py_tasks_melange: app/django/utils/synch.py@8408741aee63 (annotated)

54 03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	1	"""
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	2	Synchronization primitives:
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	3
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	4	- reader-writer lock (preference to writers)
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	5
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	6	(Contributed to Django by eugene@lazutkin.com)
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	7	"""
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	8
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	9	try:
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	10	import threading
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	11	except ImportError:
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	12	import dummy_threading as threading
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	13
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	14	class RWLock:
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	15	"""
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	16	Classic implementation of reader-writer lock with preference to writers.
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	17
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	18	Readers can access a resource simultaneously.
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	19	Writers get an exclusive access.
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	20
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	21	API is self-descriptive:
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	22	reader_enters()
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	23	reader_leaves()
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	24	writer_enters()
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	25	writer_leaves()
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	26	"""
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	27	def __init__(self):
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	28	self.mutex = threading.RLock()
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	29	self.can_read = threading.Semaphore(0)
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	30	self.can_write = threading.Semaphore(0)
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	31	self.active_readers = 0
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	32	self.active_writers = 0
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	33	self.waiting_readers = 0
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	34	self.waiting_writers = 0
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	35
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	36	def reader_enters(self):
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	37	self.mutex.acquire()
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	38	try:
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	39	if self.active_writers == 0 and self.waiting_writers == 0:
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	40	self.active_readers += 1
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	41	self.can_read.release()
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	42	else:
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	43	self.waiting_readers += 1
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	44	finally:
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	45	self.mutex.release()
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	46	self.can_read.acquire()
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	47
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	48	def reader_leaves(self):
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	49	self.mutex.acquire()
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	50	try:
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	51	self.active_readers -= 1
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	52	if self.active_readers == 0 and self.waiting_writers != 0:
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	53	self.active_writers += 1
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	54	self.waiting_writers -= 1
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	55	self.can_write.release()
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	56	finally:
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	57	self.mutex.release()
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	58
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	59	def writer_enters(self):
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	60	self.mutex.acquire()
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	61	try:
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	62	if self.active_writers == 0 and self.waiting_writers == 0 and self.active_readers == 0:
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	63	self.active_writers += 1
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	64	self.can_write.release()
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	65	else:
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	66	self.waiting_writers += 1
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	67	finally:
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	68	self.mutex.release()
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	69	self.can_write.acquire()
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	70
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	71	def writer_leaves(self):
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	72	self.mutex.acquire()
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	73	try:
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	74	self.active_writers -= 1
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	75	if self.waiting_writers != 0:
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	76	self.active_writers += 1
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	77	self.waiting_writers -= 1
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	78	self.can_write.release()
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	79	elif self.waiting_readers != 0:
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	80	t = self.waiting_readers
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	81	self.waiting_readers = 0
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	82	self.active_readers += t
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	83	while t > 0:
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	84	self.can_read.release()
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	85	t -= 1
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	86	finally:
03e267d67478 Major reorganization of the soc svn repo, to merge into a single App Engine Todd Larsen <tlarsen@google.com> parents: diff changeset	87	self.mutex.release()

author	Madhusudan.C.S <madhusudancs@gmail.com>
	Mon, 24 Aug 2009 04:31:23 +0530
changeset 2787	8408741aee63
parent 54	03e267d67478
permissions	-rw-r--r--