diff options
| -rw-r--r-- | erts/doc/src/erlang.xml | 9 | ||||
| -rw-r--r-- | lib/kernel/doc/src/application.xml | 10 | ||||
| -rw-r--r-- | lib/kernel/src/application_master.erl | 4 | ||||
| -rw-r--r-- | system/doc/design_principles/applications.xml | 10 |
4 files changed, 26 insertions, 7 deletions
diff --git a/erts/doc/src/erlang.xml b/erts/doc/src/erlang.xml index 1b973cd60e..984072076c 100644 --- a/erts/doc/src/erlang.xml +++ b/erts/doc/src/erlang.xml @@ -2068,8 +2068,15 @@ end</pre> Typically, this is used when a process started from a certain shell is to have another group leader than <c>init</c>.</p> + <p>The group leader should be rarely changed in + applications with a supervision tree, because OTP + assumes the group leader of their processes is + their application master.</p> <p>See also - <seealso marker="#group_leader/0"><c>group_leader/0</c></seealso>.</p> + <seealso marker="#group_leader/0"><c>group_leader/0</c></seealso> + and <seealso marker="doc/design_principles:applications#stopping">OTP + design principles</seealso> related to starting and stopping + applications.</p> </desc> </func> 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. diff --git a/system/doc/design_principles/applications.xml b/system/doc/design_principles/applications.xml index c673fde07e..6e5a2ce6cf 100644 --- a/system/doc/design_principles/applications.xml +++ b/system/doc/design_principles/applications.xml @@ -363,9 +363,13 @@ ok application are running.</p> <marker id="application_master"></marker> <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. - The application master starts the application by calling + <em>application master</em> 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>start/2</c> in the module, and with the start argument, defined by the <c>mod</c> key in the <c>.app</c> file.</p> |