Lecture 5 Nonblocking I/O and Multiplexing Erick Pranata © Sekolah Tinggi Teknik Surabaya 1.

Presentasi berjudul: "Lecture 5 Nonblocking I/O and Multiplexing Erick Pranata © Sekolah Tinggi Teknik Surabaya 1."— Transcript presentasi:

1 Lecture 5 Nonblocking I/O and Multiplexing Erick Pranata © Sekolah Tinggi Teknik Surabaya 1

2 2

3 » Socket I/O calls may block for several reasons ˃Data Input (if data not available) +Read() +Receive() +ReceiveFrom() ˃Data Output (if no sufficient space) +Write() +Send() +SendTo() ˃Listener (until connection established) +Accept() +AcceptSocket() +AcceptTcpClient() 3 © Sekolah Tinggi Teknik Surabaya

4 » Problems in connection establishment ˃Long round-trip times ˃High error rate connections ˃Slow (or deceased) server » Blocking method call halts the execution of application » Solution: ˃I/O Status Prechecking ˃Blocking Calls with Timeout ˃Nonblocking Sockets 4 © Sekolah Tinggi Teknik Surabaya

5 5

6 » Avoid calls that will block » Precheck I/O Status ˃Will I/O block? 6 © Sekolah Tinggi Teknik Surabaya

7 7

8 8

9 9

10 10 © Sekolah Tinggi Teknik Surabaya

11 11 © Sekolah Tinggi Teknik Surabaya

12 » Poll() method ˃Takes two options: +An integer number of microseconds – May be negative to wait indefinitely – May be zero to be used as prechecking +Mode of operation – SelectRead – SelectWrite – SelectError ˃Returns true for pending operations, ready to be processed 12 © Sekolah Tinggi Teknik Surabaya

13 13 © Sekolah Tinggi Teknik Surabaya

14 » Polling is considered very inefficient » Sometimes called busy waiting » Solution: ˃Multiplexing ˃Threads ˃Asynchronous I/O 14 © Sekolah Tinggi Teknik Surabaya

15 » Some issues ˃Write() and Send() call blocks until last byte is written into buffer ˃Socket connection establishment will block until +Connection established +Connection refused +System-imposed timeout occurs 15 © Sekolah Tinggi Teknik Surabaya

16 » Example Example 16 © Sekolah Tinggi Teknik Surabaya

17 » Change behavior of the socket into nonblocking ˃If requested operation can be completed immediately, the calls’ return will succeed ˃ If not, it throws a SocketException with ErrorCode 10035 +Catch the error, then continue… » Blocking property in Socket class » Also categorized as busy waiting technique 17 © Sekolah Tinggi Teknik Surabaya

18 » Example Example 18 © Sekolah Tinggi Teknik Surabaya

19 19

20 » I/O on multiple channels simultaneously » Example: echo service on several ports ˃Socket binds to a port ˃ At Accept(), which socket to choose? ˃ Accept() or Receive() may block +Use nonblocking sockets? 20 © Sekolah Tinggi Teknik Surabaya

21 » Socket.Select() method ˃Behavior +Specify a list of sockets to check for pending I/O +Suspends the program until one or more of the sockets in the list becomes ready to perform I/O +The list is modified to only include those Socket instances that are ready ˃Parameters +The first three: list of sockets +The fourth: time in microseconds 21 © Sekolah Tinggi Teknik Surabaya

22 » Example Example 22 © Sekolah Tinggi Teknik Surabaya

23 » David Makofske, Michael J. Donahoo, Kenneth L. Calvert, TCP/IP Sockets in C#: Practical Guide for Programmers, Morgan Kaufmann, 2004 23 © Sekolah Tinggi Teknik Surabaya