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diff --git a/erts/doc/src/erl_tracer.xml b/erts/doc/src/erl_tracer.xml new file mode 100644 index 0000000000..83eef374ca --- /dev/null +++ b/erts/doc/src/erl_tracer.xml @@ -0,0 +1,778 @@ +<?xml version="1.0" encoding="utf-8" ?> +<!DOCTYPE erlref SYSTEM "erlref.dtd"> + +<erlref> + <header> + <copyright> + <year>2016</year><year>2016</year> + <holder>Ericsson AB. All Rights Reserved.</holder> + </copyright> + <legalnotice> + Licensed under the Apache License, Version 2.0 (the "License"); + you may not use this file except in compliance with the License. + You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. + + </legalnotice> + + <title>erl_tracer</title> + <prepared></prepared> + <docno></docno> + <date></date> + <rev></rev> + </header> + <module>erl_tracer</module> + <modulesummary>Erlang tracer behavior.</modulesummary> + <description> + <p>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 <c>enabled</c> and <c>trace</c> + 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.</p> + + <note> + <p>All functions in this behavior must be implemented as NIFs. + This limitation can be removed in a future releases. + An <seealso marker="#example">example tracer module NIF</seealso> + implementation is provided at the end of this page.</p> + </note> + + <warning> + <p>Do not send messages or issue port commands to the <c>Tracee</c> + in any of the callbacks. This is not allowed and can cause all + sorts of strange behavior, including, but not limited to, infinite + recursions.</p> + </warning> + </description> + + <datatypes> + <datatype> + <name name="trace_tag_call"/> + </datatype> + <datatype> + <name name="trace_tag_gc"/> + </datatype> + <datatype> + <name name="trace_tag_ports"/> + </datatype> + <datatype> + <name name="trace_tag_procs"/> + </datatype> + <datatype> + <name name="trace_tag_receive"/> + </datatype> + <datatype> + <name name="trace_tag_running_ports"/> + </datatype> + <datatype> + <name name="trace_tag_running_procs"/> + </datatype> + <datatype> + <name name="trace_tag_send"/> + </datatype> + <datatype> + <name name="trace_tag"/> + <desc> + <p>The different trace tags that the tracer is called with. + Each trace tag is described in detail in + <seealso marker="#Module:trace/5"><c>Module:trace/5</c></seealso>.</p> + </desc> + </datatype> + <datatype> + <name name="tracee"/> + <desc> + <p>The process or port that the trace belongs to.</p> + </desc> + </datatype> + <datatype> + <name name="trace_opts"/> + <desc> + <p>The options for the tracee:</p> + <taglist> + <tag><c>timestamp</c></tag> + <item>If set the tracer has been requested to include a + time stamp.</item> + <tag><c>extra</c></tag> + <item>If set the tracepoint has included additonal data about + the trace event. What the additional data is depends on which + <c>TraceTag</c> has been triggered. The <c>extra</c> trace data + corresponds to the fifth element in the trace tuples described in + <seealso marker="erlang#trace_3_trace_messages"> + erlang:trace/3</seealso>.</item> + <tag><c>match_spec_result</c></tag> + <item>If set the tracer has been requested to include the output + of a match specification that was run.</item> + <tag><c>scheduler_id</c></tag> + <item>If set the scheduler id is to be included by the tracer.</item> + </taglist> + </desc> + </datatype> + <datatype> + <name name="tracer_state"/> + <desc> + <p>The state specified when calling + <seealso marker="erlang#trace-3"> + <c>erlang:trace(PidPortSpec,true,[{tracer,Module,TracerState}])</c></seealso>. + The tracer state is an immutable value that is passed to + <c>erl_tracer</c> callbacks and is to + contain all the data that is needed to generate the trace event.