IEG 4180 Tutorial 7

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IEG 4180 Tutorial 7

• Prepared by Shing
• (Remark Modified by Zero)

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Outline

• Traditional Blocking I/O
• Overlapped I/O
• Event Object Signaling
• Alertable I/O
• Java Basic
• Java Network Programming
• Eclipse

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Traditional Blocking I/O
Time Required A B C D
Max Rate Packet Size / Time Required
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Overlapped I/O

• When using overlapped I/O, the I/O operation will
  run in the background
• While the I/O operation runs in the background,
  the application can do some other processing
• When the I/O operation completes, the application
  is notified
• There are multiple mechanisms for notifying the
  application that an I/O operation has been
  completed
• Event Object Signaling
• Alertable I/O

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Overlapped I/O

• Advantages
• Non-blocking
• Use application buffers to receive data directly
• Allow posting multiple receive calls

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Overlapped I/O Create Overlapped Socket

• Use WSASocket() instead of socket()
• Use normal bind(), accept(), connect() etc

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Overlapped I/O Send Receive Data

• For TCP, use
• WSASend()
• WSARecv()
• For UDP, use
• WSASendTo()
• WSARecvFrom()

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Overlapped I/O Receive

• Important parameters for WSARecv and WSARecvFrom
• Socket
• Array of WSABUF structures
• Number of elements in WSABUF array
• WSAOVERLAPPED structure
• Pointer to I/O completion routine (used for
  alertable I/O)

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Overlapped I/O Receive

• The return value
• Does not return the number of bytes received.
• Only tell you it success or error.
• SOCKET_ERROR may be returned even there was no
  error.
• Use WSAGetLastError() to check, if error code is
  WSA_IO_PENDING, it means there is no error!!!

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Overlapped I/O WSABUF

• The definition of buffer for overlapped I/O
• len
• The length of buffer
• Have to be filled in advance
• buf
• The memory space that actually hold the data

typedef struct __WSABUF u_long len char
FAR buf WSABUF, LPWSABUF
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Overlapped I/O WSAOVERLAPPED structure

• A mean for notification

typedef struct _WSAOVERLAPPED DWORD Internal
DWORD InternalHigh DWORD Offset DWORD
OffsetHigh WSAEVENT hEvent WSAOVERLAPPED,
LPWSAOVERLAPPED

• hEvent
• Function call returns immediately, some
  mechanisms are needed to determine the status and
  the completion of the request
• Used in event object notification

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Overlapped I/O The Model - Use of Event Object
Need to Figure Out which Buffer is Being Filled
(or Returned)
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Overlapped I/O Event Object Notification

• Create an event object
• Similar to Mutex and Semaphore, event objects
  also have signaled or nonsignaled state
• Pass this object to hEvent of the WSAOVERLAPPED
  structure
• To know when the I/O operation complete
• WSAWaitForMultipleEvents()
• To retrieve the results of overlapped operations
• WSAGetOverlappedResult()
• Reset the event object to nonsignaled state
• WSAResetEvent()
• To free resources occupied by the event object
• WSACloseEvent()

WSAEVENT WSACreateEvent(void)
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Overlapped I/O Alertable I/O-Introduction

• Instead of using event object notification, make
  the OS calls one of your functions when I/O
  operations complete
• Completion routines
• Functions that will be called when I/O complete
• Specified in the last parameter of WSASend() /
  WSASendTo() / WSARecv() / WSARecvFrom()

int i WSARecvFrom(..., lpOverlapped,
lpCompletionRoutine)
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Overlapped I/O Alertable I/O
Move Data Processing to the Completion Routine
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Overlapped I/O Alertable I/O -Completion Routines
void CALLBACK CompletionRoutine( IN DWORD
dwError, / the error code / IN
DWORD cbTransferred, / in bytes / IN
LPWSAOVERLAPPED lpOverlapped, / the structure of
this I/O / IN DWORD dwFlags )

• cbTransferred
• Number of bytes transferred
• Equals to zero when connection is closed
• lpOverlapped
• hEvent can be freely used by your code, just like
  the LPVOID parameter in thread procedure
• You have to manage the buffer usage yourself!
• For example, you issued 10 WSARecv() with 10
  buffers
• The data will be filled in the buffers according
  to the calling order
• Reissue WSARecv() on processed buffers

