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NAME
erl_tracer - Erlang tracer behavior.
DESCRIPTION
This behavior module implements the back end of the Erlang tracing system. The functions
in this module are called whenever a trace probe is triggered. Both the enabled and trace
functions are called in the context of the entity that triggered the trace probe. This
means that the overhead by having the tracing enabled is greatly effected by how much time
is spent in these functions. So, do as little work as possible in these functions.
Note:
All functions in this behavior must be implemented as NIFs. This limitation can be removed
in a future releases. An example tracer module NIF implementation is provided at the end
of this page.
Warning:
Do not send messages or issue port commands to the Tracee in any of the callbacks. This is
not allowed and can cause all sorts of strange behavior, including, but not limited to,
infinite recursions.
DATA TYPES
trace_tag_call() =
call | return_to | return_from | exception_from
trace_tag_gc() =
gc_minor_start | gc_minor_end | gc_major_start | gc_major_end
trace_tag_ports() =
open | closed | link | unlink | getting_linked |
getting_unlinked
trace_tag_procs() =
spawn | spawned | exit | link | unlink | getting_linked |
getting_unlinked | register | unregister
trace_tag_receive() = 'receive'
trace_tag_running_ports() =
in | out | in_exiting | out_exiting | out_exited
trace_tag_running_procs() =
in | out | in_exiting | out_exiting | out_exited
trace_tag_send() = send | send_to_non_existing_process
trace_tag() =
trace_tag_send() |
trace_tag_receive() |
trace_tag_call() |
trace_tag_procs() |
trace_tag_ports() |
trace_tag_running_procs() |
trace_tag_running_ports() |
trace_tag_gc()
The different trace tags that the tracer is called with. Each trace tag is
described in detail in Module:trace/5.
tracee() = port() | pid() | undefined
The process or port that the trace belongs to.
trace_opts() =
#{extra => term(),
match_spec_result => term(),
scheduler_id => integer() >= 0,
timestamp =>
timestamp | cpu_timestamp | monotonic | strict_monotonic}
The options for the tracee:
timestamp:
If set the tracer has been requested to include a time stamp.
extra:
If set the tracepoint has included additional data about the trace event. What
the additional data is depends on which TraceTag has been triggered. The extra
trace data corresponds to the fifth element in the trace tuples described in
erlang:trace/3.
match_spec_result:
If set the tracer has been requested to include the output of a match
specification that was run.
scheduler_id:
If set the scheduler id is to be included by the tracer.
tracer_state() = term()
The state specified when calling
erlang:trace(PidPortSpec,true,[{tracer,Module,TracerState}]). The tracer state is
an immutable value that is passed to erl_tracer callbacks and is to contain all the
data that is needed to generate the trace event.
CALLBACK FUNCTIONS
The following functions are to be exported from an erl_tracer callback module:
Module:enabled/3:
Mandatory
Module:trace/5:
Mandatory
Module:enabled_call/3:
Optional
Module:trace_call/5:
Optional
Module:enabled_garbage_collection/3:
Optional
Module:trace_garbage_collection/5:
Optional
Module:enabled_ports/3:
Optional
Module:trace_ports/5:
Optional
Module:enabled_procs/3:
Optional
Module:trace_procs/5:
Optional
Module:enabled_receive/3:
Optional
Module:trace_receive/5:
Optional
Module:enabled_running_ports/3:
Optional
Module:trace_running_ports/5:
Optional
Module:enabled_running_procs/3:
Optional
Module:trace_running_procs/5:
Optional
Module:enabled_send/3:
Optional
Module:trace_send/5:
Optional
EXPORTS
Module:enabled(TraceTag, TracerState, Tracee) -> Result
Types:
TraceTag = trace_tag() | trace_status
TracerState = term()
Tracee = tracee()
Result = trace | discard | remove
This callback is called whenever a tracepoint is triggered. It allows the tracer to
decide whether a trace is to be generated or not. This check is made as early as
possible to limit the amount of overhead associated with tracing. If trace is
returned, the necessary trace data is created and the trace callback of the tracer
is called. If discard is returned, this trace call is discarded and no call to
trace is done.
trace_status is a special type of TraceTag, which is used to check if the tracer is
still to be active. It is called in multiple scenarios, but most significantly it
is used when tracing is started using this tracer. If remove is returned when the
trace_status is checked, the tracer is removed from the tracee.
This function can be called multiple times per tracepoint, so it is important that
it is both fast and without side effects.
Module:enabled_call(TraceTag, TracerState, Tracee) -> Result
Types:
TraceTag = trace_tag_call()
TracerState = term()
Tracee = tracee()
Result = trace | discard | remove
This callback is called whenever a tracepoint with trace flag call | return_to is
triggered.
If enabled_call/3 is undefined, Module:enabled/3 is called instead.
Module:enabled_garbage_collection(TraceTag, TracerState, Tracee) -> Result
Types:
TraceTag = trace_tag_gc()
TracerState = term()
Tracee = tracee()
Result = trace | discard | remove
This callback is called whenever a tracepoint with trace flag garbage_collection is
triggered.
If enabled_garbage_collection/3 is undefined, Module:enabled/3 is called instead.
Module:enabled_ports(TraceTag, TracerState, Tracee) -> Result
Types:
TraceTag = trace_tag_ports()
TracerState = term()
Tracee = tracee()
Result = trace | discard | remove
This callback is called whenever a tracepoint with trace flag ports is triggered.
If enabled_ports/3 is undefined, Module:enabled/3 is called instead.
Module:enabled_procs(TraceTag, TracerState, Tracee) -> Result
Types:
TraceTag = trace_tag_procs()
TracerState = term()
Tracee = tracee()
Result = trace | discard | remove
This callback is called whenever a tracepoint with trace flag procs is triggered.
If enabled_procs/3 is undefined, Module:enabled/3 is called instead.
Module:enabled_receive(TraceTag, TracerState, Tracee) -> Result
Types:
TraceTag = trace_tag_receive()
TracerState = term()
Tracee = tracee()
Result = trace | discard | remove
This callback is called whenever a tracepoint with trace flag 'receive' is
triggered.
If enabled_receive/3 is undefined, Module:enabled/3 is called instead.
Module:enabled_running_ports(TraceTag, TracerState, Tracee) -> Result
Types:
TraceTag = trace_tag_running_ports()
TracerState = term()
Tracee = tracee()
Result = trace | discard | remove
This callback is called whenever a tracepoint with trace flag running_ports is
triggered.
If enabled_running_ports/3 is undefined, Module:enabled/3 is called instead.
Module:enabled_running_procs(TraceTag, TracerState, Tracee) -> Result
Types:
TraceTag = trace_tag_running_procs()
TracerState = term()
Tracee = tracee()
Result = trace | discard | remove
This callback is called whenever a tracepoint with trace flag running_procs |
running is triggered.
If enabled_running_procs/3 is undefined, Module:enabled/3 is called instead.
Module:enabled_send(TraceTag, TracerState, Tracee) -> Result
Types:
TraceTag = trace_tag_send()
TracerState = term()
Tracee = tracee()
Result = trace | discard | remove
This callback is called whenever a tracepoint with trace flag send is triggered.
If enabled_send/3 is undefined, Module:enabled/3 is called instead.
Module:trace(TraceTag, TracerState, Tracee, TraceTerm, Opts) -> Result
Types:
TraceTag = trace_tag()
TracerState = term()
Tracee = tracee()
TraceTerm = term()
Opts = trace_opts()
Result = ok
This callback is called when a tracepoint is triggered and the Module:enabled/3
callback returned trace. In it any side effects needed by the tracer are to be
done. The tracepoint payload is located in the TraceTerm. The content of the
TraceTerm depends on which TraceTag is triggered. TraceTerm corresponds to the
fourth element in the trace tuples described in erlang:trace/3.
If the trace tuple has five elements, the fifth element will be sent as the extra
value in the Opts maps.
Module:trace(seq_trace, TracerState, Label, SeqTraceInfo, Opts) -> Result
Types:
TracerState = term()
Label = term()
SeqTraceInfo = term()
Opts = trace_opts()
Result = ok
The TraceTag seq_trace is handled slightly differently. There is no Tracee for
seq_trace, instead the Label associated with the seq_trace event is specified.
For more information on what Label and SeqTraceInfo can be, see seq_trace(3erl).
Module:trace_call(TraceTag, TracerState, Tracee, TraceTerm, Opts) -> Result
Types:
TraceTag = trace_tag_call()
TracerState = term()
Tracee = tracee()
TraceTerm = term()
Opts = trace_opts()
Result = ok
This callback is called when a tracepoint is triggered and the
Module:enabled_call/3 callback returned trace.
If trace_call/5 is undefined, Module:trace/5 is called instead.
Module:trace_garbage_collection(TraceTag, TracerState, Tracee, TraceTerm, Opts) -> Result
Types:
TraceTag = trace_tag_gc()
TracerState = term()
Tracee = tracee()
TraceTerm = term()
Opts = trace_opts()
Result = ok
This callback is called when a tracepoint is triggered and the
Module:enabled_garbage_collection/3 callback returned trace.
If trace_garbage_collection/5 is undefined, Module:trace/5 is called instead.
Module:trace_ports(TraceTag, TracerState, Tracee, TraceTerm, Opts) -> Result
Types:
TraceTag = trace_tag()
TracerState = term()
Tracee = tracee()
TraceTerm = term()
Opts = trace_opts()
Result = ok
This callback is called when a tracepoint is triggered and the
Module:enabled_ports/3 callback returned trace.
If trace_ports/5 is undefined, Module:trace/5 is called instead.
Module:trace_procs(TraceTag, TracerState, Tracee, TraceTerm, Opts) -> Result
Types:
TraceTag = trace_tag()
TracerState = term()
Tracee = tracee()
TraceTerm = term()
Opts = trace_opts()
Result = ok
This callback is called when a tracepoint is triggered and the
Module:enabled_procs/3 callback returned trace.
If trace_procs/5 is undefined, Module:trace/5 is called instead.
Module:trace_receive(TraceTag, TracerState, Tracee, TraceTerm, Opts) -> Result
Types:
TraceTag = trace_tag_receive()
TracerState = term()
Tracee = tracee()
TraceTerm = term()
Opts = trace_opts()
Result = ok
This callback is called when a tracepoint is triggered and the
Module:enabled_receive/3 callback returned trace.
If trace_receive/5 is undefined, Module:trace/5 is called instead.
Module:trace_running_ports(TraceTag, TracerState, Tracee, TraceTerm, Opts) -> Result
Types:
TraceTag = trace_tag_running_ports()
TracerState = term()
Tracee = tracee()
TraceTerm = term()
Opts = trace_opts()
Result = ok
This callback is called when a tracepoint is triggered and the
Module:enabled_running_ports/3 callback returned trace.
If trace_running_ports/5 is undefined, Module:trace/5 is called instead.
Module:trace_running_procs(TraceTag, TracerState, Tracee, TraceTerm, Opts) -> Result
Types:
TraceTag = trace_tag_running_procs()
TracerState = term()
Tracee = tracee()
TraceTerm = term()
Opts = trace_opts()
Result = ok
This callback is called when a tracepoint is triggered and the
Module:enabled_running_procs/3 callback returned trace.
If trace_running_procs/5 is undefined, Module:trace/5 is called instead.
Module:trace_send(TraceTag, TracerState, Tracee, TraceTerm, Opts) -> Result
Types:
TraceTag = trace_tag_send()
TracerState = term()
Tracee = tracee()
TraceTerm = term()
Opts = trace_opts()
Result = ok
This callback is called when a tracepoint is triggered and the
Module:enabled_send/3 callback returned trace.
If trace_send/5 is undefined, Module:trace/5 is called instead.
ERL TRACER MODULE EXAMPLE
In this example, a tracer module with a NIF back end sends a message for each send trace
tag containing only the sender and receiver. Using this tracer module, a much more
lightweight message tracer is used, which only records who sent messages to who.
The following is an example session using it on Linux:
$ gcc -I erts-8.0/include/ -fPIC -shared -o erl_msg_tracer.so erl_msg_tracer.c
$ erl
Erlang/OTP 19 [DEVELOPMENT] [erts-8.0] [source-ed2b56b] [64-bit] [smp:8:8] [async-threads:10] [hipe] [kernel-poll:false]
Eshell V8.0 (abort with ^G)
1> c(erl_msg_tracer), erl_msg_tracer:load().
ok
2> Tracer = spawn(fun F() -> receive M -> io:format("~p~n",[M]), F() end end).
<0.37.0>
3> erlang:trace(new, true, [send,{tracer, erl_msg_tracer, Tracer}]).
0
{trace,<0.39.0>,<0.27.0>}
4> {ok, D} = file:open("/tmp/tmp.data",[write]).
{trace,#Port<0.486>,<0.40.0>}
{trace,<0.40.0>,<0.21.0>}
{trace,#Port<0.487>,<0.4.0>}
{trace,#Port<0.488>,<0.4.0>}
{trace,#Port<0.489>,<0.4.0>}
{trace,#Port<0.490>,<0.4.0>}
{ok,<0.40.0>}
{trace,<0.41.0>,<0.27.0>}
5>
erl_msg_tracer.erl:
-module(erl_msg_tracer).
-export([enabled/3, trace/5, load/0]).
load() ->
erlang:load_nif("erl_msg_tracer", []).
enabled(_, _, _) ->
error.
trace(_, _, _, _, _) ->
error.
erl_msg_tracer.c:
#include <erl_nif.h>
/* NIF interface declarations */
static int load(ErlNifEnv* env, void** priv_data, ERL_NIF_TERM load_info);
static int upgrade(ErlNifEnv* env, void** priv_data, void** old_priv_data, ERL_NIF_TERM load_info);
static void unload(ErlNifEnv* env, void* priv_data);
/* The NIFs: */
static ERL_NIF_TERM enabled(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[]);
static ERL_NIF_TERM trace(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[]);
static ErlNifFunc nif_funcs[] = {
{"enabled", 3, enabled},
{"trace", 5, trace}
};
ERL_NIF_INIT(erl_msg_tracer, nif_funcs, load, NULL, upgrade, unload)
static int load(ErlNifEnv* env, void** priv_data, ERL_NIF_TERM load_info)
{
*priv_data = NULL;
return 0;
}
static void unload(ErlNifEnv* env, void* priv_data)
{
}
static int upgrade(ErlNifEnv* env, void** priv_data, void** old_priv_data,
ERL_NIF_TERM load_info)
{
if (*old_priv_data != NULL || *priv_data != NULL) {
return -1; /* Don't know how to do that */
}
if (load(env, priv_data, load_info)) {
return -1;
}
return 0;
}
/*
* argv[0]: TraceTag
* argv[1]: TracerState
* argv[2]: Tracee
*/
static ERL_NIF_TERM enabled(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
{
ErlNifPid to_pid;
if (enif_get_local_pid(env, argv[1], &to_pid))
if (!enif_is_process_alive(env, &to_pid))
if (enif_is_identical(enif_make_atom(env, "trace_status"), argv[0]))
/* tracer is dead so we should remove this tracepoint */
return enif_make_atom(env, "remove");
else
return enif_make_atom(env, "discard");
/* Only generate trace for when tracer != tracee */
if (enif_is_identical(argv[1], argv[2]))
return enif_make_atom(env, "discard");
/* Only trigger trace messages on 'send' */
if (enif_is_identical(enif_make_atom(env, "send"), argv[0]))
return enif_make_atom(env, "trace");
/* Have to answer trace_status */
if (enif_is_identical(enif_make_atom(env, "trace_status"), argv[0]))
return enif_make_atom(env, "trace");
return enif_make_atom(env, "discard");
}
/*
* argv[0]: TraceTag, should only be 'send'
* argv[1]: TracerState, process to send {Tracee, Recipient} to
* argv[2]: Tracee
* argv[3]: Message
* argv[4]: Options, map containing Recipient
*/
static ERL_NIF_TERM trace(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
{
ErlNifPid to_pid;
ERL_NIF_TERM recipient, msg;
if (enif_get_local_pid(env, argv[1], &to_pid)) {
if (enif_get_map_value(env, argv[4], enif_make_atom(env, "extra"), &recipient)) {
msg = enif_make_tuple3(env, enif_make_atom(env, "trace"), argv[2], recipient);
enif_send(env, &to_pid, NULL, msg);
}
}
return enif_make_atom(env, "ok");
}