{"id":837,"date":"2023-03-10T10:37:19","date_gmt":"2023-03-10T03:37:19","guid":{"rendered":"https:\/\/csharptutorial.net\/?page_id=837"},"modified":"2023-03-10T10:41:25","modified_gmt":"2023-03-10T03:41:25","slug":"csharp-whenany","status":"publish","type":"page","link":"https:\/\/www.csharptutorial.net\/csharp-concurrency\/csharp-whenany\/","title":{"rendered":"C# WhenAny"},"content":{"rendered":"\n<p><strong>Summary<\/strong>: in this tutorial, you&#8217;ll learn how to use the C# <code>WhenAny()<\/code> static method of the <code>Task<\/code> class to create a task that will complete when any of the input tasks have been completed.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Introduction to the C# WhenAny() method<\/h2>\n\n\n\n<p>The <code>Task.WhenAny()<\/code> is a static method of the <code><a href=\"https:\/\/csharptutorial.net\/csharp-concurrency\/csharp-task\/\">Task<\/a><\/code> class that allows you to wait for the first task in a collection of tasks to complete.<\/p>\n\n\n\n<p>When a task completes, the <code>Task.WhenAny()<\/code> returns a <code>Task&lt;T><\/code> object that represents the completed task.<\/p>\n\n\n\n<p>To use the <code>Task.WhenAny()<\/code> method, you follow these steps:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>First, pass a collection of tasks to the method.<\/li>\n\n\n\n<li>Second, use the <code><a href=\"https:\/\/csharptutorial.net\/csharp-concurrency\/csharp-async-await\/\">await<\/a><\/code> keyword to wait for any of the tasks in the collection to complete.<\/li>\n\n\n\n<li>Third, assign the completed task to a variable and use the <code>await<\/code> keyword again to get the result.<\/li>\n<\/ul>\n\n\n\n<p>The C# <code>WhenAny()<\/code> method is useful when you have to make multiple HTTP requests to different APIs and process the first result.<\/p>\n\n\n\n<p>For example, suppose you have an app that displays the latest news from multiple sources, each source has an API. <\/p>\n\n\n\n<p>To display the news as soon as possible, you can use the <code>Task.WhenAny()<\/code> method to wait for the first API request to complete, display the news and continue fetching the news from other APIs in parallel.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">A simple C# WhenAny() method example<\/h2>\n\n\n\n<p>The following example demonstrates how to use the <code>WhenAny()<\/code> method:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-1\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript\"><span class=\"hljs-keyword\">static<\/span> <span class=\"hljs-keyword\">async<\/span> Task&lt;int&gt; DoWork(int number, int ms)\n{\n    <span class=\"hljs-keyword\">await<\/span> Task.Delay(ms);\n    <span class=\"hljs-keyword\">return<\/span> number;\n}\n\n<span class=\"hljs-keyword\">var<\/span> t1 = Task.Run(<span class=\"hljs-function\"><span class=\"hljs-params\">()<\/span> =&gt;<\/span> DoWork(<span class=\"hljs-number\">1<\/span>, <span class=\"hljs-number\">1000<\/span>));\n<span class=\"hljs-keyword\">var<\/span> t2 = Task.Run(<span class=\"hljs-function\"><span class=\"hljs-params\">()<\/span> =&gt;<\/span> DoWork(<span class=\"hljs-number\">2<\/span>, <span class=\"hljs-number\">500<\/span>));\n\nTask&lt;int&gt; completedTask = <span class=\"hljs-keyword\">await<\/span> Task.WhenAny(t1, t2);\nint result = <span class=\"hljs-keyword\">await<\/span> completedTask;\n\nConsole.WriteLine(result);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-1\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>How it works.