JINI goals, CORBA services, OS support

Goals of JINI

JINI is Sun Microsystems' Java-based technology for building networked services that join and leave a network spontaneously. Its goals are:

• Network plug and play: a device or software service can be attached to the network and used without manual installation or configuration.
• Simplicity of use: users get services on demand; administration is minimal.
• Reliable, self-healing network: services are leased; if a service fails or leaves, its lease expires and it is removed automatically.
• Service discovery and lookup: clients find services through a lookup service by type, not by address.
• Platform independence: any device with a Java Virtual Machine can take part; code (proxy) is downloaded dynamically.
• Scalability and flexibility: small devices and large servers can be federated in one community.

CORBA services

CORBA services (COSS, Common Object Services) are a set of standard, IDL-defined, general-purpose services that every distributed object application needs. Main ones:

• Naming service: binds names to object references.
• Event and Notification service: asynchronous communication between objects (suppliers and consumers).
• Life-cycle service: create, copy, move and delete objects.
• Persistent object service: store object state on disk.
• Transaction service: atomic operations across objects.
• Concurrency control service: locks.
• Security service: authentication, access control, encryption.
• Trading service: find objects by properties.
• Relationship, Query and Time services.

Operating system support for distributed systems

The OS gives the base on which middleware and applications run:

• Processes and threads: concurrent servers handle many clients at once.
• Communication primitives: sockets, message passing, RPC support (kernel IPC).
• Memory management: virtual memory and shared memory for fast local communication.
• Protection: address spaces and kernel/user mode, access rights on resources.
• Naming, file and device access: network file systems and remote devices.
• Scheduling and synchronisation of threads and processes.
• A microkernel design provides only the basic mechanisms (threads, IPC, memory) so that other services run as user-level servers and can be replaced.