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authorXavier Noria <[email protected]>2018-04-05 01:40:20 +0200
committerXavier Noria <[email protected]>2018-06-13 12:04:08 +0200
commitb0900fc2f7daab1c77dd8878c39ab24591bb076b (patch)
treea7f75ae939076a1e54213b3db883fd3478097548 /lib/kernel
parente754f23ead59f8592f3a1cbb66e22cfdba73517d (diff)
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Explain why the AM becomes group leader
Diffstat (limited to 'lib/kernel')
-rw-r--r--lib/kernel/doc/src/application.xml10
-rw-r--r--lib/kernel/src/application_master.erl4
2 files changed, 11 insertions, 3 deletions
diff --git a/lib/kernel/doc/src/application.xml b/lib/kernel/doc/src/application.xml
index 886286b76d..be914aee87 100644
--- a/lib/kernel/doc/src/application.xml
+++ b/lib/kernel/doc/src/application.xml
@@ -318,8 +318,13 @@ Nodes = [cp1@cave, {cp2@cave, cp3@cave}]</code>
<c>{error,{not_started,App}}</c> is returned, where <c>App</c>
is the name of the missing application.</p>
<p>The application controller then creates an <em>application master</em>
- for the application. The application master is
- the group leader of all the processes in the application.
+ for the application. The application master becomes the
+ group leader of all the processes in the application. I/O is
+ forwarded to the previous group leader, though, this is just
+ a way to identify processes that belong to the application.
+ Used for example to find itself from any process, or,
+ reciprocally, to kill them all when it terminates.</p>
+ <p>
The application master starts the application by calling
the application callback function <c>Module:start/2</c> as
defined by the application specification key <c>mod</c>.</p>
@@ -608,4 +613,3 @@ Nodes = [cp1@cave, {cp2@cave, cp3@cave}]</code>
<seealso marker="app">app(4)</seealso></p>
</section>
</erlref>
-
diff --git a/lib/kernel/src/application_master.erl b/lib/kernel/src/application_master.erl
index 5da2b0b06c..06991b45e1 100644
--- a/lib/kernel/src/application_master.erl
+++ b/lib/kernel/src/application_master.erl
@@ -118,6 +118,10 @@ init(Parent, Starter, ApplData, Type) ->
link(Parent),
process_flag(trap_exit, true),
OldGleader = group_leader(),
+ %% We become the group leader, but forward all I/O to OldGleader.
+ %% This is just a way to identify processes that belong to the
+ %% application. Used for example to find ourselves from any
+ %% process, or, reciprocally, to kill them all when we terminate.
group_leader(self(), self()),
%% Insert ourselves as master for the process. This ensures that
%% the processes in the application can use get_env/1 at startup.