<\/p>\n\n\n\n<p>First, define the <code>DoWork()<\/code> method that accepts two parameters: <code>number<\/code>, an integer, and <code>ms<\/code>, a number of milliseconds. The method returns the <code>number<\/code> after a delay of <code>ms<\/code> milliseconds:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-2\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript\"><span class=\"hljs-keyword\">static<\/span> <span class=\"hljs-keyword\">async<\/span> Task&lt;int&gt; DoWork(int number, int ms)\n{\n    <span class=\"hljs-keyword\">await<\/span> Task.Delay(ms);\n    <span class=\"hljs-keyword\">return<\/span> number;\n}<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-2\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Second, create two tasks <code>t1<\/code> and <code>t2<\/code> using the <code>Task.Run()<\/code> method. The tasks execute the <code>DoWork()<\/code> method with different parameters:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><code>t1<\/code> call <code>DoWork(1,1000)<\/code> that delays for <code>1000<\/code> milliseconds before returning the number <code>1<\/code>.<\/li>\n\n\n\n<li><code>t2<\/code> call <code>DoWork(2,500)<\/code> that delays for <code>500<\/code> milliseconds before returning the number <code>2<\/code>.<\/li>\n<\/ul>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-3\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript\"><span class=\"hljs-keyword\">var<\/span> t1 = Task.Run(<span class=\"hljs-function\"><span class=\"hljs-params\">()<\/span> =&gt;<\/span> DoWork(<span class=\"hljs-number\">1<\/span>, <span class=\"hljs-number\">1000<\/span>));\n<span class=\"hljs-keyword\">var<\/span> t2 = Task.Run(<span class=\"hljs-function\"><span class=\"hljs-params\">()<\/span> =&gt;<\/span> DoWork(<span class=\"hljs-number\">2<\/span>, <span class=\"hljs-number\">500<\/span>));<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-3\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Third, use the <code>Task.WhenAny()<\/code> method to wait for either <code>t1<\/code> or <code>t2<\/code> to complete, whichever finishes first. When one of the tasks completes,  the <code>Task.WhenAny()<\/code> method returns a <code>Task&lt;int><\/code> object that represents the completed task. <\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-4\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript\">Task&lt;int&gt; completedTask = <span class=\"hljs-keyword\">await<\/span> Task.WhenAny(t1, t2);\nint result = <span class=\"hljs-keyword\">await<\/span> completedTask;<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-4\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Fourth, use the <code>await<\/code> keyword to wait for the <code>Task&lt;int&gt;<\/code> object to complete and assign the result to <code>completedTask<\/code> variable:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-5\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript\">int result = <span class=\"hljs-keyword\">await<\/span> completedTask;<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-5\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Finally, output the result to the console:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-6\" data-shcb-language-name=\"CSS\" data-shcb-language-slug=\"css\"><span><code class=\"hljs language-css\"><span class=\"hljs-selector-tag\">Console<\/span><span class=\"hljs-selector-class\">.WriteLine<\/span>(<span class=\"hljs-selector-tag\">result<\/span>);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-6\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">CSS<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">css<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<h2 class=\"wp-block-heading\">Practical use of the C# WhenAny() method<\/h2>\n\n\n\n<p>The following program attempts to download two images from different URLs and saves the first one using the C# WhenAny() method:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-7\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript\">\r<span class=\"hljs-comment\">\/\/ Define the URLs of the two images<\/span>\r\nstring url1 = <span class=\"hljs-string\">\"https:\/\/via.placeholder.com\/600\/771796\"<\/span>;\r\nstring url2 = <span class=\"hljs-string\">\"https:\/\/via.placeholder.com\/600\/24f355\"<\/span>;\r\n\r\n<span