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v8: implement v8.takeCoverage() and v8.stopCoverage() #33807

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18c2cd0
v8: implement v8.takeCoverage()
joyeecheung Jun 9, 2020
cb08d1e
v8: implement v8.stopCoverage()
joyeecheung Jun 9, 2020
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28 changes: 28 additions & 0 deletions doc/api/v8.md
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Original file line number Diff line number Diff line change
Expand Up @@ -214,6 +214,32 @@ v8.setFlagsFromString('--trace_gc');
setTimeout(() => { v8.setFlagsFromString('--notrace_gc'); }, 60e3);
```

## `v8.takeCoverage()`

<!-- YAML
added: REPLACEME
-->

The `v8.takeCoverage()` method allows the user to write the coverage started by
[`NODE_V8_COVERAGE`][] to disk on demand. This method can be invoked multiple
times during the lifetime of the process, each time the execution counter will
be reset and a new coverage report will be written to the directory specified
by [`NODE_V8_COVERAGE`][].

When the process is about to exit, one last coverage will still be written to
disk, unless [`v8.stopCoverage()`][] is invoked before the process exits.

## `v8.stopCoverage()`

<!-- YAML
added: REPLACEME
-->

The `v8.stopCoverage()` method allows the user to stop the coverage collection
started by [`NODE_V8_COVERAGE`][], so that V8 can release the execution count
records and optimize code. This can be used in conjunction with
`v8.takeCoverage()` if the user wants to collect the coverage on demand.

## `v8.writeHeapSnapshot([filename])`
<!-- YAML
added: v11.13.0
Expand Down Expand Up @@ -511,6 +537,7 @@ A subclass of [`Deserializer`][] corresponding to the format written by
[`Deserializer`]: #v8_class_v8_deserializer
[`Error`]: errors.md#errors_class_error
[`GetHeapSpaceStatistics`]: https://v8docs.nodesource.com/node-13.2/d5/dda/classv8_1_1_isolate.html#ac673576f24fdc7a33378f8f57e1d13a4
[`NODE_V8_COVERAGE`]: cli.md#cli_node_v8_coverage_dir
[`Serializer`]: #v8_class_v8_serializer
[`deserializer._readHostObject()`]: #v8_deserializer_readhostobject
[`deserializer.transferArrayBuffer()`]: #v8_deserializer_transferarraybuffer_id_arraybuffer
Expand All @@ -520,5 +547,6 @@ A subclass of [`Deserializer`][] corresponding to the format written by
[`serializer.releaseBuffer()`]: #v8_serializer_releasebuffer
[`serializer.transferArrayBuffer()`]: #v8_serializer_transferarraybuffer_id_arraybuffer
[`serializer.writeRawBytes()`]: #v8_serializer_writerawbytes_buffer
[`v8.stopCoverage()`]: #v8_v8_stopcoverage
[`vm.Script`]: vm.md#vm_new_vm_script_code_options
[worker threads]: worker_threads.md
8 changes: 8 additions & 0 deletions lib/v8.js
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Original file line number Diff line number Diff line change
Expand Up @@ -37,6 +37,12 @@ const {
Serializer: _Serializer,
Deserializer: _Deserializer
} = internalBinding('serdes');

let profiler = {};
if (internalBinding('config').hasInspector) {
profiler = internalBinding('profiler');
}

const assert = require('internal/assert');
const { copy } = internalBinding('buffer');
const { inspect } = require('internal/util/inspect');
Expand Down Expand Up @@ -275,6 +281,8 @@ module.exports = {
DefaultSerializer,
DefaultDeserializer,
deserialize,
takeCoverage: profiler.takeCoverage,
stopCoverage: profiler.stopCoverage,
serialize,
writeHeapSnapshot,
};
207 changes: 132 additions & 75 deletions src/inspector_profiler.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,7 @@
#include "util-inl.h"
#include "v8-inspector.h"

#include <cinttypes>
#include <sstream>

namespace node {
Expand Down Expand Up @@ -36,10 +37,11 @@ V8ProfilerConnection::V8ProfilerConnection(Environment* env)
false)),
env_(env) {}

size_t V8ProfilerConnection::DispatchMessage(const char* method,
const char* params) {
uint32_t V8ProfilerConnection::DispatchMessage(const char* method,
const char* params,
bool is_profile_request) {
std::stringstream ss;
size_t id = next_id();
uint32_t id = next_id();
ss << R"({ "id": )" << id;
DCHECK(method != nullptr);
ss << R"(, "method": ")" << method << '"';
Expand All @@ -50,12 +52,15 @@ size_t V8ProfilerConnection::DispatchMessage(const char* method,
std::string message = ss.str();
const uint8_t* message_data =
reinterpret_cast<const uint8_t*>(message.c_str());
// Save the id of the profile request to identify its response.
