View Source erl_tracer behaviour (erts v15.2)
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
Traceein 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
-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 whichTraceTaghas been triggered. Theextratrace 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.
-type 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.
-type trace_tag_call() :: call | return_to | return_from | exception_from.
-type trace_tag_gc() :: gc_minor_start | gc_minor_end | gc_major_start | gc_major_end.
-type trace_tag_ports() :: open | closed | link | unlink | getting_linked | getting_unlinked.
-type trace_tag_procs() ::
spawn | spawned | exit | link | unlink | getting_linked | getting_unlinked | register |
unregister.
-type trace_tag_receive() :: 'receive'.
-type trace_tag_running_ports() :: in | out | in_exiting | out_exiting | out_exited.
-type trace_tag_running_procs() :: in | out | in_exiting | out_exiting | out_exited.
-type trace_tag_send() :: send | send_to_non_existing_process.
The process or port that the trace belongs to.
Callbacks
-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.
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.
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.
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.
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.
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.
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.
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.
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.
-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.
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.
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.
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.
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.
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.
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.
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.
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.