</p> + </desc> + </datatype> + </datatypes> + + <section> + <title>Callback Functions</title> + <p>The following functions are to be exported from an <c>erl_tracer</c> + callback module:</p> + + <taglist> + <tag><seealso marker="#Module:enabled/3"> + <c>Module:enabled/3</c></seealso></tag> + <item>Mandatory</item> + <tag><seealso marker="#Module:trace/5"> + <c>Module:trace/5</c></seealso></tag> + <item>Mandatory</item> + <tag><seealso marker="#Module:enabled_call/3"> + <c>Module:enabled_call/3</c></seealso></tag> + <item>Optional</item> + <tag><seealso marker="#Module:trace_call/5"> + <c>Module:trace_call/5</c></seealso></tag> + <item>Optional</item> + <tag><seealso marker="#Module:enabled_garbage_collection/3"> + <c>Module:enabled_garbage_collection/3</c></seealso></tag> + <item>Optional</item> + <tag><seealso marker="#Module:trace_garbage_collection/5"> + <c>Module:trace_garbage_collection/5</c></seealso></tag> + <item>Optional</item> + <tag><seealso marker="#Module:enabled_ports/3"> + <c>Module:enabled_ports/3</c></seealso></tag> + <item>Optional</item> + <tag><seealso marker="#Module:trace_ports/5"> + <c>Module:trace_ports/5</c></seealso></tag> + <item>Optional</item> + <tag><seealso marker="#Module:enabled_procs/3"> + <c>Module:enabled_procs/3</c></seealso></tag> + <item>Optional</item> + <tag><seealso marker="#Module:trace_procs/5"> + <c>Module:trace_procs/5</c></seealso></tag> + <item>Optional</item> + <tag><seealso marker="#Module:enabled_receive/3"> + <c>Module:enabled_receive/3</c></seealso></tag> + <item>Optional</item> + <tag><seealso marker="#Module:trace_receive/5"> + <c>Module:trace_receive/5</c></seealso></tag> + <item>Optional</item> + <tag><seealso marker="#Module:enabled_running_ports/3"> + <c>Module:enabled_running_ports/3</c></seealso></tag> + <item>Optional</item> + <tag><seealso marker="#Module:trace_running_ports/5"> + <c>Module:trace_running_ports/5</c></seealso></tag> + <item>Optional</item> + <tag><seealso marker="#Module:enabled_running_procs/3"> + <c>Module:enabled_running_procs/3</c></seealso></tag> + <item>Optional</item> + <tag><seealso marker="#Module:trace_running_procs/5"> + <c>Module:trace_running_procs/5</c></seealso></tag> + <item>Optional</item> + <tag><seealso marker="#Module:enabled_send/3"> + <c>Module:enabled_send/3</c></seealso></tag> + <item>Optional</item> + <tag><seealso marker="#Module:trace_send/5"> + <c>Module:trace_send/5</c></seealso></tag> + <item>Optional</item> + </taglist> + </section> + + <funcs> + <func> + <name>Module:enabled(TraceTag, TracerState, Tracee) -> Result</name> + <fsummary>Check if a trace event is to be generated.</fsummary> + <type> + <v>TraceTag = <seealso marker="#type-trace_tag"> + trace_tag()</seealso> | trace_status</v> + <v>TracerState = term()</v> + <v>Tracee = <seealso marker="#type-tracee">tracee()</seealso></v> + <v>Result = trace | discard | remove</v> + </type> + <desc> + <p>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 <c>trace</c> is returned, the + necessary trace data is created and the trace callback of the tracer + is called. If <c>discard</c> is returned, this trace call is + discarded and no call to trace is done.</p> + <p><c>trace_status</c> is a special type of <c>TraceTag</c>, 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 <c>remove</c> is returned when the + <c>trace_status</c> is checked, the tracer is removed from the + tracee.</p> + <p>This function can be called multiple times per tracepoint, so it + is important that it is both fast and without side effects.</p> + </desc> + </func> + + <func> + <name>Module:enabled_call(TraceTag, TracerState, Tracee) -> Result</name> + <fsummary>Check if a trace event is to be generated.</fsummary> + <type> + <v>TraceTag = <seealso marker="#type-trace_tag_call"> + trace_tag_call()</seealso></v> + <v>TracerState = term()</v> + <v>Tracee = <seealso marker="#type-tracee">tracee()</seealso></v> + <v>Result = trace | discard | remove</v> + </type> + <desc> + <p>This callback is called whenever a tracepoint with trace flag + <seealso marker="erlang#trace-3"><c>call | return_to</c></seealso> + is triggered.