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<!-- Generated by pkgdown: do not edit by hand --><html lang="en"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><meta charset="utf-8"><meta http-equiv="X-UA-Compatible" content="IE=edge"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Task or computation that proceeds in the background — ExtendedTask • shiny</title><!-- jquery --><script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.7.1/jquery.min.js" integrity="sha512-v2CJ7UaYy4JwqLDIrZUI/4hqeoQieOmAZNXBeQyjo21dadnwR+8ZaIJVT8EE2iyI61OV8e6M8PP2/4hpQINQ/g==" crossorigin="anonymous" referrerpolicy="no-referrer"></script><!-- Bootstrap --><link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.4.1/css/bootstrap.min.css" integrity="sha256-bZLfwXAP04zRMK2BjiO8iu9pf4FbLqX6zitd+tIvLhE=" crossorigin="anonymous"><script src="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.4.1/js/bootstrap.min.js" integrity="sha256-nuL8/2cJ5NDSSwnKD8VqreErSWHtnEP9E7AySL+1ev4=" crossorigin="anonymous"></script><!-- bootstrap-toc --><link rel="stylesheet" href="../bootstrap-toc.css"><script src="../bootstrap-toc.js"></script><!-- Font Awesome icons --><link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/5.12.1/css/all.min.css" integrity="sha256-mmgLkCYLUQbXn0B1SRqzHar6dCnv9oZFPEC1g1cwlkk=" crossorigin="anonymous"><link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/5.12.1/css/v4-shims.min.css" integrity="sha256-wZjR52fzng1pJHwx4aV2AO3yyTOXrcDW7jBpJtTwVxw=" crossorigin="anonymous"><!-- clipboard.js --><script src="https://cdnjs.cloudflare.com/ajax/libs/clipboard.js/2.0.6/clipboard.min.js" integrity="sha256-inc5kl9MA1hkeYUt+EC3BhlIgyp/2jDIyBLS6k3UxPI=" crossorigin="anonymous"></script><!-- headroom.js --><script src="https://cdnjs.cloudflare.com/ajax/libs/headroom/0.11.0/headroom.min.js" integrity="sha256-AsUX4SJE1+yuDu5+mAVzJbuYNPHj/WroHuZ8Ir/CkE0=" crossorigin="anonymous"></script><script src="https://cdnjs.cloudflare.com/ajax/libs/headroom/0.11.0/jQuery.headroom.min.js" integrity="sha256-ZX/yNShbjqsohH1k95liqY9Gd8uOiE1S4vZc+9KQ1K4=" crossorigin="anonymous"></script><!-- pkgdown --><link href="../pkgdown.css" rel="stylesheet"><script src="../pkgdown.js"></script><meta property="og:title" content="Task or computation that proceeds in the background — ExtendedTask"><meta property="og:description" content="In normal Shiny reactive code, whenever an observer, calc, or
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output is busy computing, it blocks the current session from receiving any
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inputs or attempting to proceed with any other computation related to that
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session.
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The ExtendedTask class allows you to have an expensive operation that is
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started by a reactive effect, and whose (eventual) results can be accessed
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by a regular observer, calc, or output; but during the course of the
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operation, the current session is completely unblocked, allowing the user
|
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to continue using the rest of the app while the operation proceeds in the
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background.
