Asynchrony, in

computer programming Computer programming is the process of performing a particular computation (or more generally, accomplishing a specific computing result), usually by designing and building an executable computer program. Programming involves tasks such as ana ...

, refers to the occurrence of events independent of the main

program flow In computer science, control flow (or flow of control) is the order in which individual statements, instructions or function calls of an imperative program are executed or evaluated. The emphasis on explicit control flow distinguishes an ''imp ...

and ways to deal with such events. These may be "outside" events such as the arrival of

signals In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The ''IEEE Transactions on Signal Processing'' ...

, or actions instigated by a program that take place concurrently with program execution, without the program blocking to wait for results.

Asynchronous input/output In computer science, asynchronous I/O (also non-sequential 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 overlapp ...

is an example of the latter case of asynchrony, and lets programs issue commands to storage or network devices that service these requests while the

processor Processor may refer to: Computing Hardware * Processor (computing) **Central processing unit (CPU), the hardware within a computer that executes a program *** Microprocessor, a central processing unit contained on a single integrated circuit (I ...

continues executing the program. Doing so provides a degree of parallelism. A common way for dealing with asynchrony in a

programming interface An application programming interface (API) is a way for two or more computer programs to communicate with each other. It is a type of software interface, offering a service to other pieces of software. A document or standard that describes how t ...

is to provide

subroutine In computer programming, a function or subroutine is a sequence of program instructions that performs a specific task, packaged as a unit. This unit can then be used in programs wherever that particular task should be performed. Functions may ...

s that return a future or promise that represents the ongoing operation, and a synchronizing operation that blocks until the future or promise is completed. Some programming languages, such as

Cilk Cilk, Cilk++, Cilk Plus and OpenCilk are general-purpose programming languages designed for multithreaded parallel computing. They are based on the C and C++ programming languages, which they extend with constructs to express parallel loops ...

, have special syntax for expressing an asynchronous procedure call. Examples of asynchrony include the following: *

Asynchronous procedure call Asynchronous procedure call is a unit of work in a computer. Usually a program works by executing a series of synchronous procedure calls on some thread. But if some data are not ready (for example, a program waits user to reply), then keeping thr ...

, a method to run a procedure concurrently, a lightweight alternative to Threads. *

Ajax Ajax may refer to: Greek mythology and tragedy * Ajax the Great, a Greek mythological hero, son of King Telamon and Periboea * Ajax the Lesser, a Greek mythological hero, son of Oileus, the king of Locris * ''Ajax'' (play), by the ancient Greek ...

is a set of

client-side Client-side refers to operations that are performed by the client in a client–server relationship in a computer network. General concepts Typically, a client is a computer application, such as a web browser, that runs on a user's local comput ...

web technologies used on the to create asynchronous I/O

web application A web application (or web app) is application software that is accessed using a web browser. Web applications are delivered on the World Wide Web to users with an active network connection. History In earlier computing models like client-serve ...

s. * Asynchronous method dispatch (AMD), a data communication method used when there is a need for the server side to handle a large number of long lasting client requests.ICE usage of AMD
Using synchronous method dispatch (SMD), this scenario may turn the server into an unavailable busy state resulting in a connection failure response caused by a

network Network, networking and networked may refer to: Science and technology * Network theory, the study of graphs as a representation of relations between discrete objects * Network science, an academic field that studies complex networks Mathematics ...

connection request

timeout Time-out, Time Out, or timeout may refer to: Time * Time-out (sport), in various sports, a break in play, called by a team * Television timeout, a break in sporting action so that a commercial break may be taken * Timeout (computing), an enginee ...

. The servicing of a client request is immediately dispatched to an available thread from a pool of threads and the client is put in a blocking state. Upon the completion of the task, the server is notified by a callback. The server unblocks the client and transmits the response back to the client. In case of thread

starvation Starvation is a severe deficiency in caloric energy intake, below the level needed to maintain an organism's life. It is the most extreme form of malnutrition. In humans, prolonged starvation can cause permanent organ damage and eventually, dea ...

, clients are blocked waiting for threads to become available.

References

Computer programming Inter-process communication Middleware {{comp-sci-stub

See also

References