JavaSpaces is a powerful Jini service that provides a high-level tool for creating .. In a tutorial style, we cover the mechanics of creating a space-based. Selection from JavaSpaces™ Principles, Patterns, and Practice [Book] access to videos, live online training, learning paths, books, tutorials, and more. If you want more detail, I recommend Jan Newmarch’s Jini Tutorial. A JavaSpace is a Jini service that stores Java objects in memory. This makes it very useful.
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A network architecture for the construction of distributed systems where scale, rate of change, and complexity of interactions within and between networks are extremely important and cannot be satisfactorily addressed by existing technologies.
Jini technology provides a flexible infrastructure for delivering services in a network and for creating spontaneous interactions between clients that use these services regardless of their hardware or software implementations.
Jini-based systems are described as “network plug and play,” which is a reference to the dynamic, discovery-based nature of interactions between clients and services in a Jini tutoria. Jini provides both an infrastructure and a programming model.
The Jini infrastructure consists of a series of core service components that enable the distribution, discovery, security, and use of a federation of services.
These core services include service registration and lookup, distributed event notification and messaging, principal and access control list security, and a model for distributed transactions. Although Jini is not a complete grid framework, its core services provide a foundation for the construction of grid-like heterogeneous systems. Several initiatives are under javaspacces to extend the core Jini services to provide further grid-like functionality, such as scheduling and wide-area service discovery.
An example of one such effort is the JGrid project, which is hosted at http: The Jini programming model extends the core Java classes to include semantics for distributed computing. This programming model is based on a set of interfaces defining public requirements for behaviors such as transactionality across nodes and distributed event subscription and notification.
Another key concept of the model is embodied by the lease interface, which incorporates the notion of time into a reference to a non-local object.
A Jini lease grants access to a service for a certain time period and can be renewable. Leases allow for the dynamic nature of a grid environment, in which services and clients join and leave the system. When a lease expires, resources allocated for the service can be freed on both the client and the provider. Leases on a service can be shared or exclusive.
In addition to its core services, Jini includes JavaSpaceswhich is a distributed, associative, network-accessible, shared memory system implemented as a Jini service.
JavaSpaces™ Principles, Patterns, and Practice
At the highest level, a JavaSpace provides synchronized, transactional, read, write, and associative search access to objects in a persistent shared memory space. Contents of a JavaSpace are associative, meaning that they are addressed searched by their contents instead of a specific location identifier. Clients to a JavaSpace can use it to share information, including divisions of a problem that can be solved in a distributed and parallel fashion. JavaSpaces lends itself to blackboard-style processing, in which specialized processes take items from the shared board, perform their function, and then return results to the shared memory space.
JavaSpaces is described in a Sun Microsystems specification as part of Jini, and a reference implementation called Outrigger is distributed with the Jini Starter Kit.
On their own, the concepts behind JavaSpaces are neither directly related nor limited to grid computing. JavaSpaces can, however, serve as an enabling technology for a class of useful services implemented on a grid.
Jini and JavaSpaces
The JavaSpaces associative blackboard-style system provides a very simple mechanism for communication between the nodes in a distributed system. Using the space as a means of communication and synchronization simplifies distributed design and development as opposed to something like direct RPC [Remote Procedure Calls] or inter-node message passing. Nodes in the distributed system javas;aces not need to be directly aware of tuutorial other, do not need to share the same process or hardware, and can javaspces asynchronously.
You might think of the blackboard as an implementation of the Mediator pattern, which reduces the coupling between objects. As a result, the blackboard method of communication alleviates the need for a centralized or even distributed resource border or meta-scheduler. The Linda model defines a shared “tuple-space,” which functions like a blackboard in which nodes in a distributed system can read from and write to.
A tuple in the space is a vector of data values.
The nodes use simple operations to access the tuple-space blackboard. A typical distributed system based on a tuple space has producers and consumers of tuples. Producer nodes populate the space with some kind of tuple representing partitions of a problem.
javaspacess Consumer nodes take javaspzces from the space and perform some task, possibly placing results back into the space as different tuples. This arrangement is sometimes referred to as the Master-Worker or Compute Server pattern. Reads a entry from the space based on a template.
Removes an entry from the space based on a template. Requests notification when an entry matching a template is written to the space. The JavaSpace version of a Linda tuple is called an entry and described by the net. An entry is defined by its public reference-typed, serializable attributes, which are the only part of an entry that will be moved to and from the space. For those familiar with Linda, an entry differs from a Linda tuple in that it is strongly typed and may contain behavior methods in addition to data attributes.
JavaSpaces and tuple spaces in general are well-suited to solve problems that avail themselves to blackboard-style solutions or more generally, implementations following the compute-server pattern.
These problems are usually not IO-intensive and are easily subdivided and parametrized. See All Related Store Items.
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