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Note that each ExtendedTask object does not represent a single
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invocation of its long-running function. Rather, it's an object that is
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used to invoke the function with different arguments, keeps track of
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whether an invocation is in progress, and provides ways to get at the
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current status or results of the operation. A single ExtendedTask object
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does not permit overlapping invocations: if the invoke() method is called
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before the previous invoke() is completed, the new invocation will not
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begin until the previous invocation has completed."><meta property="og:image" content="/logo.png"><!-- mathjax --><script src="https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.5/MathJax.js" integrity="sha256-nvJJv9wWKEm88qvoQl9ekL2J+k/RWIsaSScxxlsrv8k=" crossorigin="anonymous"></script><script src="https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.5/config/TeX-AMS-MML_HTMLorMML.js" integrity="sha256-84DKXVJXs0/F8OTMzX4UR909+jtl4G7SPypPavF+GfA=" crossorigin="anonymous"></script><!--[if lt IE 9]>
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<span class="version label label-default" data-toggle="tooltip" data-placement="bottom" title="">1.12.0.9000</span>
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</header><div class="row">
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<div class="col-md-9 contents">
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<div class="page-header">
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<h1>Task or computation that proceeds in the background</h1>
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<small class="dont-index">Source: <a href="https://github.com/rstudio/shiny/blob/rc-v1.12.1/R/extended-task.R" class="external-link"><code>R/extended-task.R</code></a></small>
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<div class="hidden name"><code>ExtendedTask.Rd</code></div>
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</div>
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<div class="ref-description">
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<p>In normal Shiny reactive code, whenever an observer, calc, or
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output is busy computing, it blocks the current session from receiving any
|
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inputs or attempting to proceed with any other computation related to that
|
||
session.</p>
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<p>The <code>ExtendedTask</code> class allows you to have an expensive operation that is
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started by a reactive effect, and whose (eventual) results can be accessed
|
||
by a regular observer, calc, or output; but during the course of the
|
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operation, the current session is completely unblocked, allowing the user
|
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to continue using the rest of the app while the operation proceeds in the
|
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background.</p>
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<p>Note that each <code>ExtendedTask</code> object does not represent a <em>single
|
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invocation</em> of its long-running function. Rather, it's an object that is
|
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used to invoke the function with different arguments, keeps track of
|
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whether an invocation is in progress, and provides ways to get at the
|
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current status or results of the operation. A single <code>ExtendedTask</code> object
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does not permit overlapping invocations: if the <code>invoke()</code> method is called
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before the previous <code>invoke()</code> is completed, the new invocation will not
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begin until the previous invocation has completed.</p>
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</div>
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<div id="extendedtask-versus-asynchronous-reactives">
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<h2><code>ExtendedTask</code> versus asynchronous reactives</h2>
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<p>Shiny has long supported <a href="https://rstudio.github.io/promises/articles/promises_06_shiny.html" class="external-link">using {promises}</a>
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to write asynchronous observers, calcs, or outputs. You may be wondering
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what the differences are between those techniques and this class.</p>
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<p>Asynchronous observers, calcs, and outputs are not–and have never
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been–designed to let a user start a long-running operation, while keeping
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that very same (browser) session responsive to other interactions. Instead,
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they unblock other sessions, so you can take a long-running operation that
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would normally bring the entire R process to a halt and limit the blocking