class=\"hljs-comment\">\/\/ Create two tasks to request the two images asynchronously<\/span>\r\nHttpClient client = <span class=\"hljs-keyword\">new<\/span>();\r\n\r\n<span class=\"hljs-keyword\">var<\/span> t1 = client.GetByteArrayAsync(url1);\r\n<span class=\"hljs-keyword\">var<\/span> t2 = client.GetByteArrayAsync(url2);\r\n\r\n<span class=\"hljs-comment\">\/\/ Wait for the first task to complete<\/span>\r\n<span class=\"hljs-keyword\">var<\/span> completedTask = <span class=\"hljs-keyword\">await<\/span> Task.WhenAny(t1, t2);\r\n\r\n<span class=\"hljs-comment\">\/\/ Save the result of the first task to a file<\/span>\r\nbyte&#91;] bytes = <span class=\"hljs-keyword\">await<\/span> completedTask;\r\nstring fileName = <span class=\"hljs-string\">\"image.jpg\"<\/span>;\r\nFile.WriteAllBytes(fileName, bytes);\r\n\r\nConsole.WriteLine($<span class=\"hljs-string\">\"The picture has been saved to {fileName}\"<\/span>);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-7\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>How it works.<\/p>\n\n\n\n<p>First, define the URLs of the two images to download:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-8\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript\">string url1 = <span class=\"hljs-string\">\"https:\/\/via.placeholder.com\/600\/771796\"<\/span>;\r\nstring url2 = <span class=\"hljs-string\">\"https:\/\/via.placeholder.com\/600\/24f355\"<\/span>;<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-8\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Second, create a new instance of the <code>HttpClient<\/code> class to make HTTP requests:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-9\" data-shcb-language-name=\"C#\" data-shcb-language-slug=\"cs\"><span><code class=\"hljs language-cs\">HttpClient client = <span class=\"hljs-keyword\">new<\/span>();<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-9\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">C#<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">cs<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Third, create two tasks that download the two pictures asynchronously. The <code>GetByteArrayAsync()<\/code> method returns a <code>Task&lt;byte[]><\/code> object:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-10\" data-shcb-language-name=\"C#\" data-shcb-language-slug=\"cs\"><span><code class=\"hljs language-cs\"><span class=\"hljs-keyword\">var<\/span> t1 = client.GetByteArrayAsync(url1);\r\n<span class=\"hljs-keyword\">var<\/span> t2 = client.GetByteArrayAsync(url2);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-10\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">C#<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">cs<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Fourth, use the Task.WhenAny() method to wait for the first task to complete:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-11\" data-shcb-language-name=\"C#\" data-shcb-language-slug=\"cs\"><span><code class=\"hljs language-cs\"><span class=\"hljs-keyword\">var<\/span> completedTask = <span class=\"hljs-keyword\">await<\/span> Task.WhenAny(t1, t2);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-11\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">C#<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">cs<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Finally, save the result of the first task into a file:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-12\" data-shcb-language-name=\"C#\" data-shcb-language-slug=\"cs\"><span><code class=\"hljs language-cs\"><span class=\"hljs-keyword\">byte<\/span>&#91;] bytes = <span class=\"hljs-keyword\">await<\/span> completedTask;\r\n<span class=\"hljs-keyword\">string<\/span> fileName = <span class=\"hljs-string\">\"image.jpg\"<\/span>;\r\nFile.WriteAllBytes(fileName, bytes);\r\n\r\nConsole.WriteLine(<span class=\"hljs-string\">$\"Saved the picture to <span class=\"hljs-subst\">{fileName}<\/span>\"<\/span>);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-12\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">C#<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">cs<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<h2 class=\"wp-block-heading\">Summary<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Use the C# <code>WhenAny()<\/code> method to wait for the first task in a collection of tasks to finish.