IEG4180 Tutorial 6 Overlapping IO Project 3 Discussion

1
IEG4180 Tutorial 6 Overlapping I/O Project 3
Discussion

• Bosco, Fong Chi Hang

(Acknowledgement some materials in this tutorial
are adopted from previous works by Shing and
Zero.)
2
Outline

• Traditional Blocking I/O Overlapped I/O
• Event Object Signaling
• Alertable I/O

3
Overlapped I/O

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

4
Overlapped I/O Create Overlapped Socket

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

5
Overlapped I/O Send Receive Data

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

6
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)

7
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!!!

8
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
9
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

10
Overlapped I/O The Model - Use of Event Object
Need to Figure Out which Buffer is Being Filled
(or Returned)
11
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)
12
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)
13
Overlapped I/O Alertable I/O
Move Data Processing to the Completion Routine
14
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

15
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 / )
16
Project 3 Overview

• Project 3 is divided into three parts.
• Web Console NetProbe Server
• SuperNetProbe
• JavaNetProbe

17
Web Console NetProbe Server

• Extend the NetProbe Server in Project 2
• Web-UI open a new TCP port to accept HTTP
  request from a web browser (Not necessary to use
  select-based I/O for this port)
• Use web browser to connect to the NetProbe
  Server, returning a webpage(a form) for user to
  configure
• Maximum number of connections
• Start/Stop the Server in receiving Clients
  connections
• Killing a particular client connection
• Another page (with AJAX) to show
• Number of concurrent transmissions
• Statistics of each connection

18
SuperNetProbe JavaNetProbe

• SuperNetProbe
• Threading (Project 2)
• Message-Driven I/O (Project 2)
• Alertable overlapped I/O
• JavaNetProbe (with GUI)
• Threading
• New I/O

19
HTTP Request

• Browser normally analyze the URL in
• If no port given, browser normally determines the
  port number by protocol
• And send (suppose HTTP is used) the following to
  host at port

protocol//hostport/path
GET /path HTTP/version supported
20
HTTP Response

• The server then responds
• Status

HTTP/1.0 200 OK Date Fri, 31 Dec 1999 235959
GMT Content-Type text/html Content-Length 1354
lthtmlgt ltbodygt lt/bodygt lt/htmlgt
200 OK The request succeeded, and the resulting
resource (e.g. file or script output) is returned
in the message body.
21
Introduction

• AJAX Asynchronous JavaScript and XML
• Mainly based on
• HTML (DOM)
• JavaScript
• XML
• Goods
• Smoother experience
• No need to refresh the whole page
• Asynchronize request
• Rich Internet Application
• Reference
• http//www.w3schools.com

22
Idea

• On specific event (e.g. onload, onClick,)
• Create XMLHttpRequest object
• Use XMLHttpRequest to submit further requests
• Handle the response when necessary

23
Example
24
Project Code