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Not too long ago, parallel applications typically ran in multiprocessor machines. The run-time environment requires: Is it possible to monitor Java programs? An object inherits the methods of its class when it is instantiated. Practical Guide for Programmers , with its focused, tutorial-based coverage, helps you master the tasks and techniques essential to virtually all client-server projects using sockets in Java. A plain HTML document that the Web server daemon retrieves is static, which means it exists in a constant state:
Develop or adapt a run-time environment to support the execution of the parallel program generated by the development environment previously described. The run-time environment requires: Develop a performance measurement tool for the proposed environment. The performance evaluation tool requires: The goal is to detail the trends inside each research topic of this project. This has given rise to a wide range of models, chief of which is the multiple instruction stream, multiple data stream MIMD model .
The design of such systems requires careful consideration of the number of processors and their interconnection network topology .
Other models of systems exist: However, the MIMD has been considered as the most exible of these models and itself supporting a plethora of distinct implementations . The shared-memory MIMD model or multiprocessors , where the processors are connected to a number of memory modules to form a common global shared memory, was the basis of the earliest MIMD machines.
One of the major problems with this model was that severe memory contention can occur when processors try to access data residing in the same memory module. This memory contention problem can be solved by using the distributed-memory model mul- ticomputers where the memory is distributed among processors. If data needs to be accessed from the local memory of another processor, then they are transferred using the interconnection network.
However, initial programming experience indicates that shared-memory systems are easier to use and to program compared to distributed-memory systems which require more intricate programming . Another possibility of merging is the development of clusters of sym- metric multiprocessors SMP.
Symmetric multiprocessors share a common memory and each processor is mutually equivalent with each other. There is not a master-slave relation. Although not scalable, these machines perform well for high granularity parallel applications and currently many workstations and PCs are symmetric multiprocessors. There are studies in order to break the scalability problem through substitution of the internal bus by a crossbar switch.
A cluster is then a network of symmetric multiprocessors. Inside a SMP, you have a shared-memory model. Among SMPs, you have a distributed memory model. It is important to observe that this is true not only in a parallel context, but in a sequential one also. Among these paradigms, object-oriented programming has grown from a radical concept of the s to routine practice among serial programmers in the s.
The concept of object programming is strongly related to the concept of data type, restricted operations on types, and information hiding in the form of encapsulation of both data and the implementation of operations that access the data. The best way to achieve multiple copies of an object is to use the concept of inheritance. An object inherits the methods of its class when it is instantiated. Two or more objects of the same type share one copy of the code for their methods. Inheritance can be cumulative if we organize the classes in an inheritance hierarchy .
There are several approaches for parallel and distributed object orientation. For example: Concurrent OOP. In this model, objects are dynamically created and manipulated. Processing is performed by sending and receiving messages among objects.
Concurrent programming models are built up from low-level objects such as processes, queues, and semaphores into high-level objects like monitors and program modules. The popularity of concurrent object-oriented programming COOP is attributed to three application demands : The increased use of intercalating processes by individual users, such as the use of multiple X windows. Multiprocessor technology has advanced to the point of providing supercomputing power at a fraction of the traditional cost.
As a matter of fact, program abstraction leads to program modularity and software reusab- ility as is often found in OOP. Objects are program entities which encapsulate data and operations into single computational units. It turns out that concurrency is a natural con- sequence of the concept of objects.
In fact, the concurrent use of coroutines in conventional programming is very similar to the concurrent manipulation of objects in OOP. The development of concurrent object-oriented programming provides an alternative model for concurrent computing on multiprocessors or on multicomputers. The Actor Model. Actors are self-contained, interactive, independent components of a computing system that communicate by asynchronous message passing.
In an actor model, message passing is attached with semantics. Basic actor primitives include : Creating an actor from a behavior description and a set of parameters. Sending a message to another actor. An actor replacing its own behavior by a new behavior. The replacement mechanism allows one to aggregate changes and to avoid unnecessary control- ow dependences. Concurrent computations are visualized in terms of concurrent actor creations, simultaneous commu- nication events, and behavior replacements.
