Fix unbalanced background task creation in CCTUploader (#3837)

Author: mikehaney24

GoogleDataTransportCCTSupport/GDTCCTLibrary/GDTCCTUploader.m

@@ -35,7 +35,7 @@ @interface GDTCCTUploader ()
 @property(nullable, nonatomic, readwrite) NSURLSessionUploadTask *currentTask;
 
 /** If running in the background, the current background ID. */
-@property(nonatomic) GDTBackgroundIdentifier backgroundID;
+@property(nonatomic) BOOL runningInBackground;
 
 @end
 
@@ -61,7 +61,6 @@ - (instancetype)init {
     _uploaderQueue = dispatch_queue_create("com.google.GDTCCTUploader", DISPATCH_QUEUE_SERIAL);
     NSURLSessionConfiguration *config = [NSURLSessionConfiguration defaultSessionConfiguration];
     _uploaderSession = [NSURLSession sessionWithConfiguration:config];
-    _backgroundID = GDTBackgroundIdentifierInvalid;
   }
   return self;
 }
@@ -86,6 +85,15 @@ - (NSURL *)defaultServerURL {
 }
 
 - (void)uploadPackage:(GDTUploadPackage *)package {
+  GDTBackgroundIdentifier bgID = GDTBackgroundIdentifierInvalid;
+  if (_runningInBackground) {
+    bgID = [[GDTApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{
+      if (bgID != GDTBackgroundIdentifierInvalid) {
+        [[GDTApplication sharedApplication] endBackgroundTask:bgID];
+      }
+    }];
+  }
+
   dispatch_async(_uploaderQueue, ^{
     if (self->_currentTask || self->_currentUploadPackage) {
       GDTLogWarning(GDTMCWUploadFailed, @"%@",
@@ -112,9 +120,10 @@ - (void)uploadPackage:(GDTUploadPackage *)package {
           }
           pb_release(gdt_cct_LogResponse_fields, &logResponse);
           [package completeDelivery];
-          if (self->_backgroundID != GDTBackgroundIdentifierInvalid) {
-            [[GDTApplication sharedApplication] endBackgroundTask:self->_backgroundID];
-            self->_backgroundID = GDTBackgroundIdentifierInvalid;
+
+          // End the background task if there was one.
+          if (bgID != GDTBackgroundIdentifierInvalid) {
+            [[GDTApplication sharedApplication] endBackgroundTask:bgID];
           }
           self.currentTask = nil;
           self.currentUploadPackage = nil;
@@ -191,12 +200,21 @@ - (void)packageExpired:(GDTUploadPackage *)package {
 #pragma mark - GDTLifecycleProtocol
 
 - (void)appWillBackground:(GDTApplication *)app {
-  _backgroundID = [app beginBackgroundTaskWithExpirationHandler:^{
-    if (self->_backgroundID != GDTBackgroundIdentifierInvalid) {
-      [app endBackgroundTask:self->_backgroundID];
-      self->_backgroundID = GDTBackgroundIdentifierInvalid;
+  _runningInBackground = YES;
+  __block GDTBackgroundIdentifier bgID = [app beginBackgroundTaskWithExpirationHandler:^{
+    if (bgID != GDTBackgroundIdentifierInvalid) {
+      [app endBackgroundTask:bgID];
     }
   }];
+  if (bgID != GDTBackgroundIdentifierInvalid) {
+    dispatch_async(_uploaderQueue, ^{
+      [[GDTApplication sharedApplication] endBackgroundTask:bgID];
+    });
+  }
+}
+
+- (void)appWillForeground:(GDTApplication *)app {
+  _runningInBackground = NO;
 }
 
 - (void)appWillTerminate:(GDTApplication *)application {