</p> + <p>If <c>enabled_call/3</c> is undefined, + <seealso marker="#Module:enabled/3"><c>Module:enabled/3</c></seealso> + is called instead.</p> + </desc> + </func> + + <func> + <name>Module:enabled_garbage_collection(TraceTag, TracerState, Tracee) -> Result</name> + <fsummary>Check if a trace event is to be generated.</fsummary> + <type> + <v>TraceTag = <seealso marker="#type-trace_tag_gc"> + trace_tag_gc()</seealso></v> + <v>TracerState = term()</v> + <v>Tracee = <seealso marker="#type-tracee">tracee()</seealso></v> + <v>Result = trace | discard | remove</v> + </type> + <desc> + <p>This callback is called whenever a tracepoint with trace flag + <seealso marker="erlang#trace-3"><c>garbage_collection</c></seealso> + is triggered.</p> + <p>If <c>enabled_garbage_collection/3</c> is undefined, + <seealso marker="#Module:enabled/3"><c>Module:enabled/3</c></seealso> + is called instead.</p> + </desc> + </func> + + <func> + <name>Module:enabled_ports(TraceTag, TracerState, Tracee) -> Result</name> + <fsummary>Check if a trace event is to be generated.</fsummary> + <type> + <v>TraceTag = <seealso marker="#type-trace_tag_ports"> + trace_tag_ports()</seealso></v> + <v>TracerState = term()</v> + <v>Tracee = <seealso marker="#type-tracee">tracee()</seealso></v> + <v>Result = trace | discard | remove</v> + </type> + <desc> + <p>This callback is called whenever a tracepoint with trace flag + <seealso marker="erlang#trace-3"><c>ports</c></seealso> + is triggered.</p> + <p>If <c>enabled_ports/3</c> is undefined, + <seealso marker="#Module:enabled/3"><c>Module:enabled/3</c></seealso> + is called instead.</p> + </desc> + </func> + + <func> + <name>Module:enabled_procs(TraceTag, TracerState, Tracee) -> Result</name> + <fsummary>Check if a trace event is to be generated.</fsummary> + <type> + <v>TraceTag = <seealso marker="#type-trace_tag_procs"> + trace_tag_procs()</seealso></v> + <v>TracerState = term()</v> + <v>Tracee = <seealso marker="#type-tracee">tracee()</seealso></v> + <v>Result = trace | discard | remove</v> + </type> + <desc> + <p>This callback is called whenever a tracepoint with trace flag + <seealso marker="erlang#trace-3"><c>procs</c></seealso> + is triggered.</p> + <p>If <c>enabled_procs/3</c> is undefined, + <seealso marker="#Module:enabled/3"><c>Module:enabled/3</c></seealso> + is called instead.</p> + </desc> + </func> + + <func> + <name>Module:enabled_receive(TraceTag, TracerState, Tracee) -> Result + </name> + <fsummary>Check if a trace event is to be generated.</fsummary> + <type> + <v>TraceTag = <seealso marker="#type-trace_tag_receive"> + trace_tag_receive()</seealso></v> + <v>TracerState = term()</v> + <v>Tracee = <seealso marker="#type-tracee">tracee()</seealso></v> + <v>Result = trace | discard | remove</v> + </type> + <desc> + <p>This callback is called whenever a tracepoint with trace flag + <seealso marker="erlang#trace-3"><c>'receive'</c></seealso> + is triggered.</p> + <p>If <c>enabled_receive/3</c> is undefined, + <seealso marker="#Module:enabled/3"><c>Module:enabled/3</c></seealso> + is called instead.</p> + </desc> + </func> + + <func> + <name>Module:enabled_running_ports(TraceTag, TracerState, Tracee) -> + Result</name> + <fsummary>Check if a trace event is to be generated.</fsummary> + <type> + <v>TraceTag = <seealso marker="#type-trace_tag_running_ports"> + trace_tag_running_ports()</seealso></v> + <v>TracerState = term()</v> + <v>Tracee = <seealso marker="#type-tracee">tracee()</seealso></v> + <v>Result = trace | discard | remove</v> + </type> + <desc> + <p>This callback is called whenever a tracepoint with trace flag + <seealso marker="erlang#trace-3"><c>running_ports</c></seealso> + is triggered.</p> + <p>If <c>enabled_running_ports/3</c> is undefined, + <seealso marker="#Module:enabled/3"><c>Module:enabled/3</c></seealso> + is called instead.