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Overlapped I/O Alertable Wait state

• The thread using alertable I/O has to enter
  alertable wait state, so that the completion
  routines can be called
• To enter alertable wait state
• Just like the ordinary Sleep()
• Return when timeout or completion

DWORD SleepEx( DWORD dwMilliseconds, BOOL
bAlertable / set to true / )
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Java Basic

• Write the program
• Filename extension .java
• Filename should be the same as the public class
  name
• One public class one source file
• Compile and run the program
• javac HelloWorldApp.java (you will have
  HellpWorldApp.class)
• java HelloWorldApp (no extension)

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Hello World
Define class name(So filename is
HelloWorldApp.java)

• public class HelloWorldApp public static void
  main (String args) System.out.println(Hello
  World!)

Application entry point similar to C
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Data Type

• Primitive Type
• int, boolean, short, char, etc.
• Reference Type
• All class object
• E.g. String, Integer, Socket, etc.

int a //a represent the integer itself a 123
//just declare and use it
Integer a //a is only a reference pointer a
new Integer(123) //you must call new to create
the object
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Illustration

• Primitive Type
• Reference Type

int a a 123 a 456
123
456
Integer a a new Integer(123) a new
Integer(456)
1010
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String

• String variable1 Hello
• String variable2 new String(Hello)
• variable1 World
• Convert String to int
• int a Integer.parseInt(10)
• Convert int to String
• String b String.valueOf(10)
• String b 10

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Array

• Array of primitive ? new once
• int arrayInt new int10 // int arrayInt
• arrayInt0 123
• Array of reference ? new twice
• ClassApple apples new ClassApple10
• for (int i0 iltapples.lenght i)
• applesi new ClassApple()

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Memory Management

• Java programmer never free allocated object
  manually.
• JVM will reclaim unreferenced memory through
  garbage collection.
• Garbage collection is performed automatically
  when system is idle or runs out-of memory
• Force garbage collection to start by calling

System.gc() //Force the system to start garbage
collection
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Handling Exception

• To handle exception you either
• Catch it
• Throw it

try Socket s new Socket(host, port)
// Thread.currentThread().sleep(10)
catch (IOException e) e.printStackTrace()
catch (Exception e) System.out.println(e.to
String())
public void connect() throws IOException
Socket s new Socket(host, port)
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The finally clause

• Some codes may not be executed due to exception
• Using the finally clause

try PrintWriter out new PrintWriter(new
FileWriter(out.txt)) for (int i0 iltSIZE
i) out.println(v.elementAt(i)) out.close(
) // may not be executed catch (IOException e)
System.err.println(Caught IOException)
try PrintWriter out new PrintWriter(new
FileWriter(out.txt)) for (int i0 iltSIZE
i) out.println(v.elementAt(i)) catch
(IOException e) System.err.println(Caught
IOException) finally if (out ! null)
out.close()
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Inheritance

• public ClassA extends ClassB implements ClassC,
  ClassD
• extends only one Class but implements multiple
  Interface

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Creating Thread

• Method 1 Extend the Thread class

class Primethread extends Thread long
minPrime PrimeThread(long minPrime)
this.minPrime minPrime public void run()
// compute primes larger than minPrime

PrimeThread p new PrimeThread(143) // create
the thread p.start() // start the thread
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Creating Thread

• Method 2 Implement Runnable and run by a thread

class PrimeRun implements Runnable long
minPrime PrimeRun(long minPrime)
this.minPrime minPrime public void run()
// compute primes larger than minPrime

Thread aThread new Thread(new
PrimeRun(143)) aThread.start()
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Mutual Exclusion

• Java has the keyword synchronized for mutual
  Exclusion
• It is applicable to a class, method and a block
  of code
• Any Java Objects can be used for synchronization
  while the Built-in type(int, fload) cannot

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Mutual Exclusion

• Synchronization on a Block / Statement Level (Use
  object for synchronization)
• Class newThread
• Static Object Lock new Object()
• public someMethod()
• synchronized(Lock)
• // the code that need mutual exclusion
• As Lock is static, so only one instance exists no
  matter how many newThread instance exists
  already. As a result, only one thread can run the
  Lock code concurrently

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Mutual Exclusion

• Synchronization on a Method / Instance Level
• class newThread implements Runnable
• synchronized void someMethod()
• It ensure that only one thread can call an
  objects method at a time
• But if there are two instances of newThread, then
  someMethod() can be executed by two different
  threads concurrently.