Each message may cause an object actor to modify its state, create new objects, and send new messages. Concurrency control structures represent particular patterns of message passing.
The actor primitives provide a low-level description of concurrent systems. High-level constructs are also needed for raising the granularity of descriptions and for encapsulating faults. The actor model is particularly suitable for multicomputer implementations.
The Server Paradigm. A server is a task, or cluster of tasks, which implement the methods of an object as cooperating subtasks. Servers execute the methods of an object in parallel. They provide a natural way to implement object programs with a minimum of synchron- ization and locking. This means that servers are relatively self-contained programs that implement one or more tasks of a parallel program. A server is an object in motion. In the server model, a parallel program is a collection of miniature programs running independ- ently, but occasionally interacting with one another by message passing.
In this view of parallel programming, every object is a miniature program that communic- ates with other objects by message passing.
When objects are activated in this manner, we call them servers . Other approaches exist. According to Hwang , three common patterns of parallelism have been found in the practice of COOP: In this case, there is no interaction between the procedures solving the subproblems. Object orientation means more abstraction: Parallel Software The construction of distributed memory MIMD systems is now commer- cially viable, and it is feasible to build systems involving large numbers of processors.
Four main approaches have been suggested as a basis for designing programming languages that would promote the wider use of parallel systems: Occam2 ; 2. Linda ; 3. Cray Fortran , and 4. The last approach composes the essentials of the underlying software platform we are focusing while using the Java paradigm see Section 3.
The approach based on introducing features to an existing language that deal explicitly with parallelism should enable existing software to be adapted and transferred to parallel machines, where appropriate, by existing programmers. This category is the one receiving most attention at present. This is a consequence of the fact that the majority of the users of parallel machines are scientists and engineers whose main working language has been Fortran. Although, variants are nonstandard, the underlying language is a standard.
However, the production of a standard for such languages is not impossible e. However, considering that Java is an object-oriented language, the extended features, which will eventually be introduced to it, must follow the trend of concurrent object paradigm. In this sense, the main characteristics of an OO approach, such as encapsulation, information hiding, inheritance and the potential for software reuse should reinforced.
Nevertheless, may it be completely transparent, object communication in distributed systems is actually implemented in its lowest level through message passing schemes. These systems are usually called distributed systems, in contrast to the previous centralized systems, based on a single CPU, memory, peripherals, and some termin- als. It has been remarked that these systems are being employed as shared parallel computers.
Operating systems for these environments can be called distributed operating systems. Distributed systems involve two essential features: Therefore, as the work environment in this project, we consider independent computers implying on a distributed memory model.
There will always be an available processor to execute a certain task. It is the role of the distributed operating system to support this transparency. Distributed operating systems are software components with special functions. They can be programmed using the approaches presented in the previous paragraphs about parallel paradigms and parallel softwares.
Communication, resources allocation, task scheduling, lightweight processes, all of these elements are performed by operating systems. Current commercial operating systems have support for distributed applications: Not too long ago, parallel applications typically ran in multiprocessor machines. More recently, it is common to use a cluster of work- stations connected through a LAN to cooperate in executing a parallel task.
Fiber optics and high-bandwidth electronics together have enabled telecommunications to shift from a technology designed for 10Hz signals to one designed for 1GHz signals, and to achieve the new bandwidth at low cost.
These advances in communication infra-structure allowed the development of the Internet. The Internet has made wide-area distributed applications a reality. DNS servers scattered throughout the world maintain portions of the DNS naming database and cooperate in resolving Internet host names and addresses.
Below, we overview the evolution of the Internet: Internet Evolution In the early 's, data communication had already become a fun- damental part of computing. At the time, most existing networks were independent entities dedicated to the needs of isolated groups of people. The big challenge was to deal with the hardware and protocol heterogeneity of the existing networking infra-structure, since replacing it was economically impractical. The only other way was to accommodate heterogeneity by interconnecting the existing networks, or internetworking.
