<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE erlref SYSTEM "erlref.dtd">

<erlref>
  <header>
    <copyright>
      <year>1996</year>
      <year>2022</year>
      <holder>Ericsson AB, All Rights Reserved</holder>
    </copyright>
    <legalnotice>
  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at
 
      http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.

  The Initial Developer of the Original Code is Ericsson AB.
    </legalnotice>

    <title>supervisor_bridge</title>
    <prepared></prepared>
    <docno></docno>
    <date></date>
    <rev></rev>
  </header>
  <module since="">supervisor_bridge</module>
  <modulesummary>Generic supervisor bridge behavior.</modulesummary>
  <description>
    <p>This behavior module provides a supervisor bridge, a process
      that connects a subsystem not designed according to the OTP design
      principles to a supervision tree. The supervisor bridge sits between
      a supervisor and the subsystem. It behaves like a real supervisor to
      its own supervisor, but has a different interface than a real
      supervisor to the subsystem. For more information, see
      <seeguide marker="system/design_principles:sup_princ">
	Supervisor Behaviour</seeguide> in OTP Design Principles.
    </p>

    <p>A supervisor bridge assumes the functions for starting and stopping
      the subsystem to be located in a callback module exporting a
      predefined set of functions.</p>

    <p>The <seeerl marker="sys"><c>sys(3)</c></seeerl> module can be used
      for debugging a supervisor bridge.</p>

    <p>Unless otherwise stated, all functions in this module fail if
      the specified supervisor bridge does not exist or if bad arguments are
      specified.</p>
  </description>

  <funcs>
    <func>
      <name name="start_link" arity="2" since=""/>
      <name name="start_link" arity="3" since=""/>
      <fsummary>Create a supervisor bridge process.</fsummary>
      <desc>
        <p>Creates a supervisor bridge process, linked to the calling process,
          which calls <c><anno>Module</anno>:init/1</c> to start the subsystem.
          To ensure a synchronized startup procedure, this function does
          not return until <c><anno>Module</anno>:init/1</c> has returned.</p>
        <list type="bulleted">
          <item>
            <p>If <c><anno>SupBridgeName</anno>={local,<anno>Name</anno>}</c>,
              the supervisor bridge is registered locally as
              <c><anno>Name</anno></c> using <c>register/2</c>.</p>
          </item>
          <item>
            <p>If <c><anno>SupBridgeName</anno>={global,<anno>GlobalName</anno>}</c>,
              the supervisor bridge is registered globally as
              <c><anno>GlobalName</anno></c> using
              <seemfa marker="kernel:global#register_name/2">
              <c>global:register_name/2</c></seemfa>.</p>
          </item>
          <item>
            <p>If
            <c><anno>SupBridgeName</anno>={via,<anno>Module</anno>,<anno>ViaName</anno>}</c>,
            the supervisor bridge is registered as <c><anno>ViaName</anno></c>
            using a registry represented by <anno>Module</anno>. The
            <c>Module</c> callback is to export functions
            <c>register_name/2</c>, <c>unregister_name/1</c>, and <c>send/2</c>,
            which are to behave like the corresponding functions in
            <seeerl marker="kernel:global"><c>global</c></seeerl>.
            Thus, <c>{via,global,GlobalName}</c> is a valid reference.</p>
          </item>
        </list>
        <p>If no name is provided, the supervisor bridge is not registered.</p>
        <p><c><anno>Module</anno></c> is the name of the callback module.</p>
        <p><c><anno>Args</anno></c> is an arbitrary term that is passed as the
          argument to <c><anno>Module</anno>:init/1</c>.</p>
        <list type="bulleted">
          <item>
            <p>If the supervisor bridge and the subsystem are successfully
              started, the function returns <c>{ok,<anno>Pid</anno>}</c>, where
              <c><anno>Pid</anno></c> is is the pid of the supervisor
              bridge.</p>
          </item>
          <item>
            <p>If there already exists a process with the specified
              <c><anno>SupBridgeName</anno></c>, the function returns
              <c>{error,{already_started,<anno>Pid</anno>}}</c>, where
              <c><anno>Pid</anno></c> is the pid of that process.</p>
          </item>
          <item>
            <p>If <c><anno>Module</anno>:init/1</c> returns <c>ignore</c>, this
              function returns <c>ignore</c> as well and the supervisor bridge
              terminates with reason <c>normal</c>.</p>
          </item>
          <item>
            <p>If <c><anno>Module</anno>:init/1</c> fails or returns an error
              tuple or an incorrect value, this function returns
              <c>{error,<anno>Error</anno>}</c>, where
              <c><anno>Error</anno></c> is a term with information about the
              error, and the supervisor bridge
              terminates with reason <c><anno>Error</anno></c>.</p>
          </item>
        </list>
      </desc>
    </func>
  </funcs>

 

  <funcs>
    <fsdescription>
      <title>Callback Functions</title>
      <p>The following functions must be exported from a
        <c>supervisor_bridge</c> callback module.</p>
    </fsdescription>
    <func>
      <name since="">Module:init(Args) -> Result</name>
      <fsummary>Initialize process and start subsystem.</fsummary>
      <type>
        <v>Args = term()</v>
        <v>Result = {ok,Pid,State} | ignore | {error,Error}</v>
        <v>&nbsp;Pid = pid()</v>
        <v>&nbsp;State = term()</v>
        <v>&nbsp;Error = term()</v>
      </type>
      <desc>
        <p>Whenever a supervisor bridge is started using
          <seemfa marker="#start_link/2"><c>start_link/2,3</c></seemfa>,
          this function is called
          by the new process to start the subsystem and initialize.</p>
        <p><c>Args</c> is the <c>Args</c> argument provided to the start
          function.</p>
        <p>The function is to return <c>{ok,Pid,State}</c>, where <c>Pid</c>
          is the pid of the main process in the subsystem and <c>State</c>
          is any term.</p>
        <p>If later <c>Pid</c> terminates with a reason <c>Reason</c>,
          the supervisor bridge terminates with reason <c>Reason</c> as well.
          If later the supervisor bridge is stopped by its supervisor with
          reason <c>Reason</c>, it calls
          <c>Module:terminate(Reason,State)</c> to terminate.</p>
        <p>If the initialization fails, the function is to return
          <c>{error,Error}</c>, where <c>Error</c> is any term,
          or <c>ignore</c>.</p>
      </desc>
    </func>

    <func>
      <name since="">Module:terminate(Reason, State)</name>
      <fsummary>Clean up and stop subsystem.</fsummary>
      <type>
        <v>Reason = shutdown | term()</v>
        <v>State = term()</v>
      </type>
      <desc>
        <p>This function is called by the supervisor bridge when it is about
          to terminate. It is to be the opposite of <c>Module:init/1</c>
          and stop the subsystem and do any necessary cleaning up.
          The return value is ignored.</p>
        <p><c>Reason</c> is <c>shutdown</c> if the supervisor bridge is
          terminated by its supervisor. If the supervisor bridge terminates
          because a a linked process (apart from the main process of
          the subsystem) has terminated with reason <c>Term</c>,
          then <c>Reason</c> becomes <c>Term</c>.</p>
        <p><c>State</c> is taken from the return value of
          <c>Module:init/1</c>.</p>
      </desc>
    </func>
  </funcs>

  <section>
    <title>See Also</title>
    <p><seeerl marker="supervisor"><c>supervisor(3)</c></seeerl>, 
      <seeerl marker="sys"><c>sys(3)</c></seeerl></p>
  </section>
</erlref>

