *)contactIdentifier
+{
+    AssertIsOnSessionStoreQueue();
+
     NSDictionary *dictionary =
         [self objectForKey:contactIdentifier inCollection:TSStorageManagerSessionStoreCollection];
 
@@ -45,7 +57,10 @@
     return subDevicesSessions;
 }
 
-- (void)storeSession:(NSString *)contactIdentifier deviceId:(int)deviceId session:(SessionRecord *)session {
+- (void)storeSession:(NSString *)contactIdentifier deviceId:(int)deviceId session:(SessionRecord *)session
+{
+    AssertIsOnSessionStoreQueue();
+
     // We need to ensure subsequent usage of this SessionRecord does not consider this session as "fresh". Normally this
     // is achieved by marking things as "not fresh" at the point of deserialization - when we fetch a SessionRecord from
     // YapDB (initWithCoder:). However, because YapDB has an object cache, rather than fetching/deserializing, it's
@@ -65,11 +80,17 @@
     [self setObject:dictionary forKey:contactIdentifier inCollection:TSStorageManagerSessionStoreCollection];
 }
 
-- (BOOL)containsSession:(NSString *)contactIdentifier deviceId:(int)deviceId {
+- (BOOL)containsSession:(NSString *)contactIdentifier deviceId:(int)deviceId
+{
+    AssertIsOnSessionStoreQueue();
+
     return [self loadSession:contactIdentifier deviceId:deviceId].sessionState.hasSenderChain;
 }
 
-- (void)deleteSessionForContact:(NSString *)contactIdentifier deviceId:(int)deviceId {
+- (void)deleteSessionForContact:(NSString *)contactIdentifier deviceId:(int)deviceId
+{
+    AssertIsOnSessionStoreQueue();
+
     NSMutableDictionary *dictionary =
         [[self dictionaryForKey:contactIdentifier inCollection:TSStorageManagerSessionStoreCollection] mutableCopy];
 
@@ -82,7 +103,10 @@
     [self setObject:dictionary forKey:contactIdentifier inCollection:TSStorageManagerSessionStoreCollection];
 }
 
-- (void)deleteAllSessionsForContact:(NSString *)contactIdentifier {
+- (void)deleteAllSessionsForContact:(NSString *)contactIdentifier
+{
+    AssertIsOnSessionStoreQueue();
+
     [self removeObjectForKey:contactIdentifier inCollection:TSStorageManagerSessionStoreCollection];
 }
 
@@ -96,6 +120,8 @@
 
 - (void)printAllSessions
 {
+    AssertIsOnSessionStoreQueue();
+
     NSString *tag = @"[TSStorageManager (SessionStore)]";
     [self.dbConnection readWithBlock:^(YapDatabaseReadTransaction *_Nonnull transaction) {
         DDLogDebug(@"%@ All Sessions:", tag);