diff --git a/zipline/component.py b/zipline/component.py
index 7bcd8500..e4af443c 100644
--- a/zipline/component.py
+++ b/zipline/component.py
@@ -503,13 +503,6 @@ class Component(object):
 
         """
         raise NotImplementedError
-        
-    @property
-    def is_blocking(self):
-        """
-        True if a zipline be held open for this component.
-        """
-        return False
 
     @property
     def get_pure(self):
diff --git a/zipline/finance/trading.py b/zipline/finance/trading.py
index cab1051a..97d8cebb 100644
--- a/zipline/finance/trading.py
+++ b/zipline/finance/trading.py
@@ -212,15 +212,6 @@ class OrderDataSource(qmsg.DataSource):
     def get_type(self):
         return zp.DATASOURCE_TYPE.ORDER
         
-    #
-    @property
-    def is_blocking(self):
-        """
-        This datasource is in a loop with the TradingSimulationClient,
-        so we don't want it to block processing.
-        """
-        return True
-        
     def open(self):
         qmsg.DataSource.open(self)
         self.order_socket = self.bind_order()
@@ -243,7 +234,8 @@ class OrderDataSource(qmsg.DataSource):
             # to potentially receive the client's done message before the 
             # controller or heartbeat times out.
             
-            # TODO: shouldn't this block until we receive a message?
+            # this will block for timeout/2, and return an empty dict if there
+            # are no messages.
             socks = dict(self.poll.poll(self.heartbeat_timeout/2))
 
             # see if the poller has results for the result_feed
@@ -294,19 +286,6 @@ class TransactionSimulator(qmsg.BaseTransform):
         elif style == SIMULATION_STYLE.NOOP:
             self.apply_trade_to_open_orders = self.simulate_noop
             
-    #
-    @property
-    def is_blocking(self):
-        """
-        Including this explicitly for clarity, even though we are using the 
-        default value. TransactionSimulator has a defined action for every
-        event type. Downstream components depend on the presence of the 
-        TRANSACTION transform in all cases. When no transaction happens,
-        None is the value. Thus, we do want merging to block on the 
-        availability of transaction messages.
-        """
-        return True
-            
     def transform(self, event):
         """
         Pulls one message from the event feed, then
diff --git a/zipline/messaging.py b/zipline/messaging.py
index b36dea95..03764807 100644
--- a/zipline/messaging.py
+++ b/zipline/messaging.py
@@ -83,13 +83,9 @@ class ComponentHost(Component):
             self.sync_register[component.get_id] = datetime.datetime.utcnow()
 
             if isinstance(component, DataSource):
-                self.feed.add_source(component.get_id, component.is_blocking)
-                if not component.is_blocking:
-                    self.feed.ds_finished_counter +=1 
+                self.feed.add_source(component.get_id)
             if isinstance(component, BaseTransform):
-                self.merge.add_source(component.get_id, component.is_blocking)
-                if not component.is_blocking:
-                    self.feed.ds_finished_counter +=1
+                self.merge.add_source(component.get_id)
                         
     def unregister_component(self, component_id):
         del self.components[component_id]
@@ -199,9 +195,6 @@ class Feed(Component):
         self.sent_counters          = Counter()
         self.recv_counters          = Counter()
         
-        # source_id -> boolean. True is for blocking
-        self.is_blocking_map = {}
-
     def init(self):
         pass
 
@@ -350,9 +343,6 @@ class Feed(Component):
         all un-DONE, blocking sources.
         """
         for source_id, events in self.data_buffer.iteritems():
-            if not self.is_blocking_map[source_id]:
-                continue
-                
             if len(events) == 0:
                 return False
         return True
@@ -367,12 +357,11 @@ class Feed(Component):
             total += len(events)
         return total
 
-    def add_source(self, source_id, is_blocking=True):
+    def add_source(self, source_id):
         """
         Add a data source to the buffer.
         """
         self.data_buffer[source_id] = []
-        self.is_blocking_map[source_id] = is_blocking
 
     def __len__(self):
         """
@@ -478,10 +467,6 @@ class BaseTransform(Component):
     def get_type(self):
         return COMPONENT_TYPE.CONDUIT
 
-    @property
-    def is_blocking(self):
-        return True
-
     def open(self):
         """
         Establishes zmq connections.
@@ -630,10 +615,6 @@ class DataSource(Component):
     @property
     def get_id(self):
         return self.id
-        
-    @property
-    def is_blocking(self):
-        return True
 
     @property
     def get_type(self):