Interprocess Communication

 

INTERPROCESS COMMUNICATION (IPC) — BRIEF OUTLINE

Interprocess Communication (IPC) refers to mechanisms that allow processes to exchange data and coordinate their execution. In Linux/UNIX systems, several IPC mechanisms exist, each suited for different communication needs.
The three most commonly used IPC mechanisms are:

1. Pipes

Overview

  • Pipes provide a unidirectional communication channel between related processes, typically a parent and child.

  • Data flows in a first-in-first-out (FIFO) manner, similar to a queue.

  • Implemented using the pipe() system call.

  • Acts like an in-memory file used for communication.

Characteristics

  • Half-duplex: data flows in only one direction.

  • Requires a parent-child relation (for unnamed pipes).

  • Uses file descriptors:

    • fd[0] → read end

    • fd[1] → write end

Use Cases

  • Simple data transfer between parent and child processes.

  • Passing small amounts of data such as computation results.

  • Shell pipelines (ls | grep txt).

2. Message Queues

Overview

  • Message queues allow processes to exchange structured messages.

  • Data is stored in the queue until the receiving process reads it.

  • Identified using a key via msgget(), msgsnd(), and msgrcv().

Characteristics

  • Support for asynchronous communication (receiver does not need to wait).

  • Multiple processes can read/write messages.

  • Messages are grouped by message type, allowing selective retrieval.

  • Kernel manages the queue memory.

Advantages

  • Allows communication between unrelated processes.

  • Supports prioritization via message types.

  • Suitable for larger and structured data.

Use Cases

  • Server-client communication.

  • Logging systems.

  • Multi-process applications requiring asynchronous messaging.

3. Shared Memory

Overview

  • Shared memory allows multiple processes to access the same memory region.

  • Fastest IPC mechanism because data is not copied between processes.

  • Created using shmget(), attached using shmat(), and detached with shmdt().

Characteristics

  • Provides bidirectional communication.

  • Requires synchronization mechanisms (semaphores, mutexes) to prevent race conditions.

  • Efficient for large data transfers.

Advantages

  • Maximum speed — processes read/write directly in memory.

  • Ideal for real-time data exchange.

Limitations

  • No built-in synchronization—must use semaphores to avoid concurrent access issues.

  • Memory region persists until explicitly removed.

Use Cases

  • Large data sharing between multiple processes.

  • Producer–consumer implementations.

  • Shared buffers in high-performance applications.

Comparison Summary

FeaturePipesMessage QueuesShared Memory
DirectionUnidirectionalBidirectionalBidirectional
Relation neededRelated (unnamed pipe)Unrelated possibleUnrelated possible
Data StyleStream of bytesStructured messagesRaw memory
SpeedMediumSlow–MediumFastest
SynchronizationNot requiredNot requiredRequired
CapacityLimitedModerately largeVery large

Summary

  • Pipes → simple, parent-child, stream-based communication.

  • Message Queues → asynchronous, structured messages, suitable for multi-process systems.

  • Shared Memory → fastest IPC, used for large data, but needs synchronization.

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