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to just the session that started the operation. (For more details, see the
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section on <a href="https://rstudio.github.io/promises/articles/promises_06_shiny.html#the-flush-cycle" class="external-link">"The Flush Cycle"</a>.)</p>
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<p><code>ExtendedTask</code>, on the other hand, invokes an asynchronous function (that
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is, a function that quickly returns a promise) and allows even that very
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session to immediately unblock and carry on with other user interactions.</p>
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</div>
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<div id="methods">
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<h2>Methods</h2>
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<div class="section">
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<h3 id="public-methods">Public methods<a class="anchor" aria-label="anchor" href="#public-methods"></a></h3>
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<ul><li><p><a href="#method-ExtendedTask-new"><code>ExtendedTask$new()</code></a></p></li>
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<li><p><a href="#method-ExtendedTask-invoke"><code>ExtendedTask$invoke()</code></a></p></li>
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<li><p><a href="#method-ExtendedTask-status"><code>ExtendedTask$status()</code></a></p></li>
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<li><p><a href="#method-ExtendedTask-result"><code>ExtendedTask$result()</code></a></p></li>
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</ul></div><p></p><hr><a id="method-ExtendedTask-new"></a><div class="section">
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<h3 id="method-new-">Method <code><a href="https://rdrr.io/r/methods/new.html" class="external-link">new()</a></code><a class="anchor" aria-label="anchor" href="#method-new-"></a></h3>
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<p>Creates a new <code>ExtendedTask</code> object. <code>ExtendedTask</code> should generally be
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created either at the top of a server function, or at the top of a module
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server function.</p><div class="section">
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<h4 id="usage">Usage<a class="anchor" aria-label="anchor" href="#usage"></a></h4>
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<p></p><div class="r"><div class="sourceCode"><pre><code><span><span class="va"><a href="../reference/ExtendedTask.html">ExtendedTask</a></span><span class="op">$</span><span class="fu">new</span><span class="op">(</span><span class="va">func</span><span class="op">)</span></span></code></pre></div><p></p></div>
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</div>
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<div class="section">
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<h4 id="arguments">Arguments<a class="anchor" aria-label="anchor" href="#arguments"></a></h4>
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<p></p><div class="arguments"><dl><dt><code>func</code></dt>
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<dd><p>The long-running operation to execute. This should be an
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asynchronous function, meaning, it should use the
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<a href="https://rstudio.github.io/promises/" class="external-link">{promises}</a> package, most
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likely in conjunction with the
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<a href="https://mirai.r-lib.org" class="external-link">{mirai}</a> or
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<a href="https://rstudio.github.io/promises/articles/promises_04_futures.html" class="external-link">{future}</a>
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package. (In short, the return value of <code>func</code> should be a
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<code><a href="https://mirai.r-lib.org/reference/mirai.html" class="external-link">mirai</a></code>, <code><a href="https://future.futureverse.org/reference/future.html" class="external-link">Future</a></code>, <code>promise</code>,
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or something else that <code><a href="https://rstudio.github.io/promises/reference/is.promise.html" class="external-link">promises::as.promise()</a></code> understands.)</p>
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<p>It's also important that this logic does not read from any
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reactive inputs/sources, as inputs may change after the function is
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invoked; instead, if the function needs to access reactive inputs, it
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should take parameters and the caller of the <code>invoke()</code> method should
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read reactive inputs and pass them as arguments.</p></dd>
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</dl><p></p></div>
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</div>
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</div><p></p><hr><a id="method-ExtendedTask-invoke"></a><div class="section">
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<h3 id="method-invoke-">Method <code>invoke()</code><a class="anchor" aria-label="anchor" href="#method-invoke-"></a></h3>
