Interprocess Communication

Modern operating systems aren't just about running one program at a time. They're designed to run multiple processes simultaneously, and often, these processes need to talk to each other, coordinate tasks, or share data. That’s where Interprocess Communication (IPC) comes into play.

📘 What is IPC?

Interprocess Communication (IPC) is a set of mechanisms that allows processes to exchange data and synchronize their actions while running in parallel on an operating system.

In simple terms, IPC is how independent processes “talk” to each other in a safe and structured way.

Without IPC, processes would operate in isolation, limiting the capabilities of modern multi-process applications like web browsers, databases, and operating systems themselves.

🧠 Why IPC is Needed

• 🔄 Data Sharing: Processes need to share information (e.g., a logging service and the main app).
• ⚙️ Resource Sharing: Devices, files, and memory regions are shared across processes.
• 🧮 Computation Division: Large tasks are split across multiple processes for performance.
• 🛑 Event Notification: One process may notify others about changes or events.
• 🧵 Process Synchronization: Ensures processes don’t conflict when accessing shared data.

🧩 IPC Categories and Mechanisms

Let’s explore the main types of IPC, grouped into categories:

🗃️ 1. Shared Memory

Processes share a portion of memory and communicate by reading/writing to this region.

• Pros: Fast (no system call needed after setup)
• Cons: Requires synchronization (e.g., mutexes or semaphores)
• Examples:
  • POSIX Shared Memory (shm_open)
  • System V Shared Memory (shmget)

🔧 Use Case: High-speed data exchange in scientific computing or graphics pipelines.

💬 2. Message Passing

Processes send messages to each other using the OS as an intermediary.

• Types:
  • Synchronous (blocking)
  • Asynchronous (non-blocking)
  • Direct (send to a specific process)
  • Indirect (via mailboxes/message queues)
• Examples:
  • POSIX Message Queues
  • System V Message Queues
  • MPI (for distributed systems)

🔧 Use Case: Communication between microservices or isolated worker processes.

🔗 3. Pipes and FIFOs

Used to create a unidirectional or bidirectional data stream between processes.

• Unnamed Pipes: Parent-child communication
• Named Pipes (FIFOs): Communication between unrelated processes

🔧 Use Case: Command pipelines in UNIX (ls | grep txt), inter-service data transfer.

🌐 4. Sockets

Used for communication over a network or locally.

• Unix Domain Sockets: Local IPC
• Internet Sockets (TCP/UDP): Remote communication

🔧 Use Case: Web servers, network daemons, database access.

🚨 5. Signals

Asynchronous notifications sent by the OS or another process.

• Used for simple events like termination, pause, or custom-defined actions.
• Example: kill -SIGTERM <pid>

🔧 Use Case: Informing a process to reload configuration or shut down.

🔒 6. Semaphores and Mutexes

Though technically for synchronization, they are essential to control access in IPC, especially with shared memory.

• Binary Semaphores (mutexes): Mutual exclusion
• Counting Semaphores: Control access to a pool of resources

🔧 Use Case: Managing concurrent access to shared memory buffers.

📞 7. Remote Procedure Call (RPC)

One process can invoke a function in another (possibly remote) process as if it were local.

• Examples: gRPC, ONC RPC, D-Bus

🔧 Use Case: Client-server interactions in distributed systems.

🧠 Challenges in IPC

• 🔒 Synchronization issues: Race conditions, deadlocks
• 🚫 Security: Unauthorized access to shared memory or messages
• ⏱️ Latency: Overhead in message delivery (especially over sockets)
• 📐 Design complexity: Choosing the right IPC mechanism for the job