def test_multiple_readers(self):
"""Test non-exclusive access to readers"""
rw_lock = RWLock()
rw_buffer = ['A']
threads = [Reader(rw_lock, rw_buffer, 0, 0.05),
Reader(rw_lock, rw_buffer, 0.01, 0),
Writer(rw_lock, rw_buffer, 0.02, 0.02, 'Z'),
Reader(rw_lock, rw_buffer, 0.03, 0)]
for th in threads:
th.start()
for th in threads:
th.join()
self.assertEqual(rw_buffer, ['Z'])
self.assertEqual(threads[0].rdata, ['A'])
self.assertEqual(threads[1].rdata, ['A'])
self.assertEqual(threads[3].rdata, ['Z'])
# Second reader started after the first one finishing
# before it. This means there is no mutual exclusion
# between readers.
self.assertLess(threads[0].entry_time, threads[1].entry_time)
self.assertGreater(threads[0].exit_time, threads[1].exit_time)
def test_exclusion_writers(self):
"""Test if only one writer can access the resource at the same time"""
rw_lock = RWLock()
rw_buffer = ['A']
threads = [Reader(rw_lock, rw_buffer, 0, 0.02),
Writer(rw_lock, rw_buffer, 0.02, 0.03, 'Z'),
Writer(rw_lock, rw_buffer, 0.03, 0, 'X'),
Reader(rw_lock, rw_buffer, 0.04, 0)]
for th in threads:
th.start()
for th in threads:
th.join()
self.assertEqual(rw_buffer, ['X'])
self.assertEqual(threads[0].rdata, ['A'])
self.assertEqual(threads[3].rdata, ['X'])
# First writting lasts more than the time that the second
# writer needs to access the critical section. But, the
# second writer will wait till the first writer ends its work.
self.assertLess(threads[1].entry_time, threads[2].entry_time)
self.assertLess(threads[1].exit_time, threads[2].exit_time)
# The last thread (a reader) will wait till the last writer ends.
self.assertLess(threads[2].entry_time, threads[3].entry_time)
self.assertLess(threads[2].exit_time, threads[3].exit_time)