Go class: Walk example

This example builds out a tool to find files that have the same content as determined by a secure hash (ignoring file names, paths, mod dates, etc.).

In each case, we ignore files of length 0 as their hashes would always be a trivial match.

Of course, with the trivial test directory (and/or a small VM in repl.it) it will not be possible to see the real performance gains; you need to run this against a large filesystem.

Each of these four variations becomes progressively faster (although most of the benefit shows in the second program, as reading & hashing the files is the largest part of the work).

Sequential program

walk0.go runs without goroutines and does a sequential file walk.

$ go run ./walk1 test
864c9c6 2
   test/f1.txt
   test/local/f2.txt

Method 1

walk1.go uses a fixed pool of worker goroutines and a sequential file walk to send file paths to the workers.

$ go run ./walk2 test
864c9c6 2
   test/f1.txt
   test/local/f2.txt

Method 2

walk2.go uses a fixed pool of goroutines, but also starts a new file walk goroutine for each directory in the tree.

$ go run ./walk2 test
864c9c6 2
   test/f1.txt
   test/local/f2.txt

Method 3

walk3.go creates a goroutine for each file and directory, but limits the number of goroutines that are allowed to do file system operations (to limit contention).

$ go run ./walk3 test
864c9c6 2
   test/f1.txt
   test/local/f2.txt