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+# A parallelized "find(1)" using the thread module (SGI only for now).
+
+# 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.
+
+# 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
+# group or world write permission.)
+
+# Usage: parfind.py [-w nworkers] [directory] ...
+# Default nworkers is 4, maximum appears to be 8 (on Irix 4.0.2)
+
+
+import sys
+import getopt
+import string
+import time
+import os
+from stat import *
+import 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, job):
+		if not job:
+			raise TypeError, 'cannot add null job'
+		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):
+		while 1:
+			job = self._getwork()
+			if not job:
+				break
+			func, args = job
+			apply(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 = string.atoi(arg)
+	if not args:
+		args = [os.curdir]
+
+	wq = WorkQ()
+	for dir in args:
+		wq.addwork(find, (dir, selector, wq))
+
+	t1 = time.millitimer()
+	wq.run(nworkers)
+	t2 = time.millitimer()
+
+	sys.stderr.write('Total time ' + `t2-t1` + ' msec.\n')
+
+
+# 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 group or world writable files
+	return (stat[ST_MODE] & 0022) != 0
+
+
+# The find procedure -- calls wq.addwork() for subdirectories
+
+def find(dir, pred, wq):
+	try:
+		names = os.listdir(dir)
+	except os.error, msg:
+		print `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, msg:
+				print `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()