C++ Micro Services: ModuleContext Class Reference
ModuleContext Class Reference

A module's execution context within the framework. More...

Public Member Functions

 ~ModuleContext ()
 
ModuleGetModule () const
 Returns the Module object associated with this ModuleContext. More...
 
ModuleGetModule (long id) const
 Returns the module with the specified identifier. More...
 
void GetModules (std::vector< Module * > &modules) const
 Returns a list of all known modules. More...
 
ServiceRegistration RegisterService (const std::list< std::string > &clazzes, us::Base *service, const ServiceProperties &properties=ServiceProperties())
 Registers the specified service object with the specified properties under the specified class names into the framework. More...
 
ServiceRegistration RegisterService (const char *clazz, us::Base *service, const ServiceProperties &properties=ServiceProperties())
 Registers the specified service object with the specified properties under the specified class name with the framework. More...
 
template<class S >
ServiceRegistration RegisterService (us::Base *service, const ServiceProperties &properties=ServiceProperties())
 Registers the specified service object with the specified properties using the specified template argument with the framework. More...
 
std::list< ServiceReferenceGetServiceReferences (const std::string &clazz, const std::string &filter=std::string())
 Returns a list of ServiceReference objects. More...
 
template<class S >
std::list< ServiceReferenceGetServiceReferences (const std::string &filter=std::string())
 Returns a list of ServiceReference objects. More...
 
ServiceReference GetServiceReference (const std::string &clazz)
 Returns a ServiceReference object for a service that implements and was registered under the specified class. More...
 
template<class S >
ServiceReference GetServiceReference ()
 Returns a ServiceReference object for a service that implements and was registered under the specified template class argument. More...
 
us::Base * GetService (const ServiceReference &reference)
 Returns the service object referenced by the specified ServiceReference object. More...
 
template<class S >
S * GetService (const ServiceReference &reference)
 Returns the service object referenced by the specified ServiceReference object. More...
 
bool UngetService (const ServiceReference &reference)
 Releases the service object referenced by the specified ServiceReference object. More...
 
void AddServiceListener (const ServiceListener &delegate, const std::string &filter=std::string())
 
void RemoveServiceListener (const ServiceListener &delegate)
 
void AddModuleListener (const ModuleListener &delegate)
 
void RemoveModuleListener (const ModuleListener &delegate)
 
template<class R >
void AddServiceListener (R *receiver, void(R::*callback)(const ServiceEvent), const std::string &filter=std::string())
 Adds the specified callback with the specified filter to the context modules's list of listeners. More...
 
template<class R >
void RemoveServiceListener (R *receiver, void(R::*callback)(const ServiceEvent))
 Removes the specified callback from the context module's list of listeners. More...
 
template<class R >
void AddModuleListener (R *receiver, void(R::*callback)(const ModuleEvent))
 Adds the specified callback to the context modules's list of listeners. More...
 
template<class R >
void RemoveModuleListener (R *receiver, void(R::*callback)(const ModuleEvent))
 Removes the specified callback from the context module's list of listeners. More...
 

Detailed Description

A module's execution context within the framework.

The context is used to grant access to other methods so that this module can interact with the Micro Services Framework.

ModuleContext methods allow a module to:

  • Subscribe to events published by the framework.
  • Register service objects with the framework service registry.
  • Retrieve ServiceReferences from the framework service registry.
  • Get and release service objects for a referenced service.
  • Get the list of modules loaded in the framework.
  • Get the Module object for a module.

A ModuleContext object will be created and provided to the module associated with this context when it is loaded using the ModuleActivator::Load method. The same ModuleContext object will be passed to the module associated with this context when it is unloaded using the ModuleActivator::Unload method. A ModuleContext object is generally for the private use of its associated module and is not meant to be shared with other modules in the module environment.

The Module object associated with a ModuleContext object is called the context module.

