View Source erl_tracer behaviour (erts v15.1.1)

Erlang tracer behavior.

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 below.

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.

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");
}

Summary

Types

The options for the tracee

The different trace tags that the tracer is called with.

The process or port that the trace belongs to.

Callbacks

This callback is called whenever a tracepoint is triggered.

This callback is called whenever a tracepoint with trace flag call | return_to is triggered.

This callback is called whenever a tracepoint with trace flag garbage_collection is triggered.

This callback is called whenever a tracepoint with trace flag ports is triggered.

This callback is called whenever a tracepoint with trace flag procs is triggered.

This callback is called whenever a tracepoint with trace flag 'receive' is triggered.

This callback is called whenever a tracepoint with trace flag running_ports is triggered.

This callback is called whenever a tracepoint with trace flag running_procs | running is triggered.

This callback is called whenever a tracepoint with trace flag send is triggered.

This callback is called when a tracepoint is triggered and the Module:enabled/3 callback returned trace.

This callback is called when a tracepoint is triggered and the Module:enabled_call/3 callback returned trace.

This callback is called when a tracepoint is triggered and the Module:enabled_garbage_collection/3 callback returned trace.

This callback is called when a tracepoint is triggered and the Module:enabled_ports/3 callback returned trace.

This callback is called when a tracepoint is triggered and the Module:enabled_procs/3 callback returned trace.

This callback is called when a tracepoint is triggered and the Module:enabled_receive/3 callback returned trace.

This callback is called when a tracepoint is triggered and the Module:enabled_running_ports/3 callback returned trace.

This callback is called when a tracepoint is triggered and the Module:enabled_running_procs/3 callback returned trace.

This callback is called when a tracepoint is triggered and the Module:enabled_send/3 callback returned trace.

Types

Link to this type

trace_opts()

View Source (since OTP 19.0)
-type trace_opts() ::
          #{extra => term(),
            match_spec_result => term(),
            scheduler_id => non_neg_integer(),
            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 trace:process/4.

  • 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.

Link to this type

trace_tag()

View Source (since OTP 19.0)

The different trace tags that the tracer is called with.

Each trace tag is described in detail in Module:trace/5.

Link to this type

trace_tag_call()

View Source (since OTP 19.0)
-type trace_tag_call() :: call | return_to | return_from | exception_from.
Link to this type

trace_tag_gc()

View Source (since OTP 19.0)
-type trace_tag_gc() :: gc_minor_start | gc_minor_end | gc_major_start | gc_major_end.
Link to this type

trace_tag_ports()

View Source (since OTP 19.0)
-type trace_tag_ports() :: open | closed | link | unlink | getting_linked | getting_unlinked.
Link to this type

trace_tag_procs()

View Source (since OTP 19.0)
-type trace_tag_procs() ::
          spawn | spawned | exit | link | unlink | getting_linked | getting_unlinked | register |
          unregister.
Link to this type

trace_tag_receive()

View Source (since OTP 19.0)
-type trace_tag_receive() :: 'receive'.
Link to this type

trace_tag_running_ports()

View Source (since OTP 19.0)
-type trace_tag_running_ports() :: in | out | in_exiting | out_exiting | out_exited.
Link to this type

trace_tag_running_procs()

View Source (since OTP 19.0)
-type trace_tag_running_procs() :: in | out | in_exiting | out_exiting | out_exited.
Link to this type

trace_tag_send()

View Source (since OTP 19.0)
-type trace_tag_send() :: send | send_to_non_existing_process.
Link to this type

tracee()

View Source (since OTP 19.0)
-type tracee() :: port() | pid() | undefined.

The process or port that the trace belongs to.

Callbacks

Link to this callback

enabled(TraceTag, TracerState, Tracee)

View Source (since OTP 19.0)
-callback enabled(TraceTag, TracerState, Tracee) -> Result
                     when
                         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.

Link to this callback

enabled_call(TraceTag, TracerState, Tracee)

View Source (optional) (since OTP 19.0)
-callback enabled_call(TraceTag, TracerState, Tracee) -> Result
                          when
                              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.

Link to this callback

enabled_garbage_collection(TraceTag, TracerState, Tracee)

View Source (optional) (since OTP 19.0)
-callback enabled_garbage_collection(TraceTag, TracerState, Tracee) -> Result
                                        when
                                            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.

