issue #186: add PushFileService

This is like FileService but blocks until the file is pushed by a parent
context, with deduplicating behaviour at each level in the hierarchy. It
does not stream large files, so it is only suitable for small files like
Python modules.

Additionally add SerializedInvoker for use with PushFileService, which
ensures all method calls to a single service occur in sequence.

docs/services.rst

@@ -17,8 +17,9 @@ Overview
 Service
 
 * User-supplied class with explicitly exposed methods.
-* Identified in calls by its canonical name (e.g. mypkg.mymod.MyClass).
 * May be auto-imported/constructed in a child from a parent simply by calling it
+* Identified in calls by its canonical name (e.g. mypkg.mymod.MyClass) by
+  default, but may use any naming scheme the configured activator understands.
 * Children receive refusals if the class is not already activated by a aprent
 * Has an associated Select instance which may be dynamically loaded with
   receivers over time, on_message_received() invoked if any receiver becomes
@@ -28,9 +29,12 @@ Invoker
 
 * Abstracts mechanism for calling a service method and verifying permissions.
 * Built-in 'service.Invoker': concurrent execution of all methods on the thread pool.
+* Built-in 'service.SerializedInvoker': serialization of all calls on a single
+  thread borrowed from the pool while any request is pending.
 * Built-in 'service.DeduplicatingInvoker': requests are aggregated by distinct
-  (method, kwargs) key, only one such method executes, return value is cached
-  and broadcast to all requesters.
+  (method, kwargs) key, only one such method ever executes, return value is
+  cached and broadcast to all request waiters. Waiters do not block additional
+  pool threads.
 
 Activator
 

mitogen/service.py

@@ -195,12 +195,12 @@ class Activator(object):
 
     def activate(self, pool, service_name, msg):
         mod_name, _, class_name = service_name.rpartition('.')
-        if not self.is_permitted(mod_name, class_name, msg):
+        if msg and not self.is_permitted(mod_name, class_name, msg):
             raise mitogen.core.CallError(self.not_active_msg, service_name)
 
         module = mitogen.core.import_module(mod_name)
         klass = getattr(module, class_name)
-        service = klass(pool.router)
+        service = klass(router=pool.router)
         pool.add(service)
         return service
 
@@ -261,6 +261,50 @@ class Invoker(object):
             msg.reply(response)
 
 
+class SerializedInvoker(Invoker):
+    def __init__(self, **kwargs):
+        super(SerializedInvoker, self).__init__(**kwargs)
+        self._lock = threading.Lock()
+        self._queue = []
+        self._running = False
+
+    def _pop(self):
+        self._lock.acquire()
+        try:
+            try:
+                return self._queue.pop(0)
+            except IndexError:
+                self._running = False
+        finally:
+            self._lock.release()
+
+    def _run(self):
+        while True:
+            tup = self._pop()
+            if tup is None:
+                return
+            method_name, kwargs, msg = tup
+            try:
+                super(SerializedInvoker, self).invoke(method_name, kwargs, msg)
+            except Exception:
+                LOG.exception('%r: while invoking %r of %r',
+                              self, method_name, self.service)
+                msg.reply(mitogen.core.Message.dead())
+
+    def invoke(self, method_name, kwargs, msg):
+        self._lock.acquire()
+        try:
+            self._queue.append((method_name, kwargs, msg))
+            first = not self._running
+            self._running = True
+        finally:
+            self._lock.release()
+
+        if first:
+            self._run()
+        return Service.NO_REPLY
+
+
 class DeduplicatingInvoker(Invoker):
     """
     A service that deduplicates and caches expensive responses. Requests are
@@ -419,7 +463,7 @@ class Pool(object):
         if name in self._invoker_by_name:
             raise Error('service named %r already registered' % (name,))
         assert service.select not in self._func_by_recv
-        invoker = service.invoker_class(service)
+        invoker = service.invoker_class(service=service)
         self._invoker_by_name[name] = invoker
         self._func_by_recv[service.select] = service.on_message
 
