CORBA Overview Distributed Systems &Middleware ICS243f 22 November 2015 Arvind S. Krishna Info & Comp Science Dept University of California, Irvine

Brief History - OMG OMG Formation OMG created in 1989 with aim of promoting object technology in Distributed Systems OMG realizes its goals through creating standards which allow interoperability and portability of distributed object oriented applications Do not produce software define standards OMA – Object Management Architecture Consists of four components divided into two parts: System oriented components  Object Request Brokers and Object Services and Application oriented components  Application Objects and Common Facilities Object Request Broker is the one which constitutes the foundation of OMA and manages all communication between its components

CORBA CORBA – Common Object Request Broker Architecture Motivation To allow objects to interact in Heterogeneous distributed environment independent of the platforms on which these objects reside techniques used to implement them (languages) CORBA – Common Object Request Broker Architecture Motivation To allow objects to interact in Heterogeneous distributed environment independent of the platforms on which these objects reside techniques used to implement them (languages) CORBA – Architecture Object Request Broker (ORB) ORB encompasses all communication infrastructure necessary to identify and locate objects, handle connection management Marshalling & de-marshalling data and deliver data. The ORB is not required to be a single component; it is simply defined by its interfaces. The ORB Core is the most crucial part of the Object Request Broker; Minimum run-time layer required in every peer CORBA – Architecture Object Request Broker (ORB) ORB encompasses all communication infrastructure necessary to identify and locate objects, handle connection management Marshalling & de-marshalling data and deliver data. The ORB is not required to be a single component; it is simply defined by its interfaces. The ORB Core is the most crucial part of the Object Request Broker; Minimum run-time layer required in every peer

Overview of CORBA Components Standard CORBA Components Object  This is a CORBA programming entity that consists of an identity, an interface, and an implementation, which is known as a Servant. Servant  This is an implementation programming language entity that defines the operations that support a CORBA IDL interface. Servants can be written in a variety of languages, including C, C++, Java, Smalltalk, and Ada. Standard CORBA Components Object  This is a CORBA programming entity that consists of an identity, an interface, and an implementation, which is known as a Servant. Servant  This is an implementation programming language entity that defines the operations that support a CORBA IDL interface. Servants can be written in a variety of languages, including C, C++, Java, Smalltalk, and Ada. Client  This is the program entity that invokes an operation on an object implementation. Accessing the services of a remote object should be transparent to the caller. Ideally, it should be as simple as calling a method on an object, i.e., obj->op(args)

Component Overview – (contd) ORB Interface  An ORB is a logical entity that may be implemented in various ways (such as one or more processes or a set of libraries). To decouple applications from implementation details, the CORBA specification defines an abstract interface for an ORB. This interface provides various helper functions such as converting object references to strings and vice versa CORBA IDL stubs and skeletons  CORBA IDL stubs and skeletons serve as the ``glue'' between the client and server applications The transformation between CORBA IDL definitions to languages automated IDL compiler The compiler allows for compiler optimization and automation of repetitive tasks Object Adapter  This assists the ORB with delivering requests to the object and with activating the object. More importantly, an object adapter associates object implementations with the ORB. Object adapters can be specialized to provide support for certain object implementation styles The QoS requirements for a POA specified using policies passed to it at creation time OMG provides seven standard policies and policy values Lifespan policy with policy values PERSISTENT and TRANSPERANT ORB Interface  An ORB is a logical entity that may be implemented in various ways (such as one or more processes or a set of libraries). To decouple applications from implementation details, the CORBA specification defines an abstract interface for an ORB. This interface provides various helper functions such as converting object references to strings and vice versa CORBA IDL stubs and skeletons  CORBA IDL stubs and skeletons serve as the ``glue'' between the client and server applications The transformation between CORBA IDL definitions to languages automated IDL compiler The compiler allows for compiler optimization and automation of repetitive tasks Object Adapter  This assists the ORB with delivering requests to the object and with activating the object. More importantly, an object adapter associates object implementations with the ORB. Object adapters can be specialized to provide support for certain object implementation styles The QoS requirements for a POA specified using policies passed to it at creation time OMG provides seven standard policies and policy values Lifespan policy with policy values PERSISTENT and TRANSPERANT

