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Reactor Pattern
The reactor design pattern is an event handling pattern for handling service requests delivered concurrently to a service handler by one or more inputs. The service handler then demultiplexes the incoming requests and dispatches them synchronously to the associated request handlers. Structure ;Resources: Any resource that can provide input to or consume output from the system. ;Synchronous Event Demultiplexer: Uses an event loop to block on all resources. The demultiplexer sends the resource to the dispatcher when it is possible to start a synchronous operation on a resource without blocking (''Example:'' a synchronous call to read() will block if there is no data to read. The demultiplexer uses select() on the resource, which blocks until the resource is available for reading. In this case, a synchronous call to read() won't block, and the demultiplexer can send the resource to the dispatcher.) ;Dispatcher: Handles registering and unregistering of request handlers. Dispatches ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Design Pattern (computer Science)
In software engineering, a software design pattern is a general, reusable solution to a commonly occurring problem within a given context in software design. It is not a finished design that can be transformed directly into source or machine code. Rather, it is a description or template for how to solve a problem that can be used in many different situations. Design patterns are formalized best practices that the programmer can use to solve common problems when designing an application or system. Object-oriented design patterns typically show relationships and interactions between classes or objects, without specifying the final application classes or objects that are involved. Patterns that imply mutable state may be unsuited for functional programming languages. Some patterns can be rendered unnecessary in languages that have built-in support for solving the problem they are trying to solve, and object-oriented patterns are not necessarily suitable for non-object-oriented langua ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Event Handling
In programming and software design, an event is an action or occurrence recognized by software, often originating asynchronously from the external environment, that may be handled by the software. Computer events can be generated or triggered by the system, by the user, or in other ways. Typically, events are handled synchronously with the program flow; that is, the software may have one or more dedicated places where events are handled, frequently an event loop. A source of events includes the user, who may interact with the software through the computer's peripherals - for example, by typing on the keyboard. Another source is a hardware device such as a timer. Software can also trigger its own set of events into the event loop, e.g. to communicate the completion of a task. Software that changes its behavior in response to events is said to be event-driven, often with the goal of being interactive. Description Event driven systems are typically used when there is so ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Concurrency (computer Science)
In computer science, concurrency is the ability of different parts or units of a program, algorithm, or problem to be executed out-of-order or in partial order, without affecting the outcome. This allows for parallel execution of the concurrent units, which can significantly improve overall speed of the execution in multi-processor and multi-core systems. In more technical terms, concurrency refers to the decomposability of a program, algorithm, or problem into order-independent or partially-ordered components or units of computation. According to Rob Pike, concurrency is the composition of independently executing computations, and concurrency is not parallelism: concurrency is about dealing with lots of things at once but parallelism is about doing lots of things at once. Concurrency is about structure, parallelism is about execution, concurrency provides a way to structure a solution to solve a problem that may (but not necessarily) be parallelizable. A number of mathema ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Demultiplex
In telecommunications and computer networking, multiplexing (sometimes contracted to muxing) is a method by which multiple analog or digital signals are combined into one signal over a shared medium. The aim is to share a scarce resource - a physical transmission medium. For example, in telecommunications, several telephone calls may be carried using one wire. Multiplexing originated in telegraphy in the 1870s, and is now widely applied in communications. In telephony, George Owen Squier is credited with the development of telephone carrier multiplexing in 1910. The multiplexed signal is transmitted over a communication channel such as a cable. The multiplexing divides the capacity of the communication channel into several logical channels, one for each message signal or data stream to be transferred. A reverse process, known as demultiplexing, extracts the original channels on the receiver end. A device that performs the multiplexing is called a multiplexer (MUX), and a devi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Event Loop
In computer science, the event loop is a programming construct or design pattern that waits for and dispatches events or messages in a program. The event loop works by making a request to some internal or external "event provider" (that generally blocks the request until an event has arrived), then calls the relevant event handler ("dispatches the event"). The event loop is also sometimes referred to as the message dispatcher, message loop, message pump, or run loop. The event-loop may be used in conjunction with a reactor, if the event provider follows the file interface, which can be selected or 'polled' (the Unix system call, not actual polling). The event loop almost always operates asynchronously with the message originator. When the event loop forms the central control flow construct of a program, as it often does, it may be termed the main loop or main event loop. This title is appropriate, because such an event loop is at the highest level of control within the program. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Read (system Call)
