diff --git a/ptvsd/messaging.py b/ptvsd/messaging.py
index 77835d6f..2ae91c11 100644
--- a/ptvsd/messaging.py
+++ b/ptvsd/messaging.py
@@ -125,12 +125,89 @@ class JsonIOStream(object):
         self._writer.write(body)
 
 
+class Request(object):
+    """Represents an incoming or an outgoing request.
+
+    Incoming requests are represented by instances of this class.
+
+    Outgoing requests are represented by instances of OutgoingRequest, which
+    provides additional functionality to handle responses.
+    """
+
+    def __init__(self, channel, seq, command, arguments):
+        self.channel = channel
+        self.seq = seq
+        self.command = command
+        self.arguments = arguments
+
+
+class OutgoingRequest(Request):
+    """Represents an outgoing request, for which it is possible to wait for a
+    response to be received, and register a response callback.
+    """
+
+    def __init__(self, *args):
+        super(OutgoingRequest, self).__init__(*args)
+        self.response = None
+        self._lock = threading.Lock()
+        self._got_response = threading.Event()
+        self._callback = lambda _: None
+
+    def _handle_response(self, seq, command, body):
+        assert self.response is None
+        with self._lock:
+            response = Response(self.channel, seq, self, body)
+            self.response = response
+            callback = self._callback
+        callback(response)
+        self._got_response.set()
+
+    def wait_for_response(self, raise_if_failed=True):
+        """Waits until a response is received for this request, records that
+        response as a new Response object accessible via self.response, and
+        returns self.response.body.
+
+        If raise_if_failed is True, and the received response does not indicate
+        success, raises RequestFailure. Otherwise, self.response.body has to be
+        inspected to determine whether the request failed or succeeded.
+        """
+
+        self._got_response.wait()
+        if raise_if_failed and not self.response.success:
+            raise self.response.body
+        return self.response.body
+
+    def on_response(self, callback):
+        """Registers a callback to invoke when a response is received for this
+        request. If response was already received, invokes callback immediately.
+        Callback is invoked with Response as the sole arugment.
+
+        To get access to the entire Response object in the callback, the callback
+        should be a lambda capturing the request on which on_response was called.
+        Then, request.response can be inspected inside the callback.
+
+        The callback is invoked on an unspecified background thread that performs
+        processing of incoming messages; therefore, no further message processing
+        occurs until the callback returns.
+        """
+
+        with self._lock:
+            response = self.response
+            if response is None:
+                self._callback = callback
+                return
+        callback(response)
+
+
 class Response(object):
     """Represents a response to a Request.
     """
 
-    def __init__(self, request, body):
-        self.request = None
+    def __init__(self, channel, seq, request, body):
+        self.channel = channel
+        self.seq = seq
+
+        self.request = request
         """Request object that this is a response to.
         """
 
@@ -150,13 +227,16 @@ class Response(object):
     def success(self):
         return not isinstance(self.body, Exception)
 
-    def __eq__(self, other):
-        if not isinstance(other, Response):
-            return NotImplemented
-        return self.request is other.request and self.body == other.body
 
-    def __ne__(self, other):
-        return not self == other
+class Event(object):
+    """Represents a received event.
+    """
+
+    def __init__(self, channel, seq, event, body):
+        self.channel = channel
+        self.seq = seq
+        self.event = event
+        self.body = body
 
 
 class RequestFailure(Exception):
@@ -164,71 +244,18 @@ class RequestFailure(Exception):
         self.message = message
 
     def __eq__(self, other):
-        if isinstance(other, RequestFailure) and other.message == self.message:
-            return True
-        return NotImplemented
+        if not isinstance(other, RequestFailure):
+            return NotImplemented
+        return self.message == other.message
 
