Make findNearestUsers() code in soc/logic/site/id_user.py more generic and
move it to soc/logic/model.py. Orginal findNearest...() functions in
id_user.py are now convenience wrappers.
Add typed-query string construction functions to model.py.
Move getFulLClassName() from key_name.py model.py, since it has more to do
with Model types than key names.
Swap 'offset' and 'limit' and make 'limit' arguments non-optional. Also,
stop adding 1 inside the ...ForLimitAndOffset() functions and make the
callers do it (since it was being added for a very UI-specific reason of
whether or not to display a "Next>" link).
Patch by: Todd Larsen
Review by: Pawel Solyga
Review URL: http://codereviews.googleopensourceprograms.com/1401
"""
Synchronization primitives:
- reader-writer lock (preference to writers)
(Contributed to Django by eugene@lazutkin.com)
"""
try:
import threading
except ImportError:
import dummy_threading as threading
class RWLock:
"""
Classic implementation of reader-writer lock with preference to writers.
Readers can access a resource simultaneously.
Writers get an exclusive access.
API is self-descriptive:
reader_enters()
reader_leaves()
writer_enters()
writer_leaves()
"""
def __init__(self):
self.mutex = threading.RLock()
self.can_read = threading.Semaphore(0)
self.can_write = threading.Semaphore(0)
self.active_readers = 0
self.active_writers = 0
self.waiting_readers = 0
self.waiting_writers = 0
def reader_enters(self):
self.mutex.acquire()
try:
if self.active_writers == 0 and self.waiting_writers == 0:
self.active_readers += 1
self.can_read.release()
else:
self.waiting_readers += 1
finally:
self.mutex.release()
self.can_read.acquire()
def reader_leaves(self):
self.mutex.acquire()
try:
self.active_readers -= 1
if self.active_readers == 0 and self.waiting_writers != 0:
self.active_writers += 1
self.waiting_writers -= 1
self.can_write.release()
finally:
self.mutex.release()
def writer_enters(self):
self.mutex.acquire()
try:
if self.active_writers == 0 and self.waiting_writers == 0 and self.active_readers == 0:
self.active_writers += 1
self.can_write.release()
else:
self.waiting_writers += 1
finally:
self.mutex.release()
self.can_write.acquire()
def writer_leaves(self):
self.mutex.acquire()
try:
self.active_writers -= 1
if self.waiting_writers != 0:
self.active_writers += 1
self.waiting_writers -= 1
self.can_write.release()
elif self.waiting_readers != 0:
t = self.waiting_readers
self.waiting_readers = 0
self.active_readers += t
while t > 0:
self.can_read.release()
t -= 1
finally:
self.mutex.release()