Servers: publishing objects

This chapter explains how you write code that publishes objects to be remotely accessible. These objects are then called Pyro objects and the program that provides them, is often called a server program.

(The program that calls the objects is usually called the client. Both roles can be mixed in a single program.)

Make sure you are familiar with Pyro’s Key concepts before reading on.

See also

Configuring Pyro for several config items that you can use to tweak various server side aspects.

Pyro Daemon: publishing Pyro objects

To publish a regular Python object and turn it into a Pyro object, you have to tell Pyro about it. After that, your code has to tell Pyro to start listening for incoming requests and to process them. Both are handled by the Pyro daemon.

In its most basic form, you create one or more objects that you want to publish as Pyro objects, you create a daemon, register the object(s) with the daemon, and then enter the daemon’s request loop:

import Pyro4

class MyPyroThing(object):
    pass

thing=MyPyroThing()
daemon=Pyro4.Daemon()
uri=daemon.register(thing)
print uri
daemon.requestLoop()

After printing the uri, the server sits waiting for requests. The uri that is being printed looks a bit like this: PYRO:obj_dcf713ac20ce4fb2a6e72acaeba57dfd@localhost:51850 It can be used in a client program to create a proxy and access your Pyro object with.

Note

You can publish any regular Python object as a Pyro object. However since Pyro adds a few Pyro-specific attributes to the object, you can’t use:

  • types that don’t allow custom attributes, such as the builtin types (str and int for instance)
  • types with __slots__ (a possible way around this is to add Pyro’s custom attributes to your __slots__, but that isn’t very nice)

Oneliner Pyro object publishing

Ok not really a one-liner, but one statement: use serveSimple to publish a dict of objects and start Pyro’s request loop. The code above could also be written as:

import Pyro4

class MyPyroThing(object):
    pass

Pyro4.Daemon.serveSimple(
    {
        MyPyroThing(): None
    },
    ns=False, verbose=True)

Verbose is set to True because you want it to print out the generated random object uri, otherwise there is no way to connect to your object. You can also choose to provide object names yourself, to use or not use the name server, etc. See Pyro4.core.Daemon.serveSimple().

Note that the amount of options you can provide is quite limited. If you want to control the way the Pyro daemon is constructed, you have to do that by setting the appropriate config options before calling serveSimple. Or you can create a daemon object yourself with the right arguments, and pass that to serveSimple so that it doesn’t create a default daemon itself. Because they are so frequently used, serveSimple has a host and port parameter that you can use to control the host and port of the daemon that it creates (useful if you want to make it run on something else as localhost).

Creating a Daemon

Pyro’s daemon is Pyro4.core.Daemon and you can also access it by its shortcut Pyro4.Daemon. It has a few optional arguments when you create it:

Daemon([host=None, port=0, unixsocket=None, nathost=None, natport=None])

Create a new Pyro daemon.

Parameters:
  • host (str or None) – the hostname or IP address to bind the server on. Default is None which means it uses the configured default (which is localhost).
  • port (int) – port to bind the server on. Defaults to 0, which means to pick a random port.
  • unixsocket (str or None) – the name of a Unix domain socket to use instead of a TCP/IP socket. Default is None (don’t use).
  • nathost – hostname to use in published addresses (useful when running behind a NAT firewall/router). Default is None which means to just use the normal host. For more details about NAT, see Pyro behind a NAT router/firewall.
  • natport – port to use in published addresses (useful when running behind a NAT firewall/router). If you use 0 here, Pyro will replace the NAT-port by the internal port number to facilitate one-to-one NAT port mappings.

Registering objects

Every object you want to publish as a Pyro object needs to be registered with the daemon. You can let Pyro choose a unique object id for you, or provide a more readable one yourself.

Daemon.register(obj[, objectId=None])

Registers an object with the daemon to turn it into a Pyro object.

Parameters:
  • obj – the object to register
  • objectId (str or None) – optional custom object id (must be unique). Default is to let Pyro create one for you.
Returns:

an uri for the object

Return type:

Pyro4.core.URI

It is important to do something with the uri that is returned: it is the key to access the Pyro object. You can save it somewhere, or perhaps print it to the screen. The point is, your client programs need it to be able to access your object (they need to create a proxy with it).

Maybe the easiest thing is to store it in the Pyro name server. That way it is almost trivial for clients to obtain the proper uri and connect to your object. See Name Server for more information (Registering object names), but it boils down to getting a name server proxy and using its register method:

uri = daemon.register(some_object)
ns = Pyro4.locateNS()
ns.register("example.objectname", uri)

Note

If you ever need to create a new uri for an object, you can use Pyro4.core.Daemon.uriFor(). The reason this method exists on the daemon is because an uri contains location information and the daemon is the one that knows about this.