if (is_profile_request) {
profile_ids_.insert(id);
}
Debug(env(),
DebugCategory::INSPECTOR_PROFILER,
"Dispatching message %s\n",
message.c_str());
session_->Dispatch(StringView(message_data, message.length()));
// TODO(joyeecheung): use this to identify the ending message.
return id;
}

Expand All @@ -77,33 +82,73 @@ void V8ProfilerConnection::V8ProfilerSessionDelegate::SendMessageToFrontend(
Environment* env = connection_->env();
Isolate* isolate = env->isolate();
HandleScope handle_scope(isolate);
Context::Scope context_scope(env->context());
Local<Context> context = env->context();
Context::Scope context_scope(context);

// TODO(joyeecheung): always parse the message so that we can use the id to
// identify ending messages as well as printing the message in the debug
// output when there is an error.
const char* type = connection_->type();
Debug(env,
DebugCategory::INSPECTOR_PROFILER,
"Receive %s profile message, ending = %s\n",
type,
connection_->ending() ? "true" : "false");
if (!connection_->ending()) {
return;
}

// Convert StringView to a Local<String>.
Local<String> message_str;
if (!String::NewFromTwoByte(isolate,
message.characters16(),
NewStringType::kNormal,
message.length())
.ToLocal(&message_str)) {
fprintf(stderr, "Failed to convert %s profile message\n", type);
fprintf(
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@devsnek devsnek Jun 9, 2020

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it would be nice if this was available as an error callback or something, since the calling code can't really read stderr

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@bnoordhuis bnoordhuis Jun 11, 2020

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The only reason I could see it failing is when message.length() > kStringMaxLength which:

  1. I don't think can realistically happen, and
  2. Isn't actionable for users when it does (except by opening a bug report here)

Maybe the error message could include the size and perhaps the first N bytes of the message.

Similar reasoning applies to the error code paths below. Failure likely means we need to fix something on our end.

stderr, "Failed to convert %s profile message to V8 string\n", type);
return;
}

Debug(env,
DebugCategory::INSPECTOR_PROFILER,
"Receive %s profile message\n",
type);

Local<Value> parsed;
if (!v8::JSON::Parse(context, message_str).ToLocal(&parsed) ||
!parsed->IsObject()) {
fprintf(stderr, "Failed to parse %s profile result as JSON object\n", type);
return;
}

Local<Object> response = parsed.As<Object>();
Local<Value> id_v;
if (!response->Get(context, FIXED_ONE_BYTE_STRING(isolate, "id"))
.ToLocal(&id_v) ||
!id_v->IsUint32()) {
Utf8Value str(isolate, message_str);
fprintf(
stderr, "Cannot retrieve id from the response message:\n%s\n", *str);
return;
}
uint32_t id = id_v.As<v8::Uint32>()->Value();

connection_->WriteProfile(message_str);
if (!connection_->HasProfileId(id)) {
Utf8Value str(isolate, message_str);
Debug(env, DebugCategory::INSPECTOR_PROFILER, "%s\n", *str);
return;
} else {
Debug(env,
DebugCategory::INSPECTOR_PROFILER,
"Writing profile response (id = %" PRIu64 ")\n",
static_cast<uint64_t>(id));
}

// Get message.result from the response.