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Mutual Exclusion

• Synchronization on a Class Level
• class newThread implements Runnable
• static synchronized void someMethod()
• This one can be applied for any (Threaded) class
  methods

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Java NIO

• Java New IO package java.nio
• New features
• Buffer for data of primitive type.
• Character-set encoders and decoders.
• Channels, a new primitive I/O abstraction.
• A multiplexed, non-blocking I/O facility for
  writing scalable servers.

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Read/Write Through Channel

• Read/Write is done through buffer objects instead
  of input and output streams.
• Send/Receive chars

Charset charset Charset.forName("US-ASCII") Cha
rsetEncoder encoder charset.newEncoder() Charse
tDecoder decoder charset.newDecoder() // write
string sChannel.write(encoder.encode(CharBuffer.wr
ap("Your msg."))) // read string ByteBuffer dbuf
ByteBuffer.allocateDirect(1024) sChannel.read(d
buf) dbuf.flip() String msg
decoder.decode(dbuf).toString()
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Read/Write Through Channel

• Read/Write is done through buffer objects instead
  of input and output streams.
• Send/Receive raw-bytes

// writing raw-bytes // wrap you data in byte
array buf into ByteBuffer object ByteBuffer
buffer ByteBuffer.wrap(buf) sChannel.write(buff
er) // read string ByteBuffer buffer
ByteBuffer.allocateDirect(1024) sChannel.read(buf
fer)
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ServerSocketChannel

• The ServerSocketChannel class is channel-based
  socket listener.
• It performs the same basic task as the familiar
  ServerSocket class.
• To create a ServerSocketChannel that listen on a
  particular port.

ServerSocketChannel ssc ServerSocketChannel.open
() ServerSocket serverSocket
ssc.socket() serverSocket.bind(new
InetSocketAddress(1234))
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SocketChannel

• SocketChannel acts as the client, initiating a
  connection to listening server.
• It is the channel-based counterpart of the Socket
  class.
• To create a SocketChannel that connects to remote
  server

SocketChannel socketChannel SocketChannel.open()
socketChannel.connect(new InetSocketAddress("som
eHost", somePort))
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Non-Blocking I/O

• We can configure the I/O operation of a channel
  to be blocking and non-blocking.
• To configure a channel to be non-blocking

serverSocketChannel.configureBlocking(false) sock
etChannel.configureBlocking(false)
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Introduction

• Another IDE
• Originally for Java
• C, PHP, COBOL, etc. are also supported
• Similar to NetBean
• Written in Java
• Require JVM
• Vast amount of plugins available

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Where to get it?

• Project homepagehttp//www.eclipse.org/
• GUI building requires Visual Editor
  (VE)http//www.eclipse.org/vep/WebContent/main.ph
  pDownload http//download.eclipse.org/tools/ve/d
  ownloads/index.php
• Latest VE support up to Eclipse
  3.2http//archive.eclipse.org/eclipse/downloads/d
  rops/R-3.2.2-200702121330/
• For simplicity, download Eclipse, VE, EMF and GEF
  fromhttp//download.eclipse.org/tools/ve/download
  s/drops/R-1.2.3_jem-200701301117/index.html

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Startup
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Step 1

• New
• Project
• Java Project"

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Console Program - Step 2

• New
• ClassCheck the public static void for
  startup class

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Console Program - Step 3

• Run / Debug
• Java ApplicationSelect (or use the detected)
  class as Main class

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GUI Program - Step 2

• New
• Visual ClassCheck the public static void
  for startup classThis example use JFrame

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GUI Program - Step 3

• Run / Debug
• Java BeanSelect (or use the detected) class as
  Java Bean