In modern POSIX compliant operating systems, a program that needs to access data from a file stored in a file system uses the read system call. The file is identified by a file descriptor that is normally obtained from a previous call to open. This system call reads in data in bytes, the number of which is specified by the caller, from the file and stores then into a buffer supplied by the calling process. The read system call takes three arguments: # The file descriptor of the file. # the buffer where the read data is to be stored and # the number of bytes to be read from the file. POSIX usage The read system call interface is standardized by the POSIX specification. Data from a file is read by calling the read function: ssize_t read(int fd, void *buf, size_t count); The value returned is the number of bytes read (zero indicates end of file) and the file position is advanced by this number. It is not an error if this number is smaller than the number of bytes requested; this ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Select (Unix)
is a system call and application programming interface (API) in Unix-like and POSIX-compliant operating systems for examining the status of file descriptors of open input/output channels. The select system call is similar to the ' facility introduced in UNIX System V and later operating systems. However, with the c10k problem, both select and poll have been superseded by the likes of kqueue, epoll, /dev/poll and I/O completion ports. One common use of select outside of its stated use of waiting on filehandles is to implement a portable sub-second Sleep (system call), sleep. This can be achieved by passing NULL for all three fd_set arguments, and the duration of the desired sleep as the timeout argument. In the C (programming language), C programming language, the select system call is declared in the header file sys/select.h or unistd.h, and has the following syntax: int select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *errorfds, struct timeval *timeout); fd_se ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thread (computer Science)
In computer science, a thread of execution is the smallest sequence of programmed instructions that can be managed independently by a scheduler, which is typically a part of the operating system. The implementation of threads and processes differs between operating systems. In Modern Operating Systems, Tanenbaum shows that many distinct models of process organization are possible.TANENBAUM, Andrew S. Modern Operating Systems. 1992. Prentice-Hall International Editions, ISBN 0-13-595752-4. In many cases, a thread is a component of a process. The multiple threads of a given process may be executed concurrently (via multithreading capabilities), sharing resources such as memory, while different processes do not share these resources. In particular, the threads of a process share its executable code and the values of its dynamically allocated variables and non- thread-local global variables at any given time. History Threads made an early appearance under the name of "tasks ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Debugging
In computer programming and software development, debugging is the process of finding and resolving '' bugs'' (defects or problems that prevent correct operation) within computer programs, software, or systems. Debugging tactics can involve interactive debugging, control flow analysis, unit testing, integration testing, log file analysis, monitoring at the application or system level, memory dumps, and profiling. Many programming languages and software development tools also offer programs to aid in debugging, known as ''debuggers''. Etymology The terms "bug" and "debugging" are popularly attributed to Admiral Grace Hopper in the 1940s. While she was working on a Mark II computer at Harvard University, her associates discovered a moth stuck in a relay and thereby impeding operation, whereupon she remarked that they were "debugging" the system. However, the term "bug", in the sense of "technical error", dates back at least to 1878 and Thomas Edison who describes the "litt ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Symmetric Multiprocessing
Symmetric multiprocessing or shared-memory multiprocessing (SMP) involves a multiprocessor computer hardware and software architecture where two or more identical processors are connected to a single, shared main memory, have full access to all input and output devices, and are controlled by a single operating system instance that treats all processors equally, reserving none for special purposes. Most multiprocessor systems today use an SMP architecture. In the case of multi-core processors, the SMP architecture applies to the cores, treating them as separate processors. Professor John D. Kubiatowicz considers traditionally SMP systems to contain processors without caches. Culler and Pal-Singh in their 1998 book "Parallel Computer Architecture: A Hardware/Software Approach" mention: "The term SMP is widely used but causes a bit of confusion. ..The more precise description of what is intended by SMP is a shared memory multiprocessor where the cost of accessing a memory location ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Proactor Pattern
Proactor is a software design pattern for event handling in which long running activities are running in an asynchronous part. A ''completion handler'' is called after the asynchronous part has terminated. The proactor pattern can be considered to be an asynchronous variant of the synchronous reactor pattern.Pattern-Oriented Software Architecture, Volume 2, Schmidt et al., Jon Wiley & Sons, Ltd, 2000 Interaction Operation specific actors: * The ''Proactive Initiator'' starts the asynchronous operation via the Asynchronous Operation Processor and defines the Completion Handler * ''Completion Handler'' is a call at the end of the operation from the Asynchronous Operation Processor * ''Asynchronous Operation'' Standardized actors * The ''Asynchronous Operation Processor'' controls the whole asynchronous operation * The ''Completion Dispatcher'' handles the call, depending on the execution environment. Implementations Proactor and Boost.Asio(C++) * Adaptive Communication Environ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Application Server
An application server is a server that hosts applications or software that delivers a business application through a communication protocol. An application server framework is a service layer model. It includes software components available to a software developer through an application programming interface. An application server may have features such as clustering, fail-over, and load-balancing. The goal is for developers to focus on the business logic. Java application servers Jakarta EE (formerly Java EE or J2EE) defines the core set of API and features of Java application servers. The Jakarta EE infrastructure is partitioned into logical containers. *EJB container: Enterprise Beans are used to manage transactions. According to the Java BluePrints, the business logic of an application resides in Enterprise Beans—a modular server component providing many features, including declarative transaction management, and improving application scalability. * Web container: the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
