Server Software Design Examples Chuan-Ming Liu Computer Science - - PowerPoint PPT Presentation

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Feb 16, 2023 170 likes •420 views

Mobile Computing & Software Engineering Lab Mobile Computing & Software Engineering Lab Server Software Design Examples Chuan-Ming Liu Computer Science and Information Engineering National Taipei University of Technology NTUT,

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Server Software Design Examples

Chuan-Ming Liu Computer Science and Information Engineering National Taipei University of Technology

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Examples

Iterative, Connectionless Server (UDP) Iterative, Connected-Oriented Server (TCP) Concurrent, Connection-Oriented Server (TCP)

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Iterative, Connectionless Server (UDP)

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Creating Passive Socket

To hide the allocation of socket, use

passiveUDP (passiveUDP.c) passiveTCP (passiveTCP.c)

two high-level procedures Both procedures call passivesock() to perform socket allocation – passivesock.c

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Port Privilege

To use well-known services (lower port number), the server process needs special privilege Two servers on a given computer can not use the same port number at the same time How to overcome the port privilege?

Using portbase

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Portbase

Programmer does not need to modify all references to port numbers – safety Solves the problem in general way – generality Solving the possible port conflicts – no conflicts

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Process Structure

server

OS AP

Socket at well-known port used for all communication

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Example

The UDPtimed.c example

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Iterative, Connection-Oriented Server (UDP)

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Creating Passive Socket

Use passiveTCP to allocate a stream socket and bind it to the well-known port Two arguments in passiveTCP:

Name of service Size of the queue for requests

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Why Iterative?

Each request for the time is simple and easy to process Server does not need to optimize for speed

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Process Structure

server

OS AP

Socket for connection requests Socket for an individual connection

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Example

The TCPdaytimed.c example The call to accept blocks the server thread until a connection arrives

When a connection request arrives TCP protocol engages 3-way handshake to establish a connection After completing the handshake, the system allocates a new socket and the call to accept returns The server continues to execute

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Connection Termination

Daytime server can close a connection Usually, the termination is decided by clients Allowing a client to control connection duration can be dangerous because it allows clients to control resource use Avoid vulnerability when designing servers

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Concurrent, Connection- Oriented Servers (TCP)

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Multiple Single-threaded Processes

Recall Algorithm 8.4 OS’s support for concurrent processing Master process for connection requests Slave processes for handling communication with clients Each process contains a single thread

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Echo Service

Echo server responds to each client Alternates between reading and writing Closes the connection when it encounters an end-of-file condition Iterative or concurrent?

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Process Structure

Master

OS Application Processes (or threads)

Socket for connection requests Sockets for individual connections slave1 slave2 slaven

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Example – TCPechod.c

The call to accept blocks the server thread until a connection arrives Note the call to fork(): after the fork()

Master process needs to close the child socket The new child process needs to close the master socket Sockets only disappear in the processes not the system Before system deallocates a socket, all the processes own the socket need to close it

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Exit call

Linux interprets the exit call as a request to terminate the process and uses the argument as a process exit code Conventionally, a process uses exit code zero to denote normal termination

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Errant Processes

Incompletely terminated processes due to the dynamic allocation of processes Linux solves this by sending a signal to the parent whenever a child process exits

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Errant Processes

Existing process remains in a zombie state until the parent executes a wait3 system call Server needs to catch the child termination signal and executes a signal handling function

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Signal

signal(SIGCHLD,reaper) informs the OS

The master process should execute reaper function whenever it receives a signal that a child process has exited

reaper function calls wait3() system call

To complete terminate a child that exits Wait3 blocks until one or more children exit WNOHANG argument specifies that wait3 should not block waiting for a process to exit