Reference Manual

Version 3.4

Table of Contents




Module Summary

Generic supervisor bridge behavior.


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(3) 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.


start_link(Module, Args) -> Result
start_link(SupBridgeName, Module, Args) -> Result


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.


Module:init(Args) -> Result


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)


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