16f6c0aecf
Inline adoc files when they are included exactly once. Also fix language tags because this inlining gives us better information on what language the code is written in.
106 lines
3.1 KiB
Plaintext
106 lines
3.1 KiB
Plaintext
== Why is this an issue?
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An ``++async++`` method with a ``++void++`` return type is a "fire and forget" method best reserved for event handlers because there's no way to wait for the method's execution to complete and respond accordingly. There's also no way to ``++catch++`` exceptions thrown from the method.
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Having an ``++async void++`` method that is not an event handler could mean your program works some times and not others because of timing issues. Instead, ``++async++`` methods should return ``++Task++``.
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This rule raises an issue when non-event handler methods are both ``++async++`` and ``++void++``.
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=== Noncompliant code example
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[source,csharp]
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----
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class HttpPrinter
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{
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private string content;
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public async void CallNetwork(string url) //Noncompliant
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{
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var client = new HttpClient();
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var response = await client.GetAsync(url);
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content = await response.Content.ReadAsStringAsync();
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}
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public async Task PrintContent(string url) // works correctly if web request finishes in under 1 second, otherwise content will be null
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{
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CallNetwork(url);
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await Task.Delay(1000);
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Console.Write(content);
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}
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}
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----
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=== Compliant solution
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[source,csharp]
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----
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class HttpPrinter
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{
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private string content;
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public async Task CallNetwork(string url)
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{
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var client = new HttpClient();
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var response = await client.GetAsync(url);
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content = await response.Content.ReadAsStringAsync();
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}
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public async Task PrintContent(string url)
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{
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await CallNetwork(url); // <----- call changed here. If await is not added warning CS4014 will be triggered
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await Task.Delay(1000);
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Console.Write(content);
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}
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}
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----
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=== Exceptions
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Event handlers, i.e. methods with two arguments, first one matching type ``++object++`` or name ``++sender++`` and the second being or inheriting from ``++EventArgs++``, are ignored.
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Methods named as ``++OnSomething++`` are also ignored.
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ifdef::env-github,rspecator-view[]
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'''
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== Implementation Specification
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(visible only on this page)
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=== Message
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Return "Task" instead.
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'''
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== Comments And Links
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(visible only on this page)
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=== on 30 Jun 2015, 13:36:13 Ann Campbell wrote:
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\[~tamas.vajk] I don't understand the code snippets. The ``++async Task++`` method doesn't return anything.
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Also, could you morph the Noncompliant Example into a Compliant Solution, please?
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=== on 1 Jul 2015, 07:10:48 Tamas Vajk wrote:
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\[~ann.campbell.2] I added the compliant solution.
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A method with ``++async++`` keyword returning a ``++Task++`` is like a non ``++async++`` method with ``++void++`` return type. Similarly in an ``++async Task<int>++`` method we can return a simple ``++int++``. (\https://msdn.microsoft.com/en-us/library/hh524395.aspx)
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=== on 1 Jul 2015, 11:31:53 Ann Campbell wrote:
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\[~tamas.vajk] that makes me wonder if we should generalize this rule to catch _any_ ``++async++`` method that does not return a ``++Task++``...?
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=== on 1 Jul 2015, 11:49:54 Tamas Vajk wrote:
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\[~ann.campbell.2] That's a compiler error (CS1983, _The return type of async must be void, Task or Task<T>_).
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=== on 1 Jul 2015, 11:59:39 Ann Campbell wrote:
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Okay, thanks [~tamas.vajk]
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endif::env-github,rspecator-view[]
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