Week 13 - August 5-9

Introduction

This week we will look at the last method of inter-process communications - shared memory. Shared memory is different from the others stored because it is primarily a hardware-based form of inter-process communications. It is faster than the other methods studied, but it is also the most primitive form of interprocess communication.

We will also have a final exam review.

Videos

Quiz

• Quiz 11 will be on shared memory. Study chapter 48 of The Linux Programming Interface

Final Assessment

• Final Review: see FinalReview.docx.

Lecture Material

• Shared Memory - Chapter 48 of The Linux Programming Interface.

Labs

• Lab 9 - Server with Multiple Clients and a Receive Thread with Mutexing.
• Lab 10 - Semaphores with Shared Memory.
  

Assignment(s)

Assignment 2.

Sample Code

Shared Memory

• Code that demonstrates shared memory via Linux utilities can be found in client.h, client1.cpp and client2.cpp with its Makefile.
• Code that demonstrates shared memory via a memory pool can be found in client.h, client1.cpp and client2.cpp with its Makefile. This will give a segmentation fault. The address of the memory pool of client1 has been passed to client2, therefore it should be possible to read the contents of the memory pool in client2. However, each process has its own virtual address space, so the address passed by client1 will not be the same address when read by client2. THIS DOES NOT WORK.
  Linux has its own shared memory utilities. It is better to use those.
• Code for two processes which send messages to each other via shared memory can be found at: client.h, client1.cpp and client2.cpp with its Makefile.
  The messages passed back and forth between the clients have been taken from the Monty Python skit: The Funniest Joke.
• Code that simulates 16 clients trying to write to a radio with four channels can be found at: client.h, client.cpp, memoryManager.cpp and Makefile.
  The memory map can be seen at: RadioChannelsMemoryMap.docx.
  Scripts for starting and stopping the simulation can be found at: start.sh and stop.sh.
  Each channel uses a part of shared memory. The clients write to one of the channels by writing into the channel's shared memory. The use of semaphores ensures that the number of clients writing to the radio's channels is limited to four.