     def __ne__(self, other):
         return not self == other
 
+    def __repr__(self):
+        return 'RequestFailure(%r)' % self.message
 
-class Request(object):
-    """Represents a request that was sent to the other party, and is awaiting or has
-    already received a response.
-    """
-
-    def __init__(self, channel, seq, command, arguments):
-        self.channel = channel
-        self.seq = seq
-        self.command = command
-        self.arguments = arguments
-
-        self.response = None
-        self._lock = threading.Lock()
-        self._got_response = threading.Event()
-        self._callback = lambda _: None
-
-    def _handle_response(self, command, body):
-        assert self.response is None
-        with self._lock:
-            response = Response(self, body)
-            self.response = response
-            callback = self._callback
-        callback(response.body)
-        self._got_response.set()
-
-    def wait_for_response(self, raise_if_failed=True):
-        """Waits until a response is received for this request, records that
-        response as a new Response object accessible via self.response,
-        and returns self.response.body.
-
-        If raise_if_failed is True, and the received response does not indicate
-        success, raises RequestFailure. Otherwise, self.response.success has to
-        be inspected to determine whether the request failed or succeeded, since
-        self.response.body can be None in either case.
-        """
-
-        self._got_response.wait()
-        if raise_if_failed and not self.response.success:
-            raise self.response.body
-        return self.response.body
-
-    def on_response(self, callback):
-        """Registers a callback to invoke when a response is received for this
-        request. If response was already received, invokes callback immediately.
-        Callback is invoked with Response object as the sole argument.
-
-        The callback is invoked on an unspecified background thread that performs
-        processing of incoming messages; therefore, no further message processing
-        occurs until the callback returns.
-        """
-
-        with self._lock:
-            response = self.response
-            if response is None:
-                self._callback = callback
-                return
-        callback(response.body)
+    def __str__(self):
+        return self.message
 
 
 class JsonMessageChannel(object):
@@ -277,7 +304,7 @@ class JsonMessageChannel(object):
         if arguments is not None:
             d['arguments'] = arguments
         with self._send_message('request', d) as seq:
-            request = Request(self, seq, command, arguments)
+            request = OutgoingRequest(self, seq, command, arguments)
             self._requests[seq] = request
         return request
 
@@ -327,34 +354,32 @@ class JsonMessageChannel(object):
 
     def on_request(self, seq, command, arguments):
         handler_name = '%s_request' % command
-        specific_handler = getattr(self._handlers, handler_name, None)
-        if specific_handler is not None:
-            handler = lambda: specific_handler(self, arguments)
-        else:
+        handler = getattr(self._handlers, handler_name, None)
+        if handler is None:
             try:
-                generic_handler = getattr(self._handlers, 'request')
+                handler = getattr(self._handlers, 'request')
             except AttributeError:
                 raise AttributeError('%r has no handler for request %r' % (self._handlers, command))
-            handler = lambda: generic_handler(self, command, arguments)
+        request = Request(self, seq, command, arguments)
         try:
-            response_body = handler()
+            response_body = handler(request)
         except Exception as ex:
             self._send_response(seq, False, command, str(ex), None)
         else:
-            self._send_response(seq, True, command, None, response_body)
+            if isinstance(response_body, Exception):
+                self._send_response(seq, False, command, str(response_body), None)
+            else:
+                self._send_response(seq, True, command, None, response_body)
 
     def on_event(self, seq, event, body):
         handler_name = '%s_event' % event
-        specific_handler = getattr(self._handlers, handler_name, None)
-        if specific_handler is not None:
-            handler = lambda: specific_handler(self, body)
-        else:
+        handler = getattr(self._handlers, handler_name, None)
+        if handler is None:
             try:
-                generic_handler = getattr(self._handlers, 'event')
+                handler = getattr(self._handlers, 'event')
             except AttributeError:
                 raise AttributeError('%r has no handler for event %r' % (self._handlers, event))
-            handler = lambda: generic_handler(self, event, body)
-        handler()
+        handler(Event(self, seq, event, body))
 
     def on_response(self, seq, request_seq, success, command, error_message, body):
         try:
@@ -364,7 +389,7 @@ class JsonMessageChannel(object):
             raise KeyError('Received response to unknown request %d', request_seq)
         if not success:
             body = RequestFailure(error_message)
-        return request._handle_response(command, body)
+        return request._handle_response(seq, command, body)
 
     def _process_incoming_messages(self):
         try:
@@ -384,7 +409,7 @@ class JsonMessageChannel(object):
             # must be marked as failed to unblock anyone waiting on them.
             with self._lock:
                 for request in self._requests.values():
-                    request._handle_response(request.command, EOFError('No response'))
+                    request._handle_response(None, request.command, EOFError('No response'))
 
 
 class MessageHandlers(object):
diff --git a/ptvsd/multiproc.py b/ptvsd/multiproc.py
index 01ac7f7a..45cc08e6 100644
--- a/ptvsd/multiproc.py
+++ b/ptvsd/multiproc.py
@@ -11,6 +11,7 @@ import re
 import socket
 import sys
 import time
+import traceback
 
 try:
     import queue
@@ -99,18 +100,19 @@ def _subprocess_listener():
 
 def _handle_subprocess(n, stream):
     class Handlers(object):
-        def ptvsd_subprocess_request(self, channel, body):
+        def ptvsd_subprocess_request(self, request):
             # When child process is spawned, the notification it sends only
             # contains information about itself and its immediate parent.
             # Add information about the root process before passing it on.
-            body.update({
+            arguments = dict(request.arguments)
+            arguments.update({
                 'rootProcessId': os.getpid(),
                 'rootStartRequest': root_start_request,
             })
 