Intermission: Example 1: server and client not using name server

A little code example that shows the very basics of creating a daemon and publishing a Pyro object with it. Server code:

import Pyro4

class Thing(object):
    def method(self, arg):
        return arg*2

# ------ normal code ------
daemon = Pyro4.Daemon()
uri = daemon.register(Thing())
print "uri=",uri
daemon.requestLoop()

# ------ alternatively, using serveSimple -----
Pyro4.Daemon.serveSimple(
    {
        Thing(): None
    },
    ns=False, verbose=True)

Client code example to connect to this object:

import Pyro4
# use the URI that the server printed:
uri = "PYRO:obj_b2459c80671b4d76ac78839ea2b0fb1f@localhost:49383"
thing = Pyro4.Proxy(uri)
print thing.method(42)   # prints 84

With correct additional parameters –described elsewhere in this chapter– you can control on which port the daemon is listening, on what network interface (ip address/hostname), what the object id is, etc.

Intermission: Example 2: server and client, with name server

A little code example that shows the very basics of creating a daemon and publishing a Pyro object with it, this time using the name server for easier object lookup. Server code:

import Pyro4

class Thing(object):
    def method(self, arg):
        return arg*2

# ------ normal code ------
daemon = Pyro4.Daemon()
ns = Pyro4.locateNS()
uri = daemon.register(Thing())
ns.register("mythingy", uri)
daemon.requestLoop()

# ------ alternatively, using serveSimple -----
Pyro4.Daemon.serveSimple(
    {
        Thing(): "mythingy"
    },
    ns=True, verbose=True)

Client code example to connect to this object:

import Pyro4
thing = Pyro4.Proxy("PYRONAME:mythingy")
print thing.method(42)   # prints 84

Unregistering objects

When you no longer want to publish an object, you need to unregister it from the daemon:

Daemon.unregister(objectOrId)
Parameters:objectOrId (object itself or its id string) – the object to unregister

Running the request loop

Once you’ve registered your Pyro object you’ll need to run the daemon’s request loop to make Pyro wait for incoming requests.

Daemon.requestLoop([loopCondition])
Parameters:loopCondition – optional callable returning a boolean, if it returns False the request loop will be aborted and the call returns

This is Pyro’s event loop and it will take over your program until it returns (it might never.) If this is not what you want, you can control it a tiny bit with the loopCondition, or read the next paragraph.

Integrating Pyro in your own event loop

If you want to use a Pyro daemon in your own program that already has an event loop (aka main loop), you can’t simply call requestLoop because that will block your program. A daemon provides a few tools to let you integrate it into your own event loop:

  • Pyro4.core.Daemon.sockets - list of all socket objects used by the daemon, to inject in your own event loop
  • Pyro4.core.Daemon.events() - method to call from your own event loop when Pyro needs to process requests. Argument is a list of sockets that triggered.

For more details and example code, see the eventloop and gui_eventloop examples. They show how to use Pyro including a name server, in your own event loop, and also possible ways to use Pyro from within a GUI program with its own event loop.

Cleaning up

To clean up the daemon itself (release its resources) either use the daemon object as a context manager in a with statement, or manually call Pyro4.core.Daemon.close().

Autoproxying

Pyro will automatically take care of any Pyro objects that you pass around through remote method calls. It will replace them by a proxy automatically, so the receiving side can call methods on it and be sure to talk to the remote object instead of a local copy. There is no need to create a proxy object manually. All you have to do is to register the new object with the appropriate daemon:

def some_pyro_method(self):
    thing=SomethingNew()
    self._pyroDaemon.register(thing)
    return thing    # just return it, no need to return a proxy

This feature can be enabled or disabled by a config item, see Configuring Pyro. (it is on by default). If it is off, a copy of the object itself is returned, and the client won’t be able to interact with the actual new Pyro object in the server. There is a autoproxy example that shows the use of this feature, and several other examples also make use of it.

Note that when using the marshal serializer, this feature doesn’t work. You have to use one of the other serializers to use autoproxying.

Server types and Object concurrency model

Pyro supports multiple server types (the way the Daemon listens for requests). Select the desired type by setting the SERVERTYPE config item. It depends very much on what you are doing in your Pyro objects what server type is most suitable. For instance, if your Pyro object does a lot of I/O, it may benefit from the parallelism provided by the thread pool server. However if it is doing a lot of CPU intensive calculations, the multiplexed server may be more appropriate. If in doubt, go with the default setting.