</p> + </desc> + </func> + + <func> + <name>Module:enabled_running_procs(TraceTag, TracerState, Tracee) -> + Result</name> + <fsummary>Check if a trace event is to be generated.</fsummary> + <type> + <v>TraceTag = <seealso marker="#type-trace_tag_running_procs"> + trace_tag_running_procs()</seealso></v> + <v>TracerState = term()</v> + <v>Tracee = <seealso marker="#type-tracee">tracee()</seealso></v> + <v>Result = trace | discard | remove</v> + </type> + <desc> + <p>This callback is called whenever a tracepoint with trace flag + <seealso marker="erlang#trace-3"> + <c>running_procs | running</c></seealso> + is triggered.</p> + <p>If <c>enabled_running_procs/3</c> is undefined, + <seealso marker="#Module:enabled/3"><c>Module:enabled/3</c></seealso> + is called instead.</p> + </desc> + </func> + + <func> + <name>Module:enabled_send(TraceTag, TracerState, Tracee) -> Result</name> + <fsummary>Check if a trace event is to be generated.</fsummary> + <type> + <v>TraceTag = <seealso marker="#type-trace_tag_send"> + trace_tag_send()</seealso></v> + <v>TracerState = term()</v> + <v>Tracee = <seealso marker="#type-tracee">tracee()</seealso></v> + <v>Result = trace | discard | remove</v> + </type> + <desc> + <p>This callback is called whenever a tracepoint with trace flag + <seealso marker="erlang#trace-3"><c>send</c></seealso> + is triggered.</p> + <p>If <c>enabled_send/3</c> is undefined, + <seealso marker="#Module:enabled/3"><c>Module:enabled/3</c></seealso> + is called instead.</p> + </desc> + </func> + + <func> + <name>Module:trace(TraceTag, TracerState, Tracee, TraceTerm, + Opts) -> Result</name> + <fsummary>Check if a trace event is to be generated.</fsummary> + <type> + <v>TraceTag = <seealso marker="#type-trace_tag"> + trace_tag()</seealso></v> + <v>TracerState = term()</v> + <v>Tracee = <seealso marker="#type-tracee">tracee()</seealso></v> + <v>TraceTerm = term()</v> + <v>Opts = <seealso marker="#type-trace_opts">trace_opts()</seealso></v> + <v>Result = ok</v> + </type> + <desc> + <p>This callback is called when a tracepoint is triggered and the + <seealso marker="#Module:enabled/3"><c>Module:enabled/3</c></seealso> + callback returned <c>trace</c>. In it any side effects needed by + the tracer are to be done. The tracepoint payload is located in + the <c>TraceTerm</c>. The content of the <c>TraceTerm</c> + depends on which <c>TraceTag</c> is triggered. + <c>TraceTerm</c> corresponds to the + fourth element in the trace tuples described in + <seealso marker="erlang#trace_3_trace_messages"> + <c>erlang:trace/3</c></seealso>.</p> + <p>If the trace tuple has five elements, the fifth element + will be sent as the <c>extra</c> value in the <c>Opts</c> maps.</p> + </desc> + </func> + + <func> + <name name="trace">Module:trace(seq_trace, TracerState, Label, + SeqTraceInfo, Opts) -> Result</name> + <fsummary>Check if a sequence trace event is to be generated.</fsummary> + <type> + <v>TracerState = term()</v> + <v>Label = term()</v> + <v>SeqTraceInfo = term()</v> + <v>Opts = <seealso marker="#type-trace_opts">trace_opts()</seealso></v> + <v>Result = ok</v> + </type> + <desc> + <p>The <c>TraceTag</c> <c>seq_trace</c> is handled slightly + differently. There is no <c>Tracee</c> for <c>seq_trace</c>, instead + the <c>Label</c> associated with the <c>seq_trace</c> event is + specified.</p> + <p>For more information on what <c>Label</c> and <c>SeqTraceInfo</c> + can be, see <seealso marker="kernel:seq_trace"> + <c>seq_trace(3)</c></seealso>.</p> + </desc> + </func> + + <func> + <name>Module:trace_call(TraceTag, TracerState, Tracee, TraceTerm, + Opts) -> Result</name> + <fsummary>Check if a trace event is to be generated.</fsummary> + <type> + <v>TraceTag = <seealso marker="#type-trace_tag_call"> + trace_tag_call()</seealso></v> + <v>TracerState = term()</v> + <v>Tracee = <seealso marker="#type-tracee">tracee()</seealso></v> + <v>TraceTerm = term()</v> + <v>Opts = <seealso marker="#type-trace_opts">trace_opts()</seealso></v> + <v>Result = ok</v> + </type> + <desc> + <p>This callback is called when a tracepoint is triggered and the + <seealso marker="#Module:enabled_call/3"> + <c>Module:enabled_call/3</c></seealso> + callback returned <c>trace</c>.