app/django/utils/synch.py
author Lennard de Rijk <ljvderijk@gmail.com>
Mon, 16 Feb 2009 20:38:35 +0000
changeset 1364 b2709805fafe
parent 54 03e267d67478
permissions -rw-r--r--
Update org bulk accept script. The script now: 1) leaves correctly control to the browser to update the GUI of the progress bar during ajax communication. 2) Displays an error if something went wrong (I've tried in my box stopping the server while doing the requests), and show a retry button to fetch again the list of the applications that are still not accepted and iterate over them again (seems to recover correctly restarting the server after the error in my box) 3) doesn't display any text at the beginning, and the button has the correct CSS class assigned 4) Check if there are applications to accept, if not displays a message stating that there are no orgs to accept. 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()