@@ -439,13 +483,17 @@ class Pool(object):
             invoker = self._invoker_by_name.get(name)
             if not invoker:
                 service = self._activator.activate(self, name, msg)
-                invoker = service.invoker_class(service)
+                invoker = service.invoker_class(service=service)
                 self._invoker_by_name[name] = invoker
         finally:
             self._lock.release()
 
         return invoker
 
+    def get_service(self, name):
+        invoker = self.get_invoker(name, None)
+        return invoker.service
+
     def _validate(self, msg):
         tup = msg.unpickle(throw=False)
         if not (isinstance(tup, tuple) and
@@ -466,7 +514,8 @@ class Pool(object):
             LOG.warning('%r: call error: %s: %s', self, msg, e)
             msg.reply(e)
         except Exception:
-            LOG.exception('While invoking %r._invoke()', self)
+            LOG.exception('%r: while invoking %r of %r',
+                          self, method_name, service_name)
             e = sys.exc_info()[1]
             msg.reply(mitogen.core.CallError(e))
 
@@ -513,6 +562,111 @@ class FileStreamState(object):
         self.lock = threading.Lock()
 
 
+class PushFileService(Service):
+    """
+    Push-based file service. Files are delivered and cached in RAM, sent
+    recursively from parent to child. A child that requests a file via
+    :meth:`get` will block until it has ben delivered by a parent.
+
+    This service will eventually be merged into FileService.
+    """
+    invoker_class = SerializedInvoker
+
+    def __init__(self, **kwargs):
+        super(PushFileService, self).__init__(**kwargs)
+        self._lock = threading.Lock()
+        self._cache = {}
+        self._waiters = {}
+        self._sent_by_stream = {}
+
+    def get(self, path):
+        self._lock.acquire()
+        try:
+            if path in self._cache:
+                return self._cache[path]
+            waiters = self._waiters.setdefault(path, [])
+            latch = mitogen.core.Latch()
+            waiters.append(lambda: latch.put(None))
+        finally:
+            self._lock.release()
+
+        latch.get()
+        LOG.debug('%r.get(%r) -> %r', self, path, self._cache[path])
+        return self._cache[path]
+
+    def _forward(self, context, path):
+        stream = self.router.stream_by_id(context.context_id)
+        child = mitogen.core.Context(self.router, stream.remote_id)
+        sent = self._sent_by_stream.setdefault(stream, set())
+        if path in sent and child.context_id != context.context_id:
+            child.call_service_async(
+                service_name=self.name(),
+                method_name='forward',
+                path=path,
+                context=context
+            ).close()
+        else:
+            child.call_service_async(
+                service_name=self.name(),
+                method_name='store_and_forward',
+                path=path,
+                data=self._cache[path],
+                context=context
+            ).close()
+
+    @expose(policy=AllowParents())
+    @arg_spec({
+        'context': mitogen.core.Context,
+        'path': basestring,
+    })
+    def propagate_to(self, context, path):
+        LOG.debug('%r.propagate_to(%r, %r)', self, context, path)
+        if path not in self._cache:
+            fp = open(path, 'rb')
+            try:
+                self._cache[path] = mitogen.core.Blob(fp.read())
+            finally:
+                fp.close()
+        self._forward(context, path)
+
+    def _store(self, path, data):
+        self._lock.acquire()
+        try:
+            self._cache[path] = data
+            return self._waiters.pop(path, [])
+        finally:
+            self._lock.release()
+
+    @expose(policy=AllowParents())
+    @no_reply()
+    @arg_spec({
+        'path': basestring,
+        'data': mitogen.core.Blob,
+        'context': mitogen.core.Context,
+    })
+    def store_and_forward(self, path, data, context):
+        LOG.debug('%r.store_and_forward(%r, %r, %r)',
+                  self, path, data, context)
+        waiters = self._store(path, data)
+        if context.context_id != mitogen.context_id:
+            self._forward(path, context)
+        for callback in waiters:
+            callback()
+
+    @expose(policy=AllowParents())
+    @no_reply()
+    @arg_spec({
+        'path': basestring,
+        'context': mitogen.core.Context,
+    })
+    def forward(self, path, context):
+        LOG.debug('%r.forward(%r, %r)', self, path, context)
+        if path not in self._cache:
+            LOG.error('%r: %r is not in local cache', self, path)
+            return
+        self._forward(path, context)
+
+
 class FileService(Service):
     """
     Streaming file server, used to serve small files and huge files alike.