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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:
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 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.
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.
 |
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
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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.
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.
This is the default.
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.
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.
Types:
Snapshot = {Pid, Function, Status, Info}
Pid = pid()
Function = {Module,Name,Args}
Module = Name = atom()
Args = [term()]
Status = idle | running | waiting | break | exit
| no_conn
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={}.
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).