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<h1>
<small class="visible-xs">Elixir v1.7.2</small>
GenEvent <small>behaviour</small>
<a href="https://github.com/elixir-lang/elixir/blob/v1.7.2/lib/elixir/lib/gen_event.ex#L1" title="View Source" class="view-source" rel="help">
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</h1>
<div class="deprecated">
This behaviour is deprecated. Use Erlang/OTP's :gen_event module instead.
</div>
<section id="moduledoc">
<p>A event manager with event handlers behaviour.</p>
<p>If you are interested in implementing an event manager, please read the
“Alternatives” section below. If you have to implement an event handler to
integrate with an existing system, such as Elixir’s Logger, please use
<code class="inline">:gen_event</code> instead.</p>
<h2 id="module-alternatives" class="section-heading">
<a href="#module-alternatives" class="hover-link"><span class="icon-link" aria-hidden="true"></span></a>
Alternatives
</h2>
<p>There are a few suitable alternatives to replace GenEvent. Each of them can be
the most beneficial based on the use case.</p>
<h3 id="module-supervisor-and-genservers" class="section-heading">
<a href="#module-supervisor-and-genservers" class="hover-link"><span class="icon-link" aria-hidden="true"></span></a>
Supervisor and GenServers
</h3>
<p>One alternative to GenEvent is a very minimal solution consisting of using a
supervisor and multiple GenServers started under it. The supervisor acts as
the “event manager” and the children GenServers act as the “event handlers”.
This approach has some shortcomings (it provides no backpressure for example)
but can still replace GenEvent for low-profile usages of it. <a href="http://blog.plataformatec.com.br/2016/11/replacing-genevent-by-a-supervisor-genserver/">This blog post
by José
Valim</a>
has more detailed information on this approach.</p>
<h3 id="module-genstage" class="section-heading">
<a href="#module-genstage" class="hover-link"><span class="icon-link" aria-hidden="true"></span></a>
GenStage
</h3>
<p>If the use case where you were using GenEvent requires more complex logic,
<a href="https://github.com/elixir-lang/gen_stage">GenStage</a> provides a great
alternative. GenStage is an external Elixir library maintained by the Elixir
team; it provides a tool to implement systems that exchange events in a
demand-driven way with built-in support for backpressure. See the <a href="https://hexdocs.pm/gen_stage">GenStage
documentation</a> for more information.</p>
<h3 id="module-gen_event" class="section-heading">
<a href="#module-gen_event" class="hover-link"><span class="icon-link" aria-hidden="true"></span></a>
<code class="inline">:gen_event</code>
</h3>
<p>If your use case requires exactly what GenEvent provided, or you have to
integrate with an existing <code class="inline">:gen_event</code>-based system, you can still use the
<a href="http://erlang.org/doc/man/gen_event.html"><code class="inline">:gen_event</code></a> Erlang module.</p>
</section>
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Summary
</h1>
<div class="summary-types summary">
<h2>
<a href="#types">Types</a>
</h2>
<div class="summary-row">
<div class="summary-signature">
<a href="#t:handler/0">handler()</a>
</div>
</div>
<div class="summary-row">
<div class="summary-signature">
<a href="#t:manager/0">manager()</a>
</div>
</div>
<div class="summary-row">
<div class="summary-signature">
<a href="#t:name/0">name()</a>
</div>
</div>
<div class="summary-row">
<div class="summary-signature">
<a href="#t:on_start/0">on_start()</a>
</div>
</div>
<div class="summary-row">
<div class="summary-signature">
<a href="#t:options/0">options()</a>
</div>
</div>
</div>
<div class="summary-callbacks summary">
<h2>
<a href="#callbacks">Callbacks</a>
</h2>
<div class="summary-row">
<div class="summary-signature">
<a href="#c:code_change/3">code_change(old_vsn, state, extra)</a>
</div>
</div>
<div class="summary-row">
<div class="summary-signature">
<a href="#c:handle_call/2">handle_call(request, state)</a>
</div>
</div>
<div class="summary-row">
<div class="summary-signature">
<a href="#c:handle_event/2">handle_event(event, state)</a>
</div>
</div>
<div class="summary-row">
<div class="summary-signature">
<a href="#c:handle_info/2">handle_info(msg, state)</a>
</div>
</div>
<div class="summary-row">
<div class="summary-signature">
<a href="#c:init/1">init(args)</a>
</div>
</div>
<div class="summary-row">
<div class="summary-signature">
<a href="#c:terminate/2">terminate(reason, state)</a>
</div>
</div>
</div>
</section>
<section id="types" class="details-list">
<h1 class="section-heading">
<a class="hover-link" href="#types">
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Types
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<span class="signature">handler()</span>
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<div class="specs">
<pre>handler() :: <a href="typespecs.html#basic-types">atom</a>() | {<a href="typespecs.html#basic-types">atom</a>(), <a href="typespecs.html#built-in-types">term</a>()}</pre>
</div>
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<section class="docstring">
</section>
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<div class="detail" id="t:manager/0">
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<span class="signature">manager()</span>
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</a>
<div class="specs">
<pre>manager() :: <a href="typespecs.html#basic-types">pid</a>() | <a href="#t:name/0">name</a>() | {<a href="typespecs.html#basic-types">atom</a>(), <a href="typespecs.html#built-in-types">node</a>()}</pre>
</div>
</div>
<section class="docstring">
</section>
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<div class="detail" id="t:name/0">
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<span class="signature">name()</span>
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</a>
<div class="specs">
<pre>name() :: <a href="typespecs.html#basic-types">atom</a>() | {:global, <a href="typespecs.html#built-in-types">term</a>()} | {:via, <a href="typespecs.html#built-in-types">module</a>(), <a href="typespecs.html#built-in-types">term</a>()}</pre>
