Asynchrony (computer programming)

Asynchrony, in <a href="/facts/Computer_programming/QmSsFnu0">computer programming</a>, refers to the occurrence of events independent of the main <a href="/facts/Control_flow/2XTDfErC">program flow</a> and ways to deal with such events. These may be "outside" events such as the arrival of <a href="/facts/Unix_signal/IN6VK6r8">signals</a>, or actions instigated by a program that take place <a href="/facts/Concurrent_computing/yVzQBPr9">concurrently</a> with program execution, without the program <a href="/facts/Hang_(computing)/4Tx1l7xs">hanging</a> to wait for results. <a href="/facts/Asynchronous_I%2fO/6A7V3P89">Asynchronous input/output</a> 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 <a href="/facts/Central_processing_unit/Jxp1bqMV">processor</a> continues executing the program. Doing so provides a degree of <a href="/facts/Concurrency_(computer_science)/Ctnrrq4A">concurrency</a>.
A common way for dealing with asynchrony in a <a href="/facts/Application_programming_interface/GMlN4vUr">programming interface</a> is to provide <a href="/facts/Subroutine/9vFJrg0A">subroutines</a> that return a <a href="/facts/Futures_and_promises/5Mpgxv4m">future or promise</a> that represents the ongoing operation, and a synchronizing operation that <a href="/facts/Blocking_(computing)/6vvBpp7A">blocks</a> until the future or promise is completed. Some programming languages, such as <a href="/facts/Cilk/nIftzSWW">Cilk</a>, have special syntax for expressing an asynchronous procedure call.
Examples of asynchrony include the following:

<ul><li><a href="/facts/Asynchronous_procedure_call/Eyg3p9D3">Asynchronous procedure call</a>, a method to run a procedure concurrently, a lightweight alternative to <a href="/facts/Thread_(computing)/hh8WHyPd">threads</a>.</li>
<li><a href="/facts/Ajax_(programming)/cS0P0whT">Ajax</a> is a set of <a href="/facts/Client-side/v7DVfjsH">client-side</a> <a href="/facts/Web_development/UW5ypSzj">web technologies</a> used by the client to create asynchronous I/O <a href="/facts/Web_application/BLkF3BIN">web applications</a>.</li>
<li>Asynchronous method dispatch (AMD), a <a href="/facts/Data_communication/1yAhaANd">data communication</a> method used when there is a need for the server side to handle a large number of long lasting client requests. 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 <a href="/facts/Computer_network/3w5RM99p">network</a> connection request <a href="/facts/Timeout_(computing)/va8CczEQ">timeout</a>. The servicing of a client request is immediately dispatched to an available <a href="/facts/Thread_(computer_science)/hh8WHyPd">thread</a> from a <a href="/facts/Thread_pool_pattern/lFJlm6hL">pool of threads</a> 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 <a href="/facts/Starvation_(computer_science)/E9UjtIWS">starvation</a>, clients are blocked waiting for threads to become available.</li></ul>

Asynchrony (computer programming) open-in-new

Asynchrony (computer programming)