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v8: implement v8.stopCoverage()
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Add a v8.stopCoverage() API to stop the coverage collection
started by NODE_V8_COVERAGE - this would be useful in
conjunction with v8.takeCoverage() if the user don't want
to emit the coverage at the process exit but still want
to collect it on demand at some point.

PR-URL: #33807
Backport-PR-URL: #36352
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Ben Coe <bencoe@gmail.com>
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joyeecheung authored and richardlau committed Mar 17, 2021
1 parent 8ddea3f commit 86f34ee
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16 changes: 14 additions & 2 deletions doc/api/v8.md
Original file line number Diff line number Diff line change
Expand Up @@ -227,7 +227,18 @@ 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.
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
Expand Down Expand Up @@ -524,7 +535,7 @@ A subclass of [`Deserializer`][] corresponding to the format written by
[`Deserializer`]: #v8_class_v8_deserializer
[`Error`]: errors.html#errors_class_error
[`GetHeapSpaceStatistics`]: https://v8docs.nodesource.com/node-13.2/d5/dda/classv8_1_1_isolate.html#ac673576f24fdc7a33378f8f57e1d13a4
[`NODE_V8_COVERAGE`]: cli.html#cli_node_v8_coverage_dir
[`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 @@ -534,6 +545,7 @@ 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.html#vm_new_vm_script_code_options
[HTML structured clone algorithm]: https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Structured_clone_algorithm
[V8]: https://developers.google.com/v8/
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1 change: 1 addition & 0 deletions lib/v8.js
Original file line number Diff line number Diff line change
Expand Up @@ -293,6 +293,7 @@ module.exports = {
DefaultDeserializer,
deserialize,
takeCoverage: profiler.takeCoverage,
stopCoverage: profiler.stopCoverage,
serialize,
writeHeapSnapshot,
};
20 changes: 20 additions & 0 deletions src/inspector_profiler.cc
Original file line number Diff line number Diff line change
Expand Up @@ -295,6 +295,10 @@ void V8CoverageConnection::TakeCoverage() {
DispatchMessage("Profiler.takePreciseCoverage", nullptr, true);
}

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

void V8CoverageConnection::End() {
Debug(env_,
DebugCategory::INSPECTOR_PROFILER,
Expand Down Expand Up @@ -505,6 +509,21 @@ static void TakeCoverage(const FunctionCallbackInfo<Value>& args) {
}
}

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,
Expand All @@ -513,6 +532,7 @@ static void Initialize(Local<Object> target,
env->SetMethod(target, "setCoverageDirectory", SetCoverageDirectory);
env->SetMethod(target, "setSourceMapCacheGetter", SetSourceMapCacheGetter);
env->SetMethod(target, "takeCoverage", TakeCoverage);
env->SetMethod(target, "stopCoverage", StopCoverage);
}

} // namespace profiler
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1 change: 1 addition & 0 deletions src/inspector_profiler.h
Original file line number Diff line number Diff line change
Expand Up @@ -95,6 +95,7 @@ class V8CoverageConnection : public V8ProfilerConnection {
void WriteProfile(v8::Local<v8::Object> result) override;
void WriteSourceMapCache();
void TakeCoverage();
void StopCoverage();

private:
std::unique_ptr<inspector::InspectorSession> session_;
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3 changes: 3 additions & 0 deletions test/fixtures/v8-coverage/stop-coverage.js
Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
'use strict';
const v8 = require('v8');
v8.stopCoverage();
34 changes: 34 additions & 0 deletions test/parallel/test-v8-stop-coverage.js
Original file line number Diff line number Diff line change
@@ -0,0 +1,34 @@
'use strict';

if (!process.features.inspector) return;

require('../common');
const fixtures = require('../common/fixtures');
const tmpdir = require('../common/tmpdir');
const assert = require('assert');
const fs = require('fs');
const { spawnSync } = require('child_process');

tmpdir.refresh();
const intervals = 20;

{
const output = spawnSync(process.execPath, [
'-r',
fixtures.path('v8-coverage', 'stop-coverage'),
'-r',
fixtures.path('v8-coverage', 'take-coverage'),
fixtures.path('v8-coverage', 'interval'),
], {
env: {
...process.env,
NODE_V8_COVERAGE: tmpdir.path,
NODE_DEBUG_NATIVE: 'INSPECTOR_PROFILER',
TEST_INTERVALS: intervals
},
});
console.log(output.stderr.toString());
assert.strictEqual(output.status, 0);
const coverageFiles = fs.readdirSync(tmpdir.path);
assert.strictEqual(coverageFiles.length, 0);
}

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