def __init__(self):
"""Create a new DNSCache"""
self.cache = {}
self.rCache = {}
self.callbacks = {}
self.lock = threading.RLock()
self.queue = TimeoutQueue()
self.threads = []
self.nLiveThreads = 0
self.nBusyThreads = 0
self._isShutdown = 0
self.cleanCache()
class DNSCache:
"""Class to cache answers to DNS requests and manager DNS threads."""
## Fields:
# _isShutdown: boolean: are the threads shutting down? (While the
# threads are shutting down, we don't answer any requests.)
# cache: map from name to PENDING or getIP result.
# rCache: map from (family,lowercase IP) to (hostname, time).
# callbacks: map from name to list of callback functions. (See lookup
# for definition of callback.)
# lock: Lock to control access to this class's shared state.
# nBusyThreads: Number of threads that are currently handling requests.
# nLiveThreads: Number of threads that are currently running.
# queue: Instance of TimeoutQueue that holds either names to resolve,
# or instances of None to shutdown threads.
# threads: List of DNSThreads, some of which may be dead.
def __init__(self):
"""Create a new DNSCache"""
self.cache = {}
self.rCache = {}
self.callbacks = {}
self.lock = threading.RLock()
self.queue = TimeoutQueue()
self.threads = []
self.nLiveThreads = 0
self.nBusyThreads = 0
self._isShutdown = 0
self.cleanCache()
def getNonblocking(self, name):
"""Return the cached result for the lookup of name. If we're
waiting for an answer, return PENDING. If there is no cached
result, return None.
"""
try:
self.lock.acquire()
return self.cache.get(name)
finally:
self.lock.release()
def getNameByAddressNonblocking(self, addr, family=None):
"""Given an IP address (and optionally a family), if we have gotten
the address as a result in the past, return the hostname that
most recently resolved to the address, or None if no such hostname
is found."""
if family is None:
if ':' in addr:
family = mixminion.NetUtils.AF_INET6
else:
family = mixminion.NetUtils.AF_INET
try:
self.lock.acquire()
v = self.rCache.get((family,addr.lower()))
if v is None:
return None
else:
return v[0]
finally:
self.lock.release()
def lookup(self,name,cb):
"""Look up the name 'name', and pass the result to the callback
function 'cb' when we're done. The result will be of the
same form as the return value of NetUtils.getIP: either
(Family, Address, Time) or ('NOENT', Reason, Time).
Note: The callback may be invoked from a different thread. Either
this thread or a DNS thread will block until the callback finishes,
so it shouldn't be especially time-consuming.
"""
# Check for a static IP first; no need to resolve that.
v = mixminion.NetUtils.nameIsStaticIP(name)
if v is not None:
cb(name,v)
return
try:
self.lock.acquire()
v = self.cache.get(name)
# If we don't have a cached answer, add cb to self.callbacks
if v is None or v is PENDING:
self.callbacks.setdefault(name, []).append(cb)
# If we aren't looking up the answer, start looking it up.
if v is None:
LOG.trace("DNS cache starting lookup of %r", name)
self._beginLookup(name)
finally:
self.lock.release()
# If we _did_ have an answer, invoke the callback now.
if v is not None and v is not PENDING:
LOG.trace("DNS cache returning cached value %s for %r",
v,name)
cb(name,v)
def shutdown(self, wait=0):
"""Tell all the DNS threads to shut down. If 'wait' is true,
don't wait until all the theads have completed."""
try:
self.lock.acquire()
self._isShutdown = 1
self.queue.clear()
for _ in xrange(self.nLiveThreads*2):
self.queue.put(None)
finally:
self.lock.release()
if wait:
for thr in self.threads:
thr.join()
def cleanCache(self,now=None):
"""Remove all expired entries from the cache."""
if now is None:
now = time.time()
try:
self.lock.acquire()
# Purge old entries from the caches.
cache = self.cache
for name in cache.keys():
v = cache[name]
if v is PENDING: continue
if now-v[2] > MAX_ENTRY_TTL:
del cache[name]
rCache = self.rCache
for name in rCache.keys():
v=rCache[name]
if now-v[1] > MAX_RENTRY_TTL:
del rCache[name]
# Remove dead threads from self.threads.
liveThreads = [ thr for thr in self.threads if thr.isAlive() ]
self.threads = liveThreads
# Make sure we have enough threads.
if len(self.threads) < MIN_THREADS:
for _ in xrange(len(self.threads)-MIN_THREADS):
self.threads.append(DNSThread(self))
self.threads[-1].start()
finally:
self.lock.release()
def _beginLookup(self,name):
"""Helper function: Begin looking up 'name'.
Caller must hold self.lock
"""
self.cache[name] = PENDING
if self._isShutdown:
# If we've shut down the threads, don't queue the request at
# all; it'll stay pending indefinitely.
return
# Queue the request.
self.queue.put(name)
# If there aren't enough idle threads, and if we haven't maxed
# out the threads, start a new one.
if (self.nLiveThreads < self.nBusyThreads + MIN_FREE_THREADS
and self.nLiveThreads < MAX_THREADS):
thread = DNSThread(self)
thread.start()
self.threads.append(thread)
def _lookupDone(self,name,val):
"""Helper function: invoked when we get the answer 'val' for
a lookup of 'name'.
"""
try:
self.lock.acquire()
# Insert the value in the cache.
self.cache[name]=val
# Insert the value in the reverse cache.
if val[0] != 'NOENT':
self.rCache[(val[0], val[1].lower())] = (name.lower(),val[2])
# Get the callbacks for the name, if any.
cbs = self.callbacks.get(name,[])
try:
del self.callbacks[name]
except KeyError:
pass
finally:
self.lock.release()
# Now that we've released the lock, invoke the callbacks.
for cb in cbs:
cb(name,val)
def _adjLiveThreads(self,n):
"""Helper: adjust the number of live threads by n"""
self.lock.acquire()
self.nLiveThreads += n
self.lock.release()
def _adjBusyThreads(self,n):
"""Helper: adjust the number of busy threads by n"""
self.lock.acquire()
self.nBusyThreads += n
self.lock.release()