It also provided a new operating system abstraction known as socket that allows application programs to access the kernel-level communication protocols. Within seven years from its inception, the Internet already spanned hundreds of individual networks located throughout the US and Europe, connecting nearly 20, computers at uni- versities, laboratories, and government agencies. The size and use of the Internet continued to grow much faster than expected.
By , the connected Internet included 3, active networks and over , hosts. The rapid growth resulted in scalability problems not anticipated in the original design. By mid 's, it was clear that a centralized database would not scale. The Internet name space was partitioned, distributed and replicated in several DNS servers. These servers are responsible for performing host name to Internet address mapping.
It does not guarantee reliability nor in-order delivery. This service is useful to applications that do not need to pay the overhead incurred by the connection-oriented service described below. At the transport level, the communication end points establish a connection to send a data stream reliably.
More recent distributed real-time applications, such as multimedia conferencing have more demanding service require- ments. Moreover, many of these applications perform multipoint communication with several senders and several receivers. This trend in modern, distributed applications has motivated ex- tensive research in developing a new Internet architecture and service models.
Gopher and WWW are probably the most well-known among the browsing tools. Indexing tools, on the other hand, organize searchable information into index- ing databases and respond to user queries by searching their databases for relevant information. Currently, the Web is undoubtfully one of the most popular Internet services. WWW organizes data into a distributed hypertext, where nodes are either full-text objects, directory objects called Web pages, or indices.
The WWW architecture is based on the client-server model.
The WWW client provides users with a hypertext-like browsing interface. NNTP allows access to Internet news groups and news articles. News articles may contain references to other articles or news groups, which are represented as hypertext links. HTTP allows document retrieval and full-text search operations. A plain HTML document that the Web server daemon retrieves is static, which means it exists in a constant state: A CGI program, on the other hand, is executed in real-time on the server, so that it can output dynamic information.
The output of the CGI program will be sent to the client. CGI programs made the Web more dynamic since they allow servers to generate the data required by the client on-demand by executing the appropriate CGI program.
The next step towards a dynamic Web is to allow the execution to happen on the client side. What is Java? Java provides a completely new way to think about distributed computing. Just as when the desktop computers freed individuals from depending upon a single mainframe from everyday work, Java frees client computers on the Internet from the dependence upon host computers for the execution of dynamic content.
Up to now, everything presented in a Web page was completely static. It had the electronic version of a printed document. However, Java provides functionality by allowing the execution of the code that can be distributed across the Internet in a portable, robust, secure, high-performance environment . The Java architecture provides an overview of how Java works, and the basics of the under- lying design.
The Java environment refers to the programs you can use to run Java programs.
Java is an interpreted language, and therefore needs a run-time system on every computer on which the applications are going to be run. This run-time system, or interpreter, can exist both inside other programs, such as HotJava or a WWW browser, or stand alone. By setting up and using these programs, individuals are able to execute Java programs that exist on Web pages, or are downloaded from an ftp site .
The Java language is a tentative of providing a truly object-oriented, portable, robust, secure, high-performance, development environment for distributing dynamic content over the Internet. The Java language changes the passive nature of the Internet and WWW by allowing architec- turally neutral code to be dynamically loaded and run on a heterogeneous network of machines such as the Internet. Java provides this functionality by incorporating the following features into its architecture, which make Java a promising candidate to be a major protocol for the Internet in the near future.
This means that it can run on any machine that has Java interpreter ported to it. The feature of the language and run-time environment make sure that the code is well behaved. This comes primarily as a result of the push to portability, and the need for solid applications that will not bring down a system when a user stumbles across a home page with a small animation.
In addition to protecting the client against unintentional attacks, the Java environment must protect it against intentional ones as well.
The language is object-oriented at the foundations of the language, and allows the inheritance and reuse of code both in a static and dynamic fashion. The dynamic nature of Java, which is an extension of its object-oriented design, allows for run-time extensibility. The Java language supports several high-performance features such as multithreading, just-in-time compiling, and native code usage. At the same time, the environment takes over many of the error prone tasks from the programmer such as pointers and memory management.
