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我想在收到推送通知后启动后台任务。到目前为止，我有以下内容：

  -(void)application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)notification fetchCompletionHandler:(void (^)(UIBackgroundFetchResult))completionHandler {

  NSString* taskName = [NSString stringWithFormat:@"PushNotificationTask-%@", [[NSUUID UUID] UUIDString]];

  NSLog(@"Starting bg-task for push notification %@", taskName);

  self.pnBgTask = [application beginBackgroundTaskWithName:taskName expirationHandler:^{
    NSLog(@"Expiring bg-task for push notification %@", taskName);

    [application endBackgroundTask:self.pnBgTask];
    self.pnBgTask = UIBackgroundTaskInvalid;
  }];

  dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

    // do work here

    NSLog(@"Ending bg-task for push notification %@", taskName);
    [application endBackgroundTask:self.pnBgTask];
    self.pnBgTask = UIBackgroundTaskInvalid;
  });

在前一个后台任务完成之前推送通知到达的情况下，此代码将失败，因为一个任务将覆盖另一个任务。

有人可以提出一个好的模式来解决这个问题吗？

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