[RUBY] I understood the very basics of character input

Background

When I touch Vim, some action occurs every time I enter a character, so I was technically interested in how it works, so I tried reading the source code.

Knowledge level

I know that I can input line by line with getc () and gets (), but I don't know how to process each key input.

Expected behavior

I imagined that the simple idea from my own knowledge was to monitor the character input in another thread and notify the main thread when there was a key input.

Look at wincons.rb

I remember writing a Ruby console library called wincons.rb a long time ago that it would end after entering a single character, and I was wondering how this was achieved.

You can get the source from the following. http://texcell.co.jp/ruby/Lib/winconsole.html

Looking at it, it seems that it is realized by calling a function called PeekConsoleInputW of win32api.

http://texcell.co.jp/ruby/PLC/rubyc24.html ↑ Looking at the example here, it seems that the key input check is always performed in the loop and it ends when q comes.

Look at the Vim source code

Is the way wincons.rb really correct? I also had a question, so I decided to take a look at the Vim source code as well.

You can get the source code from github. https://github.com/vim/vim

When I searched for the part where PeekConsoleInputW mentioned earlier was used, I found that it was used in the function read_console_input of src / os_win32.c.

This read_console_input seems to be called from quite a few places, and I didn't know which one was directly connected to keyboard input, so I gave up.

View the readline source code

The readline that comes with ruby calls the completion Proc when you press the TAB key. I guess it must have a process such as calling Proc when the TAB key is pressed.

First, code read the readline that comes with ruby

You can see the source of ruby from the following. https://github.com/ruby/ruby

The source for readline is around ʻext / readline`.

After a lot of research, I found that the function that calls Proc looks like readline_attempted_completion_function. That function is bound to rl_attempted_completion_function.

The rl_attempted_completion_function is not in the ruby code, but in the GNU readline code, so read that.

You can see the source of GNU readline from the following. https://github.com/JuliaLang/readline

It's not exactly the real source of GNU readline, but I don't think it's a problem for this understanding.

The rl_attempted_completion_function is in complete.c, but I couldn't get to that point by going back in the function.

Find out how to use readline

Looking around here, readline looks like a root, so I decided to check it step by step from the root. http://d.hatena.ne.jp/cocoatomo/20071112/1194855728

readline () is located in readline.c. If you follow the function more and more, it seems that kbhit () in rl_gather_tyi () of ʻinput.c` is the key to key input.

What is kbhit ()?

If you look here http://tricky-code.net/mine/c/mc07kbhit.php

The kbhit function returns a non-zero value when any key is pressed, A function that returns 0 if no key is pressed.

It seems that this itself does not determine which key was pressed.

It seems that what is actually taken is to call the read () function in rl_getc (stream) and read one character from the IO passed as an argument.

By turning it around in a loop, it seems that the key input is always checked and checked character by character.

There was no thread.

Summary

readline checks for keystrokes in a loop without using threads.

I use kbhit () to determine if there was a keystroke

To get the characters, use read () to get the characters one by one.

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