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<p>Starts executing the long-running operation. If this <code>ExtendedTask</code> is
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already running (meaning, a previous call to <code>invoke()</code> is not yet
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complete) then enqueues this invocation until after the current
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invocation, and any already-enqueued invocation, completes.</p><div class="section">
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<h4 id="usage-1">Usage<a class="anchor" aria-label="anchor" href="#usage-1"></a></h4>
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<p></p><div class="r"><div class="sourceCode"><pre><code><span><span class="va">ExtendedTask</span><span class="op">$</span><span class="fu">invoke</span><span class="op">(</span><span class="va">...</span><span class="op">)</span></span></code></pre></div><p></p></div>
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</div>
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<div class="section">
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<h4 id="arguments-1">Arguments<a class="anchor" aria-label="anchor" href="#arguments-1"></a></h4>
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<p></p><div class="arguments"><dl><dt><code>...</code></dt>
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<dd><p>Parameters to use for this invocation of the underlying
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function. If reactive inputs are needed by the underlying function,
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they should be read by the caller of <code>invoke</code> and passed in as
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arguments.</p></dd>
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</dl><p></p></div>
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</div>
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</div><p></p><hr><a id="method-ExtendedTask-status"></a><div class="section">
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<h3 id="method-status-">Method <code><a href="https://mirai.r-lib.org/reference/status.html" class="external-link">status()</a></code><a class="anchor" aria-label="anchor" href="#method-status-"></a></h3>
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<p>This is a reactive read that invalidates the caller when the task's
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status changes.</p>
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<p>Returns one of the following values:</p><ul><li><p><code>"initial"</code>: This <code>ExtendedTask</code> has not yet been invoked</p></li>
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<li><p><code>"running"</code>: An invocation is currently running</p></li>
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<li><p><code>"success"</code>: An invocation completed successfully, and a value can be
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retrieved via the <code>result()</code> method</p></li>
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<li><p><code>"error"</code>: An invocation completed with an error, which will be
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re-thrown if you call the <code>result()</code> method</p></li>
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</ul><div class="section">
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<h4 id="usage-2">Usage<a class="anchor" aria-label="anchor" href="#usage-2"></a></h4>
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<p></p><div class="r"><div class="sourceCode"><pre><code><span><span class="va">ExtendedTask</span><span class="op">$</span><span class="fu">status</span><span class="op">(</span><span class="op">)</span></span></code></pre></div><p></p></div>
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</div>
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</div><p></p><hr><a id="method-ExtendedTask-result"></a><div class="section">
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<h3 id="method-result-">Method <code>result()</code><a class="anchor" aria-label="anchor" href="#method-result-"></a></h3>
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<p>Attempts to read the results of the most recent invocation. This is a
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reactive read that invalidates as the task's status changes.</p>
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<p>The actual behavior differs greatly depending on the current status of
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the task:</p><ul><li><p><code>"initial"</code>: Throws a silent error (like <code><a href="req.html">req(FALSE)</a></code>). If
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this happens during output rendering, the output will be blanked out.</p></li>
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<li><p><code>"running"</code>: Throws a special silent error that, if it happens during
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output rendering, makes the output appear "in progress" until further
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notice.</p></li>
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<li><p><code>"success"</code>: Returns the return value of the most recent invocation.</p></li>
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<li><p><code>"error"</code>: Throws whatever error was thrown by the most recent
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invocation.</p></li>
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</ul><p>This method is intended to be called fairly naively by any output or
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reactive expression that cares about the output–you just have to be
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aware that if the result isn't ready for whatever reason, processing will