Link to this callback

enabled_ports(TraceTag, TracerState, Tracee)

View Source (optional) (since OTP 19.0)
-callback enabled_ports(TraceTag, TracerState, Tracee) -> Result
                           when
                               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.

Link to this callback

enabled_procs(TraceTag, TracerState, Tracee)

View Source (optional) (since OTP 19.0)
-callback enabled_procs(TraceTag, TracerState, Tracee) -> Result
                           when
                               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.

Link to this callback

enabled_receive(TraceTag, TracerState, Tracee)

View Source (optional) (since OTP 19.0)
-callback enabled_receive(TraceTag, TracerState, Tracee) -> Result
                             when
                                 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.

Link to this callback

enabled_running_ports(TraceTag, TracerState, Tracee)

View Source (optional) (since OTP 19.0)
-callback enabled_running_ports(TraceTag, TracerState, Tracee) -> Result
                                   when
                                       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.

Link to this callback

enabled_running_procs(TraceTag, TracerState, Tracee)

View Source (since OTP 19.0)
-callback enabled_running_procs(TraceTag, TracerState, Tracee) -> Result
                                   when
                                       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.

Link to this callback

enabled_send(TraceTag, TracerState, Tracee)

View Source (optional) (since OTP 19.0)
-callback enabled_send(TraceTag, TracerState, Tracee) -> Result
                          when
                              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.

Link to this callback

trace(Tag, TracerState, Tracee, Msg, Opts)

View Source (since OTP 19.0)
-callback trace(seq_trace, TracerState, Label, SeqTraceInfo, Opts) -> Result
                   when
                       TracerState :: term(),
                       Label :: term(),
                       SeqTraceInfo :: term(),
                       Opts :: trace_opts(),
                       Result :: ok;
               (TraceTag, TracerState, Tracee, TraceTerm, Opts) -> Result
                   when
                       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 trace:process/4.

If the trace tuple has five elements, the fifth element will be sent as the extra value in the Opts maps.

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.

Link to this callback

trace_call(TraceTag, TracerState, Tracee, TraceTerm, Opts)

View Source (optional) (since OTP 19.0)
-callback trace_call(TraceTag, TracerState, Tracee, TraceTerm, Opts) -> Result
                        when
                            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.

Link to this callback

trace_garbage_collection(TraceTag, TracerState, Tracee, TraceTerm, Opts)

View Source (optional) (since OTP 19.0)
-callback trace_garbage_collection(TraceTag, TracerState, Tracee, TraceTerm, Opts) -> Result
                                      when
                                          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.

Link to this callback

trace_ports(TraceTag, TracerState, Tracee, TraceTerm, Opts)

View Source (optional) (since OTP 19.0)
-callback trace_ports(TraceTag, TracerState, Tracee, TraceTerm, Opts) -> Result
                         when
                             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.

Link to this callback

trace_procs(TraceTag, TracerState, Tracee, TraceTerm, Opts)

View Source (optional) (since OTP 19.0)
-callback trace_procs(TraceTag, TracerState, Tracee, TraceTerm, Opts) -> Result
                         when
                             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.

Link to this callback

trace_receive(TraceTag, TracerState, Tracee, TraceTerm, Opts)

View Source (optional) (since OTP 19.0)
-callback trace_receive(TraceTag, TracerState, Tracee, TraceTerm, Opts) -> Result
                           when
                               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.

Link to this callback

trace_running_ports(TraceTag, TracerState, Tracee, TraceTerm, Opts)

View Source (optional) (since OTP 19.0)
-callback trace_running_ports(TraceTag, TracerState, Tracee, TraceTerm, Opts) -> Result
                                 when
                                     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.

Link to this callback

trace_running_procs(TraceTag, TracerState, Tracee, TraceTerm, Opts)

View Source (since OTP 19.0)
-callback trace_running_procs(TraceTag, TracerState, Tracee, TraceTerm, Opts) -> Result
                                 when
                                     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.

Link to this callback

trace_send(TraceTag, TracerState, Tracee, TraceTerm, Opts)

View Source (optional) (since OTP 19.0)
-callback trace_send(TraceTag, TracerState, Tracee, TraceTerm, Opts) -> Result
                        when
                            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.