app/django/utils/synch.py
author Lennard de Rijk <ljvderijk@gmail.com>
Sat, 14 Feb 2009 21:18:12 +0000
changeset 1328 cd175dddc15c
parent 54 03e267d67478
permissions -rw-r--r--
Added bulk acceptance and progress bar in review org applications view. In the list of organization applications for reviewing, if you click the button "click here" the whole first text line will fade out and the progress bar will fade in while starting to contact the server for the list of orgs to accept and then make synchronous calls for acceptance, while updating the progress bar, the name of the organization currently accepting and the number of orgs already accepted against the total. Inside the script, what's inside the parenthesis is converted due to regexp (in this case (link_id)) and then read the json_object.applications[index].link_id. By doing this with an eval(), you can use other names as well and the script will be reading for example json_object.applications[index].attribute_name if you insert "(attribute_name)" inside the link returned by {{ bulk_accept_link }}. Notes by Lennard: -Put Done outside the for-loop so that it also shows when there are 0 pre-accepted organizations. -Made some minor style fixes Patch by: Mario Ferraro Reviewed by: Lennard de Rijk

"""
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()