Demo/threads/find.py

# A parallelized "find(1)" using the thread module.

# This demonstrates the use of a work queue and worker threads.
# It really does do more stats/sec when using multiple threads,
# although the improvement is only about 20-30 percent.
# (That was 8 years ago.  In 2002, on Linux, I can't measure
# a speedup. :-( )

# I'm too lazy to write a command line parser for the full find(1)
# command line syntax, so the predicate it searches for is wired-in,
# see function selector() below.  (It currently searches for files with
# world write permission.)

# Usage: parfind.py [-w nworkers] [directory] ...
# Default nworkers is 4


import sys
import getopt
import time
import os
from stat import *
import _thread as thread


# Work queue class.  Usage:
#   wq = WorkQ()
#   wq.addwork(func, (arg1, arg2, ...)) # one or more calls
#   wq.run(nworkers)
# The work is done when wq.run() completes.
# The function calls executed by the workers may add more work.
# Don't use keyboard interrupts!

class WorkQ:

    # Invariants:

    # - busy and work are only modified when mutex is locked
    # - len(work) is the number of jobs ready to be taken
    # - busy is the number of jobs being done
    # - todo is locked iff there is no work and somebody is busy

    def __init__(self):
        self.mutex = thread.allocate()
        self.todo = thread.allocate()
        self.todo.acquire()
        self.work = []
        self.busy = 0

    def addwork(self, func, args):
        job = (func, args)
        self.mutex.acquire()
        self.work.append(job)
        self.mutex.release()
        if len(self.work) == 1:
            self.todo.release()

    def _getwork(self):
        self.todo.acquire()
        self.mutex.acquire()
        if self.busy == 0 and len(self.work) == 0:
            self.mutex.release()
            self.todo.release()
            return None
        job = self.work[0]
        del self.work[0]
        self.busy = self.busy + 1
        self.mutex.release()
        if len(self.work) > 0:
            self.todo.release()
        return job

    def _donework(self):
        self.mutex.acquire()
        self.busy = self.busy - 1
        if self.busy == 0 and len(self.work) == 0:
            self.todo.release()
        self.mutex.release()

    def _worker(self):
        time.sleep(0.00001)     # Let other threads run
        while 1:
            job = self._getwork()
            if not job:
                break
            func, args = job
            func(*args)
            self._donework()

    def run(self, nworkers):
        if not self.work:
            return # Nothing to do
        for i in range(nworkers-1):
            thread.start_new(self._worker, ())
        self._worker()
        self.todo.acquire()


# Main program

def main():
    nworkers = 4
    opts, args = getopt.getopt(sys.argv[1:], '-w:')
    for opt, arg in opts:
        if opt == '-w':
            nworkers = int(arg)
    if not args:
        args = [os.curdir]

    wq = WorkQ()
    for dir in args:
        wq.addwork(find, (dir, selector, wq))

    t1 = time.time()
    wq.run(nworkers)
    t2 = time.time()

    sys.stderr.write('Total time %r sec.\n' % (t2-t1))


# The predicate -- defines what files we look for.
# Feel free to change this to suit your purpose

def selector(dir, name, fullname, stat):
    # Look for world writable files that are not symlinks
    return (stat[ST_MODE] & 0o002) != 0 and not S_ISLNK(stat[ST_MODE])


# The find procedure -- calls wq.addwork() for subdirectories

def find(dir, pred, wq):
    try:
        names = os.listdir(dir)
    except os.error as msg:
        print(repr(dir), ':', msg)
        return
    for name in names:
        if name not in (os.curdir, os.pardir):
            fullname = os.path.join(dir, name)
            try:
                stat = os.lstat(fullname)
            except os.error as msg:
                print(repr(fullname), ':', msg)
                continue
            if pred(dir, name, fullname, stat):
                print(fullname)
            if S_ISDIR(stat[ST_MODE]):
                if not os.path.ismount(fullname):
                    wq.addwork(find, (fullname, pred, wq))


# Call the main program

main()