#! /usr/bin/env python

# The following example shows how several build processes can collaborate
# to stop spawning new processes when a special task of type K is executed
# this may be useful for link tasks for example

def options(opt):
	opt.add_option('--loops', action='store', type='int', default=5, help='amount of cpu-intensive loops to perform')

def configure(conf):
	busy = conf.path.find_node('look_busy.py').abspath()
	conf.env.NOT_BUSY = ('%s 0' % busy).split()
	conf.env.VERY_BUSY = ('%s %d' % (busy, conf.options.loops)).split()

def build(bld):
	bld.link_limit = 1
	bld.lockfile = bld.path.parent.make_node('busy_lock.txt').abspath()
	for i in range(2):
		for k in range(5):
			bld(rule='${NOT_BUSY}', always=True)

		bld(rule='${VERY_BUSY}', always=True, exclusive=True)

		for k in range(10):
			bld(rule='${NOT_BUSY}', always=True)

import os, fcntl, threading, errno, time
from waflib import Task

lock = threading.Lock()

def lock_maxjob(self):
	# lock the file, telling other build processes to avoid spawining tasks during that time
	while True:
		try:
			self.lockfd = os.open(self.generator.bld.lockfile, os.O_TRUNC | os.O_CREAT | os.O_RDWR)
			fcntl.flock(self.lockfd, fcntl.LOCK_EX | fcntl.LOCK_NB)
		except EnvironmentError as e:
			if e.errno in (errno.EACCES, errno.EAGAIN):
				time.sleep(0.3)
				continue
			raise
		os.write(self.lockfd, "%d" % os.getpid())
		self.start_time = time.time()
		break

def release_maxjob(self):
	# release the lock file
	print("> long task %d" % (time.time() - self.start_time))
	try:
		os.remove(self.generator.bld.lockfile)
		os.close(self.lockfd)
	except OSError, e:
		# of someone else has removed the lock... bad luck! but do not fail here
		print "unexpected failure", e
		pass

def wait_maxjob(self):
	# wait on the lock file.. up to a certain limit
	while True:
		try:
			ini = os.stat(self.generator.bld.lockfile).st_mtime
		except OSError, e:
			return
		diff = time.time() - ini
		if diff > 300: # stale lock file? wait 5 minutes
			return
		time.sleep(0.5)

# the method process is called by threads...
def process2(self):

	if getattr(self.generator, 'exclusive', False):
		lock.acquire()
		try:
			self.lock_maxjob()
		finally:
			lock.release()
	else:
		self.wait_maxjob()

	ret = self.process_bound_maxjobs()

	if getattr(self.generator, 'exclusive', False):
		lock.acquire()
		try:
			self.release_maxjob()
		finally:
			lock.release()
	return ret

def process(self):
	try:
		process2(self)
	except Exception, e:
		print type(e), e

Task.Task.process_bound_maxjobs = Task.Task.process
Task.Task.process = process
Task.Task.lock_maxjob = lock_maxjob
Task.Task.release_maxjob = release_maxjob
Task.Task.wait_maxjob = wait_maxjob