</p> + <p>If <c>trace_call/5</c> is undefined, + <seealso marker="#Module:trace/5"><c>Module:trace/5</c></seealso> + is called instead.</p> + </desc> + </func> + + <func> + <name>Module:trace_garbage_collection(TraceTag, TracerState, Tracee, + TraceTerm, Opts) -> Result</name> + <fsummary>Check if a trace event is to be generated.</fsummary> + <type> + <v>TraceTag = <seealso marker="#type-trace_tag_gc"> + trace_tag_gc()</seealso></v> + <v>TracerState = term()</v> + <v>Tracee = <seealso marker="#type-tracee">tracee()</seealso></v> + <v>TraceTerm = term()</v> + <v>Opts = <seealso marker="#type-trace_opts">trace_opts()</seealso></v> + <v>Result = ok</v> + </type> + <desc> + <p>This callback is called when a tracepoint is triggered and the + <seealso marker="#Module:enabled_garbage_collection/3"> + <c>Module:enabled_garbage_collection/3</c></seealso> + callback returned <c>trace</c>.</p> + <p>If <c>trace_garbage_collection/5</c> is undefined, + <seealso marker="#Module:trace/5"><c>Module:trace/5</c></seealso> + is called instead.</p> + </desc> + </func> + + <func> + <name>Module:trace_ports(TraceTag, TracerState, Tracee, TraceTerm, + Opts) -> Result</name> + <fsummary>Check if a trace event is to be generated.</fsummary> + <type> + <v>TraceTag = <seealso marker="#type-trace_tag_ports"> + trace_tag()</seealso></v> + <v>TracerState = term()</v> + <v>Tracee = <seealso marker="#type-tracee">tracee()</seealso></v> + <v>TraceTerm = term()</v> + <v>Opts = <seealso marker="#type-trace_opts">trace_opts()</seealso></v> + <v>Result = ok</v> + </type> + <desc> + <p>This callback is called when a tracepoint is triggered and the + <seealso marker="#Module:enabled_ports/3"> + <c>Module:enabled_ports/3</c></seealso> + callback returned <c>trace</c>.</p> + <p>If <c>trace_ports/5</c> is undefined, + <seealso marker="#Module:trace/5"><c>Module:trace/5</c></seealso> + is called instead.</p> + </desc> + </func> + + <func> + <name>Module:trace_procs(TraceTag, TracerState, Tracee, TraceTerm, + Opts) -> Result</name> + <fsummary>Check if a trace event is to be generated.</fsummary> + <type> + <v>TraceTag = <seealso marker="#type-trace_tag_procs"> + trace_tag()</seealso></v> + <v>TracerState = term()</v> + <v>Tracee = <seealso marker="#type-tracee">tracee()</seealso></v> + <v>TraceTerm = term()</v> + <v>Opts = <seealso marker="#type-trace_opts">trace_opts()</seealso></v> + <v>Result = ok</v> + </type> + <desc> + <p>This callback is called when a tracepoint is triggered and the + <seealso marker="#Module:enabled_procs/3"> + <c>Module:enabled_procs/3</c></seealso> + callback returned <c>trace</c>.</p> + <p>If <c>trace_procs/5</c> is undefined, + <seealso marker="#Module:trace/5"><c>Module:trace/5</c></seealso> + is called instead.</p> + </desc> + </func> + + <func> + <name>Module:trace_receive(TraceTag, TracerState, Tracee, TraceTerm, + Opts) -> Result</name> + <fsummary>Check if a trace event is to be generated.</fsummary> + <type> + <v>TraceTag = <seealso marker="#type-trace_tag_receive"> + trace_tag_receive()</seealso></v> + <v>TracerState = term()</v> + <v>Tracee = <seealso marker="#type-tracee">tracee()</seealso></v> + <v>TraceTerm = term()</v> + <v>Opts = <seealso marker="#type-trace_opts">trace_opts()</seealso></v> + <v>Result = ok</v> + </type> + <desc> + <p>This callback is called when a tracepoint is triggered and the + <seealso marker="#Module:enabled_receive/3"> + <c>Module:enabled_receive/3</c></seealso> + callback returned <c>trace</c>.</p> + <p>If <c>trace_receive/5</c> is undefined, + <seealso marker="#Module:trace/5"><c>Module:trace/5</c></seealso> + is called instead.