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stop in much the same way as <code>req(FALSE)</code> does, but when the result is
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ready you'll get invalidated, and when you run again the result should be
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there.</p>
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<p>Note that the <code>result()</code> method is generally not meant to be used with
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<code><a href="observeEvent.html">observeEvent()</a></code>, <code><a href="observeEvent.html">eventReactive()</a></code>, <code><a href="bindEvent.html">bindEvent()</a></code>, or <code><a href="isolate.html">isolate()</a></code> as the
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invalidation will be ignored.</p><div class="section">
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<h4 id="usage-3">Usage<a class="anchor" aria-label="anchor" href="#usage-3"></a></h4>
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<p></p><div class="r"><div class="sourceCode"><pre><code><span><span class="va">ExtendedTask</span><span class="op">$</span><span class="fu">result</span><span class="op">(</span><span class="op">)</span></span></code></pre></div><p></p></div>
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</div>
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</div>
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</div>
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<div id="ref-examples">
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<h2>Examples</h2>
|
||
<div class="sourceCode"><pre class="sourceCode r"><code><span class="r-in"><span><span class="kw">if</span> <span class="op">(</span><span class="cn">FALSE</span><span class="op">)</span> <span class="op">{</span> <span class="co"># rlang::is_interactive() && rlang::is_installed("mirai")</span></span></span>
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<span class="r-in"><span><span class="kw"><a href="https://rdrr.io/r/base/library.html" class="external-link">library</a></span><span class="op">(</span><span class="va"><a href="https://shiny.posit.co/" class="external-link">shiny</a></span><span class="op">)</span></span></span>
|
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<span class="r-in"><span><span class="kw"><a href="https://rdrr.io/r/base/library.html" class="external-link">library</a></span><span class="op">(</span><span class="va"><a href="https://rstudio.github.io/bslib/" class="external-link">bslib</a></span><span class="op">)</span></span></span>
|
||
<span class="r-in"><span><span class="kw"><a href="https://rdrr.io/r/base/library.html" class="external-link">library</a></span><span class="op">(</span><span class="va"><a href="https://mirai.r-lib.org" class="external-link">mirai</a></span><span class="op">)</span></span></span>
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<span class="r-in"><span></span></span>
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<span class="r-in"><span><span class="co"># Set background processes for running tasks</span></span></span>
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<span class="r-in"><span><span class="fu"><a href="https://mirai.r-lib.org/reference/daemons.html" class="external-link">daemons</a></span><span class="op">(</span><span class="fl">1</span><span class="op">)</span></span></span>
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<span class="r-in"><span><span class="co"># Reset when the app is stopped</span></span></span>
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||
<span class="r-in"><span><span class="fu"><a href="onStop.html">onStop</a></span><span class="op">(</span><span class="kw">function</span><span class="op">(</span><span class="op">)</span> <span class="fu"><a href="https://mirai.r-lib.org/reference/daemons.html" class="external-link">daemons</a></span><span class="op">(</span><span class="fl">0</span><span class="op">)</span><span class="op">)</span></span></span>
|
||
<span class="r-in"><span></span></span>
|
||
<span class="r-in"><span><span class="va">ui</span> <span class="op"><-</span> <span class="fu"><a href="https://rstudio.github.io/bslib/reference/page.html" class="external-link">page_fluid</a></span><span class="op">(</span></span></span>
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||
<span class="r-in"><span> <span class="fu"><a href="titlePanel.html">titlePanel</a></span><span class="op">(</span><span class="st">"Extended Task Demo"</span><span class="op">)</span>,</span></span>
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||
<span class="r-in"><span> <span class="fu"><a href="https://rstudio.github.io/htmltools/reference/builder.html" class="external-link">p</a></span><span class="op">(</span></span></span>
|
||
<span class="r-in"><span> <span class="st">'Click the button below to perform a "calculation"'</span>,</span></span>
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<span class="r-in"><span> <span class="st">"that takes a while to perform."</span></span></span>
|
||
<span class="r-in"><span> <span class="op">)</span>,</span></span>
|
||
<span class="r-in"><span> <span class="fu"><a href="https://rstudio.github.io/bslib/reference/input_task_button.html" class="external-link">input_task_button</a></span><span class="op">(</span><span class="st">"recalculate"</span>, <span class="st">"Recalculate"</span><span class="op">)</span>,</span></span>
|
||
<span class="r-in"><span> <span class="fu"><a href="https://rstudio.github.io/htmltools/reference/builder.html" class="external-link">p</a></span><span class="op">(</span><span class="fu"><a href="textOutput.html">textOutput</a></span><span class="op">(</span><span class="st">"result"</span><span class="op">)</span><span class="op">)</span></span></span>
