-spec change_code(Name, Module, OldVsn, Extra) -> ok | {error, Reason}
                     when
                         Name :: name(),
                         Module :: module(),
                         OldVsn :: undefined | term(),
                         Extra :: term(),
                         Reason :: term().

Equivalent to change_code(Name, Module, OldVsn, Extra, 5000).

-spec change_code(Name, Module, OldVsn, Extra, Timeout) -> ok | {error, Reason}
                     when
                         Name :: name(),
                         Module :: module(),
                         OldVsn :: undefined | term(),
                         Extra :: term(),
                         Timeout :: timeout(),
                         Reason :: term().

Tells the process to change code.

The process must be suspended to handle this message. Argument Extra is reserved for each process to use as its own. Function Module:system_code_change/4 is called. OldVsn is the old version of the Module.

-spec get_state(Name) -> State when Name :: name(), State :: term().

Equivalent to get_state(Name, 5000).

-spec get_state(Name, Timeout) -> State when Name :: name(), Timeout :: timeout(), State :: term().

Gets the state of the process.

Note

These functions are intended only to help with debugging. They are provided for convenience, allowing developers to avoid having to create their own state extraction functions and also avoid having to interactively extract the state from the return values of get_status/1 or get_status/2 while debugging.

The value of State varies for different types of processes, as follows:

• For a gen_server process, the returned State is the state of the callback module.
• For a gen_statem process, State is the tuple {CurrentState,CurrentData}.
• For a gen_event process, State is a list of tuples, where each tuple corresponds to an event handler registered in the process and contains {Module, Id, HandlerState}, as follows:

  • Module - The module name of the event handler.

  • Id - The ID of the handler (which is false if it was registered without an ID).

  • HandlerState - The state of the handler.

If the callback module exports a function system_get_state/1, it is called in the target process to get its state. Its argument is the same as the Misc value returned by get_status/1,2, and function Module:system_get_state/1 is expected to extract the state of the callback module from it. Function system_get_state/1 must return {ok, State}, where State is the state of the callback module.

If the callback module does not export a system_get_state/1 function, get_state/1,2 assumes that the Misc value is the state of the callback module and returns it directly instead.

If the callback module's system_get_state/1 function crashes or throws an exception, the caller exits with error {callback_failed, {Module, system_get_state}, {Class, Reason}}, where Module is the name of the callback module and Class and Reason indicate details of the exception.

Function system_get_state/1 is primarily useful for user-defined behaviors and modules that implement OTP special processes. The gen_server, gen_statem, and gen_event OTP behavior modules export this function, so callback modules for those behaviors need not to supply their own.

For more information about a process, including its state, see get_status/1 and get_status/2.

-spec get_status(Name) -> Status
                    when
                        Name :: name(),
                        Status :: {status, Pid :: pid(), {module, Module :: module()}, [SItem]},
                        SItem ::
                            (PDict :: [{Key :: term(), Value :: term()}]) |
                            (SysState :: running | suspended) |
                            (Parent :: pid()) |
                            (Dbg :: [dbg_opt()]) |
                            (Misc :: term()).

Equivalent to get_status(Name, 5000).

-spec get_status(Name, Timeout) -> Status
                    when
                        Name :: name(),
                        Timeout :: timeout(),
                        Status :: {status, Pid :: pid(), {module, Module :: module()}, [SItem]},
                        SItem ::
                            (PDict :: [{Key :: term(), Value :: term()}]) |
                            (SysState :: running | suspended) |
                            (Parent :: pid()) |
                            (Dbg :: [dbg_opt()]) |
                            (Misc :: term()).

Gets the status of the process.

The value of Misc varies for different types of processes, for example:

• A gen_server process returns the state of the callback module.
• A gen_statem process returns information, such as its current state name and state data.
• A gen_event process returns information about each of its registered handlers.
• A bare sys process returns the value passed as Misc to handle_system_message/6.

Callback modules for gen_server, gen_statem, and gen_event can also change the value of Misc by exporting a function format_status/1, which contributes module-specific information. For details, see gen_server:format_status/1, gen_statem:format_status/1, and gen_event:format_status/1.

-spec install(Name, FuncSpec) -> ok
                 when
                     Name :: name(),
                     FuncSpec :: {Func, FuncState} | {FuncId, Func, FuncState},
                     FuncId :: term(),
                     Func :: dbg_fun(),
                     FuncState :: term().