The ModuleContext object is only valid during the execution of its context module; that is, during the period when the context module is loaded. If the ModuleContext object is used subsequently, a std::logic_error is thrown. The ModuleContext object is never reused after its context module is unloaded.

The framework is the only entity that can create ModuleContext objects.

Remarks
This class is thread safe.

Constructor & Destructor Documentation

ModuleContext::~ModuleContext ( )

Member Function Documentation

void ModuleContext::AddModuleListener ( const ModuleListener &  delegate)
template<class R >
void ModuleContext::AddModuleListener ( R *  receiver,
void(R::*)(const ModuleEvent callback 
)
inline

Adds the specified callback to the context modules's list of listeners.

Listeners are notified when a module has a lifecycle state change.

If the context module's list of listeners already contains a pair (r,c) of receiver and callback such that (r == receiver && c == callback), then this method does nothing.

Template Parameters
RThe type of the receiver (containing the member function to be called)
Parameters
receiverThe object to connect to.
callbackThe member function pointer to call.
Exceptions
std::logic_errorIf this ModuleContext is no longer valid.
See Also
ModuleEvent
void ModuleContext::AddServiceListener ( const ServiceListener &  delegate,
const std::string &  filter = std::string() 
)
template<class R >
void ModuleContext::AddServiceListener ( R *  receiver,
void(R::*)(const ServiceEvent callback,
const std::string &  filter = std::string() 
)
inline

Adds the specified callback with the specified filter to the context modules's list of listeners.

See LDAPFilter for a description of the filter syntax. Listeners are notified when a service has a lifecycle state change.

You must take care to remove registered listeners befor the receiver object is destroyed. However, the Micro Services framework takes care of removing all listeners registered by this context module's classes after the module is unloaded.

If the context module's list of listeners already contains a pair (r,c) of receiver and callback such that (r == receiver && c == callback), then this method replaces that callback's filter (which may be empty) with the specified one (which may be empty).

The callback is called if the filter criteria is met. To filter based upon the class of the service, the filter should reference the ServiceConstants::OBJECTCLASS() property. If filter is empty, all services are considered to match the filter.

When using a filter, it is possible that the ServiceEvents for the complete lifecycle of a service will not be delivered to the callback. For example, if the filter only matches when the property x has the value 1, the callback will not be called if the service is registered with the property x not set to the value 1. Subsequently, when the service is modified setting property x to the value 1, the filter will match and the callback will be called with a ServiceEvent of type MODIFIED. Thus, the callback will not be called with a ServiceEvent of type REGISTERED.

Template Parameters
RThe type of the receiver (containing the member function to be called)
Parameters
receiverThe object to connect to.
callbackThe member function pointer to call.
filterThe filter criteria.
Exceptions
std::invalid_argumentIf filter contains an invalid filter string that cannot be parsed.
std::logic_errorIf this ModuleContext is no longer valid.
See Also
ServiceEvent
RemoveServiceListener()
Module* ModuleContext::GetModule ( ) const

Returns the Module object associated with this ModuleContext.

This module is called the context module.

Returns
The Module object associated with this ModuleContext.
Exceptions
std::logic_errorIf this ModuleContext is no longer valid.
Module* ModuleContext::GetModule ( long  id) const

Returns the module with the specified identifier.

Parameters
idThe identifier of the module to retrieve.
Returns
A Module object or 0 if the identifier does not match any previously loaded module.
void ModuleContext::GetModules ( std::vector< Module * > &  modules) const

Returns a list of all known modules.

This method returns a list of all modules loaded in the module environment at the time of the call to this method. This list will also contain modules which might already have been unloaded.

Parameters
modulesA std::vector of Module objects which will hold one object per known module.
us::Base* ModuleContext::GetService ( const ServiceReference reference)

Returns the service object referenced by the specified ServiceReference object.

A module's use of a service is tracked by the module's use count of that service. Each time a service's service object is returned by GetService(const ServiceReference&) the context module's use count for that service is incremented by one. Each time the service is released by UngetService(const ServiceReference&) the context module's use count for that service is decremented by one.

