1. Inter-process Communication
An Overview of
Shared Memory and Messaging

2. Overview Inter-process Communication (IPC) Shared Memory Messaging
Concept
Associated Linux Commands
Messaging
Summary of Concepts

3. Scope of Presentation Impart General Concepts
Assumption Audience has General Programming Knowledge
Present Two of Many IPC Strategies
Recognition of Other IPC Methodologies

4. Overview of IPC
Definition – Ability for processes to share information and resources , as well as provide critical notices of process status to other processes.
Coordination of Processes
Integrity of Data
Protection of Order of Operations
Complex problem solving
Non-linear Problems
Linear Problems

5. Traditional Linear Problem
Problem Solver Process
Processor
Master Process

6. Linear Problem with Answer Caching (using IPC and multiple processors)
Master Process
Problem Solver Process
Processor 1
Processor 2
Potential Problem Answer Cache
Message Queue
Cache Problem Solver Processes
Processor 3

7. Management of IPC Operating System Level Process Level
Two Common Techniques
Shared Memory
Messaging

8. Shared Memory
Allow two or more processes access to the same address space for reading and writing.
What could go wrong!
Process Level Management of Access
Protecting Access with a Semaphore

9. Semaphore
A semaphore is a global memory variable that processes use to manage access to memory and resources.
Analogy: Classroom Speaking Permission Card
No speaking unless card is in Student’s Possession
Student Must Get the Card and Return the Card
Simple Semaphore – Reading and Writing
Complex Semaphore – Bank of Printers

10. Shared Memory Pros and Cons
Good speed once access is granted.
Simple implementation
Cons
Performance degradation as user access requests increase
Limited scalability and applicability to purpose

11. Linux OS: Semaphore Commands (not inclusive)
semget() – Initializes or gains access to a semaphore.
semop() - Performs operations on a semaphore set.
semctl() - Changes permissions and other characteristics of existing semaphore sets.

12. Messaging
Allow processes to communicate via messages that are managed by the OS.
Data Requests
Processing Requests
Process Control Through Message Forwarding
Direct Messaging
Synchronous (ex. Requesting data)
Asynchronous (ex. Print job)
Indirect Messaging
Mailbox Concept
OS Controlled Queue

13. Messaging Pros and Cons
Strong ability to scale solutions and retain performance
Ability to queue requests and allow processes to continue
Flexibility to create complex dependent operations through message redirection
Cons
Complex implementation

14. Linux OS: Messaging Commands (not inclusive)
msgget() - Initializes a new message queue.
msgsnd() – Used to send messages to a message queue.
msgrcv() – Used to receive messages from a message queue.

15. Summary of Concepts Inter-process Communication Shared Memory
Messaging
Customized Operating Systems
Messaging Commands
Semaphore
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Limits of IPC