On 6-Jul-07, at 6:45 AM, Yaakov Nemoy wrote:

>

I don't know how it is done in general, but for reference, here are
some of the unittests for my read/write lock class:

 def testReadCount(self):
     wrlock = ReadWriteLock()
     read, write = wrlock.reader, wrlock.writer

     self.assertEqual(wrlock.readerCount, 0)
     read.acquire()
     self.assertEqual(wrlock.readerCount, 1)
     read.acquire()
     self.assertEqual(wrlock.readerCount, 2)
     read.release()
     self.assertEqual(wrlock.readerCount, 1)
     read.release()
     self.assertEqual(wrlock.readerCount, 0)

 def testContention(self):
     wrlock = ReadWriteLock()
     read, write = wrlock.reader, wrlock.writer

     class Writer(Thread):
         gotit = False
         def run(self):
             write.acquire()
             self.gotit = True
             write.release()
     writer = Writer()

     self.assertEqual(wrlock.readerCount, 0)
     read.acquire()
     self.assertEqual(wrlock.readerCount, 1)
     writer.start()
     self.assertFalse(writer.gotit)

     read.acquire()
     self.assertEqual(wrlock.readerCount, 2)
     self.assertFalse(writer.gotit)

     read.release()
     self.assertEqual(wrlock.readerCount, 1)
     self.assertFalse(writer.gotit)

     read.release()
     self.assertEqual(wrlock.readerCount, 0)
     time.sleep(.1)
     self.assertTrue(writer.gotit)

 def testWRAcquire(self):
     wrlock = ReadWriteLock()
     read, write = wrlock.reader, wrlock.writer

     self.assertEqual(wrlock.readerCount, 0)
     write.acquire()
     write.acquire()
     write.release()
     write.release()

     read.acquire()
     self.assertEqual(wrlock.readerCount, 1)
     read.acquire()
     self.assertEqual(wrlock.readerCount, 2)
     read.release()
     self.assertEqual(wrlock.readerCount, 1)
     read.release()
     self.assertEqual(wrlock.readerCount, 0)
     write.acquire()
     write.release()

 def testOwnAcquire(self):
     wrlock = ReadWriteLock()
     read, write = wrlock.reader, wrlock.writer

     class Writer(Thread):
         gotit = False
         def run(self):
             write.acquire()
             self.gotit = True
             write.release()
     writer = Writer()

     self.assertEqual(wrlock.readerCount, 0)
     read.acquire()
     self.assertEqual(wrlock.readerCount, 1)
     writer.start()
     self.assertFalse(writer.gotit)

     # can acquire the write lock if only
     # this thread has the read lock
     write.acquire()
     write.release()

     read.acquire()
     self.assertEqual(wrlock.readerCount, 2)
     self.assertFalse(writer.gotit)

     read.release()
     self.assertEqual(wrlock.readerCount, 1)
     self.assertFalse(writer.gotit)

     read.release()
     self.assertEqual(wrlock.readerCount, 0)
     time.sleep(.1)
     self.assertTrue(writer.gotit)


 def testDeadlock(self):
     wrlock = ReadWriteLock()
     read, write = wrlock.reader, wrlock.writer

     errors = []

     # a situation which can readily deadlock if care isn't taken
     class LockThread(threading.Thread):
         def __init__(self):
             threading.Thread.__init__(self)
             self.q = Queue.Queue()
         def run(self):
             while True:
                 task, lock, delay = self.q.get()
                 if not task:
                     break
                 time.sleep(delay)
                 if task == 'acquire':
                     for delay in waittime(maxTime=5.0):
                         if lock.acquire(False):
                             break
                         time.sleep(delay)
                     else:
                         errors.append("Couldn't acquire %s" % str 

(lock)) else: lock.release()

     thrd = LockThread()
     thrd.start()

     thrd.q.put(('acquire', read, 0))
     time.sleep(.2)
     read.acquire()
     thrd.q.put(('acquire', write, 0))
     thrd.q.put(('release', write, .5))
     thrd.q.put(('release', read, 0))
     write.acquire()
     time.sleep(0.0)
     write.release()
     read.release()

     # end
     thrd.q.put((None, None, None))
     thrd.join()

     self.assertFalse(errors, "Errors: %s" % errors)