Local<Value> result_v;
if (!response->Get(context, FIXED_ONE_BYTE_STRING(isolate, "result"))
.ToLocal(&result_v)) {
fprintf(stderr, "Failed to get 'result' from %s profile response\n", type);
return;
}

if (!result_v->IsObject()) {
fprintf(
stderr, "'result' from %s profile response is not an object\n", type);
return;
}

connection_->WriteProfile(result_v.As<Object>());
connection_->RemoveProfileId(id);
}

static bool EnsureDirectory(const std::string& directory, const char* type) {
Expand Down Expand Up @@ -138,45 +183,9 @@ std::string V8CoverageConnection::GetFilename() const {
return filename;
}

static MaybeLocal<Object> ParseProfile(Environment* env,
Local<String> message,
const char* type) {
Local<Context> context = env->context();
Isolate* isolate = env->isolate();

// Get message.result from the response
Local<Value> parsed;
if (!v8::JSON::Parse(context, message).ToLocal(&parsed) ||
!parsed->IsObject()) {
fprintf(stderr, "Failed to parse %s profile result as JSON object\n", type);
return MaybeLocal<Object>();
}

Local<Value> result_v;
if (!parsed.As<Object>()
->Get(context, FIXED_ONE_BYTE_STRING(isolate, "result"))
.ToLocal(&result_v)) {
fprintf(stderr, "Failed to get 'result' from %s profile message\n", type);
return MaybeLocal<Object>();
}

if (!result_v->IsObject()) {
fprintf(
stderr, "'result' from %s profile message is not an object\n", type);
return MaybeLocal<Object>();
}

return result_v.As<Object>();
}

void V8ProfilerConnection::WriteProfile(Local<String> message) {
void V8ProfilerConnection::WriteProfile(Local<Object> result) {
Local<Context> context = env_->context();

// Get message.result from the response.
Local<Object> result;
if (!ParseProfile(env_, message, type()).ToLocal(&result)) {
return;
}
// Generate the profile output from the subclass.
Local<Object> profile;
if (!GetProfile(result).ToLocal(&profile)) {
Expand All @@ -203,7 +212,7 @@ void V8ProfilerConnection::WriteProfile(Local<String> message) {
WriteResult(env_, path.c_str(), result_s);
}

void V8CoverageConnection::WriteProfile(Local<String> message) {
void V8CoverageConnection::WriteProfile(Local<Object> result) {
Isolate* isolate = env_->isolate();
Local<Context> context = env_->context();
HandleScope handle_scope(isolate);
Expand All @@ -219,11 +228,6 @@ void V8CoverageConnection::WriteProfile(Local<String> message) {
return;
}

// Get message.result from the response.
Local<Object> result;
if (!ParseProfile(env_, message, type()).ToLocal(&result)) {
return;
}
// Generate the profile output from the subclass.
