stats: added IStatsProducer interface, fixed stats provider startup

this adds an interface, IStatsProducer, defining the get_stats() method
which the stats provider calls upon and registered producer, and made the
register_producer() method check that interface is implemented.

also refine the startup logic, so that the stats provider doesn't try and
connect out to the stats gatherer until after the node declares the tub
'ready'.  this is to address an issue whereby providers would attach to
the gatherer without providing a valid furl, and hence the gatherer would
be unable to determine the tubid of the connected client, leading to lost
samples.

src/allmydata/client.py

@@ -84,8 +84,7 @@ class Client(node.Node, Referenceable, testutil.PollMixin):
     def init_stats_provider(self):
         gatherer_furl = self.get_config('stats_gatherer.furl')
         if gatherer_furl:
-            nickname = self.get_config('nickname')
-            self.stats_provider = StatsProvider(self.tub, nickname, gatherer_furl)
+            self.stats_provider = StatsProvider(self, gatherer_furl)
             self.add_service(self.stats_provider)
         else:
             self.stats_provider = None

src/allmydata/interfaces.py

@@ -1341,3 +1341,10 @@ class RIStatsGatherer(RemoteInterface):
         return None
 
 
+class IStatsProducer(Interface):
+    def get_stats():
+        """
+        returns a dictionary, with str keys representing the names of stats
+        to be monitored, and numeric values.
+        """
+

src/allmydata/stats.py

@@ -14,9 +14,11 @@ import foolscap
 from foolscap.logging.gatherer import get_local_ip_for
 
 from allmydata.util import log
-from allmydata.interfaces import RIStatsProvider, RIStatsGatherer
+from allmydata.interfaces import RIStatsProvider, RIStatsGatherer, IStatsProducer
 
 class LoadMonitor(service.MultiService):
+    implements(IStatsProducer)
+
     loop_interval = 1
     num_samples = 60
 
@@ -65,8 +67,9 @@ class LoadMonitor(service.MultiService):
 class StatsProvider(foolscap.Referenceable, service.MultiService):
     implements(RIStatsProvider)
 
-    def __init__(self, tub, nickname, gatherer_furl):
+    def __init__(self, node, gatherer_furl):
         service.MultiService.__init__(self)
+        self.node = node
         self.gatherer_furl = gatherer_furl
 
         self.counters = {}
@@ -76,15 +79,20 @@ class StatsProvider(foolscap.Referenceable, service.MultiService):
         self.load_monitor.setServiceParent(self)
         self.register_producer(self.load_monitor)
 
-        if tub:
-            tub.connectTo(gatherer_furl, self._connected_to_gatherer, nickname)
+    def startService(self):
+        if self.node:
+            d = self.node.when_tub_ready()
+            def connect(junk):
+                nickname = self.node.get_config('nickname')
+                self.node.tub.connectTo(self.gatherer_furl, self._connected, nickname)
+            d.addCallback(connect)
 
     def count(self, name, delta):
         val = self.counters.setdefault(name, 0)
         self.counters[name] = val + delta
 
     def register_producer(self, stats_producer):
-        self.stats_producers.append(stats_producer)
+        self.stats_producers.append(IStatsProducer(stats_producer))
 
     def remote_get_stats(self):
         stats = {}
@@ -92,7 +100,7 @@ class StatsProvider(foolscap.Referenceable, service.MultiService):
             stats.update(sp.get_stats())
         return { 'counters': self.counters, 'stats': stats }
 
-    def _connected_to_gatherer(self, gatherer, nickname):
+    def _connected(self, gatherer, nickname):
         gatherer.callRemote('provide', self, nickname or '')
 
 class StatsGatherer(foolscap.Referenceable, service.MultiService):

src/allmydata/storage.py

@@ -8,7 +8,7 @@ from twisted.internet import defer
 from zope.interface import implements
 from allmydata.interfaces import RIStorageServer, RIBucketWriter, \
      RIBucketReader, IStorageBucketWriter, IStorageBucketReader, HASH_SIZE, \
-     BadWriteEnablerError
+     BadWriteEnablerError, IStatsProducer
 from allmydata.util import fileutil, idlib, mathutil, log
 from allmydata.util.assertutil import precondition, _assert
 
@@ -666,7 +666,7 @@ def create_mutable_sharefile(filename, my_nodeid, write_enabler, parent):
 
 
 class StorageServer(service.MultiService, Referenceable):
-    implements(RIStorageServer)
+    implements(RIStorageServer, IStatsProducer)
     name = 'storageserver'
 
     def __init__(self, storedir, sizelimit=None, no_storage=False, stats_provider=None):