Equivalent to install(Name, FuncSpec, 5000).

-spec install(Name, FuncSpec, Timeout) -> ok
                 when
                     Name :: name(),
                     FuncSpec :: {Func, FuncState} | {FuncId, Func, FuncState},
                     FuncId :: term(),
                     Func :: dbg_fun(),
                     FuncState :: term(),
                     Timeout :: timeout().

Enables installation of alternative debug functions. An example of such a function is a trigger, a function that waits for some special event and performs some action when the event is generated. For example, turning on low-level tracing.

Func is called whenever a system event is generated. This function is to return done, or a new Func state. In the first case, the function is removed. It is also removed if the function fails. If one debug function should be installed more times, a unique FuncId must be specified for each installation.

-spec log(Name, Flag) -> ok | {ok, [system_event()]}
             when Name :: name(), Flag :: true | {true, N :: pos_integer()} | false | get | print.

Equivalent to log(Name, Flag, 5000).

-spec log(Name, Flag, Timeout) -> ok | {ok, [system_event()]}
             when
                 Name :: name(),
                 Flag :: true | {true, N :: pos_integer()} | false | get | print,
                 Timeout :: timeout().

Turns the logging of system events on or off. If on, a maximum of N events are kept in the debug structure (default is 10).

If Flag is get, a list of all logged events is returned.

If Flag is print, the logged events are printed to standard_io.

The events are formatted with a function that is defined by the process that generated the event (with a call to handle_debug/4).

-spec log_to_file(Name, Flag) -> ok | {error, open_file}
                     when Name :: name(), Flag :: (FileName :: string()) | false.

Equivalent to log_to_file(Name, FileName, 5000).

-spec log_to_file(Name, Flag, Timeout) -> ok | {error, open_file}
                     when Name :: name(), Flag :: (FileName :: string()) | false, Timeout :: timeout().

Enables or disables the logging of all system events in text format to the file. The events are formatted with a function that is defined by the process that generated the event (with a call to handle_debug/4). The file is opened with encoding UTF-8.

-spec no_debug(Name) -> ok when Name :: name().

Equivalent to no_debug(Name, 5000).

-spec no_debug(Name, Timeout) -> ok when Name :: name(), Timeout :: timeout().

Turns off all debugging for the process. This includes functions that are installed explicitly with function install/2,3, for example, triggers.

-spec remove(Name, Func | FuncId) -> ok when Name :: name(), Func :: dbg_fun(), FuncId :: term().

Equivalent to remove(Name, FuncOrFuncId, 5000).

-spec remove(Name, Func | FuncId, Timeout) -> ok
                when Name :: name(), Func :: dbg_fun(), FuncId :: term(), Timeout :: timeout().

Removes an installed debug function from the process. Func or FuncId must be the same as previously installed.

-spec replace_state(Name, StateFun) -> NewState
                       when
                           Name :: name(),
                           StateFun :: fun((State :: term()) -> NewState :: term()),
                           NewState :: term().

Equivalent to replace_state(Name, StateFun, 5000).

-spec replace_state(Name, StateFun, Timeout) -> NewState
                       when
                           Name :: name(),
                           StateFun :: fun((State :: term()) -> NewState :: term()),
                           Timeout :: timeout(),
                           NewState :: term().

Replaces the state of the process, and returns the new state.

Note

These functions are intended only to help with debugging, and are not to be called from normal code. They are provided for convenience, allowing developers to avoid having to create their own custom state replacement functions.

Function StateFun provides a new state for the process. Argument State and the NewState return value of StateFun vary for different types of processes as follows:

• For a gen_server process, State is the state of the callback module and NewState is a new instance of that state.

• For a gen_statem process, State is the tuple {CurrentState,CurrentData}, and NewState is a similar tuple, which can contain a new current state, new state data, or both.

• For a gen_event process, State is the tuple {Module, Id, HandlerState} as follows:

  • Module - The module name of the event handler.

  • Id - The ID of the handler (which is false if it was registered without an ID).

  • HandlerState - The state of the handler.

  NewState is a similar tuple where Module and Id are to have the same values as in State, but the value of HandlerState can be different. Returning a NewState, whose Module or Id values differ from those of State, leaves the state of the event handler unchanged. For a gen_event process, StateFun is called once for each event handler registered in the gen_event process.