Interface Definition Language IDL - motivation CORBA language independent OMG does not provide implementations Left to ORB implementer OMG defines architecture of the system in terms of “interfaces” and the operations on these interfaces IDL – in Motion IDL is a language that has been developed for distribution of architecture Each ORB implementer writes an IDL compiler to generate programming language code IDL – Mapping OMG also defines a mapping from the IDL to the programming language IDL is a declarative language – cannot define data members Example, interfaces are mapped to the Java classes or to abstract classes in C++ Arguments must also specify the direction e.g. in means only input cannot hold output, inout holds both input and output IDL - motivation CORBA language independent OMG does not provide implementations Left to ORB implementer OMG defines architecture of the system in terms of “interfaces” and the operations on these interfaces IDL – in Motion IDL is a language that has been developed for distribution of architecture Each ORB implementer writes an IDL compiler to generate programming language code IDL – Mapping OMG also defines a mapping from the IDL to the programming language IDL is a declarative language – cannot define data members Example, interfaces are mapped to the Java classes or to abstract classes in C++ Arguments must also specify the direction e.g. in means only input cannot hold output, inout holds both input and output interface Drone { void turn (in float degrees); void speed (in short mph); void reset_odometer (); short odometer (); // … }; interface Drone { void turn (in float degrees); void speed (in short mph); void reset_odometer (); short odometer (); // … };

CORBA Communication Model CORBA Communication Heterogeneous languages, platforms and also operating systems Big endian (Sparc)Little endian architectures (Intel) Problem Traditionally programmers have had to handle these Offloaded to middleware Protocol definition General Internet Inter-ORB protocol Standard marshalling and demarshalling parameters Client marshals a request i.e. wraps a request in a given format includes padding etc GIOP maps to various protocols TCP/IP mapping of the protocol is IIOP same as that used by java RMI Standardized exchange enabling two different ORB implementations to inter operate Supports standardized uni-cast communication reliable one-way, two-way communication CORBA Communication Heterogeneous languages, platforms and also operating systems Big endian (Sparc)Little endian architectures (Intel) Problem Traditionally programmers have had to handle these Offloaded to middleware Protocol definition General Internet Inter-ORB protocol Standard marshalling and demarshalling parameters Client marshals a request i.e. wraps a request in a given format includes padding etc GIOP maps to various protocols TCP/IP mapping of the protocol is IIOP same as that used by java RMI Standardized exchange enabling two different ORB implementations to inter operate Supports standardized uni-cast communication reliable one-way, two-way communication Three broad mechanisms of communication –synchronous – deferred synchronous – asynchronous Three broad mechanisms of communication –synchronous – deferred synchronous – asynchronous

Object References Inter-operability Many ORBs how can these ORBs talk to each other? OMG standardizes the generation of Object references An object reference is an ORB-specific entity that can contain a Repository ID, which identifies its interface type Transport address information, e.g., a server’s TCP/IP host/port address(es) An object key that identifies which object in the server the request is destined for An object reference similar to a C++ “pointer” that’s been enhanced to identify objects in remote address spaces Object references can be passed among processes on separate hosts The underlying CORBA ORB will correctly convert object references into a form that can be transmitted over the network The ORB provides the receiver with a pointer to a proxy in its own address space This proxy refers to the remote object implementation Object references are a powerful feature of CORBA e.g., they support peer-to-peer interactions and distributed callbacks Inter-operability Many ORBs how can these ORBs talk to each other? OMG standardizes the generation of Object references An object reference is an ORB-specific entity that can contain a Repository ID, which identifies its interface type Transport address information, e.g., a server’s TCP/IP host/port address(es) An object key that identifies which object in the server the request is destined for An object reference similar to a C++ “pointer” that’s been enhanced to identify objects in remote address spaces Object references can be passed among processes on separate hosts The underlying CORBA ORB will correctly convert object references into a form that can be transmitted over the network The ORB provides the receiver with a pointer to a proxy in its own address space This proxy refers to the remote object implementation Object references are a powerful feature of CORBA e.g., they support peer-to-peer interactions and distributed callbacks Standardized Format Standardized Format ORB-specific Format ORB-specific Format

