1. Overview of the Lab 1 Assignment: Multiplexing Inter-Process Communication
Chris Gill
CSE 522S – Advanced Operating Systems
Washington University in St. Louis
St. Louis, MO 63143

2. CSE 522S – Advanced Operating Systems
Overall Design
Server & clients work to reassemble a file from shuffled fragments
A form of distributed merge sort
Server loads a file listing fragments, then coordinates with clients
Reads in and sends a fragment to each client as soon as that client connects
When all fragments have been sent to clients, stops accepting new connections
Reads back and merges streams of sorted (numbered) lines from clients
Outputs the assembled file
Clients process file fragments
Each client reads in a stream of (numbered) lines from the server
Stores lines then sorts them according to their line numbers
Streams the (numbered) lines back to the server
Server
Client
Client
Client
CSE 522S – Advanced Operating Systems

3. CSE 522S – Advanced Operating Systems
Server Nuances
Server needs to multiplex events within a single thread of execution
Using epoll() or select() or poll() to handle events from multiple sockets concurrently
Dispatching a single call to accept() or read() or write() for each new event
Stores and manage results dynamically
Use malloc and free to support arbitrary numbers of clients, text lengths, numbers of text fragments, etc.
Use dynamic, not static, data structures
Don’t assume fixed sizes/numbers for things that may vary per program inputs
Even with a single thread, work concurrently
Small fragments of text are written/read
Data structures store interim results
Server stays busy (assuming client turnaround is reasonably quick)
Server Event Loop
select()
accept()
write()
read()
CSE 522S – Advanced Operating Systems

4. CSE 522S – Advanced Operating Systems
Client Nuances
Client may be single-threaded without using an event multiplexing loop
Workflow is largely sequential
Stays busy once server starts feeding it data
Stores and manage results dynamically
Use malloc and free to support arbitrary lengths and numbers of text fragments, etc.
Use dynamic, not static, data structures
Don’t assume fixed sizes/numbers for things that may vary per program inputs
Each read or write may send or receive only part of a buffer of data
Need to manage pointers within linked list of text fragments, in order to make sure everything is sent
This issue also affects server code
Client workflow
connect()
while(!done) {
read() }
sort()
write()
close()
CSE 522S – Advanced Operating Systems

5. CSE 522S – Advanced Operating Systems
Lab Write-up
As you work, please record your observations in detail
It’s a good idea to read the entire assignment, and to plan and design a bit before starting to work on it
It’s also a good idea to develop and test incrementally
Run different combinations of file lengths, #s of fragments
Use the file fragmentation program that’s linked from the assignment to generate your own test cases
Write a cohesive report that analyzes, integrates, and offers explanations for what you observed
Document the thinking behind your design
Attribute sources for any code or design ideas you obtained from elsewhere (caveat – only use what you understand, and know to be correct)
Explain not only what you did and what you saw, but also why you did that, and why you think what you saw happened
CSE 522S – Advanced Operating Systems