#!/usr/bin/env python3

from glob import glob
from os import lstat,mkdir
from random import randint
from os.path import isdir,exists
from pathlib import Path
from time import sleep
from subprocess import run
from multiprocessing import Pool

def drop_caches():
    with open('/proc/sys/vm/drop_caches','w') as f:
        f.write('3')

def enable_bfq():
    with open('/sys/block/sda/queue/scheduler','w') as f:
        f.write('bfq')

def sync():
    run(('sync'))

def prepare_tree(name):
    def populate(dir, depth=6):
        if not depth:
            return
        for fname in range(1,20):
            if randint(0,100) > 80:
                dirname = "{}{}/".format(dir,fname)
                mkdir(dirname)
                populate(dirname, depth - 1)
                continue
            fname = "{}{}".format(dir, fname)
            Path(fname).touch(exist_ok=True)
            
    if not isdir(name):
        mkdir(name)
    if not name.endswith('/'):
        name = '{}/'.format(name)
    populate(name)
    
        

def traverse(dir):
    drop_caches()
    for inode in glob("{}/*".format(dir)):
        if isdir(inode):
            traverse(inode)
        else:
            lstat(inode)
            if randint(0,10) > 6:
                sleep(0)

def main():
    nproc = 16
    dirname = 'testdir'
    if not exists(dirname):
        prepare_tree(dirname)
    sync()
    drop_caches()
    enable_bfq()
    drop_caches()

    with Pool(nproc) as pool:
        dirs = (dirname,) * nproc
        pool.map(traverse,dirs)
            
main()