</p> + </desc> + </func> + + <func> + <name>Module:trace_running_ports(TraceTag, TracerState, Tracee, + TraceTerm, Opts) -> Result</name> + <fsummary>Check if a trace event is to be generated.</fsummary> + <type> + <v>TraceTag = <seealso marker="#type-trace_tag_running_ports"> + trace_tag_running_ports()</seealso></v> + <v>TracerState = term()</v> + <v>Tracee = <seealso marker="#type-tracee">tracee()</seealso></v> + <v>TraceTerm = term()</v> + <v>Opts = <seealso marker="#type-trace_opts">trace_opts()</seealso></v> + <v>Result = ok</v> + </type> + <desc> + <p>This callback is called when a tracepoint is triggered and the + <seealso marker="#Module:enabled_running_ports/3"> + <c>Module:enabled_running_ports/3</c></seealso> + callback returned <c>trace</c>.</p> + <p>If <c>trace_running_ports/5</c> is undefined, + <seealso marker="#Module:trace/5"><c>Module:trace/5</c></seealso> + is called instead.</p> + </desc> + </func> + + <func> + <name>Module:trace_running_procs(TraceTag, TracerState, Tracee, + TraceTerm, Opts) -> Result</name> + <fsummary>Check if a trace event is to be generated.</fsummary> + <type> + <v>TraceTag = <seealso marker="#type-trace_tag_running_procs"> + trace_tag_running_procs()</seealso></v> + <v>TracerState = term()</v> + <v>Tracee = <seealso marker="#type-tracee">tracee()</seealso></v> + <v>TraceTerm = term()</v> + <v>Opts = <seealso marker="#type-trace_opts">trace_opts()</seealso></v> + <v>Result = ok</v> + </type> + <desc> + <p>This callback is called when a tracepoint is triggered and the + <seealso marker="#Module:enabled_running_procs/3"> + <c>Module:enabled_running_procs/3</c></seealso> + callback returned <c>trace</c>.</p> + <p>If <c>trace_running_procs/5</c> is undefined, + <seealso marker="#Module:trace/5"><c>Module:trace/5</c></seealso> + is called instead.</p> + </desc> + </func> + + <func> + <name>Module:trace_send(TraceTag, TracerState, Tracee, TraceTerm, + Opts) -> Result</name> + <fsummary>Check if a trace event is to be generated.</fsummary> + <type> + <v>TraceTag = <seealso marker="#type-trace_tag_send"> + trace_tag_send()</seealso></v> + <v>TracerState = term()</v> + <v>Tracee = <seealso marker="#type-tracee">tracee()</seealso></v> + <v>TraceTerm = term()</v> + <v>Opts = <seealso marker="#type-trace_opts">trace_opts()</seealso></v> + <v>Result = ok</v> + </type> + <desc> + <p>This callback is called when a tracepoint is triggered and the + <seealso marker="#Module:enabled_send/3"> + <c>Module:enabled_send/3</c></seealso> + callback returned <c>trace</c>.</p> + <p>If <c>trace_send/5</c> is undefined, + <seealso marker="#Module:trace/5"><c>Module:trace/5</c></seealso> + is called instead.</p> + </desc> + </func> + </funcs> + + <section> + <marker id="example"></marker> + <title>Erl Tracer Module Example</title> + <p>In this example, a tracer module with a NIF back end sends a + message for each <c>send</c> 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.</p> + + <p>The following is an example session using it on Linux:</p> + + <pre> +$ 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 +{<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></pre> + + <p><c>erl_msg_tracer.erl</c>:</p> + + <pre> +-module(erl_msg_tracer). + +-export([enabled/3, trace/5, load/0]). + +load() -> + erlang:load_nif("erl_msg_tracer", []). + +enabled(_, _, _) -> + error. + +trace(_, _, _, _, _) -> + error.</pre> + + <p><c>erl_msg_tracer.c</c>:</p> + + <pre> +#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 {argv[2], argv[4]} to + * argv[2]: Tracee + * argv[3]: Recipient + * argv[4]: Options, ignored + */ +static ERL_NIF_TERM trace(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[]) +{ + ErlNifPid to_pid; + + if (enif_get_local_pid(env, argv[1], &to_pid)) { + ERL_NIF_TERM msg = enif_make_tuple3(env, enif_make_atom(env, "trace"), argv[2], argv[4]); + enif_send(env, &to_pid, NULL, msg); + } + + return enif_make_atom(env, "ok"); +}</pre> + </section> +</erlref> |