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# supervisor_bridge

### MODULE

supervisor_bridge

### MODULE SUMMARY

Generic Supervisor Bridge Behaviour.

### DESCRIPTION

A behaviour module for implementing a supervisor_bridge, a process which 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. Refer to OTP Design Principles for more information.

A supervisor_bridge assumes the functions for starting and stopping the subsystem to be located in a callback module exporting a pre-defined set of functions.

The sys module can be used for debugging a supervisor_bridge.

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

### 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 start-up 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 no name is provided, the supervisor_bridge is not registered. 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.

Module is the name of the callback module.

Args is an arbitrary term which 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 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 should 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 supervisor_bridge: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 should 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 will terminate with reason Reason as well. If later the supervisor_bridge is stopped by its supervisor with reason Reason, it will call Module:terminate(Reason,State) to terminate.

If something goes wrong during the initialization the function should 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 should 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, Reason will be Term.

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

### SEE ALSO

supervisor(3), sys(3)