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-rw-r--r--lib/stdlib/doc/src/gen_event.xml18
1 files changed, 18 insertions, 0 deletions
diff --git a/lib/stdlib/doc/src/gen_event.xml b/lib/stdlib/doc/src/gen_event.xml
index 42e952fd46..56cb7974a2 100644
--- a/lib/stdlib/doc/src/gen_event.xml
+++ b/lib/stdlib/doc/src/gen_event.xml
@@ -579,6 +579,13 @@ gen_event:stop -----> Module:terminate/2
<v>Extra = term()</v>
</type>
<desc>
+ <note>
+ <p>This callback is optional, so callback modules need not export it.
+ If a release upgrade/downgrade with <c>Change={advanced,Extra}</c>
+ specified in the <c>.appup</c> file is made when <c>code_change/3</c>
+ isn't implemented the event handler will crash with an <c>undef</c> error
+ reason.</p>
+ </note>
<p>This function is called for an installed event handler that
is to update its internal state during a release
upgrade/downgrade, that is, when the instruction
@@ -759,6 +766,12 @@ gen_event:stop -----> Module:terminate/2
<v>&nbsp;&nbsp;Id = term()</v>
</type>
<desc>
+ <note>
+ <p>This callback is optional, so callback modules need not
+ export it. The <c>gen_event</c> module provides a default
+ implementation of this function that logs about the unexpected
+ <c>Info</c> message, drops it and returns <c>{noreply, State}</c>.</p>
+ </note>
<p>This function is called for each installed event handler when
an event manager receives any other message than an event or
a synchronous request (or a system message).</p>
@@ -815,6 +828,11 @@ gen_event:stop -----> Module:terminate/2
<v>&nbsp;Args = Reason = Term = term()</v>
</type>
<desc>
+ <note>
+ <p>This callback is optional, so callback modules need not
+ export it. The <c>gen_event</c> module provides a default
+ implementation without cleanup.</p>
+ </note>
<p>Whenever an event handler is deleted from an event manager,
this function is called. It is to be the opposite of
<seealso marker="#Module:init/1"><c>Module:init/1</c></seealso>