C# FluentNHibernate-无法从输入流（XmlDocument）配置数据存储

我有一个使用FluentNHibernate的传统WCF服务（以及EF和存储过程）。这项服务在一年多的时间里运作良好。最近，我们将apppool回收设置从默认设置更改为每天上午10点进行apppool回收。自从那次更改以来，我的WCF服务至少两次失败，出现以下异常

FluentNHibernate.Cfg.FluentConfigurationException: An invalid or incomplete configuration was used while creating a SessionFactory. Check PotentialReasons collection, and InnerException for more detail.

 ---> FluentNHibernate.Cfg.FluentConfigurationException: An invalid or incomplete configuration was used while creating a SessionFactory. Check PotentialReasons collection, and InnerException for more detail.

 ---> NHibernate.MappingException: Could not configure datastore from input stream (XmlDocument) ---> System.NullReferenceException: Object reference not set to an instance of an object.
   at NHibernate.Cfg.MappingsQueue.GetNextAvailableResource()
   at NHibernate.Cfg.Configuration.AddInputStream(Stream xmlInputStream, String name)
   --- End of inner exception stack trace ---
   at NHibernate.Cfg.Configuration.LogAndThrow(Exception exception)
   at NHibernate.Cfg.Configuration.AddInputStream(Stream xmlInputStream, String name)
   at NHibernate.Cfg.Configuration.AddDocument(XmlDocument doc, String name)
   at FluentNHibernate.PersistenceModel.Configure(Configuration cfg)
   at FluentNHibernate.Cfg.MappingConfiguration.Apply(Configuration cfg)
   at FluentNHibernate.Cfg.FluentConfiguration.BuildConfiguration()
  --- End of inner exception stack trace ---
  at FluentNHibernate.Cfg.FluentConfiguration.BuildConfiguration()
  at FluentNHibernate.Cfg.FluentConfiguration.BuildSessionFactory()
  --- End of inner exception stack trace ---
  at FluentNHibernate.Cfg.FluentConfiguration.BuildSessionFactory()

有几件有趣的事要注意

这两次错误都是在apppool回收几秒钟后出现的，这让我相信这与此密切相关

这不会在每次apppool回收后发生

在apppool回收设置为IIS默认值的测试环境中不会发生这种情况

这很难在当地复制。我已经研究了以下关于相同例外情况的问题，但它们处于完全不同的环境中，这些问题的作者一致地得到了例外情况，而这里的情况并非如此

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经过数小时的调查，问题归结为多个线程试图创建会话工厂。我本以为NH会话工厂是线程安全的，但遗憾的是它不是，我不得不输入int代码使其线程安全