When a module's use count for a service drops to zero, the module should no longer use that service.

This method will always return 0 when the service associated with this reference has been unregistered.

The following steps are taken to get the service object:

  1. If the service has been unregistered, 0 is returned.
  2. The context module's use count for this service is incremented by one.
  3. If the context module's use count for the service is currently one and the service was registered with an object implementing the ServiceFactory interface, the ServiceFactory::GetService method is called to create a service object for the context module. This service object is cached by the framework. While the context module's use count for the service is greater than zero, subsequent calls to get the services's service object for the context module will return the cached service object.
    If the ServiceFactory object throws an exception, 0 is returned and a warning is logged.
  4. The service object for the service is returned.
Parameters
referenceA reference to the service.
Returns
A service object for the service associated with reference or 0 if the service is not registered or the ServiceFactory threw an exception.
Exceptions
std::logic_errorIf this ModuleContext is no longer valid.
std::invalid_argumentIf the specified ServiceReference is invalid (default constructed).
See Also
UngetService(const ServiceReference&)
ServiceFactory
template<class S >
S* ModuleContext::GetService ( const ServiceReference reference)
inline

Returns the service object referenced by the specified ServiceReference object.

This is a convenience method which is identical to US_BASECLASS_NAME* GetService(const ServiceReference&) except that it casts the service object to the supplied template argument type

Template Parameters
SThe type the service object will be cast to.
Returns
A service object for the service associated with reference or 0 if the service is not registered, the ServiceFactory threw an exception or the service could not be casted to the desired type.
Exceptions
std::logic_errorIf this ModuleContext is no longer valid.
std::invalid_argumentIf the specified ServiceReference is invalid (default constructed).
See Also
GetService(const ServiceReference&)
UngetService(const ServiceReference&)
ServiceFactory
ServiceReference ModuleContext::GetServiceReference ( const std::string &  clazz)

Returns a ServiceReference object for a service that implements and was registered under the specified class.

The returned ServiceReference object is valid at the time of the call to this method. However as the Micro Services framework is a very dynamic environment, services can be modified or unregistered at any time.

This method is the same as calling ModuleContext::GetServiceReferences(const std::string&, const std::string&) with an empty filter expression. It is provided as a convenience for when the caller is interested in any service that implements the specified class.

If multiple such services exist, the service with the highest ranking (as specified in its ServiceConstants::SERVICE_RANKING() property) is returned.

If there is a tie in ranking, the service with the lowest service ID (as specified in its ServiceConstants::SERVICE_ID() property); that is, the service that was registered first is returned.

Parameters
clazzThe class name with which the service was registered.
Returns
A ServiceReference object, or an invalid ServiceReference if no services are registered which implement the named class.
Exceptions
std::logic_errorIf this ModuleContext is no longer valid.
ServiceExceptionIf no service was registered under the given class name.
See Also
GetServiceReferences(const std::string&, const std::string&)
template<class S >
ServiceReference ModuleContext::GetServiceReference ( )
inline

Returns a ServiceReference object for a service that implements and was registered under the specified template class argument.

This method is identical to GetServiceReference(const std::string&) except that the class name for the service object is automatically deduced from the template argument.

Template Parameters
SThe type under which the requested service must have been registered.
Returns
A ServiceReference object, or an invalid ServiceReference if no services are registered which implement the type S.
Exceptions
std::logic_errorIf this ModuleContext is no longer valid.
ServiceExceptionIt no service was registered under the given class name.
See Also
GetServiceReference(const std::string&)
GetServiceReferences(const std::string&)
std::list<ServiceReference> ModuleContext::GetServiceReferences ( const std::string &  clazz,
const std::string &  filter = std::string() 
)

Returns a list of ServiceReference objects.

The returned list contains services that were registered under the specified class and match the specified filter expression.

