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Overlapped I/O is a name used for asynchronous I/O in the Windows API. It was introduced as an extension to the API in Windows NT.
Utilizing overlapped I/O requires passing an OVERLAPPED
structure to API functions that normally block, including ReadFile()
, WriteFile()
, and Winsock's WSASend()
and WSARecv()
. The requested operation is initiated by a function call which returns immediately, and is completed by the OS in the background. The caller may optionally specify a Win32 event handle to be raised when the operation completes. Alternatively, a program may receive notification of an event via an I/O completion port, which is the preferred method of receiving notification when used in symmetric multiprocessing environments or when handling I/O on a large number of files or sockets. The third and the last method to get the I/O completion notification with overlapped IO is to use ReadFileEx()
and WriteFileEx()
, which allow the User APC routine to be provided, which will be fired on the same thread on completion (User APC is the thing very similar to Unix/POSIX signal, with the main difference being that the signals are using signal numbers from the historically predefined enumeration, while the User APC can be any function declared as "void f(void* context)
"). The so-called overlapped API presents some differences depending on the Windows version used. [1]
Asynchronous I/O is particularly useful for sockets and pipes.
Unix and Linux implement the POSIX asynchronous I/O API (AIO).
DNIX is a discontinued Unix-like real-time operating system from the Swedish company Dataindustrier AB (DIAB). A version named ABCenix was developed for the ABC 1600 computer from Luxor. Daisy Systems also had a system named Daisy DNIX on some of their computer-aided design (CAD) workstations. It was unrelated to DIAB's product.
Berkeley sockets is an application programming interface (API) for Internet sockets and Unix domain sockets, used for inter-process communication (IPC). It is commonly implemented as a library of linkable modules. It originated with the 4.2BSD Unix operating system, which was released in 1983.
In computing, the Windows Sockets API (WSA), later shortened to Winsock, is an application programming interface (API) that defines how Windows network application software should access network services, especially TCP/IP. It defines a standard interface between a Windows TCP/IP client application and the underlying TCP/IP protocol stack. The nomenclature is based on the Berkeley sockets API used in BSD for communications between programs.
In computing, vectored I/O, also known as scatter/gather I/O, is a method of input and output by which a single procedure call sequentially reads data from multiple buffers and writes it to a single data stream, or reads data from a data stream and writes it to multiple buffers, as defined in a vector of buffers. Scatter/gather refers to the process of gathering data from, or scattering data into, the given set of buffers. Vectored I/O can operate synchronously or asynchronously. The main reasons for using vectored I/O are efficiency and convenience.
Signals are standardized messages sent to a running program to trigger specific behavior, such as quitting or error handling. They are a limited form of inter-process communication (IPC), typically used in Unix, Unix-like, and other POSIX-compliant operating systems.
File locking is a mechanism that restricts access to a computer file, or to a region of a file, by allowing only one user or process to modify or delete it at a specific time and to prevent reading of the file while it's being modified or deleted.
In computer science, asynchronous I/O is a form of input/output processing that permits other processing to continue before the transmission has finished. A name used for asynchronous I/O in the Windows API is overlapped I/O.
The architecture of Windows NT, a line of operating systems produced and sold by Microsoft, is a layered design that consists of two main components, user mode and kernel mode. It is a preemptive, reentrant multitasking operating system, which has been designed to work with uniprocessor and symmetrical multiprocessor (SMP)-based computers. To process input/output (I/O) requests, they use packet-driven I/O, which utilizes I/O request packets (IRPs) and asynchronous I/O. Starting with Windows XP, Microsoft began making 64-bit versions of Windows available; before this, there were only 32-bit versions of these operating systems.
A file system API is an application programming interface through which a utility or user program requests services of a file system. An operating system may provide abstractions for accessing different file systems transparently.
Core Foundation is a C application programming interface (API) written by Apple for its operating systems, and is a mix of low-level routines and wrapper functions. Most Core Foundation routines follow a certain naming convention that deal with opaque objects, for example CFDictionaryRef for functions whose names begin with CFDictionary, and these objects are often reference counted (manually) through CFRetain
and CFRelease
. Internally, Core Foundation forms the base of the types in the Objective-C standard library and the Carbon API.
Dynamic-link library (DLL) is Microsoft's implementation of the shared library concept in the Microsoft Windows and OS/2 operating systems. These libraries usually have the file extension DLL
, OCX
, or DRV
. The file formats for DLLs are the same as for Windows EXE files – that is, Portable Executable (PE) for 32-bit and 64-bit Windows, and New Executable (NE) for 16-bit Windows. As with EXEs, DLLs can contain code, data, and resources, in any combination.
In computing, ioctl
is a system call for device-specific input/output operations and other operations which cannot be expressed by regular system calls. It takes a parameter specifying a request code; the effect of a call depends completely on the request code. Request codes are often device-specific. For instance, a CD-ROM device driver which can instruct a physical device to eject a disc would provide an ioctl
request code to do so. Device-independent request codes are sometimes used to give userspace access to kernel functions which are only used by core system software or still under development.
In computer science, an anonymous pipe is a simplex FIFO communication channel that may be used for one-way interprocess communication (IPC). An implementation is often integrated into the operating system's file IO subsystem. Typically a parent program opens anonymous pipes, and creates a new process that inherits the other ends of the pipes, or creates several new processes and arranges them in a pipeline.
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", then calls the relevant event handler. The event loop is also sometimes referred to as the message dispatcher, message loop, message pump, or run loop.
A network socket is a software structure within a network node of a computer network that serves as an endpoint for sending and receiving data across the network. The structure and properties of a socket are defined by an application programming interface (API) for the networking architecture. Sockets are created only during the lifetime of a process of an application running in the node.
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.
Input/output completion port (IOCP) is an API for performing multiple simultaneous asynchronous input/output operations in Windows NT versions 3.5 and later, AIX and on Solaris 10 and later. An input/output completion port object is created and associated with a number of sockets or file handles. When I/O services are requested on the object, completion is indicated by a message queued to the I/O completion port. A process requesting I/O services is not notified of completion of the I/O services, but instead checks the I/O completion port's message queue to determine the status of its I/O requests. The I/O completion port manages multiple threads and their concurrency.
The X/Open Transport Interface (XTI) is an Open Group specification for network application programming present in UNIX System V operating systems. It provides OSI transport layer services with protocol independence. Although Open Group considers this specification withdrawn, an implementation is part of the standard programming interfaces on modern UNIX System V operating systems where it is implemented using the STREAMS character input/output mechanism.
Kqueue is a scalable event notification interface introduced in FreeBSD 4.1 in July 2000, also supported in NetBSD, OpenBSD, DragonFly BSD, and macOS. Kqueue was originally authored in 2000 by Jonathan Lemon, then involved with the FreeBSD Core Team. Kqueue makes it possible for software like nginx to solve the c10k problem.
libuv is a multi-platform C library that provides support for asynchronous I/O based on event loops. It supports epoll(4)
, kqueue(2)
, Windows IOCP, and Solaris event ports. It is primarily designed for use in Node.js but it is also used by other software projects. It was originally an abstraction around libev or Microsoft IOCP, as libev doesn't support IOCP on Windows. In node-v0.9.0's version of libuv, the dependency on libev was removed.