The program terminal

The terminal: it shows the text that a program gives as records, and it gives the keys of the person to that program (support/terminal).

The terminal starts no program. The root service starts a program and its terminal, and gives the same terminal ring and text region to the two. The terminal holds a surface, these two memory objects, and a handle that reads the state of the program: it has nothing of the role of the program. The name of the program, the size of the text and what the window shows are values of its context.

Keys: Page Up and Page Down move the view. Each other key goes to the program, and the view returns to the last lines.

Two threads:

the reader It reads the records of the terminal ring and keeps the

lines. It owns the lines: no lock exists.

the drawer The first thread. At the rate of the screen it asks the

reader for a view: the cells of the rows that the window

shows. Then it draws the view. The reader makes the view

between two groups of records: some microseconds.

The surface has two pictures: the compositor never reads

a picture that the drawer changes.

The reader does not wait for a picture, so the program that writes does not wait for a picture. A line that the window does not show costs one copy of its bytes, and no pixel.

The lines that the terminal keeps are in three areas of fixed size: the lines, the runs, the bytes. Each area starts again at its first place when it is full: the oldest lines go.