Java is aimed at being the universal standard for the transfer of dynamic, executable content over the Web. Its potential applications are quite diverse: This last feature is probably the one which has the most interest in our project.
They would actually run on diverse systems, moving from database to database attempting to gather the information you need. Java provides the perfect language for implementing such a system. Java is able to provide a secure environment within which such intelligent agents can run, without risking the security of the host system itself. Therefore, applications frequently must be ported to take advantage of improved hardware and software.
The meaning of portability seems to have been implicitly understood until real-world parallel applications began to be developed. The criteria for measuring portability can vary from one application domain to another. Because of the limitations in current tools, real-world application developers frequently use low-level tools such as libraries, and many of them have reported good performance.
Beyond IP Addresses: The Domain Name System. Internet Addressing with Java. Data Streams. How Streams Work. Filter Streams. Readers and Writers. Object Persistence and Object Serialization. User Datagram Protocol. DatagramPacket Class. DatagramSocket Class. Listening for UDP Packets.
Sending UDP Packets. User Datagram Protocol Example. Additional Information on UDP. Transmission Control Protocol. TCP Sockets and Java. Socket Class. Creating a TCP Client. ServerSocket Class. Creating a TCP Server. Exception Handling: Socket Specific Exceptions.
Multi-threaded Applications. Multi-threading in Java. Interthread Communication. Thread Groups. Thread Priorities. Implementing Application Protocols.
Application Protocol Specifications. Application Protocols Implementation. HyperText Transfer Protocol. HTTP and Java. Java Servlets. How Servlets Work. Using Servlets. Running Servlets. Writing a Simple Servlet.
ServletRequest and HttpServletRequest. ServletResponse and Http Response. Servlet Exceptions. Creating Stub and Skeleton Classes. Creating an RMI Server. Creating an RMI Client. Running the RMI System. Remote Method Invocation Packages and Classes. Remote Method Invocation Deployment Issues. Remote Object Activation.
From IDL to Java. Testing the JavaMail Installation. Advanced Messaging with JavaMail. Custom Networking https: The Java platform is highly regarded in part because of its suitability for writing programs that use and interact with the resources on the Internet and the World Wide Web.
In fact, Java-compatible browsers use this ability of the Java platform to the extreme to transport and run applets over the Internet.
This trail walks you through the complexities of writing Java applications and applets that can be used on the Internet. Overview of Networking has two sections. The first describes the networking capabilities of the Java platform that you may already be using without realizing that you are using the network.
The second provides a brief overview of networking to familiarize you with terms and concepts that you should understand before reading how to use URLs, sockets, and datagrams.
Your Java programs can use URLs to connect to and retrieve information over a network. This lesson provides a more complete definition of a URL and shows you how to create and parse a URL, how to open a connection to a URL, and how to read from and write to that connection.
All About Sockets explains how to use sockets so that your programs can communicate with other programs on the network. A socket is one endpoint of a two-way communication link between two programs running on the network. This lesson shows you how a client can connect to a standard server, the Echo server, and communicate with it via a socket. It then challenges you to rewrite the example using multicast socket instead.
Programmatic Access to Network Parameters explains why you might want to access network interface parameters and how to do so. It gives examples of how to list all the IP addresses assigned to the machine as well as other useful information such as whether the interface is running.
Working With Cookies discusses how cookies are used to create a session between a client and server, and how you can take advantage of cookies in your HTTP URL connections.
Java — Networking http: Download the tutorial: The term network programming refers to writing programs that execute across multiple devices computers , in which the devices are all connected to each other using a network.
The java. Sometimes your programs require lower-level network communication, for example, when you want to write a client-server application. In client-server applications, the server provides some service, such as processing database queries or sending out current stock prices. The client uses the service provided by the server, either displaying database query results to the user or making stock purchase recommendations to an investor.
The communication that occurs between the client and the server must be reliable.