The list is valid at the time of the call to this method. However since the Micro Services framework is a very dynamic environment, services can be modified or unregistered at any time.

The specified filter expression is used to select the registered services whose service properties contain keys and values which satisfy the filter expression. See LDAPFilter for a description of the filter syntax. If the specified filter is empty, all registered services are considered to match the filter. If the specified filter expression cannot be parsed, an std::invalid_argument will be thrown with a human readable message where the filter became unparsable.

The result is a list of ServiceReference objects for all services that meet all of the following conditions:

  • If the specified class name, clazz, is not empty, the service must have been registered with the specified class name. The complete list of class names with which a service was registered is available from the service's objectClass property.
  • If the specified filter is not empty, the filter expression must match the service.
Parameters
clazzThe class name with which the service was registered or an empty string for all services.
filterThe filter expression or empty for all services.
Returns
A list of ServiceReference objects or an empty list if no services are registered which satisfy the search.
Exceptions
std::invalid_argumentIf the specified filter contains an invalid filter expression that cannot be parsed.
std::logic_errorIf this ModuleContext is no longer valid.
template<class S >
std::list<ServiceReference> ModuleContext::GetServiceReferences ( const std::string &  filter = std::string())
inline

Returns a list of ServiceReference objects.

The returned list contains services that were registered under the interface id of the template argument S and match the specified filter expression.

This method is identical to GetServiceReferences(const std::string&, const std::string&) except that the class name for the service object is automatically deduced from the template argument.

Template Parameters
SThe type under which the requested service objects must have been registered.
Parameters
filterThe filter expression or empty for all services.
Returns
A list of ServiceReference objects or an empty list if no services are registered which satisfy the search.
Exceptions
std::invalid_argumentIf the specified filter contains an invalid filter expression that cannot be parsed.
std::logic_errorIf this ModuleContext is no longer valid.
See Also
GetServiceReferences(const std::string&, const std::string&)
ServiceRegistration ModuleContext::RegisterService ( const std::list< std::string > &  clazzes,
us::Base *  service,
const ServiceProperties properties = ServiceProperties() 
)

Registers the specified service object with the specified properties under the specified class names into the framework.

A ServiceRegistration object is returned. The ServiceRegistration object is for the private use of the module registering the service and should not be shared with other modules. The registering module is defined to be the context module. Other modules can locate the service by using either the GetServiceReferences or GetServiceReference method.

A module can register a service object that implements the ServiceFactory interface to have more flexibility in providing service objects to other modules.

The following steps are taken when registering a service:

  1. The framework adds the following service properties to the service properties from the specified ServiceProperties (which may be omitted):
    A property named ServiceConstants::SERVICE_ID() identifying the registration number of the service
    A property named ServiceConstants::OBJECTCLASS() containing all the specified classes.
    Properties with these names in the specified ServiceProperties will be ignored.
  2. The service is added to the framework service registry and may now be used by other modules.
  3. A service event of type ServiceEvent::REGISTERED is fired.
  4. A ServiceRegistration object for this registration is returned.
Parameters
clazzesThe class names under which the service can be located. The class names will be stored in the service's properties under the key ServiceConstants::OBJECTCLASS().
serviceThe service object or a ServiceFactory object.
propertiesThe properties for this service. The keys in the properties object must all be std::string objects. See ServiceConstants for a list of standard service property keys. Changes should not be made to this object after calling this method. To update the service's properties the ServiceRegistration::SetProperties method must be called. The set of properties may be omitted if the service has no properties.
Returns
A ServiceRegistration object for use by the module registering the service to update the service's properties or to unregister the service.
Exceptions
std::invalid_argumentIf one of the following is true:
  • service is 0.
  • properties contains case variants of the same key name.
std::logic_errorIf this ModuleContext is no longer valid.
See Also
ServiceRegistration
ServiceFactory
ServiceRegistration ModuleContext::RegisterService ( const char *  clazz,
us::Base *  service,
const ServiceProperties properties = ServiceProperties() 
)

Registers the specified service object with the specified properties under the specified class name with the framework.

