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MODULE

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MODULE SUMMARY

Interpreter Interface

DESCRIPTION

The Erlang interpreter provides mechanisms for breakpoints and stepwise execution of code. It is mainly intended to be used by the Debugger, see Debugger User's Guide and debugger(3).

From the shell, it is possible to:

Specify which modules should be interpreted.
Specify breakpoints.
Monitor the current status of all processes executing code in interpreted modules, also processes at other Erlang nodes.

By attaching to a process executing interpreted code, it is possible to examine variable bindings and order stepwise execution. This is done by sending and receiving information to/from the process via a third process, called the meta process. It is possible to implement your own attached process. See int.erl for available functions and dbg_ui_trace.erl for possible messages.

The interpreter depends on the Kernel, STDLIB and GS applications, which means modules belonging to any of these applications are not allowed to be interpreted as it could lead to a deadlock or emulator crash. This also applies to modules belonging to the Debugger application itself.

Breakpoints

Breakpoints are specified on a line basis. When a process executing code in an interpreted module reaches a breakpoint, it will stop. This means that that a breakpoint must be set at an executable line, that is, a line of code containing an executable expression.

A breakpoint have a status, a trigger action and may have a condition associated with it. The status is either active or inactive. An inactive breakpoint is ignored. When a breakpoint is reached, the trigger action specifies if the breakpoint should continue to be active (enable), if it should become inactive (disable), or if it should be removed (delete). A condition is a tuple {Module,Name}. When the breakpoint is reached, Module:Name(Bindings) is called. If this evaluates to true, execution will stop. If this evaluates to false, the breakpoint is ignored. Bindings contains the current variable bindings, use get_binding to retrieve the value for a given variable.

By default, a breakpoint is active, has trigger action enable and has no condition associated with it. For more detailed information about breakpoints, refer to Debugger User's Guide.

EXPORTS

i(AbsModule) -> {module,Module} | error
i(AbsModules) -> ok
ni(AbsModule) -> {module,Module} | error
ni(AbsModules) -> ok

Types:

AbsModules = [AbsModule]

AbsModule = Module | File | [Module | File]

Module = atom()

File = string()

Interprets the specified module(s). i/1 interprets the module only at the current node. ni/1 interprets the module at all known nodes.

A module may be given by its module name (atom) or by its file name. If given by its module name, the object code Module.beam is searched for in the current path. The source code Module.erl is searched for first in the same directory as the object code, then in a src directory next to it.

If given by its file name, the file name may include a path and the .erl extension may be omitted. The object code Module.beam is searched for first in the same directory as the source code, then in an ebin directory next to it, and then in the current path.

Note

The interpreter needs both the source code and the object code, and the object code must include debug information. That is, only modules compiled with the option debug_info set can be interpreted.

The functions returns {module,Module} if the module was interpreted, or error if it was not.

The argument may also be a list of modules/file names, in which case the function tries to interpret each module as specified above. The function then always returns ok, but prints some information to stdout if a module could not be interpreted.

n(AbsModule) -> ok
nn(AbsModule) -> ok

Types:

AbsModule = Module | File | [Module | File]

Module = atom()

File = string()

Stops interpreting the specified module. n/1 stops interpreting the module only at the current node. nn/1 stops interpreting the module at all known nodes.

As for i/1 and ni/1, a module may be given by either its module name or its file name.

interpreted() -> [Module]

Types:

Module = atom()

Returns a list with all interpreted modules.

file(Module) -> File | {error,not_loaded}

Types:

Module = atom()

File = string()

Returns the source code file name File for an interpreted module Module.

interpretable(AbsModule) -> true | {error,Reason}

Types:

AbsModule = Module | File

Module = atom()

File = string()

Reason = no_src | no_beam | no_debug_info | badarg | {app,App}

App = atom()

Checks if a module is possible to interpret. The module can be given by its module name Module or its source file name File. If given by a module name, the module is searched for in the code path.

The function returns true if both source code and object code for the module is found, the module has been compiled with the option debug_info set and does not belong to any of the applications Kernel, STDLIB, GS or Debugger itself.

The function returns {error,Reason} if the module for some reason is not possible to interpret.

Reason is no_src if no source code is found or no_beam if no object code is found. It is assumed that the source- and object code are located either in the same directory, or in src and ebin directories next to each other.

Reason is no_debug_info if the module has not been compiled with the option debug_info set.

Reason is badarg if AbsModule is not found. This could be because the specified file does not exist, or because code:which/1 does not return a beam file name, which is the case not only for non-existing modules but also for modules which are preloaded or cover compiled.

Reason is {app,App} where App is kernel, stdlib, gs or debugger if AbsModule belongs to one of these applications.

