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NAME

       supervisor_bridge - Generic supervisor bridge behavior.

DESCRIPTION

       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  Supervisor Behaviour in OTP Design Principles.

       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.

       The sys(3erl) module can be used for debugging a supervisor bridge.

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

EXPORTS

       start_link(Module, Args) -> Result

       start_link(SupBridgeName, Module, Args) -> Result

              Types:

                 SupBridgeName = {local, Name} | {global, Name}
                 Name = atom()
                 Module = module()
                 Args = term()
                 Result = {ok, Pid} | ignore | {error, Error}
                 Error = {already_started, Pid} | term()
                 Pid = pid()

              Creates  a  supervisor  bridge  process, linked to the calling process, which calls
              Module:init/1 to start the subsystem. To ensure a synchronized  startup  procedure,
              this function does not return until Module:init/1 has returned.

                * If  SupBridgeName={local,Name},  the supervisor bridge is registered locally as
                  Name using register/2.

                * If SupBridgeName={global,Name}, the supervisor bridge is registered globally as
                  Name using global:register_name/2.

                * If SupBridgeName={via,Module,Name}, the supervisor bridge is registered as Name
                  using a registry represented by  Module.  The  Module  callback  is  to  export
                  functions  register_name/2,  unregister_name/1, and send/2, which are to behave
                  like the corresponding functions in global. Thus, {via,global,GlobalName} is  a
                  valid reference.

              If no name is provided, the supervisor bridge is not registered.

              Module is the name of the callback module.

              Args is an arbitrary term that is passed as the argument to Module:init/1.

                * If  the  supervisor  bridge  and  the  subsystem  are successfully started, the
                  function returns {ok,Pid}, where Pid is is the pid of the supervisor bridge.

                * If there already  exists  a  process  with  the  specified  SupBridgeName,  the
                  function  returns  {error,{already_started,Pid}},  where Pid is the pid of that
                  process.

                * If Module:init/1 returns ignore, this function returns ignore as well  and  the
                  supervisor bridge terminates with reason normal.

                * If  Module:init/1  fails  or returns an error tuple or an incorrect value, this
                  function returns {error,Errorr}, where Error is a term with  information  about
                  the error, and the supervisor bridge terminates with reason Error.

CALLBACK FUNCTIONS

       The following functions must be exported from a supervisor_bridge callback module.

EXPORTS

       Module:init(Args) -> Result

              Types:

                 Args = term()
                 Result = {ok,Pid,State} | ignore | {error,Error}
                  Pid = pid()
                  State = term()
                  Error = term()

              Whenever  a  supervisor  bridge  is  started using start_link/2,3, this function is
              called by the new process to start the subsystem and initialize.

              Args is the Args argument provided to the start function.

              The function is to return {ok,Pid,State}, where Pid is the pid of the main  process
              in the subsystem and State is any term.

              If later Pid terminates with a reason Reason, the supervisor bridge terminates with
              reason Reason as well. If later the supervisor bridge is stopped by its  supervisor
              with reason Reason, it calls Module:terminate(Reason,State) to terminate.

              If  the  initialization fails, the function is to return {error,Error}, where Error
              is any term, or ignore.

       Module:terminate(Reason, State)

              Types:

                 Reason = shutdown | term()
                 State = term()

              This function is called by the supervisor bridge when it is about to terminate.  It
              is  to be the opposite of Module:init/1 and stop the subsystem and do any necessary
              cleaning up. The return value is ignored.

              Reason is shutdown 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  Term,  then  Reason  becomes
              Term.

              State is taken from the return value of Module:init/1.

SEE ALSO

       supervisor(3erl), sys(3erl)