Pipe

🧠 What is a Pipe?

A Pipe is a unidirectional communication channel that allows one process to send data to another by writing into a buffer, which the other process reads from.

Think of it as a one-way tunnel: data goes in one end and comes out the other.

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📦 Key Characteristics

Feature	Description
🔁 Direction	Unidirectional (one writes, one reads)
🧬 Relationship	Typically used between related processes (like parent ↔ child)
💾 Backed By	Kernel buffer (in-memory)
🚦 Synchronization	Automatically blocks reader/writer if the buffer is empty/full
🧠 OS Support	Managed by the kernel (usually uses file descriptors)

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🔍 How It Works

Process A (Writer)     Process B (Reader)
       |                      |
     write() ------------>  read()
          [ Kernel Pipe Buffer ]

• pipe(fd) creates two file descriptors:

  • fd[0] → read end

  • fd[1] → write end

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🛠️ Code Example in C (Parent → Child)

int fd[2];
pipe(fd);
if (fork() == 0) {
    // Child
    close(fd[1]);  // Close write end
    read(fd[0], buffer, sizeof(buffer));
} else {
    // Parent
    close(fd[0]);  // Close read end
    write(fd[1], "Hello", 5);
}

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📚 Types of Pipes

Type	Description
🔒 Anonymous Pipe	Used between related processes (created with pipe())
🧾 Named Pipe (FIFO)	Works between unrelated processes; exists in file system (mkfifo())

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⚠️ Limitations of Pipes

Limitation	Reason
⛔ Unidirectional	You need two pipes for two-way communication
🧬 Related processes only	Anonymous pipes can’t be used between unrelated processes
💽 Buffer size limited	Usually around 64 KB
📥 No message boundaries	It’s a byte stream, not message-structured

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🧠 Real-World Analogy

Imagine two people using a plastic tube — one speaks into it, the other listens.
But they can’t speak at the same time through the same tube — that’s a pipe.

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🧠 Interview-Ready Definition:

A Pipe is a unidirectional IPC mechanism provided by the OS that allows one process to write data into a buffer and another to read from it. It’s commonly used between related processes and operates through file descriptors and kernel-managed buffers.