  1. threaded server (servertype "threaded", this is the default)

    This server uses a thread pool to handle incoming proxy connections. The size of the pool is configurable via various config items. Every proxy on a client that connects to the daemon will be assigned to a thread to handle the remote method calls. This way multiple calls can potentially be processed concurrently. This means your Pyro object must be thread-safe! If you access a shared resource from your Pyro object you may need to take thread locking measures such as using Queues. If the thread pool is too small for the number of proxy connections, new proxy connections will be put to wait until another proxy disconnects from the server.

  1. multiplexed server (servertype "multiplex")

    This server uses a select (or poll, if available) based connection multiplexer to process all remote method calls sequentially. No threads are used in this server. It means only one method call is running at a time, so if it takes a while to complete, all other calls are waiting for their turn (even when they are from different proxies).

Note

If the ONEWAY_THREADED config item is enabled (it is by default), oneway method calls will be executed in a separate worker thread, regardless of the server type you’re using.

Note

It must be pretty obvious but the following is a very important concept so it is repeated once more to be 100% clear: Currently, you register objects with Pyro, not classes. This means remote method calls to a certain Pyro object always run on the single instance that you registered with Pyro.

When to choose which server type? With the threadpool server at least you have a chance to achieve concurrency, and you don’t have to worry much about blocking I/O in your remote calls. The usual trouble with using threads in Python still applies though: Python threads don’t run concurrently unless they release the GIL. If they don’t, you will still hang your server process. For instance if a particular piece of your code doesn’t release the GIL during a longer computation, the other threads will remain asleep waiting to acquire the GIL. One of these threads may be the Pyro server loop and then your whole Pyro server will become unresponsive. Doing I/O usually means the GIL is released. Some C extension modules also release it when doing their work. So, depending on your situation, not all hope is lost.

With the multiplexed server you don’t have threading problems: everything runs in a single main thread. This means your requests are processed sequentially, but it’s easier to make the Pyro server unresponsive. Any operation that uses blocking I/O or a long-running computation will block all remote calls until it has completed.

Serialization

Pyro will serialize the objects that you pass to the remote methods, so they can be sent across a network connection. Depending on the serializer that is being used for your Pyro server, there will be some limitations on what objects you can use, and what serialization format is required of the clients that connect to your server.

You specify one or more serializers that are accepted in the daemon/server by setting the SERIALIZERS_ACCEPTED config item. This is a set of serializer names that are allowed to be used with your server. It defaults to the set of ‘safe’ serializers. A client that successfully talks to your server will get responses using the same serializer as the one used to send requests to the server.

If your server also uses Pyro client code/proxies, you might also need to select the serializer for these by setting the SERIALIZER config item.

See the Configuring Pyro chapter for details about the config items. See Serialization for more details about serialization, the new config items, and how to deal with existing code that relies on pickle.

Note

Since Pyro 4.20 the default serializer is “serpent”. It used to be “pickle” in older versions. The default set of accepted serializers in the server is the set of ‘safe’ serializers, so “pickle” is not among the default.

Other features

Attributes added to Pyro objects

The following attributes will be added your object if you register it as a Pyro object:

  • _pyroId - the unique id of this object (a str)
  • _pyroDaemon - a reference to the Pyro4.core.Daemon object that contains this object

Even though they start with an underscore (and are private, in a way), you can use them as you so desire. As long as you don’t modify them! The daemon reference for instance is useful to register newly created objects with, to avoid the need of storing a global daemon object somewhere.

These attributes will be removed again once you unregister the object.

Network adapter binding

All Pyro daemons bind on localhost by default. This is because of security reasons. This means only processes on the same machine have access to your Pyro objects. If you want to make them available for remote machines, you’ll have to tell Pyro on what network interface address it must bind the daemon.

Warning

Read chapter Security before exposing Pyro objects to remote machines!

There are a few ways to tell Pyro what network address it needs to use. You can set a global config item HOST, or pass a host parameter to the constructor of a Daemon, or use a command line argument if you’re dealing with the name server. For more details, refer to the chapters in this manual about the relevant Pyro components.

Pyro provides a couple of utility functions to help you with finding the appropriate IP address to bind your servers on if you want to make them publicly accessible:

Daemon Pyro interface

A rather interesting aspect of Pyro’s Daemon is that it (partly) is a Pyro object itself. This means it exposes a couple of remote methods that you can also invoke yourself if you want. The object exposed is Pyro4.core.DaemonObject (as you can see it is a bit limited still).

You access this object by creating a proxy for the "Pyro.Daemon" object. That is a reserved object name. You can use it directly but it is preferable to use the constant Pyro4.constants.DAEMON_NAME. An example follows that accesses the daemon object from a running name server:

>>> import Pyro4
>>> daemon=Pyro4.Proxy("PYRO:"+Pyro4.constants.DAEMON_NAME+"@localhost:9090")
>>> daemon.ping()
>>> daemon.registered()
['Pyro.NameServer', 'Pyro.Daemon']