Source code for envisage.service_registry
# (C) Copyright 2007-2023 Enthought, Inc., Austin, TX
# All rights reserved.
#
# This software is provided without warranty under the terms of the BSD
# license included in LICENSE.txt and may be redistributed only under
# the conditions described in the aforementioned license. The license
# is also available online at http://www.enthought.com/licenses/BSD.txt
#
# Thanks for using Enthought open source!
""" The service registry. """
# Standard library imports.
import logging
# Enthought library imports.
from traits.api import Dict, Event, HasTraits, Int, provides
# Local imports.
from .i_service_registry import IServiceRegistry
from .import_manager import ImportManager
# Logging.
logger = logging.getLogger(__name__)
[docs]@provides(IServiceRegistry)
class ServiceRegistry(HasTraits):
"""The service registry."""
#### IServiceRegistry interface ##########################################
#: An event that is fired when a service is registered.
registered = Event
#: An event that is fired when a service is unregistered.
unregistered = Event
#### Private interface ###################################################
# The services in the registry.
#
# { service_id : (protocol_name, obj, properties) }
#
# where:
#
# 'protocol_name' is the (possible dotted) name of the interface, type or
# class that the object is registered against.
#
# 'obj' is the object that is registered (any old, Python object!).
#
# 'properties' is the arbitrary dictionary of properties that were
# registered with the object.
_services = Dict
# The next service Id (service Ids are never persisted between process
# invocations so this is simply an ever increasing integer!).
_service_id = Int
###########################################################################
# 'IServiceRegistry' interface.
###########################################################################
[docs] def get_required_service(
self, protocol, query="", minimize="", maximize=""
):
"""Return the service that matches the specified query.
Raise a 'NoSuchServiceError' exception if no such service exists.
"""
service = self.get_service(protocol, query, minimize, maximize)
if service is None:
raise NoSuchServiceError(protocol)
return service
[docs] def get_service(self, protocol, query="", minimize="", maximize=""):
"""Return at most one service that matches the specified query."""
services = self.get_services(protocol, query, minimize, maximize)
if len(services) > 0:
service = services[0]
else:
service = None
return service
[docs] def get_service_from_id(self, service_id):
"""Return the service with the specified id."""
try:
protocol, obj, properties = self._services[service_id]
except KeyError:
raise ValueError("no service with id <%d>" % service_id)
return obj
[docs] def get_services(self, protocol, query="", minimize="", maximize=""):
"""Return all services that match the specified query."""
services = []
for service_id, (name, obj, properties) in self._services.items():
if self._get_protocol_name(protocol) == name:
# If the protocol is a string then we need to import it!
if isinstance(protocol, str):
actual_protocol = ImportManager().import_symbol(protocol)
# Otherwise, it is an actual protocol, so just use it!
else:
actual_protocol = protocol
# If the registered service is actually a factory then use it
# to create the actual object.
obj = self._resolve_factory(
actual_protocol, name, obj, properties, service_id
)
# If a query was specified then only add the service if it
# matches it!
if len(query) == 0 or self._eval_query(obj, properties, query):
services.append(obj)
# Are we minimizing or maximising anything? If so then sort the list
# of services by the specified attribute/property.
if minimize != "":
services.sort(key=lambda x: getattr(x, minimize))
elif maximize != "":
services.sort(key=lambda x: getattr(x, maximize), reverse=True)
return services
[docs] def get_service_properties(self, service_id):
"""Return the dictionary of properties associated with a service."""
try:
protocol, obj, properties = self._services[service_id]
properties = properties.copy()
except KeyError:
raise ValueError("no service with id <%d>" % service_id)
return properties
[docs] def register_service(self, protocol, obj, properties=None):
"""Register a service."""
protocol_name = self._get_protocol_name(protocol)
# Make sure each service gets its own properties dictionary.
if properties is None:
properties = {}
service_id = self._next_service_id()
self._services[service_id] = (protocol_name, obj, properties)
self.registered = service_id
logger.debug("service <%d> registered %s", service_id, protocol_name)
return service_id
[docs] def set_service_properties(self, service_id, properties):
"""Set the dictionary of properties associated with a service."""
try:
protocol, obj, old_properties = self._services[service_id]
self._services[service_id] = protocol, obj, properties.copy()
except KeyError:
raise ValueError("no service with id <%d>" % service_id)
[docs] def unregister_service(self, service_id):
"""Unregister a service."""
try:
protocol, obj, properties = self._services.pop(service_id)
self.unregistered = service_id
logger.debug("service <%d> unregistered", service_id)
except KeyError:
raise ValueError("no service with id <%d>" % service_id)
###########################################################################
# Private interface.
###########################################################################
def _create_namespace(self, service, properties):
"""Create a namespace in which to evaluate a query."""
namespace = {}
namespace.update(service.__dict__)
namespace.update(properties)
return namespace
def _eval_query(self, service, properties, query):
"""Evaluate a query over a single service.
Return True if the service matches the query, otherwise return False.
"""
namespace = self._create_namespace(service, properties)
try:
result = eval(query, namespace)
except Exception:
result = False
return result
def _get_protocol_name(self, protocol_or_name):
"""Returns the full class name for a protocol."""
if isinstance(protocol_or_name, str):
name = protocol_or_name
else:
name = "%s.%s" % (
protocol_or_name.__module__,
protocol_or_name.__name__,
)
return name
def _is_service_factory(self, protocol, obj):
"""Is the object a factory for services supporting the protocol?"""
# fixme: Should we have a formal notion of service factory with an
# appropriate API, or is this good enough? An API might have lifecycle
# methods to both create and destroy the service?!?
return not isinstance(obj, protocol)
def _next_service_id(self):
"""Returns the next service ID."""
self._service_id += 1
return self._service_id
def _resolve_factory(self, protocol, name, obj, properties, service_id):
"""If 'obj' is a factory then use it to create the actual service."""
# Is the registered service actually a service *factory*?
if self._is_service_factory(protocol, obj):
# A service factory is any callable that takes two arguments, the
# first is the protocol, the second is the (possibly empty)
# dictionary of properties that were registered with the service.
#
# If the factory is specified as a symbol path then import it.
if isinstance(obj, str):
obj = ImportManager().import_symbol(obj)
obj = obj(**properties)
# The resulting service object replaces the factory in the cache
# (i.e. the factory will not get called again unless it is
# unregistered first).
self._services[service_id] = (name, obj, properties)
return obj
