c#编写的高并发数据库控制访问代码

  lock (databaseDoor)
  {
    // now there is only one request can reach below codes.
    if (currentValidSessionID == -1)
    {
      currentValidSessionID = currentRequest.SessionID;
    }
  }

if (currentValidSessionID == -1)
{
}

public static long currentValidSessionID = -1;
public static object databaseDoor = new object();
void readDatabase(Request currentRequest)
{
    // use currentValidSessionID to filter out other requests came in during the execute time gap
    if (currentValidSessionID == -1)
    {
        // use object-lock to filter out other requests came in during the variable change time gap.
        lock (databaseDoor)
        {
            // now there is only very little number of requests can reach below codes.
            if (currentValidSessionID == -1)
            {   // now there will be only one request can access the database
                currentValidSessionID = currentRequest.SessionID;
            }
        }
    }
    if (currentValidSessionID == currentRequest.SessionID)
    {   // here is the one !
        try
        {
            // use transaction to guarantee the execute time to void block
            // access database codes go here
        }
        catch()
        {
            // exception codes go here
        }
        finally
        {
            currentValidSessionID = -1;  // recover to original state
        }
    }
}