-            debug('ptvsd_subprocess: %r' % body)
+            debug('ptvsd_subprocess: %r' % arguments)
             response = {'incomingConnection': False}
-            subprocess_queue.put((body, response))
+            subprocess_queue.put((arguments, response))
             subprocess_queue.join()
             return response
 
@@ -145,7 +147,8 @@ def notify_root(port):
     try:
         response = request.wait_for_response()
     except Exception:
-        debug('Failed to send subprocess notification; exiting')
+        print('Failed to send subprocess notification; exiting', file=sys.__stderr__)
+        traceback.print_exc()
         sys.exit(0)
 
     if not response['incomingConnection']:
diff --git a/pytests/helpers/session.py b/pytests/helpers/session.py
index ae167196..d5f807e6 100644
--- a/pytests/helpers/session.py
+++ b/pytests/helpers/session.py
@@ -310,7 +310,7 @@ class DebugSession(object):
 
         request = self.timeline.record_request(command, arguments)
         request.sent = self.channel.send_request(command, arguments)
-        request.sent.on_response(lambda body: self._process_response(request, body))
+        request.sent.on_response(lambda response: self._process_response(request, response))
 
         def causing(*expectations):
             for exp in expectations:
@@ -372,13 +372,13 @@ class DebugSession(object):
 
         return start
 
-    def _process_event(self, channel, event, body):
-        self.timeline.record_event(event, body, block=False)
+    def _process_event(self, event):
+        self.timeline.record_event(event.event, event.body, block=False)
 
-    def _process_response(self, request, body):
-        self.timeline.record_response(request, body, block=False)
+    def _process_response(self, request_occ, response):
+        self.timeline.record_response(request_occ, response.body, block=False)
 
-    def _process_request(self, channel, command, arguments):
+    def _process_request(self, request):
         assert False, 'ptvsd should not be sending requests.'
 
     def setup_backchannel(self):
diff --git a/pytests/test_messaging.py b/pytests/test_messaging.py
index 572fdca9..56b2765f 100644
--- a/pytests/test_messaging.py
+++ b/pytests/test_messaging.py
@@ -12,7 +12,7 @@ import socket
 import threading
 import time
 
-from ptvsd.messaging import JsonIOStream, JsonMessageChannel, Response, RequestFailure
+from ptvsd.messaging import JsonIOStream, JsonMessageChannel, RequestFailure
 from .helpers.messaging import JsonMemoryStream, LoggingJsonStream
 
 
@@ -96,11 +96,12 @@ class TestJsonMessageChannel(object):
         events_received = []
 
         class Handlers(object):
-            def stopped_event(self, channel, body):
-                events_received.append((channel, body))
+            def stopped_event(self, event):
+                assert event.event == 'stopped'
+                events_received.append((event.channel, event.body))
 
-            def event(self, channel, event, body):
-                events_received.append((channel, event, body))
+            def event(self, event):
+                events_received.append((event.channel, event.event, event.body))
 
         input, input_exhausted = self.iter_with_event(EVENTS)
         stream = LoggingJsonStream(JsonMemoryStream(input, []))
@@ -123,15 +124,17 @@ class TestJsonMessageChannel(object):
         requests_received = []
 
         class Handlers(object):
-            def next_request(self, channel, arguments):
-                requests_received.append((channel, arguments))
+            def next_request(self, request):
+                assert request.command == 'next'
+                requests_received.append((request.channel, request.arguments))
                 return {'threadId': 7}
 
-            def request(self, channel, command, arguments):
-                requests_received.append((channel, command, arguments))
+            def request(self, request):
+                requests_received.append((request.channel, request.command, request.arguments))
 
-            def pause_request(self, channel, arguments):
-                requests_received.append((channel, arguments))
+            def pause_request(self, request):
+                assert request.command == 'pause'
+                requests_received.append((request.channel, request.arguments))
                 raise RuntimeError('pause error')
 
         input, input_exhausted = self.iter_with_event(REQUESTS)
@@ -176,44 +179,45 @@ class TestJsonMessageChannel(object):
         response1_body = request1.wait_for_response()
         response1 = request1.response
 
