Initial pass at module preloading

* Don't implement the rules for when preloading occurs yet
* Don't attempt to streamily preload modules downstream while this
  context hasn't yet received the final module. There is quite
  significant latency buried in here, but for now it's a lot of work to
  fix.

This works well enough to handle at least the mitogen package, but it's
likely broken for anything bigger.

mitogen/core.py

@@ -56,6 +56,7 @@ FORWARD_LOG = 102
 ADD_ROUTE = 103
 ALLOCATE_ID = 104
 SHUTDOWN = 105
+LOAD_MODULE = 106
 
 CHUNK_SIZE = 16384
 
@@ -305,6 +306,8 @@ def _queue_interruptible_get(queue, timeout=None, block=True):
     if timeout is not None:
         timeout += time.time()
 
+    LOG.info('timeout = %r, block = %r', timeout, block)
+
     msg = None
     while msg is None and (timeout is None or timeout > time.time()):
         try:
@@ -395,7 +398,7 @@ class Importer(object):
 
     :param context: Context to communicate via.
     """
-    def __init__(self, context, core_src):
+    def __init__(self, router, context, core_src):
         self._context = context
         self._present = {'mitogen': [
             'mitogen.ansible',
@@ -407,13 +410,19 @@ class Importer(object):
             'mitogen.sudo',
             'mitogen.utils',
         ]}
+        self._lock = threading.Lock()
+        # Presence of an entry in this map indicates in-flight GET_MODULE.
+        self._callbacks = {}
         self.tls = threading.local()
+        router.add_handler(self._on_load_module, LOAD_MODULE)
         self._cache = {}
         if core_src:
             self._cache['mitogen.core'] = (
+                'mitogen.core',
                 None,
                 'mitogen/core.py',
                 zlib.compress(core_src),
+                [],
             )
 
     def __repr__(self):
@@ -468,23 +477,53 @@ class Importer(object):
             # later.
             os.environ['PBR_VERSION'] = '0.0.0'
 
+    def _on_load_module(self, msg):
+        tup = msg.unpickle()
+        fullname = tup[0]
+        LOG.debug('Importer._on_load_module(%r)', fullname)
+
+        self._lock.acquire()
+        try:
+            self._cache[fullname] = tup
+            callbacks = self._callbacks.pop(fullname, [])
+        finally:
+            self._lock.release()
+
+        for callback in callbacks:
+            callback()
+
+    def _request_module(self, fullname, callback):
+        self._lock.acquire()
+        try:
+            present = fullname in self._cache
+            if not present:
+                funcs = self._callbacks.get(fullname)
+                if funcs is not None:
+                    LOG.debug('_request_module(%r): in flight', fullname)
+                    funcs.append(callback)
+                else:
+                    LOG.debug('_request_module(%r): new request', fullname)
+                    self._callbacks[fullname] = [callback]
+                    self._context.send(Message(data=fullname, handle=GET_MODULE))
+        finally:
+            self._lock.release()
+
+        if present:
+            callback()
+
     def load_module(self, fullname):
         LOG.debug('Importer.load_module(%r)', fullname)
         self._load_module_hacks(fullname)
 
-        try:
-            ret = self._cache[fullname]
-        except KeyError:
-            self._cache[fullname] = ret = (
-                self._context.send_await(
-                    Message(data=fullname, handle=GET_MODULE)
-                )
-            )
+        event = threading.Event()
+        self._request_module(fullname, event.set)
+        event.wait()
 
+        ret = self._cache[fullname]
         if ret is None:
             raise ImportError('Master does not have %r' % (fullname,))
 
-        pkg_present = ret[0]
+        pkg_present = ret[1]
         mod = sys.modules.setdefault(fullname, imp.new_module(fullname))
         mod.__file__ = self.get_filename(fullname)
         mod.__loader__ = self
@@ -500,11 +539,11 @@ class Importer(object):
 
     def get_filename(self, fullname):
         if fullname in self._cache:
-            return 'master:' + self._cache[fullname][1]
+            return 'master:' + self._cache[fullname][2]
 
     def get_source(self, fullname):
         if fullname in self._cache:
-            return zlib.decompress(self._cache[fullname][2])
+            return zlib.decompress(self._cache[fullname][3])
 
 
 class LogHandler(logging.Handler):
@@ -593,6 +632,7 @@ class Stream(BasicStream):
         self._router = router
         self.remote_id = remote_id
         self.name = 'default'
+        self.modules_sent = set()
         self.construct(**kwargs)
         self._output_buf = collections.deque()
 
@@ -853,6 +893,10 @@ class Router(object):
     def __repr__(self):
         return 'Router(%r)' % (self.broker,)
 
+    def stream_by_id(self, dst_id):
+        return self._stream_by_id.get(dst_id,
+            self._stream_by_id.get(mitogen.parent_id))
+
     def on_disconnect(self, stream, broker):
         """Invoked by Stream.on_disconnect()."""
         for context in self._context_by_id.itervalues():
@@ -1132,7 +1176,7 @@ class ExternalContext(object):
         else:
             core_src = None
 
-        self.importer = Importer(self.parent, core_src)
+        self.importer = Importer(self.router, self.parent, core_src)
         sys.meta_path.append(self.importer)
 
     def _setup_package(self, context_id, parent_ids):

mitogen/master.py

@@ -599,13 +599,14 @@ class ModuleFinder(object):
             stack.extend(set(fullnames).difference(found, stack, [fullname]))
             found.update(fullnames)
 
