对C#中Thread.IsBackground属性的理解

2015-12-02 11:15:51  访问(2533) 赞(0) 踩(0)



原文地址：http://blog.csdn.net/luckeryin/article/details/5649144

C#中,Thread类有一个IsBackground 的属性.MSDN上对它的解释是:获取或设置一个值，该值指示某个线程是否为后台线程。个人感觉这样的解释等于没有解释.

.Net中的线程,可以分为后台线程和前台线程。后台线程与前台线程并没有本质的区别，它们之间唯一的区别就是:后台线程不会防止应用程序的进程被终止掉。呵呵,这句话读出来好像并不那么好懂.其实,说白了就是当前台线程都结束了的时候,整个程序也就结束了,即使还有后台线程正在运行,此时,所有剩余的后台线程都会被停止且不会完成.但是,只要还有一个前台线程没有结束,那么它将阻止程序结束.这就是为什么有些设计不够完美的WinForm程序，在某种特定的情况下，即使所有的窗口都关闭了，但是在任务管理器的管理列表里仍然可以找到该程序的进程，仍然在消耗着CPU和内存资源.因此,在WinForm程序中,关闭所有窗口前,应该停止所有前台线程,千万不要遗忘了某个前台线程.应用程序进程的存亡由前台线程决定而于后台线程无关.这就是它们的区别.

知道了前后台线程的区别,就应该知道如何声明IsBackgroud属性的值了.

值得说明的一点是:改变线程从前台到后台不会以任何方式改变它在CPU协调程序中的优先级和状态。因为前台后线程与程序进程的优先级无关.

结束前摘录MSDN上一段示例码,以帮助大家便好的理解这一区别:

下面的代码示例对比了前台线程与后台线程的行为。创建一个前台线程和一个后台线程。前台线程使进程保持运行，直到它完成它的 while 循环。前台线程完成后，进程在后台线程完成它的 while 循环之前终止。

using System;

using System.Threading;


class Test

{

    static void Main()

    {

        BackgroundTest shortTest = new BackgroundTest(10);

        Thread foregroundThread = 

            new Thread(new ThreadStart(shortTest.RunLoop));

        foregroundThread.Name = "ForegroundThread";


        BackgroundTest longTest = new BackgroundTest(50);

        Thread backgroundThread = 

            new Thread(new ThreadStart(longTest.RunLoop));

        backgroundThread.Name = "BackgroundThread";

        backgroundThread.IsBackground = true;


        foregroundThread.Start();

        backgroundThread.Start();

    }

}


class BackgroundTest

{

    int maxIterations;


    public BackgroundTest(int maxIterations)

    {

        this.maxIterations = maxIterations;

    }


    public void RunLoop()

    {

        String threadName = Thread.CurrentThread.Name;

        

        for(int i = 0; i < maxIterations; i++)

        {

            Console.WriteLine("{0} count: {1}", 

                threadName, i.ToString());

            Thread.Sleep(250);

        }

        Console.WriteLine("{0} finished counting.", threadName);

    }

}


using System;
using System.Collections.Generic;
using System.Text;
using System.Threading;
using System.IO;

namespace ConsoleApplication1
{
    public class Program
    {
        static void Main()
        {
            BackgroundTest shortTest = new BackgroundTest(10,1);
            Thread foregroundThread =
                new Thread(new ThreadStart(shortTest.RunLoop));
            foregroundThread.Name = "ForegroundThread";

            BackgroundTest longTest = new BackgroundTest(50,2);
            Thread backgroundThread =
                new Thread(new ThreadStart(longTest.RunLoop));
            backgroundThread.Name = "BackgroundThread";
            backgroundThread.IsBackground = true;

            foregroundThread.Start();
            backgroundThread.Start();

            string str = "main end";

            while (Util.isWrite != 0)
            {
                continue;
            }

            Util.isWrite = 10;
            Util.WriteFile(@"d:\tmp\thread.txt", str);
            Util.isWrite = 0;

            Console.WriteLine(str);
        }
    }

    public class BackgroundTest
    {
        int maxIterations;
        int tId = 0;

        public BackgroundTest(int _maxIterations, int _tId)
        {
            this.maxIterations = _maxIterations;
            tId = _tId;
        }

        public void RunLoop()
        {
            string str = null;
            String threadName = Thread.CurrentThread.Name;

            for (int i = 0; i < maxIterations; i++)
            {
                  str = string.Format("{0} count: {1}",
                    threadName, i.ToString());

                while (Util.isWrite != 0)
                {
                    continue;
                }

