Question

我想为连接字符串实现多线程，它将从文件中检索更多的连接字符串，但它需要花费很多时间，所以我想使用多线程。以下是代码：

namespace ConsoleApplication1
{
    public  class Program
    {
        static void Main(string[] args)
        {
            Program p = new Program();
            p.WithTPLAndParallelOptions();
        }               
        private  object threadLock = new object();
        public  void ConnectDBAndExecuteQueryWithLock(string connectionString)
        {
            lock (threadLock)
            {
                try
                {
                    string mysqlQuery = "SELECT PS_CD,COUNT(*) AS OFFLINE_FIR_COUNT FROM t_fir_registration WHERE state_cd=18 AND lang_cd=99 GROUP BY PS_CD";

                    //string connectionString = @"Server=.\SQLEXPRESS;Database=AUTODATA;Password=abc@123;User ID=sa";
                    using (MySqlConnection connection = new MySqlConnection(connectionString))
                    {
                        connection.Open();
                        using (MySqlCommand command = new MySqlCommand(mysqlQuery, connection))
                        {
                            command.CommandTimeout = 80;
                            command.ExecuteNonQuery();
                            Console.WriteLine("Executed Thread.. " + Thread.CurrentThread.Name);
                        }
                    }
                }
                catch (Exception e)
                {
                    Console.WriteLine(e.Message);
                }
            }
        }     
       public  void WithTPLAndParallelOptions()
        {
            string cctns_offline_DBConnectionString = ConfigurationManager.ConnectionStrings["cctns_offline_DBConnectionString"].ConnectionString;
            string[] filePaths = Directory.GetFiles(ConfigurationManager.AppSettings["filePath"].ToString(), "*.properties",
                                          SearchOption.TopDirectoryOnly);
            int ThreadCount = filePaths.Length;
            ParallelOptions options = new ParallelOptions();
            options.MaxDegreeOfParallelism = 5;
            //Create Parallel.For to execute the task
            Parallel.For(0, ThreadCount, options, i =>
            {

                foreach (string fileName in filePaths)
                {
                    // i = i + 1;
                    // Read a text file using StreamReader
                    using (System.IO.StreamReader sr = new System.IO.StreamReader(fileName))
                    {
                        String line;
                        while ((line = sr.ReadLine()) != null)
                        {

                            if (line.StartsWith("db.url"))
                            {
                                string[] PS_CD = fileName.Split(new[] { "\\", ".", "_" }, StringSplitOptions.None);

                                string[] ip_address = line.Split(new[] { ";", "//", "/", ":" }, StringSplitOptions.None);
                                if (ip_address[3].ToString() != string.Empty && ip_address[3] != "SQL2K8CLUSTER")
                                {
                                    string connstringrpl = cctns_offline_DBConnectionString.Replace("PS_IP", ip_address[3].ToString());
                                    ConnectDBAndExecuteQueryWithLock(connstringrpl);
                                }
                            }
                        }
                    }
                }
            });
        }
      }
}

Answer 1

1）目前您的Parallel.For和foreach循环是嵌套的，这意味着外部Parallel.For循环的每次迭代都将重新执行内部foreach循环的所有迭代。因此，如果您有10个文件，ConnectDBAndExecuteQueryWithLock()将被执行10 * 10 = 100次，这可能不是您想要的，使您的程序慢得多。要解决此问题，请通过替换

删除foreach循环

foreach (string fileName in filePaths)
{
    ...
}

与

{
    var fileName = filePaths[i];
    ...
}

2）正如Jaya所指出的，lock (threadLock)导致一次只有一个线程可以执行数据库查询，使您的多线程程序几乎是单线程的。由于lock中的代码不使用任何共享变量，因此可以安全地完全删除lock。

使用多线程连接多个连接字符串

1 个答案: