Interpreter Interface.
The Erlang interpreter provides mechanisms for breakpoints and
stepwise execution of code. It is primarily intended to be used by
Debugger, see the User's Guide and
debugger(3)
.
The following can be done from the shell:
- Specify the modules to 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 through a third process, called the meta
process. You can implement your own attached process. See
int.erl
for available functions and dbg_wx_trace.erl
for possible messages.
The interpreter depends on the Kernel, STDLIB, and GS applications. This means that 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.
Breakpoints
Breakpoints are specified on a line basis. When a process executing code in an interpreted module reaches a breakpoint, it stops. This means that a breakpoint must be set at an executable line, that is, a code line containing an executable expression.
A breakpoint has the following:
- A status, which is active or inactive. An inactive breakpoint is ignored.
- A trigger action. When a breakpoint is reached, the trigger action specifies if the breakpoint is to continue as active (enable), or to become inactive (disable), or to be removed (delete).
- Optionally an associated condition. A condition is a tuple
{Module,Name}
. When the breakpoint is reached,Module:Name(Bindings)
is called. If it evaluates totrue
, execution stops. If it evaluates tofalse
, the breakpoint is ignored.Bindings
contains the current variable bindings. To retrieve the value for a specified variable, useget_binding
.
By default, a breakpoint is active, has trigger action
enable
, and has no associated condition. For details
about breakpoints, see the User's Guide.
Functions
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 can be specified by its module name (atom) or filename.
If specified 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 an src
directory next to it.
If specified by its filename, the filename can include a path
and the .erl
extension can 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 requires both the source code and the object
code. The object code must include debug
information, that is, only modules compiled with option
debug_info
set can be interpreted.
The functions returns {module,Module}
if the module
was interpreted, otherwise error
is returned.
The argument can also be a list of modules or filenames, in
which case the function tries to interpret each module as
specified earlier. The function then always returns ok
,
but prints some information to stdout
if a module
cannot be interpreted.
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 can be specified by
its module name or filename.
Module = atom()
Returns a list with all interpreted modules.
Module = atom()
File = string()
Returns the source code filename File
for an
interpreted module Module
.
AbsModule = Module | File
Module = atom()
File = string()
Reason = no_src | no_beam | no_debug_info | badarg | {app,App}
App = atom()
Checks if a module can be interpreted. The module can be
specified by its module name Module
or its source
filename File
. If specified by a module name, the module
is searched for in the code path.
The function returns true
if all of the following
apply:
- Both source code and object code for the module is found.
- The module has been compiled with option
debug_info
set. - The module does not belong to any of the applications Kernel, STDLIB, GS, or Debugger.
The function returns {error,Reason}
if the module cannot
be interpreted. Reason
can have the following values:
no_src
No source code is found.
It is assumed that the source code and object code are located
either in the same directory, or in src
and ebin
directories next to each other.
no_beam
No object code is found.
It is assumed that the source code and object code are located
either in the same directory, or in src
and ebin
directories next to each other.
no_debug_info
The module has not been compiled with option
debug_info
set.
badarg
AbsModule
is not found. This could be because
the specified file does not exist, or because
code:which/1
does not return a BEAM filename,
which is the case not only for non-existing modules but also
for modules that are preloaded or cover-compiled.
{app,App}
App
is kernel
, stdlib
, gs
,
or debugger
if AbsModule
belongs to one of these
applications.
Notice that the function can return true
for a module
that in fact is not interpretable in the case where
the module is marked as sticky or resides in a directory
marked as sticky. The reason is that this is not discovered
until the interpreter tries to load the module.
Flags = [init | break | exit]
Function = {Module,Name,Args}
Module = Name = atom()
Args = [term()]
Gets and sets when and how to attach automatically to a
process executing code in interpreted modules. false
means never attach automatically, this is the default.
Otherwise automatic attach is defined by a list of flags and
a function. The following flags can be specified:
init
- Attach when a process for the 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
is called as:
spawn(Module, Name, [Pid | Args])
Pid
is the pid of the process executing interpreted
code.
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. The following flags can be specified:
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 can be necessary to use for processes with long lifetimes and many tail recursive calls. This is the default.
false
Save no information about currentcalls.
Module = atom()
Line = int()
Creates a breakpoint at Line
in Module
.
Module = atom()
Line = int()
Deletes the breakpoint at Line
in Module
.
Module = Name = atom()
Arity = int()
Creates a breakpoint at the first line of every clause of
function Module:Name/Arity
.
Module = Name = atom()
Arity = int()
Deletes the breakpoints at the first line of every clause of
function Module:Name/Arity
.
Deletes all breakpoints, or all breakpoints in Module
.
Module = atom()
Line = int()
Makes the breakpoint at Line
in Module
inactive.
Module = atom()
Line = int()
Makes the breakpoint at Line
in Module
active.
Module = atom()
Line = int()
Action = enable | disable | delete
Sets the trigger action of the breakpoint at Line
in
Module
to Action
.
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 section
Breakpoints.
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.
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 = {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
- More information.
Status
is one of the following:
idle
- The process is no longer executing interpreted code.Info={}
.running
- The process is running.Info={}
.waiting
- The process is waiting at areceive
.Info={}
.break
- Process execution is stopped, normally at a breakpoint.Info={Module,Line}
.exit
- The process is 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.
Pid = pid()
X = Y = Z = int()
Resumes process execution for Pid
or
c:pid(X,Y,Z)
.