This method is otherwise identical to RegisterService(const std:list<std::string>&, us::Base*, const ServiceProperties&) and is provided as a convenience when service will only be registered under a single class name. Note that even in this case the value of the service's ServiceConstants::OBJECTCLASS property will be a std::list<std::string>, rather than just a single string.

Parameters
clazzThe class name under which the service can be located.
serviceThe service object or a ServiceFactory object.
propertiesThe properties for this service.
Returns
A ServiceRegistration object for use by the module registering the service to update the service's properties or to unregister the service.
Exceptions
std::logic_errorIf this ModuleContext is no longer valid.
See Also
RegisterService(const std:list<std::string>&, us::Base*, const ServiceProperties&)
template<class S >
ServiceRegistration ModuleContext::RegisterService ( us::Base *  service,
const ServiceProperties properties = ServiceProperties() 
)
inline

Registers the specified service object with the specified properties using the specified template argument with the framework.

This method is provided as a convenience when service will only be registered under a single class name whose type is available to the caller. It is otherwise identical to RegisterService(const char*, US_BASECLASS_NAME*, const ServiceProperties&) but should be preferred since it avoids errors in the string literal identifying the class name or interface identifier.

Template Parameters
SThe type under which the service can be located.
Parameters
serviceThe service object or a ServiceFactory object.
propertiesThe properties for this service.
Returns
A ServiceRegistration object for use by the module registering the service to update the service's properties or to unregister the service.
Exceptions
std::logic_errorIf this ModuleContext is no longer valid.
See Also
RegisterService(const char*, us::Base*, const ServiceProperties&)
void ModuleContext::RemoveModuleListener ( const ModuleListener &  delegate)
template<class R >
void ModuleContext::RemoveModuleListener ( R *  receiver,
void(R::*)(const ModuleEvent callback 
)
inline

Removes the specified callback from the context module's list of listeners.

If the (receiver,callback) pair is not contained in this context module's list of listeners, this method does nothing.

Template Parameters
RThe type of the receiver (containing the member function to be removed)
Parameters
receiverThe object from which to disconnect.
callbackThe member function pointer to remove.
Exceptions
std::logic_errorIf this ModuleContext is no longer valid.
See Also
AddModuleListener()
void ModuleContext::RemoveServiceListener ( const ServiceListener &  delegate)
template<class R >
void ModuleContext::RemoveServiceListener ( R *  receiver,
void(R::*)(const ServiceEvent callback 
)
inline

Removes the specified callback from the context module's list of listeners.

If the (receiver,callback) pair is not contained in this context module's list of listeners, this method does nothing.

Template Parameters
RThe type of the receiver (containing the member function to be removed)
Parameters
receiverThe object from which to disconnect.
callbackThe member function pointer to remove.
Exceptions
std::logic_errorIf this ModuleContext is no longer valid.
See Also
AddServiceListener()
bool ModuleContext::UngetService ( const ServiceReference reference)

Releases the service object referenced by the specified ServiceReference object.

If the context module's use count for the service is zero, this method returns false. Otherwise, the context modules's use count for the service is decremented by one.

The service's service object should no longer be used and all references to it should be destroyed when a module's use count for the service drops to zero.

The following steps are taken to unget the service object:

  1. If the context module's use count for the service is zero or the service has been unregistered, false is returned.
  2. The context module's use count for this service is decremented by one.
  3. If the context module's use count for the service is currently zero and the service was registered with a ServiceFactory object, the ServiceFactory::UngetService method is called to release the service object for the context module.
  4. true is returned.
Parameters
referenceA reference to the service to be released.
Returns
false if the context module's use count for the service is zero or if the service has been unregistered; true otherwise.
Exceptions
std::logic_errorIf this ModuleContext is no longer valid.
See Also
GetService
ServiceFactory