Add is_featured boolean property to the Work model, so that Works can be
designated as "featured" items in various places in the UI. This will be
used to allow Sponsors, Programs, and Organizations to select Documents that
should be included in their sidebar menus.
Perhaps featured "site" Documents, such as site-wide Terms of Service,
should probably be listed below the "User (sign-out)" menu, since the User
will have to read and agree to these before being allowed to use the site.
A collapsable Javascript sidebar is probably going to be needed soon...
Patch by: Todd Larsen
Review by: to-be-reviewed
"""
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()