CS208 Introduction to Computer Systems
Friday, 27 February 2026

+ pipes

- pipe.c

- look at the pictures for "ls -a | wc -l"
    - before
    - after fork + fork
    - what we want

- Is it important for child1 to execute before child2?
    - What if child2 goes first?
        mess with file descriptors (so stdin=pipe)
        exec wc -l
        wc tries to read from stdin, but there's nothing there
            so, child2 goes to sleep until there's
            something in the pipe to resolve the "read" operation

- what's in a pipe?
    some kind of buffer for the bytes
        (some kind of circular queue)
    a lock -- so child1 and child2 don't mess up the
        queue by trying to modify it simultaneously