From 7bfa8720135498e2f2298b46cc4c5b7d7b37a442 Mon Sep 17 00:00:00 2001
From: Joyee Cheung <joyeec9h3@gmail.com>
Date: Tue, 9 Jun 2020 21:18:25 +0800
Subject: [PATCH] v8: implement v8.stopCoverage()

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: https://github.com/nodejs/node/pull/33807
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>
---
 doc/api/v8.md                              | 16 ++++++++--
 lib/v8.js                                  |  1 +
 src/inspector_profiler.cc                  | 20 +++++++++++++
 src/inspector_profiler.h                   |  1 +
 test/fixtures/v8-coverage/stop-coverage.js |  3 ++
 test/parallel/test-v8-stop-coverage.js     | 34 ++++++++++++++++++++++
 6 files changed, 73 insertions(+), 2 deletions(-)
 create mode 100644 test/fixtures/v8-coverage/stop-coverage.js
 create mode 100644 test/parallel/test-v8-stop-coverage.js

diff --git a/doc/api/v8.md b/doc/api/v8.md
index acdc122ed6a563..72556365291cd5 100644
--- a/doc/api/v8.md
+++ b/doc/api/v8.md
@@ -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
@@ -526,7 +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.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
@@ -536,5 +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
diff --git a/lib/v8.js b/lib/v8.js
index 0442cce4083238..15fe57e63e36ce 100644
--- a/lib/v8.js
+++ b/lib/v8.js
@@ -282,6 +282,7 @@ module.exports = {
   DefaultDeserializer,
   deserialize,
   takeCoverage: profiler.takeCoverage,
+  stopCoverage: profiler.stopCoverage,
   serialize,
   writeHeapSnapshot,
 };
diff --git a/src/inspector_profiler.cc b/src/inspector_profiler.cc
index 3444a9b98952dd..092b263ada2fdd 100644
--- a/src/inspector_profiler.cc
+++ b/src/inspector_profiler.cc
@@ -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,
@@ -489,6 +493,21 @@ 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,
@@ -497,6 +516,7 @@ 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
diff --git a/src/inspector_profiler.h b/src/inspector_profiler.h
index 5e861dd0ea03b4..be74153b0c37ac 100644
--- a/src/inspector_profiler.h
+++ b/src/inspector_profiler.h
@@ -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_;
diff --git a/test/fixtures/v8-coverage/stop-coverage.js b/test/fixtures/v8-coverage/stop-coverage.js
new file mode 100644
index 00000000000000..dadfd1900bdd78
--- /dev/null
+++ b/test/fixtures/v8-coverage/stop-coverage.js
@@ -0,0 +1,3 @@
+'use strict';
+const v8 = require('v8');
+v8.stopCoverage();
diff --git a/test/parallel/test-v8-stop-coverage.js b/test/parallel/test-v8-stop-coverage.js
new file mode 100644
index 00000000000000..020e18d8747eb2
--- /dev/null
+++ b/test/parallel/test-v8-stop-coverage.js
@@ -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);
+}