Asynchrony, in
computer programming
Computer programming or coding is the composition of sequences of instructions, called computer program, programs, that computers can follow to perform tasks. It involves designing and implementing algorithms, step-by-step specifications of proc ...
, 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 Statement (computer science), statements, Instruction (computer science), instructions or function calls of an imperative programming, imperative computer pro ...
and ways to deal with such events. These may be "outside" events such as the arrival of
signals, or actions instigated by a program that take place
concurrently with program execution, without the program
hanging
Hanging is killing a person by suspending them from the neck with a noose or ligature strangulation, ligature. Hanging has been a standard method of capital punishment since the Middle Ages, and has been the primary execution method in numerou ...
to wait for results.
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 continues executing the program. Doing so provides a degree of
concurrency.
A common way for dealing with asynchrony in a
programming interface is to provide
subroutines 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, have special syntax for expressing an asynchronous procedure call.
Examples of asynchrony include the following:
*
Asynchronous procedure call, a method to run a procedure concurrently, a lightweight alternative to
threads.
*
Ajax is a set of
client-side web technologies used by the client to create asynchronous I/O
web applications.
* Asynchronous method dispatch (AMD), a
data communication
Data communication, including data transmission and data reception, is the transfer of data, transmitted and received over a point-to-point or point-to-multipoint communication channel. Examples of such channels are copper wires, optic ...
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 connection request timeout. 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, clients are blocked waiting for threads to become available.
See also
* Asynchronous system
* Asynchronous circuit
Asynchronous circuit (clockless or self-timed circuit) is a sequential logic, sequential digital logic electrical network, circuit that does not use a global clock circuit or clock signal, signal generator to synchronize its components. Instea ...
References
Computer programming
Inter-process communication
Middleware
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