<\/li>\n<\/ul>\n<div class=\"helpful-block-content\" data-title=\"\">\n\t<header>\n\t\t<div class=\"wth-question\">Was this tutorial helpful ?<\/div>\n\t\t<div class=\"wth-thumbs\">\n\t\t\t<button\n\t\t\t\tdata-post=\"837\"\n\t\t\t\tdata-post-url=\"https:\/\/www.csharptutorial.net\/csharp-concurrency\/csharp-whenany\/\"\n\t\t\t\tdata-post-title=\"C# WhenAny\"\n\t\t\t\tdata-response=\"1\"\n\t\t\t\tclass=\"wth-btn-rounded wth-yes-btn\"\n\t\t\t>\n\t\t\t\t<svg\n\t\t\t\t\txmlns=\"http:\/\/www.w3.org\/2000\/svg\"\n\t\t\t\t\tviewBox=\"0 0 24 24\"\n\t\t\t\t\tfill=\"none\"\n\t\t\t\t\tstroke=\"currentColor\"\n\t\t\t\t\tstroke-width=\"2\"\n\t\t\t\t\tstroke-linecap=\"round\"\n\t\t\t\t\tstroke-linejoin=\"round\"\n\t\t\t\t\tclass=\"feather feather-thumbs-up block w-full h-full\"\n\t\t\t\t>\n\t\t\t\t\t<path\n\t\t\t\t\t\td=\"M14 9V5a3 3 0 0 0-3-3l-4 9v11h11.28a2 2 0 0 0 2-1.7l1.38-9a2 2 0 0 0-2-2.3zM7 22H4a2 2 0 0 1-2-2v-7a2 2 0 0 1 2-2h3\"\n\t\t\t\t\t><\/path>\n\t\t\t\t<\/svg>\n\t\t\t\t<span class=\"sr-only\"> Yes <\/span>\n\t\t\t<\/button>\n\n\t\t\t<button\n\t\t\t\tdata-response=\"0\"\n\t\t\t\tdata-post=\"837\"\n\t\t\t\tdata-post-url=\"https:\/\/www.csharptutorial.net\/csharp-concurrency\/csharp-whenany\/\"\n\t\t\t\tdata-post-title=\"C# WhenAny\"\n\t\t\t\tclass=\"wth-btn-rounded wth-no-btn\"\n\t\t\t>\n\t\t\t\t<svg\n\t\t\t\t\txmlns=\"http:\/\/www.w3.org\/2000\/svg\"\n\t\t\t\t\tviewBox=\"0 0 24 24\"\n\t\t\t\t\tfill=\"none\"\n\t\t\t\t\tstroke=\"currentColor\"\n\t\t\t\t\tstroke-width=\"2\"\n\t\t\t\t\tstroke-linecap=\"round\"\n\t\t\t\t\tstroke-linejoin=\"round\"\n\t\t\t\t>\n\t\t\t\t\t<path\n\t\t\t\t\t\td=\"M10 15v4a3 3 0 0 0 3 3l4-9V2H5.72a2 2 0 0 0-2 1.7l-1.38 9a2 2 0 0 0 2 2.3zm7-13h2.67A2.31 2.31 0 0 1 22 4v7a2.31 2.31 0 0 1-2.33 2H17\"\n\t\t\t\t\t><\/path>\n\t\t\t\t<\/svg>\n\t\t\t\t<span class=\"sr-only\"> No <\/span>\n\t\t\t<\/button>\n\t\t<\/div>\n\t<\/header>\n\n\t<div class=\"wth-form hidden\">\n\t\t<div class=\"wth-form-wrapper\">\n\t\t\t<div class=\"wth-title\"><\/div>\n\t\t\t\n\t\t\t<textarea class=\"wth-message\"><\/textarea>\n\n\t\t\t<button class=\"btn btn-primary wth-btn-submit\">Send<\/button>\n\t\t\t<button class=\"btn wth-btn-cancel\">Cancel<\/button>\n\t\t\n\t\t<\/div>\n\t<\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>Learn how to use the C# WhenAny() static method of the Task class to wait for the first task in a collection of tasks to complete.<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":760,"menu_order":8,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-837","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.csharptutorial.net\/wp-json\/wp\/v2\/pages\/837","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.csharptutorial.net\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www.csharptutorial.net\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/www.csharptutorial.net\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.csharptutorial.net\/wp-json\/wp\/v2\/comments?post=837"}],"version-history":[{"count":5,"href":"https:\/\/www.csharptutorial.net\/wp-json\/wp\/v2\/pages\/837\/revisions"}],"predecessor-version":[{"id":842,"href":"https:\/\/www.csharptutorial.net\/wp-json\/wp\/v2\/pages\/837\/revisions\/842"}],"up":[{"embeddable":true,"href":"https:\/\/www.csharptutorial.net\/wp-json\/wp\/v2\/pages\/760"}],"wp:attachment":[{"href":"https:\/\/www.csharptutorial.net\/wp-json\/wp\/v2\/media?parent=837"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}