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||
<span class="r-in"><span><span class="op">)</span></span></span>
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||
<span class="r-in"><span></span></span>
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||
<span class="r-in"><span><span class="va">server</span> <span class="op"><-</span> <span class="kw">function</span><span class="op">(</span><span class="va">input</span>, <span class="va">output</span><span class="op">)</span> <span class="op">{</span></span></span>
|
||
<span class="r-in"><span> <span class="va">rand_task</span> <span class="op"><-</span> <span class="va">ExtendedTask</span><span class="op">$</span><span class="fu">new</span><span class="op">(</span><span class="kw">function</span><span class="op">(</span><span class="op">)</span> <span class="op">{</span></span></span>
|
||
<span class="r-in"><span> <span class="fu"><a href="https://mirai.r-lib.org/reference/mirai.html" class="external-link">mirai</a></span><span class="op">(</span></span></span>
|
||
<span class="r-in"><span> <span class="op">{</span></span></span>
|
||
<span class="r-in"><span> <span class="co"># Slow operation goes here</span></span></span>
|
||
<span class="r-in"><span> <span class="fu"><a href="https://rdrr.io/r/base/Sys.sleep.html" class="external-link">Sys.sleep</a></span><span class="op">(</span><span class="fl">2</span><span class="op">)</span></span></span>
|
||
<span class="r-in"><span> <span class="fu"><a href="https://rdrr.io/r/base/sample.html" class="external-link">sample</a></span><span class="op">(</span><span class="fl">1</span><span class="op">:</span><span class="fl">100</span>, <span class="fl">1</span><span class="op">)</span></span></span>
|
||
<span class="r-in"><span> <span class="op">}</span></span></span>
|
||
<span class="r-in"><span> <span class="op">)</span></span></span>
|
||
<span class="r-in"><span> <span class="op">}</span><span class="op">)</span></span></span>
|
||
<span class="r-in"><span></span></span>
|
||
<span class="r-in"><span> <span class="co"># Make button state reflect task.</span></span></span>
|
||
<span class="r-in"><span> <span class="co"># If using R >=4.1, you can do this instead:</span></span></span>
|
||
<span class="r-in"><span> <span class="co"># rand_task <- ExtendedTask$new(...) |> bind_task_button("recalculate")</span></span></span>
|
||
<span class="r-in"><span> <span class="fu"><a href="https://rstudio.github.io/bslib/reference/bind_task_button.html" class="external-link">bind_task_button</a></span><span class="op">(</span><span class="va">rand_task</span>, <span class="st">"recalculate"</span><span class="op">)</span></span></span>
|
||
<span class="r-in"><span></span></span>
|
||
<span class="r-in"><span> <span class="fu"><a href="observeEvent.html">observeEvent</a></span><span class="op">(</span><span class="va">input</span><span class="op">$</span><span class="va">recalculate</span>, <span class="op">{</span></span></span>
|
||
<span class="r-in"><span> <span class="co"># Invoke the extended in an observer</span></span></span>
|
||
<span class="r-in"><span> <span class="va">rand_task</span><span class="op">$</span><span class="fu">invoke</span><span class="op">(</span><span class="op">)</span></span></span>
|
||
<span class="r-in"><span> <span class="op">}</span><span class="op">)</span></span></span>
|
||
<span class="r-in"><span></span></span>
|
||
<span class="r-in"><span> <span class="va">output</span><span class="op">$</span><span class="va">result</span> <span class="op"><-</span> <span class="fu"><a href="renderPrint.html">renderText</a></span><span class="op">(</span><span class="op">{</span></span></span>
|
||
<span class="r-in"><span> <span class="co"># React to updated results when the task completes</span></span></span>
|
||
<span class="r-in"><span> <span class="va">number</span> <span class="op"><-</span> <span class="va">rand_task</span><span class="op">$</span><span class="fu">result</span><span class="op">(</span><span class="op">)</span></span></span>
|
||
<span class="r-in"><span> <span class="fu"><a href="https://rdrr.io/r/base/paste.html" class="external-link">paste0</a></span><span class="op">(</span><span class="st">"Your number is "</span>, <span class="va">number</span>, <span class="st">"."</span><span class="op">)</span></span></span>
|
||
<span class="r-in"><span> <span class="op">}</span><span class="op">)</span></span></span>
|
||
<span class="r-in"><span><span class="op">}</span></span></span>
|
||
<span class="r-in"><span></span></span>
|
||
<span class="r-in"><span><span class="fu"><a href="shinyApp.html">shinyApp</a></span><span class="op">(</span><span class="va">ui</span>, <span class="va">server</span><span class="op">)</span></span></span>
|
||
<span class="r-in"><span><span class="op">}</span></span></span>
|
||
</code></pre></div>
|
||
</div>
|
||
</div>
|
||
<div class="col-md-3 hidden-xs hidden-sm" id="pkgdown-sidebar">
|
||
<nav id="toc" data-toggle="toc" class="sticky-top"><h2 data-toc-skip>Contents</h2>
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||
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|
||
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||
|
||
<footer><div class="copyright">
|
||
<p></p><p>Developed by Winston Chang, Joe Cheng, JJ Allaire, Carson Sievert, Barret Schloerke, Garrick Aden-Buie, Yihui Xie, Jeff Allen, Jonathan McPherson, Alan Dipert, Barbara Borges, Posit Software, PBC.</p>
|
||
</div>
|
||
|
||
<div class="pkgdown">
|
||
<p></p><p>Site built with <a href="https://pkgdown.r-lib.org/" class="external-link">pkgdown</a> 2.2.0.</p>
|
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|
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|
||
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||
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