If a StateFun function decides not to effect any change in process state, then regardless of process type, it can return its State argument.

If a StateFun function crashes or throws an exception, the original state of the process is unchanged for gen_server, and gen_statem processes. For gen_event processes, a crashing or failing StateFun function means that only the state of the particular event handler it was working on when it failed or crashed is unchanged; it can still succeed in changing the states of other event handlers registered in the same gen_event process.

If the callback module exports a system_replace_state/2 function, it is called in the target process to replace its state using StateFun. Its two arguments are StateFun and Misc, where Misc is the same as the Misc value returned by get_status/1,2. A system_replace_state/2 function is expected to return {ok, NewState, NewMisc}, where NewState is the new state of the callback module, obtained by calling StateFun, and NewMisc is a possibly new value used to replace the original Misc (required as Misc often contains the state of the callback module within it).

If the callback module does not export a system_replace_state/2 function, replace_state/2,3 assumes that Misc is the state of the callback module, passes it to StateFun and uses the return value as both the new state and as the new value of Misc.

If the callback module's function system_replace_state/2 crashes or throws an exception, the caller exits with error {callback_failed, {Module, system_replace_state}, {Class, Reason}}, where Module is the name of the callback module and Class and Reason indicate details of the exception. If the callback module does not provide a system_replace_state/2 function and StateFun crashes or throws an exception, the caller exits with error {callback_failed, StateFun, {Class, Reason}}.

Function system_replace_state/2 is primarily useful for user-defined behaviors and modules that implement OTP special processes. The OTP behavior modules gen_server, gen_statem, and gen_event export this function, so callback modules for those behaviors need not to supply their own.

-spec resume(Name) -> ok when Name :: name().

Equivalent to resume(Name, 5000).

-spec resume(Name, Timeout) -> ok when Name :: name(), Timeout :: timeout().

Resumes a suspended process.

-spec statistics(Name, Flag) -> ok | {ok, Statistics}
                    when
                        Name :: name(),
                        Flag :: true | false | get,
                        Statistics :: [StatisticsTuple] | no_statistics,
                        StatisticsTuple ::
                            {start_time, DateTime1} |
                            {current_time, DateTime2} |
                            {reductions, non_neg_integer()} |
                            {messages_in, non_neg_integer()} |
                            {messages_out, non_neg_integer()},
                        DateTime1 :: file:date_time(),
                        DateTime2 :: file:date_time().

Equivalent to statistics(Name, Flag, 5000).

-spec statistics(Name, Flag, Timeout) -> ok | {ok, Statistics}
                    when
                        Name :: name(),
                        Flag :: true | false | get,
                        Statistics :: [StatisticsTuple] | no_statistics,
                        StatisticsTuple ::
                            {start_time, DateTime1} |
                            {current_time, DateTime2} |
                            {reductions, non_neg_integer()} |
                            {messages_in, non_neg_integer()} |
                            {messages_out, non_neg_integer()},
                        DateTime1 :: file:date_time(),
                        DateTime2 :: file:date_time(),
                        Timeout :: timeout().

Enables or disables the collection of statistics. If Flag is get, the statistical collection is returned.

-spec suspend(Name) -> ok when Name :: name().

Equivalent to suspend(Name, 5000).

-spec suspend(Name, Timeout) -> ok when Name :: name(), Timeout :: timeout().

Suspends the process. When the process is suspended, it only responds to other system messages, but not other messages.

-spec terminate(Name, Reason) -> ok when Name :: name(), Reason :: term().

Equivalent to terminate(Name, Reason, 5000).

-spec terminate(Name, Reason, Timeout) -> ok when Name :: name(), Reason :: term(), Timeout :: timeout().

Orders the process to terminate with the specified Reason. The termination is done asynchronously, so it is not guaranteed that the process is terminated when the function returns.

-spec trace(Name, Flag) -> ok when Name :: name(), Flag :: boolean().

Equivalent to trace(Name, Flag, 5000).

-spec trace(Name, Flag, Timeout) -> ok when Name :: name(), Flag :: boolean(), Timeout :: timeout().

Prints all system events on standard_io. The events are formatted with a function that is defined by the process that generated the event (with a call to handle_debug/4).