-        return found
+        return sorted(found)
 
 
 class ModuleResponder(object):
     def __init__(self, router):
         self._router = router
         self._finder = ModuleFinder()
+        self._cache = {}  # fullname -> pickled
         router.add_handler(self._on_get_module, mitogen.core.GET_MODULE)
 
     def __repr__(self):
@@ -622,40 +623,57 @@ class ModuleResponder(object):
             return src[:match.start()]
         return src
 
-    def _on_get_module(self, msg):
-        LOG.debug('%r.get_module(%r)', self, msg)
-        if msg == mitogen.core._DEAD:
-            return
+    def _build_tuple(self, fullname):
+        if fullname in self._cache:
+            return self._cache[fullname]
 
-        fullname = msg.data
-        try:
-            path, source, is_pkg = self._finder.get_module_source(fullname)
-            if source is None:
-                raise ImportError('could not find %r' % (fullname,))
-
-            if is_pkg:
-                pkg_present = get_child_modules(path, fullname)
-                LOG.debug('get_child_modules(%r, %r) -> %r',
-                          path, fullname, pkg_present)
-            else:
-                pkg_present = None
+        path, source, is_pkg = self._finder.get_module_source(fullname)
+        if source is None:
+            raise ImportError('could not find %r' % (fullname,))
 
-            if fullname == '__main__':
-                source = self.neutralize_main(source)
-            compressed = zlib.compress(source)
-            related = list(self._finder.find_related(fullname))
+        if is_pkg:
+            pkg_present = get_child_modules(path, fullname)
+            LOG.debug('_build_tuple(%r, %r) -> %r',
+                      path, fullname, pkg_present)
+        else:
+            pkg_present = None
+
+        if fullname == '__main__':
+            source = self.neutralize_main(source)
+        compressed = zlib.compress(source)
+        related = list(self._finder.find_related(fullname))
+        # 0:fullname 1:pkg_present 2:path 3:compressed 4:related
+        return fullname, pkg_present, path, compressed, related
+
+    def _send_load_module(self, msg, fullname):
+        stream = self._router.stream_by_id(msg.src_id)
+        if fullname not in stream.sent_modules:
             self._router.route(
                 mitogen.core.Message.pickled(
-                    (pkg_present, path, compressed, related),
+                    self._build_tuple(fullname),
                     dst_id=msg.src_id,
-                    handle=msg.reply_to,
+                    handle=mitogen.core.LOAD_MODULE,
                 )
             )
+            stream.sent_modules.add(fullname)
+
+    def _on_get_module(self, msg):
+        LOG.debug('%r.get_module(%r)', self, msg)
+        if msg == mitogen.core._DEAD:
+            return
+
+        fullname = msg.data
+        try:
+            tup = self._build_tuple(fullname)
+            related = tup[4]
+            for name in related + [fullname]:
+                if name not in ('mitogen', 'mitogen.core'):
+                    self._send_load_module(msg, name)
         except Exception:
             LOG.debug('While importing %r', fullname, exc_info=True)
             self._router.route(
                 mitogen.core.Message.pickled(
-                    None,
+                    (fullname, None, None, None, []),
                     dst_id=msg.src_id,
                     handle=msg.reply_to,
                 )
@@ -682,41 +700,28 @@ class ModuleForwarder(object):
             return
 
         fullname = msg.data
-        cached = self.importer._cache.get(fullname)
-        if cached:
-            LOG.debug('%r._on_get_module(): using cached %r', self, fullname)
-            self.router.route(
-                mitogen.core.Message.pickled(
-                    cached,
-                    dst_id=msg.src_id,
-                    handle=msg.reply_to,
-                )
-            )
-        else:
-            LOG.debug('%r._on_get_module(): requesting %r', self, fullname)
-            self.parent_context.send(
-                mitogen.core.Message(
-                    data=msg.data,
-                    handle=mitogen.core.GET_MODULE,
-                    reply_to=self.router.add_handler(
-                        lambda m: self._on_got_source(m, msg),
-                        persist=False
-                    )
-                )
-            )
+        callback = lambda: self._on_cache_callback(msg, fullname)
+        self.importer._request_module(fullname, callback)
 
-    def _on_got_source(self, msg, original_msg):
-        LOG.debug('%r._on_got_source(%r, %r)', self, msg, original_msg)
-        fullname = original_msg.data
-        self.importer._cache[fullname] = msg.unpickle()
+    def _send_one_module(self, msg, tup):
         self.router.route(
-            mitogen.core.Message(
-                data=msg.data,
-                dst_id=original_msg.src_id,
-                handle=original_msg.reply_to,
+            mitogen.core.Message.pickled(
+                self.importer._cache[fullname],
+                dst_id=msg.src_id,
+                handle=mitogen.core.LOAD_MODULE,
             )
         )
 
+    def _on_cache_callback(self, msg, fullname):
+        LOG.debug('%r._on_get_module(): sending %r', self, fullname)
+        tup = self.importer._cache[fullname]
+        if tup is not None:
+            for related in tup[4]:
+                rtup = self.importer._cache[fullname]
+                self._send_one_module(rtup)
+
+        self._send_one_module(tup)
+
 
 class Stream(mitogen.core.Stream):
     """
@@ -731,6 +736,10 @@ class Stream(mitogen.core.Stream):
     #: True to cause context to write /tmp/mitogen.stats.<pid>.<thread>.log.
     profiling = False
 
+    def __init__(self, *args, **kwargs):
+        super(Stream, self).__init__(*args, **kwargs)
+        self.sent_modules = set()
+
     def construct(self, remote_name=None, python_path=None, debug=False,
                   profiling=False, **kwargs):
         """Get the named context running on the local machine, creating it if