-        assert response1 == Response(request1, body={'threadId': 3})
         assert response1.success
+        assert response1.request is request1
         assert response1.body == response1_body
+        assert response1.body == {'threadId': 3}
 
         # Async callback, registered before response is received.
         request2 = channel.send_request('pause')
-        response2_body = []
+        response2 = []
         response2_received = threading.Event()
-        def response2_handler(body):
-            response2_body.append(body)
+        def response2_handler(resp):
+            response2.append(resp)
             response2_received.set()
         request2.on_response(response2_handler)
         request2_sent.set()
         response2_received.wait()
-        response2_body, = response2_body
-        response2 = request2.response
+        response2, = response2
 
-        assert response2 == Response(request2, RequestFailure('pause error'))
         assert not response2.success
-        assert response2.body == response2_body
+        assert response2.request is request2
+        assert response2 is request2.response
+        assert response2.body == RequestFailure('pause error')
 
         # Async callback, registered after response is received.
         request3 = channel.send_request('next')
         request3_sent.set()
         request3.wait_for_response()
-        response3_body = []
+        response3 = []
         response3_received = threading.Event()
-        def response3_handler(body):
-            response3_body.append(body)
+        def response3_handler(resp):
+            response3.append(resp)
             response3_received.set()
         request3.on_response(response3_handler)
         response3_received.wait()
-        response3_body, = response3_body
-        response3 = request3.response
+        response3, = response3
 
-        assert response3 == Response(request3, body={'threadId': 5})
         assert response3.success
-        assert response3.body == response3_body
+        assert response3.request is request3
+        assert response3 is request3.response
+        assert response3.body == {'threadId': 5}
 
     def test_fuzz(self):
         # Set up two channels over the same stream that send messages to each other
@@ -237,45 +241,44 @@ class TestJsonMessageChannel(object):
             def wait(self):
                 self._worker.join()
 
-            def fizz_event(self, channel, body):
+            def fizz_event(self, event):
+                assert event.event == 'fizz'
                 with self.lock:
-                    self.received.append(('event', 'fizz', body))
+                    self.received.append(('event', 'fizz', event.body))
 
-            def buzz_event(self, channel, body):
+            def buzz_event(self, event):
+                assert event.event == 'buzz'
                 with self.lock:
-                    self.received.append(('event', 'buzz', body))
+                    self.received.append(('event', 'buzz', event.body))
 
-            def event(self, channel, event, body):
+            def event(self, event):
                 with self.lock:
-                    self.received.append(('event', event, body))
+                    self.received.append(('event', event.event, event.body))
 
             def make_and_log_response(self, request):
                 x = random.randint(-100, 100)
-                if x >= 0:
-                    response = Response(request, x)
-                else:
-                    response = Response(request, RequestFailure(str(x)))
+                if x < 0:
+                    x = RequestFailure(str(x))
                 with self.lock:
-                    self.responses_sent.append(response)
-                if response.success:
-                    return x
-                else:
-                    raise response.body
+                    self.responses_sent.append((request.seq, x))
+                return x
 
-            def fizz_request(self, channel, arguments):
+            def fizz_request(self, request):
+                assert request.command == 'fizz'
                 with self.lock:
-                    self.received.append(('request', 'fizz', arguments))
-                return self.make_and_log_response('fizz')
+                    self.received.append(('request', 'fizz', request.arguments))
+                return self.make_and_log_response(request)
 
-            def buzz_request(self, channel, arguments):
+            def buzz_request(self, request):
+                assert request.command == 'buzz'
                 with self.lock:
-                    self.received.append(('request', 'buzz', arguments))
-                return self.make_and_log_response('buzz')
+                    self.received.append(('request', 'buzz', request.arguments))
+                return self.make_and_log_response(request)
 
-            def request(self, channel, command, arguments):
+            def request(self, request):
                 with self.lock:
-                    self.received.append(('request', command, arguments))
-                return self.make_and_log_response(command)
+                    self.received.append(('request', request.command, request.arguments))
+                return self.make_and_log_response(request)
 
             def _send_requests_and_events(self, channel):
                 pending_requests = [0]
@@ -291,9 +294,9 @@ class TestJsonMessageChannel(object):
                         with self.lock:
                             pending_requests[0] += 1
                         req = channel.send_request(name, body)
-                        def response_handler(body):
+                        def response_handler(response):
                             with self.lock:
-                                self.responses_received.append(Response(req, body))
+                                self.responses_received.append((response.request.seq, response.body))
                                 pending_requests[0] -= 1
                         req.on_response(response_handler)
                 # Spin until we get responses to all requests.