                Util.isWrite = this.tId;
                Util.WriteFile(@"d:\tmp\thread.txt", str);
                Util.isWrite = 0;

                Console.WriteLine(str);
                Thread.Sleep(250);
            }

            str = string.Format("{0} finished counting.", threadName);

            while (Util.isWrite != 0)
            {
                continue;
            }

            Util.isWrite = this.tId;
            Util.WriteFile(@"d:\tmp\thread.txt", str);
            Util.isWrite = 0;

            Console.WriteLine(str);
        }
    }

    public class Util
    {
        public static int isWrite = 0;

        #region 写入文件

        /// <summary>
        /// 写入文件
        /// </summary>
        /// <param name="fileName"></param>
        /// <param name="textValue"></param>
        public static void WriteFile(string fileName, string textValue)
        {
            WriteFile(fileName, textValue + System.Environment.NewLine, null, true, true);
        }

        /// <summary>
        /// 写入文件
        /// </summary>
        /// <param name="fileName"></param>
        /// <param name="textValue"></param>
        /// <param name="textEncoding"></param>
        public static void WriteFile(string fileName, string textValue, System.Text.Encoding textEncoding)
        {
            WriteFile(fileName, textValue, textEncoding, true, true);
        }

        /// <summary>
        /// 写入文件
        /// </summary>
        /// <param name="fileName"></param>
        /// <param name="textValue"></param>
        /// <param name="textEncoding"></param>
        /// <param name="IsOverwrite"></param>
        public static void WriteFile(string fileName, string textValue, System.Text.Encoding textEncoding, bool IsOverwrite)
        {
            WriteFile(fileName, textValue, textEncoding, IsOverwrite, true);
        }

        /// <summary>
        /// 写入文件
        /// </summary>
        /// <param name="fileName"></param>
        /// <param name="textValue"></param>
        /// <param name="textEncoding"></param>
        /// <param name="IsOverwrite"></param>
        /// <param name="IsAppend"></param>
        public static void WriteFile
            (
                string fileName,
                string textValue,
                System.Text.Encoding textEncoding,
                bool IsOverwrite,
                bool IsAppend
            )
        {
            if (fileName == null || fileName.Length == 0)
                return;


            FileInfo info = new FileInfo(fileName);

            if (info.Exists)
            {
                // 文件存在，且不覆盖 //
                if (!IsOverwrite)
                    return;


                // 如果不是追加 //
                if (!IsAppend)
                    File.Delete(info.FullName);
            }
            else
            {
                // 创建目录 //
                if (!info.Directory.Exists)
                {
                    Directory.CreateDirectory(info.Directory.FullName);
                }
            }


            FileStream fs = null;

            StreamWriter m_streamWriter = null;

            try
            {
                //创建一个文件流，用以写入或者创建一个StreamWriter
                fs = new FileStream(info.FullName, FileMode.OpenOrCreate, FileAccess.Write);

                if (textEncoding == null)
                {
                    m_streamWriter = new StreamWriter(fs);
                }
                else
                {
                    m_streamWriter = new StreamWriter(fs, textEncoding);
                }

                m_streamWriter.Flush();

                //  使用StreamWriter来往文件中写入内容
                if (IsAppend)
                    m_streamWriter.BaseStream.Seek(0, SeekOrigin.End);

                m_streamWriter.Write(textValue);
                m_streamWriter.Flush();
            }
            catch (Exception err)
            {
                throw err;
            }
            finally
            {
                if (m_streamWriter != null)
                {
                    m_streamWriter.Flush();
                    m_streamWriter.Close();
                }

                if (fs != null)
                {
                    fs.Close();
                }

                m_streamWriter = null;

                fs = null;
            }
        }

        #endregion 写入文件


    }
}


输出结果：

main end

BackgroundThread count: 0

ForegroundThread count: 0

BackgroundThread count: 1

ForegroundThread count: 1

BackgroundThread count: 2

ForegroundThread count: 2

BackgroundThread count: 3

ForegroundThread count: 3

BackgroundThread count: 4

ForegroundThread count: 4

BackgroundThread count: 5

ForegroundThread count: 5

BackgroundThread count: 6

ForegroundThread count: 6

BackgroundThread count: 7

ForegroundThread count: 7

BackgroundThread count: 8

ForegroundThread count: 8

BackgroundThread count: 9

ForegroundThread count: 9

BackgroundThread count: 10

ForegroundThread finished counting.


说明：

前台进程ForegroundThread运行完后，BackgroundThread就停止运行。 


标签：线程    C#    Thread.IsBackground 

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