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.
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.
WarningDo 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.
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");
}The options for the tracee
The different trace tags that the tracer is called with.
The process or port that the trace belongs to.
CallbacksThis 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 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_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_send/3 callback returned trace.
-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.
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.
-type tracee() :: port() | pid() | undefined.
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.
-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.
-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.
-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.
-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.
-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.
-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.
-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.
-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.
-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.
-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.
-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.
-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.
-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.
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.
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.
-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.
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