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What is Unix FIFO?

Published in Operating Systems 2 mins read

A Unix FIFO, or First-In, First-Out (FIFO), is a special type of file that acts as a communication channel between processes. It allows data to be written to one end of the FIFO and read from the other end, ensuring that data is processed in the order it was received.

Here's how FIFOs work:

  • Creation: You create a FIFO using the mkfifo command. This creates a named pipe on the file system.
  • Writing: One process can write data to the FIFO using standard file I/O operations, like write().
  • Reading: Another process can read data from the FIFO using read().
  • Blocking: If a process tries to read from an empty FIFO, it will block until data is available. Similarly, if a process tries to write to a full FIFO, it will block until space is available.

Practical Use Cases:

  • Inter-process communication: FIFOs are useful for passing data between different processes, especially when those processes need to communicate in a specific order.
  • Simple data queues: They can act as simple data queues, where data is processed in the order it arrives.
  • Event notifications: A process can write an event notification to a FIFO, and another process can read the notification and react accordingly.

Example:

# Create a FIFO named "myfifo"
mkfifo myfifo

# Process 1: Writes data to the FIFO
echo "Hello, world!" > myfifo

# Process 2: Reads data from the FIFO
cat myfifo

This example demonstrates how two processes can communicate using a FIFO. Process 1 writes a message to myfifo, and Process 2 reads the message from myfifo.

Key Points:

  • FIFOs are a simple and effective way to implement inter-process communication.
  • They ensure data is processed in the order it was received, making them suitable for applications that require ordered data processing.
  • FIFOs are a fundamental part of the Unix operating system and are widely used in various applications.

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