Note that the function can return true for a module which in fact is not interpretable in the case where the module is marked as sticky or resides in a directory marked as sticky, as this is not discovered until the interpreter actually tries to load the module.

auto_attach() -> false | {Flags,Function}
auto_attach(false)
auto_attach(Flags, Function)

Types:

Flags = [init | break | exit]

Function = {Module,Name,Args}

Module = Name = atom()

Args = [term()]

Gets and sets when and how to automatically attach to a process executing code in interpreted modules. false means never automatically attach, this is the default. Otherwise automatic attach is defined by a list of flags and a function. The following flags may be specified:

init - attach when a process for the very first time calls an interpreted function.
break - attach whenever a process reaches a breakpoint.
exit - attach when a process terminates.

When the specified event occurs, the function Function will be called as:

spawn(Module, Name, [Pid | Args])

Pid is the pid of the process executing interpreted code.

stack_trace() -> Flag
stack_trace(Flag)

Types:

Flag = all | no_tail | false

Gets and sets how to save call frames in the stack. Saving call frames makes it possible to inspect the call chain of a process, and is also used to emulate the stack trace if an error (an exception of class error) occurs.

all - save information about all current calls, that is, function calls that have not yet returned a value.
no_tail - save information about current calls, but discard previous information when a tail recursive call is made. This option consumes less memory and may be necessary to use for processes with long lifetimes and many tail recursive calls. This is the default.
false - do not save any information about current calls.

break(Module, Line) -> ok | {error,break_exists}

Types:

Module = atom()

Line = int()

Creates a breakpoint at Line in Module.

delete_break(Module, Line) -> ok

Types:

Module = atom()

Line = int()

Deletes the breakpoint located at Line in Module.

break_in(Module, Name, Arity) -> ok | {error,function_not_found}

Types:

Module = Name = atom()

Arity = int()

Creates a breakpoint at the first line of every clause of the Module:Name/Arity function.

del_break_in(Module, Name, Arity) -> ok | {error,function_not_found}

Types:

Module = Name = atom()

Arity = int()

Deletes the breakpoints at the first line of every clause of the Module:Name/Arity function.

no_break() -> ok
no_break(Module) -> ok

Deletes all breakpoints, or all breakpoints in Module.

disable_break(Module, Line) -> ok

Types:

Module = atom()

Line = int()

Makes the breakpoint at Line in Module inactive.

enable_break(Module, Line) -> ok

Types:

Module = atom()

Line = int()

Makes the breakpoint at Line in Module active.

action_at_break(Module, Line, Action) -> ok

Types:

Module = atom()

Line = int()

Action = enable | disable | delete

Sets the trigger action of the breakpoint at Line in Module to Action.

test_at_break(Module, Line, Function) -> ok

Types:

Module = atom()

Line = int()

Function = {Module,Name}

Name = atom()

Sets the conditional test of the breakpoint at Line in Module to Function. The function must fulfill the requirements specified in the section Breakpoints above.

get_binding(Var, Bindings) -> {value,Value} | unbound

Types:

Var = atom()

Bindings = term()

Value = term()

Retrieves the binding of Var. This function is intended to be used by the conditional function of a breakpoint.

all_breaks() -> [Break]
all_breaks(Module) -> [Break]

Types:

Break = {Point,Options}

Point = {Module,Line}

Module = atom()

Line = int()

Options = [Status,Trigger,null,Cond|]

Status = active | inactive

Trigger = enable | disable | delete

Cond = null | Function

Function = {Module,Name}

Name = atom()

Gets all breakpoints, or all breakpoints in Module.

snapshot() -> [Snapshot]

Types:

Snapshot = {Pid, Function, Status, Info}

Pid = pid()

Function = {Module,Name,Args}

Module = Name = atom()

Args = [term()]

Info = {} | {Module,Line} | ExitReason

Line = int()

ExitReason = term()

Gets information about all processes executing interpreted code.

Pid - process identifier.
Function - first interpreted function called by the process.
Status - current status of the process.
Info - additional information.

Status is one of:

idle - the process is no longer executing interpreted code. Info={}.
running - the process is running. Info={}.
waiting - the process is waiting at a receive. Info={}.
break - process execution has been stopped, normally at a breakpoint. Info={Module,Line}.
exit - the process has terminated. Info=ExitReason.
no_conn - the connection is down to the node where the process is running. Info={}.

clear() -> ok

Clears information about processes executing interpreted code by removing all information about terminated processes.

continue(Pid) -> ok | {error,not_interpreted}
continue(X,Y,Z) -> ok | {error,not_interpreted}

Types:

Pid = pid()

X = Y = Z = int()

Resume process execution for Pid, or for c:pid(X,Y,Z).