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https://github.com/clementvidon/multipipe_tutor
C multi-pipe implementation, dissection and explanation.
https://github.com/clementvidon/multipipe_tutor
42 42born2code 42cursus 42network 42paris 42projects 42school interprocess-communication microshell minishell multiprocessing pipe pipex pipex-42 pipex42 tutorial
Last synced: 8 days ago
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C multi-pipe implementation, dissection and explanation.
- Host: GitHub
- URL: https://github.com/clementvidon/multipipe_tutor
- Owner: clementvidon
- Created: 2022-12-14T17:05:45.000Z (almost 2 years ago)
- Default Branch: main
- Last Pushed: 2022-12-21T20:16:22.000Z (almost 2 years ago)
- Last Synced: 2024-10-09T08:08:00.495Z (about 1 month ago)
- Topics: 42, 42born2code, 42cursus, 42network, 42paris, 42projects, 42school, interprocess-communication, microshell, minishell, multiprocessing, pipe, pipex, pipex-42, pipex42, tutorial
- Language: C
- Homepage: https://clemedon.github.io/Multipipe_tutor/
- Size: 54.7 KB
- Stars: 28
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
Awesome Lists containing this project
README
Multipipe_tutor
Summary
·
Pipe
·
Multipipe
·
Sources
·
Contact
# Summary
This small project aims to guarantee me a quick and clear reunderstanding of my
implementation of the multi-pipe when the notion will be as rusty as a distant
memory the day I need it.
For this purpose we will **dissect** the `prg1 | prg2 | prg3` **command execution**
using a [**C multi-pipe implementation**](https://github.com/clemedon/Multipipe_tutor/tree/main/src).
*For reasons of readability the code does not include the protections.*
[**→ GitHub Page ←**](https://clemedon.github.io/Multipipe_tutor/)
[**→ GitHub Repo ←**](https://github.com/clemedon/Multipipe_tutor/)
# Pipe
- A pipe is a **unidirectional** data channel that can be used for **interprocess
communication**.
- It is made of **two descriptors**: `pipefd[0]` that refers to the **read end** of
the pipe and `pipefd[1]` that refers to the **write end** of the pipe.
- **Data written to the write end of the pipe is buffered** by the kernel until it
is read from the read end of the pipe.
```
Fig.0 Interprocess communication with a single pipe.
₍₂₎
IN→ 1=====xxxx0
⁽³⁾↓
⁽¹⁾ 1xxxx=====0 →OUT
(0) The main process (futur parent) creates a pipe and forks itself which
duplicates its pipe's set of file descriptors pipefd[1] and pipefd[0] into the
newly created (child) process.
(1) The parent process closes its pipefd[1] to prevent its process from writing
in the pipe.
(2) Simultaneously, the child process closes its pipefd[0] to prevent its
process from reading in the pipe.
(3) In the end we have a parent that can read and a child that can write, both
sharing the same pipe. If the child write in the pipe, the data stream will
find its way out in the read end of the parent process ⇒ interprocess
communication.
```
# Multipipe
- Alternating several pipes and processes we can create an interprocess
communication chain, **passing the output of one program as the input of
another program** and so on.
```
Fig.1 Overall idea of following multi-pipe example.
Stdin → PRG1 PRG2 PRG3 → Stdout
* [**Illustrations**](#illustrations)
### Instructions
```
main()
- initialize prevpipe to any valid file descriptor.
- start the while loop that iterate over each of the 3 commands (PRG).
PRG1 in ft_pipe()
- create a pipe P1[2] Size 2 array that contains P1[0] and P1[1]
- fork itself Which clones P1
Child
- close P1[0] Unused
- redirect Stdout to P1[1] Fill the pipe with PRG1 output
- close P1[1] Not needed anymore
- redirect Stdin to prevpipe Here Stdin (cf. prevpipe init)
- close prevpipe Not needed anymore
- exec
Parent
- close P1[1] Unused
- prevpipe = P1[0] Save prevpipe for PRG2 Stdin
PRG2 in ft_pipe()
- create a pipe P2[2] Size 2 array that contains P2[0] and P2[1]
- fork itself Which clones P2
Child
- close P2[0] Unused
- redirect Stdout to P2[1] Fill the pipe with PRG2 output
- close P2[1] Not needed anymore
- redirect Stdin to prevpipe Here P1[0] (the previous P[0])
- close prevpipe Not needed anymore
- exec
Parent
- close P2[1] Unused
- prevpipe = P2[0] Save prevpipe for PRG3 Stdin
PRG3 in ft_last()
- fork itself
Child
- redirect Stdin to prevpipe Here P2[0] (the previous P[0])
- close prevpipe Not needed anymore
- exec
Parent
- close prevpipe Unused
- wait for children
```
[**Return to Index ↑**](#example)
### Illustrations
The path taken by the **stream of data** during the whole execution is paved by
the **`(A)`** to **`(J)`** symbols.
```
PRG1 in ft_pipe()
P1 in the child process.
P1[1] P1[0]
―――――――――――――――――――――
(A) Stdin → PRG1 → OPEN → (B) CLOSED
―――――――――――――――――――――
P1 in the parent process.
P1[1] P1[0]
―――――――――――――――――――――
CLOSED (C) → OPEN → prevpipe (D)
―――――――――――――――――――――
PRG2 in ft_pipe()
P2 in the child process.
P2[1] P2[0]
―――――――――――――――――――――
(E) prevpipe → PRG2 → OPEN → (F) CLOSED
―――――――――――――――――――――
P2 in the parent process.
P2[1] P2[0]
―――――――――――――――――――――
CLOSED (G) → OPEN → prevpipe (H)
―――――――――――――――――――――
PRG3 in ft_last()
Last program execution.
(I) prevpipe → PRG3 → Stdout (J)
```
[**Return to Index ↑**](#example)
# Sources
- **`$ man 2 pipe`**
- [**GPT Chat**](https://chat.openai.com/chat)
# Contact
```
cvidon 42
clemedon icloud
```
Copyright 2022 Clément Vidon. All Rights Reserved.