Podcast
Questions and Answers
What will happen if the first client issues a SEND request for file1 and the second client sends the same request at the same time?
What will happen if the first client issues a SEND request for file1 and the second client sends the same request at the same time?
- Both files will be sent simultaneously.
- The server will append files in order. (correct)
- The server will crash due to a synchronization error.
- The server will ignore the second request.
What error is raised when the first client sends file1 after the second client has already sent a SEND request for the same file?
What error is raised when the first client sends file1 after the second client has already sent a SEND request for the same file?
- ValueError: I/O operation on closed file (correct)
- RuntimeError: Timeout occurred
- TypeError: Invalid file operation
- ValueError: File not found
What is identified as a primary issue with the Multi-Threaded Server's handling of client requests?
What is identified as a primary issue with the Multi-Threaded Server's handling of client requests?
- Slow processing speed of client requests
- Excessive memory usage
- Insufficient bandwidth for file transfers
- Multi-writers on shared data causing conflicts (correct)
Which synchronization problem is highlighted when multiple clients issue SEND requests?
Which synchronization problem is highlighted when multiple clients issue SEND requests?
What approach can be used to ensure that only one thread accesses shared data at a time in Python?
What approach can be used to ensure that only one thread accesses shared data at a time in Python?
What action does the client take when it receives an empty message from the server?
What action does the client take when it receives an empty message from the server?
What is the purpose of the select system call in this chat client implementation?
What is the purpose of the select system call in this chat client implementation?
When a user wants to send a message, which code snippet is executed?
When a user wants to send a message, which code snippet is executed?
What does the sys.stdout.flush() function do in the context of this chat client?
What does the sys.stdout.flush() function do in the context of this chat client?
What should the client do if the server is detected as being down?
What should the client do if the server is detected as being down?
Which of the following statements about the read_sockets list is correct?
Which of the following statements about the read_sockets list is correct?
What happens when the input from the user is processed through sys.stdin.readline()?
What happens when the input from the user is processed through sys.stdin.readline()?
What will the statement 'select.call returned' indicate in the chat client code?
What will the statement 'select.call returned' indicate in the chat client code?
What is the main advantage of using a multi-threaded chat server?
What is the main advantage of using a multi-threaded chat server?
Which transport layer protocol is recommended for the chat room application?
Which transport layer protocol is recommended for the chat room application?
What role does the chat server play in the communication between clients?
What role does the chat server play in the communication between clients?
What functionality is demonstrated when Client-1 and Client-2 are notified about Client-3 joining the chat?
What functionality is demonstrated when Client-1 and Client-2 are notified about Client-3 joining the chat?
In a chat room environment, which of the following statements is true regarding client-server communication?
In a chat room environment, which of the following statements is true regarding client-server communication?
What is one of the key features of a chat room that utilizes a client-server model?
What is one of the key features of a chat room that utilizes a client-server model?
How does the server ensure that all clients are informed when new clients join?
How does the server ensure that all clients are informed when new clients join?
What is one reason for using socket programming in network applications like chat rooms?
What is one reason for using socket programming in network applications like chat rooms?
What is the purpose of acquiring the global lock in a multi-threaded server?
What is the purpose of acquiring the global lock in a multi-threaded server?
What does the method threadLock.acquire()
do in the provided multi-threaded server code?
What does the method threadLock.acquire()
do in the provided multi-threaded server code?
What indicates that the lock has been successfully acquired by a thread?
What indicates that the lock has been successfully acquired by a thread?
What action does the server take if the written_file
is found closed?
What action does the server take if the written_file
is found closed?
What happens after a file is completely received from a client?
What happens after a file is completely received from a client?
How does the multi-threaded server handle concurrent SEND requests from multiple clients?
How does the multi-threaded server handle concurrent SEND requests from multiple clients?
What does the call to recv(1024)
accomplish in the server code?
What does the call to recv(1024)
accomplish in the server code?
What is one of the primary roles of the except
block in the server code?
What is one of the primary roles of the except
block in the server code?
What is the expected behavior if a client sends a file while another client is still connected and sending a file?
What is the expected behavior if a client sends a file while another client is still connected and sending a file?
What does the select system call wait for in the provided chat client?
What does the select system call wait for in the provided chat client?
What happens if the read_sockets list is empty after the select call times out?
What happens if the read_sockets list is empty after the select call times out?
Under what condition does the chat client send an 'is away' message to the server?
Under what condition does the chat client send an 'is away' message to the server?
What does the function socks.recv(4096) accomplish in the code?
What does the function socks.recv(4096) accomplish in the code?
What should the client do if it receives an empty message from the server?
What should the client do if it receives an empty message from the server?
How can the last time the user typed a message be updated in the chat client?
