openstack/swift
Code Issues Proposed changes

Fixing a possible memcached race condition and refactoring the incr/decr functionality

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This commit is contained in:
David Goetz 2010-10-25 20:42:28 +00:00 committed by Tarmac
commit 6e025c43fe
3 changed files with 64 additions and 35 deletions
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58
swift/common/memcached.py
View File

@ -168,23 +168,42 @@ class MemcacheRing(object):
def incr(self, key, delta=1, timeout=0):
"""
Increments a key which has a numeric value by delta.
If the key can't be found, it's added as delta.
If the key can't be found, it's added as delta or 0 if delta < 0.
If passed a negative number, will use memcached's decr. Returns
the int stored in memcached
Note: The data memcached stores as the result of incr/decr is
an unsigned int. decr's that result in a number below 0 are
stored as 0.
:param key: key
:param delta: amount to add to the value of key (or set as the value
if the key is not found)
if the key is not found) will be cast to an int
:param timeout: ttl in memcache
"""
key = md5hash(key)
command = 'incr'
if delta < 0:
command = 'decr'
delta = str(abs(int(delta)))
for (server, fp, sock) in self._get_conns(key):
try:
sock.sendall('incr %s %s\r\n' % (key, delta))
sock.sendall('%s %s %s\r\n' % (command, key, delta))
line = fp.readline().strip().split()
if line[0].upper() == 'NOT_FOUND':
line[0] = str(delta)
sock.sendall('add %s %d %d %s noreply\r\n%s\r\n' % \
(key, 0, timeout, len(line[0]), line[0]))
ret = int(line[0].strip())
add_val = delta
if command == 'decr':
add_val = '0'
sock.sendall('add %s %d %d %s\r\n%s\r\n' % \
(key, 0, timeout, len(add_val), add_val))
line = fp.readline().strip().split()
if line[0].upper() == 'NOT_STORED':
sock.sendall('%s %s %s\r\n' % (command, key, delta))
line = fp.readline().strip().split()
ret = int(line[0].strip())
else:
ret = int(add_val)
else:
ret = int(line[0].strip())
self._return_conn(server, fp, sock)
return ret
except Exception, e:
@ -192,29 +211,16 @@ class MemcacheRing(object):
def decr(self, key, delta=1, timeout=0):
"""
Decrements a key which has a numeric value by delta.
If the key can't be found, it's added as 0. Memcached
will treat data values below 0 as 0 with incr/decr.
Decrements a key which has a numeric value by delta. Calls incr with
-delta.
:param key: key
:param delta: amount to subtract to the value of key (or set
as the value if the key is not found)
:param delta: amount to subtract to the value of key (or set the
value to 0 if the key is not found) will be cast to
an int
:param timeout: ttl in memcache
"""
key = md5hash(key)
for (server, fp, sock) in self._get_conns(key):
try:
sock.sendall('decr %s %s\r\n' % (key, delta))
line = fp.readline().strip().split()
if line[0].upper() == 'NOT_FOUND':
line[0] = '0'
sock.sendall('add %s %d %d %s noreply\r\n%s\r\n' %
(key, 0, timeout, len(line[0]), line[0]))
ret = int(line[0].strip())
self._return_conn(server, fp, sock)
return ret
except Exception, e:
self._exception_occurred(server, e)
self.incr(key, delta=-delta, timeout=timeout)
def delete(self, key):
"""

13
test/unit/common/middleware/test_ratelimit.py
View File

@ -36,19 +36,14 @@ class FakeMemcache(object):
return True
def incr(self, key, delta=1, timeout=0):
if delta < 0:
raise "Cannot incr by a negative number"
self.store[key] = int(self.store.setdefault(key, 0)) + delta
return int(self.store[key])
def decr(self, key, delta=1, timeout=0):
if delta < 0:
raise "Cannot decr by a negative number"
self.store[key] = int(self.store.setdefault(key, 0)) - delta
self.store[key] = int(self.store.setdefault(key, 0)) + int(delta)
if self.store[key] < 0:
self.store[key] = 0
return int(self.store[key])
def decr(self, key, delta=1, timeout=0):
return self.incr(key, delta=-delta, timeout=timeout)
@contextmanager
def soft_lock(self, key, timeout=0, retries=5):
yield True

28
test/unit/common/test_memcached.py
View File

@ -98,6 +98,17 @@ class MockMemcached(object):
self.outbuf += str(val[2]) + '\r\n'
else:
self.outbuf += 'NOT_FOUND\r\n'
elif parts[0].lower() == 'decr':
if parts[1] in self.cache:
val = list(self.cache[parts[1]])
if int(val[2]) - int(parts[2]) > 0:
val[2] = str(int(val[2]) - int(parts[2]))
else:
val[2] = '0'
self.cache[parts[1]] = val
self.outbuf += str(val[2]) + '\r\n'
else:
self.outbuf += 'NOT_FOUND\r\n'
def readline(self):
if self.down:
raise Exception('mock is down')
@ -151,6 +162,23 @@ class TestMemcached(unittest.TestCase):
self.assertEquals(memcache_client.get('some_key'), '10')
memcache_client.incr('some_key', delta=1)
self.assertEquals(memcache_client.get('some_key'), '11')
memcache_client.incr('some_key', delta=-5)
self.assertEquals(memcache_client.get('some_key'), '6')
memcache_client.incr('some_key', delta=-15)
self.assertEquals(memcache_client.get('some_key'), '0')
def test_decr(self):
memcache_client = memcached.MemcacheRing(['1.2.3.4:11211'])
mock = MockMemcached()
memcache_client._client_cache['1.2.3.4:11211'] = [(mock, mock)] * 2
memcache_client.decr('some_key', delta=5)
self.assertEquals(memcache_client.get('some_key'), '0')
memcache_client.incr('some_key', delta=15)
self.assertEquals(memcache_client.get('some_key'), '15')
memcache_client.decr('some_key', delta=4)
self.assertEquals(memcache_client.get('some_key'), '11')
memcache_client.decr('some_key', delta=15)
self.assertEquals(memcache_client.get('some_key'), '0')
def test_retry(self):
logging.getLogger().addHandler(NullLoggingHandler())