fix(config): Address race condition from concurrent network session recreation

Fixes #15087

Author: ncooke3

FirebaseRemoteConfig/CHANGELOG.md

@@ -1,3 +1,7 @@
+# 12.2.0
+- [fixed] Fixed a race condition that could lead to a crash during network
+  session recreation. (#15087)
+
 # 12.0.0
 - [added] Improved how the SDK handles real-time requests when a Firebase
   project has exceeded its available quota for real-time services.

FirebaseRemoteConfig/Sources/FIRRemoteConfig.m

@@ -700,6 +700,8 @@ - (FIRRemoteConfigSettings *)configSettings {
   dispatch_sync(_queue, ^{
     minimumFetchInterval = self->_settings.minimumFetchInterval;
     fetchTimeout = self->_settings.fetchTimeout;
+    // The NSURLSession needs to be recreated whenever the fetch timeout may be updated.
+    [_configFetch recreateNetworkSession];
   });
   FIRLogDebug(kFIRLoggerRemoteConfig, @"I-RCN000066",
               @"Successfully read configSettings. Minimum Fetch Interval:%f, "
@@ -708,8 +710,6 @@ - (FIRRemoteConfigSettings *)configSettings {
   FIRRemoteConfigSettings *settings = [[FIRRemoteConfigSettings alloc] init];
   settings.minimumFetchInterval = minimumFetchInterval;
   settings.fetchTimeout = fetchTimeout;
-  /// The NSURLSession needs to be recreated whenever the fetch timeout may be updated.
-  [_configFetch recreateNetworkSession];
   return settings;
 }
 
@@ -721,7 +721,7 @@ - (void)setConfigSettings:(FIRRemoteConfigSettings *)configSettings {
 
     self->_settings.minimumFetchInterval = configSettings.minimumFetchInterval;
     self->_settings.fetchTimeout = configSettings.fetchTimeout;
-    /// The NSURLSession needs to be recreated whenever the fetch timeout may be updated.
+    // The NSURLSession needs to be recreated whenever the fetch timeout may be updated.
     [self->_configFetch recreateNetworkSession];
     FIRLogDebug(kFIRLoggerRemoteConfig, @"I-RCN000067",
                 @"Successfully set configSettings. Minimum Fetch Interval:%f, "

FirebaseRemoteConfig/Sources/RCNConfigFetch.m

@@ -113,6 +113,7 @@ - (instancetype)initWithContent:(RCNConfigContent *)content
 }
 
 /// Force a new NSURLSession creation for updated config.
+/// - Warning: This API is **not** thread-safe.
 - (void)recreateNetworkSession {
   if (_fetchSession) {
     [_fetchSession invalidateAndCancel];