How can the last time the user typed a message be updated in the chat client?
What is the effect of calling sys.stdout.flush() in the chat client?
What is the effect of calling sys.stdout.flush() in the chat client?
Which statement correctly describes the purpose of the timeout_period variable?
Which statement correctly describes the purpose of the timeout_period variable?
What is the outcome if the server sends a message with a length of zero?
What is the outcome if the server sends a message with a length of zero?
What will the chat client print before the select call is made?
What will the chat client print before the select call is made?
What function is responsible for broadcasting messages to all clients except the sender?
What function is responsible for broadcasting messages to all clients except the sender?
What does the server.listen(10)
call do?
What does the server.listen(10)
call do?
In the clientthread
function, what happens when a received message is empty?
In the clientthread
function, what happens when a received message is empty?
Which of the following statements best describes the remove
function?
Which of the following statements best describes the remove
function?
What is the purpose of the conn.send()
method in the client thread?
What is the purpose of the conn.send()
method in the client thread?
What does the command start_new_thread(clientthread, (conn, addr))
accomplish?
What does the command start_new_thread(clientthread, (conn, addr))
accomplish?
What does the line list_of_clients.append(conn)
do?
What does the line list_of_clients.append(conn)
do?
What happens if an exception occurs within the try
block of the broadcast
function?
What happens if an exception occurs within the try
block of the broadcast
function?
What action is taken before a client is added to the list of available clients?
What action is taken before a client is added to the list of available clients?
In what situation would conn.recv(4096)
return an empty message?
In what situation would conn.recv(4096)
return an empty message?
How does the server handle new connections?
How does the server handle new connections?
What type of server architecture is being utilized in this system?
What type of server architecture is being utilized in this system?
What does the server print when a new client connects?
What does the server print when a new client connects?
What should happen after conn.close()
in the main loop?
What should happen after conn.close()
in the main loop?
Flashcards
Multi-Threaded Server Scenario 2
Multi-Threaded Server Scenario 2
Two clients send files sequentially, with each client sending file1 then file2. The server appends all received files in order.
Multi-Threaded Server Scenario 3
Multi-Threaded Server Scenario 3
One client sends a file request but doesn't send the file immediately. Another client completes the file request and sends the file. The server raises a ValueError because it tries to write to a closed file.
Multi-Threaded Server Problem
Multi-Threaded Server Problem
Multiple clients can try to write to the same shared data (files) at the same time, leading to synchronization issues and potential data corruption.
Synchronization Problem
Synchronization Problem
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How to synchronize threads?
How to synchronize threads?
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What is a Chat Room?
What is a Chat Room?
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Why use TCP for a Chat Room?
Why use TCP for a Chat Room?
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How does a Client join a Chat Room?
How does a Client join a Chat Room?
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What is Multi-Threaded Synchronization?
What is Multi-Threaded Synchronization?
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Why is Synchronization needed in a Chat Room?
Why is Synchronization needed in a Chat Room?
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How do we address Synchronization issues?
How do we address Synchronization issues?
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What is a Client-Server model?
What is a Client-Server model?
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Why is the Client-Server model common in Chat Rooms?
Why is the Client-Server model common in Chat Rooms?
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select.select() system call
select.select() system call
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read_sockets in select.select()
read_sockets in select.select()
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write_sockets in select.select()
write_sockets in select.select()
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error_sockets in select.select()
error_sockets in select.select()
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socket.recv(4096)
socket.recv(4096)
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sys.stdin.readline()
sys.stdin.readline()
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socket.send(message)
socket.send(message)
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sys.stdout.write(message)
sys.stdout.write(message)
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Thread Lock
Thread Lock
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Global Variable Access
Global Variable Access
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Acquire Lock
Acquire Lock
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Release Lock
Release Lock
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Race Condition
Race Condition
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File Open Modes
File Open Modes
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Threading Synchronization
Threading Synchronization
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Multi-Threaded Server
Multi-Threaded Server
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Handling Client Requests
Handling Client Requests
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Thread Identifier
Thread Identifier
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Select System Call
Select System Call
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Read Sockets List
Read Sockets List
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User-Away Feature
User-Away Feature
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Time-out Period
Time-out Period
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Standard Input
Standard Input
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Standard Output
Standard Output
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Flush Buffer
Flush Buffer
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Socket Close Operation
Socket Close Operation
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Server Down Detection
Server Down Detection
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Empty Read Sockets
Empty Read Sockets
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What is a TCP Server?
What is a TCP Server?
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What does 'server.bind((IP_address, Port))' do?
What does 'server.bind((IP_address, Port))' do?
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What does 'server.listen(10)' do?
What does 'server.listen(10)' do?
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What is 'list_of_clients'?
What is 'list_of_clients'?