Object Adapter An Object Adapter maps remote client requests to servants Organization Similar to a file structure on a Unix machine POA similar to the directories Servants similar to the files in these directories Operations on servants similar to lines in a file Functionality Generate Object References Activate/objects Incarnate/Etherealize servants Demultiplex client requests to the appropriate servants Customization based on policies Key Components Adapter Activator – Dynamically activate POAs Servant Managers – create servants on demand POA Manager – Managed a collection of POAs similar to a faucet An Object Adapter maps remote client requests to servants Organization Similar to a file structure on a Unix machine POA similar to the directories Servants similar to the files in these directories Operations on servants similar to lines in a file Functionality Generate Object References Activate/objects Incarnate/Etherealize servants Demultiplex client requests to the appropriate servants Customization based on policies Key Components Adapter Activator – Dynamically activate POAs Servant Managers – create servants on demand POA Manager – Managed a collection of POAs similar to a faucet

Real-Time CORBA Overview RT CORBA adds QoS control to regular CORBA improve the application predictability, e.g., Bounding priority inversions & Managing resources end-to-end Policies & mechanisms for resource configuration/control in RT-CORBA include: 1.Processor Resources Thread pools Priority models Portable priorities 2.Communication Resources Protocol policies Explicit binding 3.Memory Resources Request buffering These capabilities address some important real-time application development challenges Real-time CORBA leverages the CORBA Messaging QoS Policy framework

Motivation for ZEN Real-time ORB Integrate best aspects of several key technologies Java: Simple, less error-prone, large user-base Real-time Java: Real-time support CORBA: Standards-based distributed applications Real-time CORBA: CORBA with Real-time QoS capabilities ZEN project goals Make development of distributed, real-time, & embedded (DRE) systems easier, faster, & more portable Provide open-source Real-time CORBA ORB written in Real-time Java to enhance international middleware R&D efforts

Overview - ZEN R&D Plan Phase I  Apply Optimization patterns and principles ORB-Core Optimizations Micro ORB Architecture  Virtual Component Pattern Connection Management  Acceptor- Connector pattern, Reactor (java’s nio package) Collocation and Buffer Management Strategies POA Optimizations Request Demultiplexing  Active Demultiplexing & Perfect Hashing Object Key Processing Strategies  Asynchronous completion token pattern Servant lookup  Reverse lookup map Concurrency Strategies  Half- Sync/Half-Async Phase I  Apply Optimization patterns and principles ORB-Core Optimizations Micro ORB Architecture  Virtual Component Pattern Connection Management  Acceptor- Connector pattern, Reactor (java’s nio package) Collocation and Buffer Management Strategies POA Optimizations Request Demultiplexing  Active Demultiplexing & Perfect Hashing Object Key Processing Strategies  Asynchronous completion token pattern Servant lookup  Reverse lookup map Concurrency Strategies  Half- Sync/Half-Async Phase II  Enhance Predictability by applying RTSJ features Associate Scoped Memory with Key ORB Components –I/O Layer : Acceptor-Connector, Transports –ORB Layer: CDR Streams, Message Parsers –POA Layer: Thread-Pools and Upcall Objects Using NoHeapRealtimeThreads –Ultimately use NHRT Threads for request/response processing –Reduce priority inversions from Garbage Collector Phase II  Enhance Predictability by applying RTSJ features Associate Scoped Memory with Key ORB Components –I/O Layer : Acceptor-Connector, Transports –ORB Layer: CDR Streams, Message Parsers –POA Layer: Thread-Pools and Upcall Objects Using NoHeapRealtimeThreads –Ultimately use NHRT Threads for request/response processing –Reduce priority inversions from Garbage Collector Phase III  Build a Real-Time CORBA ORB that runs atop a mature RTSJ Layer

References ZEN open-source download & web page: Real-time Java (JSR-1): jsr_001_real_time.html Dynamic scheduling RFP: Dynamic_Scheduling_RFP.html Distributed Real-time Java (JSR-50): jsr_050_drt.html AspectJ web page: JRate