Local<Object> profile;
if (!GetProfile(result).ToLocal(&profile)) {
Expand Down Expand Up @@ -287,10 +291,23 @@ void V8CoverageConnection::Start() {
R"({ "callCount": true, "detailed": true })");
}

void V8CoverageConnection::TakeCoverage() {
DispatchMessage("Profiler.takePreciseCoverage", nullptr, true);
}

void V8CoverageConnection::StopCoverage() {
DispatchMessage("Profiler.stopPreciseCoverage");
}

void V8CoverageConnection::End() {
CHECK_EQ(ending_, false);
Debug(env_,
DebugCategory::INSPECTOR_PROFILER,
"V8CoverageConnection::End(), ending = %d\n", ending_);
if (ending_) {
return;
}
ending_ = true;
DispatchMessage("Profiler.takePreciseCoverage");
TakeCoverage();
}

std::string V8CpuProfilerConnection::GetDirectory() const {
Expand Down Expand Up @@ -327,9 +344,14 @@ void V8CpuProfilerConnection::Start() {
}

void V8CpuProfilerConnection::End() {
CHECK_EQ(ending_, false);
Debug(env_,
DebugCategory::INSPECTOR_PROFILER,
"V8CpuProfilerConnection::End(), ending = %d\n", ending_);
if (ending_) {
return;
}
ending_ = true;
DispatchMessage("Profiler.stop");
DispatchMessage("Profiler.stop", nullptr, true);
}

std::string V8HeapProfilerConnection::GetDirectory() const {
Expand Down Expand Up @@ -365,31 +387,33 @@ void V8HeapProfilerConnection::Start() {
}

void V8HeapProfilerConnection::End() {
CHECK_EQ(ending_, false);
Debug(env_,
DebugCategory::INSPECTOR_PROFILER,
"V8HeapProfilerConnection::End(), ending = %d\n", ending_);
if (ending_) {
return;
}
ending_ = true;
DispatchMessage("HeapProfiler.stopSampling");
DispatchMessage("HeapProfiler.stopSampling", nullptr, true);
}

// For now, we only support coverage profiling, but we may add more
// in the future.
static void EndStartedProfilers(Environment* env) {
// TODO(joyeechueng): merge these connections and use one session per env.
Debug(env, DebugCategory::INSPECTOR_PROFILER, "EndStartedProfilers\n");
V8ProfilerConnection* connection = env->cpu_profiler_connection();
if (connection != nullptr && !connection->ending()) {
Debug(env, DebugCategory::INSPECTOR_PROFILER, "Ending cpu profiling\n");
if (connection != nullptr) {
connection->End();
}

connection = env->heap_profiler_connection();
if (connection != nullptr && !connection->ending()) {
Debug(env, DebugCategory::INSPECTOR_PROFILER, "Ending heap profiling\n");
if (connection != nullptr) {
connection->End();
}

connection = env->coverage_connection();
if (connection != nullptr && !connection->ending()) {
Debug(
env, DebugCategory::INSPECTOR_PROFILER, "Ending coverage collection\n");
if (connection != nullptr) {
connection->End();
}
}
Expand Down Expand Up @@ -469,13 +493,46 @@ static void SetSourceMapCacheGetter(const FunctionCallbackInfo<Value>& args) {
env->set_source_map_cache_getter(args[0].As<Function>());
}

static void TakeCoverage(const FunctionCallbackInfo<Value>& args) {
Environment* env = Environment::GetCurrent(args);
V8CoverageConnection* connection = env->coverage_connection();

Debug(
env,
DebugCategory::INSPECTOR_PROFILER,
"TakeCoverage, connection %s nullptr\n",
connection == nullptr ? "==" : "!=");

if (connection != nullptr) {
Debug(env, DebugCategory::INSPECTOR_PROFILER, "taking coverage\n");
connection->TakeCoverage();
}
}

static void StopCoverage(const FunctionCallbackInfo<Value>& args) {
Environment* env = Environment::GetCurrent(args);
V8CoverageConnection* connection = env->coverage_connection();

Debug(env,
DebugCategory::INSPECTOR_PROFILER,
"StopCoverage, connection %s nullptr\n",
connection == nullptr ? "==" : "!=");

if (connection != nullptr) {
Debug(env, DebugCategory::INSPECTOR_PROFILER, "Stopping coverage\n");
connection->StopCoverage();
}
}

static void Initialize(Local<Object> target,
Local<Value> unused,
Local<Context> context,
void* priv) {
Environment* env = Environment::GetCurrent(context);
env->SetMethod(target, "setCoverageDirectory", SetCoverageDirectory);
env->SetMethod(target, "setSourceMapCacheGetter", SetSourceMapCacheGetter);
env->SetMethod(target, "takeCoverage", TakeCoverage);
env->SetMethod(target, "stopCoverage", StopCoverage);
}

} // namespace profiler
Expand Down
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