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What is 'clientthread'?
What is 'clientthread'?
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What does 'conn.send("Welcome to Network Programming chatroom!")' do?
What does 'conn.send("Welcome to Network Programming chatroom!")' do?
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How does the server broadcast a message to all clients?
How does the server broadcast a message to all clients?
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What does 'conn.recv(4096)' do?
What does 'conn.recv(4096)' do?
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How does the server handle a connection error?
How does the server handle a connection error?
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What does 'remove(conn)' do?
What does 'remove(conn)' do?
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What does 'conn, addr = server.accept()' do?
What does 'conn, addr = server.accept()' do?
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How does the server handle multiple clients concurrently?
How does the server handle multiple clients concurrently?
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What happens when the server process exits?
What happens when the server process exits?
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How does the server ensure synchronized access to shared resources?
How does the server ensure synchronized access to shared resources?
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Study Notes
Network Programming: Multi-Threaded Synchronization
- Presented by Dr. Ala Altaweel, University of Sharjah, Department of Computer Engineering
- Focuses on application layer, network principles, socket programming (UDP and TCP), single-threaded vs. multi-threaded server architectures, multi-threaded synchronization, web and HTTP, and the Domain Name System (DNS)
Application Layer: Overview
- Covers principles of network applications, socket programming with UDP and TCP
- Discusses single-threaded vs. multi-threaded servers, including multi-threaded server, multi-threaded synchronization, and multi-threaded chat server
- Includes web and HTTP, and the Domain Name System (DNS)
An Enhancement to the Multi-Threaded Server
- Current version of the multi-threaded server only stores one copy of client-sent files, stored as
from_client
- Aims to improve by storing all sent files in one file named
all_received
using a global variable
Multi-Threaded TCP Server
- Demonstrates Python code for a multi-threaded TCP server that appends all received files
- Includes example code for the
Python TCPServer
- Uses a global variable
written_file
to manage the file to append to
Multi-Threaded TCP Server (SEND Command)
- Python code snippet for handling the
SEND
command from a client - Includes checking if the
written_file
is closed and reopening it if necessary - Emphasizes the use of synchronized threads to access the global file safely
Testing the Multi-Threaded Server
- Presents test scenarios (e.g., scenario 1, scenario 2, scenario 3) for evaluating how the server handles client requests
- Outlines how the multi-threaded server is expected to handle such requests and the expected results, particularly focusing on file appending order.
- Highlights potential errors, like
ValueError("I/O operation on closed file")
Problems of Multi-Threaded Servers
- Synchronization problems arise when multiple threads access shared data concurrently.
- Crucial for the server to ensure a client's request receives handling before any other client request.
- Multi-writer and reader-writer (producer-consumer) problems need to be addressed properly
How to Synchronize Threads
- Uses
lock
objects from the threading module to guarantee only one thread accesses the shared data at any given time lock.acquire()
acquires the lock, andlock.release()
releases it- Emphasizes that the lock must have been previously acquired, not necessarily by the same thread
- This method ensures safe access to avoid data corruption by using threads.
Multi-Threaded TCP Server with Synchronization
- Modification of the Python code for
TCPServer
which integrates a synchronization mechanism using thethreading
module. - Emphasizes using the
threading.Lock()
object for mutual exclusive access, avoiding unexpected results
Multi-Threaded Chat Server
- A design for a multi-threaded chat server that allows multiple clients to communicate with each other
- Discusses the client-server model's role in the process
- Key points include clients joining/leaving, clients sending/receiving messages, and maintaining user activity within the system, using sockets, threads, and synchronization primitives
Chat Client with Synchronization
- Demonstrates a Chat Client capable of handling user-away features, implemented using the
select
module to handle multiple input/output (I/O) events concurrently. - Presents scenarios where the client/server is ready to receive/send data and handles the messages via these sockets and I/O operations.
- Provides implementation using the socket module, system calls (e.g.,
recv
,send
,connect
,close
,bind
etc) along with error handling, with select
select Module for Multiple I/O
- Introduced the
select
module for efficient I/O multiplexing - Shows how it monitors various I/O sources (like sockets, files, pipes) until something is ready for reading or writing
- Highlights its use to avoid busy-waiting loops
stdin and stdout and their usage
- Expands on the
stdin
(standard input),stdout
(standard output) related functions from the Pythonsys
module. - Includes example code that shows how to read input form the terminal and print output to the console using
sys.stdin.readlines()
andsys.stdout.write()
for efficient data streams.
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Description
This quiz explores key concepts in network programming, with a focus on multi-threaded synchronization and server architectures. Topics include socket programming with UDP and TCP, as well as web and HTTP principles. Enhance your understanding of how multi-threaded servers function and their applications in network environments.