</div>
</div>
<section class="docstring">
</section>
</div>
<div class="detail" id="t:on_start/0">
<div class="detail-header">
<a href="#t:on_start/0" class="detail-link" title="Link to this type">
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<span class="signature">on_start()</span>
<a href="https://github.com/elixir-lang/elixir/blob/v1.7.2/lib/elixir/lib/gen_event.ex#L78" class="view-source" rel="help" title="View Source">
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<div class="specs">
<pre>on_start() :: {:ok, <a href="typespecs.html#basic-types">pid</a>()} | {:error, {:already_started, <a href="typespecs.html#basic-types">pid</a>()}}</pre>
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<section class="docstring">
</section>
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<div class="detail" id="t:options/0">
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<span class="signature">options()</span>
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<div class="specs">
<pre>options() :: [{:name, <a href="#t:name/0">name</a>()}]</pre>
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<section class="docstring">
</section>
</div>
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</section>
<section id="callbacks" class="details-list">
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Callbacks
</h1>
<div class="detail" id="c:code_change/3">
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<span class="signature">code_change(old_vsn, state, extra)</span>
<a href="https://github.com/elixir-lang/elixir/blob/v1.7.2/lib/elixir/lib/gen_event.ex#L75" class="view-source" rel="help" title="View Source">
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<div class="specs">
<pre>code_change(old_vsn, state :: <a href="typespecs.html#built-in-types">term</a>(), extra :: <a href="typespecs.html#built-in-types">term</a>()) ::
{:ok, new_state :: <a href="typespecs.html#built-in-types">term</a>()}
when old_vsn: <a href="typespecs.html#built-in-types">term</a>() | {:down, <a href="typespecs.html#built-in-types">term</a>()}</pre>
</div>
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</section>
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<div class="detail" id="c:handle_call/2">
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<span class="signature">handle_call(request, state)</span>
<a href="https://github.com/elixir-lang/elixir/blob/v1.7.2/lib/elixir/lib/gen_event.ex#L60" class="view-source" rel="help" title="View Source">
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<div class="specs">
<pre>handle_call(request :: <a href="typespecs.html#built-in-types">term</a>(), state :: <a href="typespecs.html#built-in-types">term</a>()) ::
{:ok, reply, new_state}
| {:ok, reply, new_state, :hibernate}
| {:remove_handler, reply}
when reply: <a href="typespecs.html#built-in-types">term</a>(), new_state: <a href="typespecs.html#built-in-types">term</a>()</pre>
</div>
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<section class="docstring">
</section>
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<div class="detail" id="c:handle_event/2">
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<span class="signature">handle_event(event, state)</span>
<a href="https://github.com/elixir-lang/elixir/blob/v1.7.2/lib/elixir/lib/gen_event.ex#L54" class="view-source" rel="help" title="View Source">
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<div class="specs">
<pre>handle_event(event :: <a href="typespecs.html#built-in-types">term</a>(), state :: <a href="typespecs.html#built-in-types">term</a>()) ::
{:ok, new_state} | {:ok, new_state, :hibernate} | :remove_handler
when new_state: <a href="typespecs.html#built-in-types">term</a>()</pre>
</div>
</div>
<section class="docstring">
</section>
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<div class="detail" id="c:handle_info/2">
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<span class="signature">handle_info(msg, state)</span>
<a href="https://github.com/elixir-lang/elixir/blob/v1.7.2/lib/elixir/lib/gen_event.ex#L66" class="view-source" rel="help" title="View Source">
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<div class="specs">
<pre>handle_info(msg :: <a href="typespecs.html#built-in-types">term</a>(), state :: <a href="typespecs.html#built-in-types">term</a>()) ::
{:ok, new_state} | {:ok, new_state, :hibernate} | :remove_handler
when new_state: <a href="typespecs.html#built-in-types">term</a>()</pre>
</div>
</div>
<section class="docstring">
</section>
</div>
<div class="detail" id="c:init/1">
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<span class="signature">init(args)</span>
<a href="https://github.com/elixir-lang/elixir/blob/v1.7.2/lib/elixir/lib/gen_event.ex#L48" class="view-source" rel="help" title="View Source">
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<div class="specs">
<pre>init(args :: <a href="typespecs.html#built-in-types">term</a>()) ::
{:ok, state} | {:ok, state, :hibernate} | {:error, reason :: <a href="typespecs.html#basic-types">any</a>()}
when state: <a href="typespecs.html#basic-types">any</a>()</pre>
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</section>
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<div class="detail" id="c:terminate/2">
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<span class="signature">terminate(reason, state)</span>
<a href="https://github.com/elixir-lang/elixir/blob/v1.7.2/lib/elixir/lib/gen_event.ex#L72" class="view-source" rel="help" title="View Source">
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<div class="specs">
<pre>terminate(reason, state :: <a href="typespecs.html#built-in-types">term</a>()) :: <a href="typespecs.html#built-in-types">term</a>()
when reason:
:stop | {:stop, <a href="typespecs.html#built-in-types">term</a>()} | :remove_handler | {:error, <a href="typespecs.html#built-in-types">term</a>()} | <a href="typespecs.html#built-in-types">term</a>()</pre>
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