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Thread Synchronization (C# Programming Guide) (2010-02-05)

นำไปประยุกต์ใช้กับ multithreaded applications ในการเข้าถึง resources ที่ใช้ร่วมกันแบบง่ายๆ ก่อนนะครับ

อันแรกใช้ Lock Statement ครับ

For example:

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

namespace SyncronizeThread
{
  
    class Program
    {
        public static Int32 counter = new Int32();
        static System.Object myLock = new object();
        private static Mutex mut = new Mutex();

        static void Main(string[] args)
        {

            counter = 1;
            Thread t = new Thread(Run);
            t.Name = "a";
            t.Start();
            t = new Thread(Run);
            t.Name = "b";
            t.Start();
            t = new Thread(Run);
            t.Name = "c";
            t.Start();
            
            Console.ReadKey();
        }

        public static void Run()
        {
            Console.WriteLine(Thread.CurrentThread.Name + " Starting ");
            lock (myLock)
            {
                for (int i = 0; i < 10; i++)
                {
                    Console.WriteLine(Thread.CurrentThread.Name + "===>" + (counter++));
                    Thread.Sleep(500);
                }
            }

        }
    }
} 
อีกอันนึงใช้ mutex    using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;

namespace SyncronizeThread
{
  
    class Program
    {
        public static Int32 counter = new Int32();
        static System.Object myLock = new object();
        private static Mutex mut = new Mutex();

        static void Main(string[] args)
        {

            counter = 1;
            Thread t = new Thread(Run);
            t.Name = "a";
            t.Start();
            t = new Thread(Run);
            t.Name = "b";
            t.Start();
            t = new Thread(Run);
            t.Name = "c";
            t.Start();
            
            Console.ReadKey();
        }

        public static void Run()
        {
            Console.WriteLine(Thread.CurrentThread.Name + " Starting ");
            mut.WaitOne();
            for (int i = 0; i < 10; i++ )
            {
                    Console.WriteLine(Thread.CurrentThread.Name + "===>" + (counter++));
                    Thread.Sleep(500);
            }
            mut.ReleaseMutex();

        }
    }
}  อันนี้ใช้ Semaphore  using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;

namespace SyncronizeThread
{
  
    class Program
    {
        public static Int32 counter = new Int32();
        static System.Object myLock = new object();
        private static Mutex mut = new Mutex();
        static Semaphore s = new Semaphore(2, 2);

        static void Main(string[] args)
        {

            counter = 1;
            Thread t = new Thread(Run);
            t.Name = "a";
            t.Start();
            t = new Thread(Run);
            t.Name = "b";
            t.Start();
            t = new Thread(Run);
            t.Name = "c";
            t.Start();
            
            Console.ReadKey();
        }

        public static void Run()
        {
            Console.WriteLine(Thread.CurrentThread.Name + " Starting ");
            s.WaitOne();
            for (int i = 0; i < 10; i++ )
            {
                    Console.WriteLine(Thread.CurrentThread.Name + "===>" + (counter++));
                    Thread.Sleep(500);
            }
            s.Release();

        }
    }
}

ผลการรันด้วย Lock Statement

a Starting
a===>1
b Starting
c Starting
a===>2
a===>3
a===>4
a===>5
a===>6
a===>7
a===>8
a===>9
a===>10
c===>11
c===>12
c===>13
c===>14
c===>15
c===>16
c===>17
c===>18
c===>19
c===>20
b===>21
b===>22
b===>23
b===>24
b===>25
b===>26
b===>27
b===>28
b===>29
b===>30

ผลการรันด้วย Mutex

ผลการรันด้วย Semaphore

a Starting
a===>1
c Starting
c===>2
b Starting
a===>3
c===>4
a===>5
c===>6
a===>7
c===>8
a===>9
c===>10
a===>11
c===>12
a===>13
c===>14
a===>15
c===>16
a===>17
c===>18
a===>19
c===>20
b===>21
b===>22
b===>23
b===>24
b===>25
b===>26
b===>27
b===>28
b===>29
b===>30

จะเห็นว่าสามารถเข้าใช้งานตัวแปร counter (resouce)ได้พร้อมกัน สอง thread

จะเห็นว่า Lock กับ Mutext thread จะใช้ resource ได้ทีละ thread, ต่างกันตรง Mutex มี scope การทำงานข้าม Process ได้
โดยระบุชื่อของ mutex เช่น Mutex mut = new Mutex(false, "mutexName");
แต่ Lock จำกัดอยู่ใน Process เดียวเท่านั้น ส่วน Semaphore ระบุจำนวน thread ที่จะเข้ามาใช้ resource ได้ครับ สุดยอดไปเรยยยยยยย

บทความที่น่าสนใจ www.c-sharpcorner.com/UploadFile/mmehta/Multithreading311162005045743AM/Multithreading3.aspx

Thread State Diagram

Writing Binary Files :

with known internal structures the BinaryReader and BinaryWriter classes offer streaming functionality that's oriented towards particular data types. The good thing about writing binary files are you cannot read the files by just opening them in the notepad also binary files can be of very large size. Lets look at the code to create Binary files.

private void Button1_Click(object sender System.EventArgs e)
{
          FileStream fs = File.Create(Server.MapPath("test.dat"));
    BinaryWriter bw = new BinaryWriter(fs);

    int x = 10;
    decimal d = 3.234M;
    string str = "Hello World";

    bw.Write(x);
    bw.Write(d);
    bw.Write(str);

    bw.Close();
    fs.Close();
}

nks>nks>

Okay now lets see what's happening in the code:

First we made the FileStream object but in this case we are writing the .dat file which means the data file.

We created an object of the BinaryWriter class.

Later we declared three variables of type int decimal and string.

Finally we wrote the three variables in the binary file.

If you go and see the file and try to open the file in notepad you will only see some strange characters. In other words you won't be able to see the text.

Reading Binary Files :

Lets see how we can read the Binary files.

private void Button1_Click(object sender System.EventArgs e)
{
      FileStream  fs = File.OpenRead(Server.MapPath("test.dat")); 	
      BinaryReader br = new BinaryReader(fs); 
			
      Response.Write(br.ReadInt32()); 
      Response.Write(br.ReadDecimal()); 
      Response.Write(br.ReadString()); 
 			
      br.Close(); 
      fs.Close(); 
}

As you can see the Reading code for Binary Files is also very simple. If you have noticed the code is a bit different from which we saw earlier for reading Text files. Here we are extracting the data types that we wrote in the binary file. We use ReadInt32() method to read the integer out from the binary file. We use ReadDecimal() to read the decimal values from the binary file and so on.

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