diff --git a/node.gyp b/node.gyp
index ae25427819..e0bd57dde5 100644
--- a/node.gyp
+++ b/node.gyp
@@ -490,12 +490,14 @@
             'src/inspector_js_api.cc',
             'src/inspector_socket.cc',
             'src/inspector_socket_server.cc',
-            'src/inspector/tracing_agent.cc',
+            'src/inspector/main_thread_interface.cc',
             'src/inspector/node_string.cc',
+            'src/inspector/tracing_agent.cc',
             'src/inspector_agent.h',
             'src/inspector_io.h',
             'src/inspector_socket.h',
             'src/inspector_socket_server.h',
+            'src/inspector/main_thread_interface.h',
             'src/inspector/node_string.h',
             'src/inspector/tracing_agent.h',
             '<@(node_inspector_generated_sources)'
diff --git a/src/inspector/main_thread_interface.cc b/src/inspector/main_thread_interface.cc
new file mode 100644
index 0000000000..da43c95bea
--- /dev/null
+++ b/src/inspector/main_thread_interface.cc
@@ -0,0 +1,317 @@
+#include "main_thread_interface.h"
+
+#include "node_mutex.h"
+#include "v8-inspector.h"
+
+#include <unicode/unistr.h>
+
+namespace node {
+namespace inspector {
+namespace {
+
+using v8_inspector::StringView;
+using v8_inspector::StringBuffer;
+
+template <typename T>
+class DeleteRequest : public Request {
+ public:
+  explicit DeleteRequest(T* object) : object_(object) {}
+  void Call() override {
+    delete object_;
+  }
+
+ private:
+  T* object_;
+};
+
+template <typename Target, typename Arg>
+class SingleArgumentFunctionCall : public Request {
+ public:
+  using Fn = void (Target::*)(Arg);
+
+  SingleArgumentFunctionCall(Target* target, Fn fn, Arg argument)
+                             : target_(target),
+                               fn_(fn),
+                               arg_(std::move(argument)) {}
+
+  void Call() override {
+    Apply(target_, fn_, std::move(arg_));
+  }
+
+ private:
+  template <typename Element>
+  void Apply(Element* target, Fn fn, Arg arg) {
+    (target->*fn)(std::move(arg));
+  }
+
+  Target* target_;
+  Fn fn_;
+  Arg arg_;
+};
+
+class PostMessageRequest : public Request {
+ public:
+  PostMessageRequest(InspectorSessionDelegate* delegate,
+                     StringView message)
+                     : delegate_(delegate),
+                       message_(StringBuffer::create(message)) {}
+
+  void Call() override {
+    delegate_->SendMessageToFrontend(message_->string());
+  }
+
+ private:
+  InspectorSessionDelegate* delegate_;
+  std::unique_ptr<StringBuffer> message_;
+};
+
+class DispatchMessagesTask : public v8::Task {
+ public:
+  explicit DispatchMessagesTask(MainThreadInterface* thread)
+                                : thread_(thread) {}
+
+  void Run() override {
+    thread_->DispatchMessages();
+  }
+
+ private:
+  MainThreadInterface* thread_;
+};
+
+void DisposePairCallback(uv_handle_t* ref) {
+  using AsyncAndInterface = std::pair<uv_async_t, MainThreadInterface*>;
+  AsyncAndInterface* pair = node::ContainerOf(
+      &AsyncAndInterface::first, reinterpret_cast<uv_async_t*>(ref));
+  delete pair;
+}
+
+template <typename T>
+class AnotherThreadObjectReference {
+ public:
+  // We create it on whatever thread, just make sure it gets disposed on the
+  // proper thread.
+  AnotherThreadObjectReference(std::shared_ptr<MainThreadHandle> thread,
+                               T* object)
+                               : thread_(thread), object_(object) {
+  }
+  AnotherThreadObjectReference(AnotherThreadObjectReference&) = delete;
+
+  ~AnotherThreadObjectReference() {
+    // Disappearing thread may cause a memory leak
+    CHECK(thread_->Post(
+        std::unique_ptr<DeleteRequest<T>>(new DeleteRequest<T>(object_))));
+    object_ = nullptr;
+  }
+
+  template <typename Fn, typename Arg>
+  void Post(Fn fn, Arg argument) const {
+    using R = SingleArgumentFunctionCall<T, Arg>;
+    thread_->Post(std::unique_ptr<R>(new R(object_, fn, std::move(argument))));
+  }
+
+  T* get() const {
+    return object_;
+  }
+
+ private:
+  std::shared_ptr<MainThreadHandle> thread_;
+  T* object_;
+};
+
+class MainThreadSessionState {
+ public:
+  MainThreadSessionState(
+      std::shared_ptr<MainThreadHandle> thread,
+      bool prevent_shutdown) : thread_(thread),
+                               prevent_shutdown_(prevent_shutdown) {}
+
+  void Connect(std::unique_ptr<InspectorSessionDelegate> delegate) {
+    Agent* agent = thread_->GetInspectorAgent();
+    if (agent != nullptr)
+      session_ = agent->Connect(std::move(delegate), prevent_shutdown_);
+  }
+
+  void Dispatch(std::unique_ptr<StringBuffer> message) {
+    session_->Dispatch(message->string());
+  }
+
+ private:
+  std::shared_ptr<MainThreadHandle> thread_;
+  bool prevent_shutdown_;
+  std::unique_ptr<InspectorSession> session_;
+};
+
+class CrossThreadInspectorSession : public InspectorSession {
+ public:
+  CrossThreadInspectorSession(
+      int id,
+      std::shared_ptr<MainThreadHandle> thread,
+      std::unique_ptr<InspectorSessionDelegate> delegate,
+      bool prevent_shutdown)
+      : state_(thread, new MainThreadSessionState(thread, prevent_shutdown)) {
+    state_.Post(&MainThreadSessionState::Connect, std::move(delegate));
+  }
+
+  void Dispatch(const StringView& message) override {
+    state_.Post(&MainThreadSessionState::Dispatch,
+                StringBuffer::create(message));
+  }
+
+ private:
+  AnotherThreadObjectReference<MainThreadSessionState> state_;
+};
+
+class ThreadSafeDelegate : public InspectorSessionDelegate {
+ public:
+  ThreadSafeDelegate(std::shared_ptr<MainThreadHandle> thread,
+                     std::unique_ptr<InspectorSessionDelegate> delegate)
+                     : thread_(thread), delegate_(thread, delegate.release()) {}
+
+  void SendMessageToFrontend(const v8_inspector::StringView& message) override {
+    thread_->Post(std::unique_ptr<Request>(
+        new PostMessageRequest(delegate_.get(), message)));
+  }
+
+ private:
+  std::shared_ptr<MainThreadHandle> thread_;
+  AnotherThreadObjectReference<InspectorSessionDelegate> delegate_;
+};
+}  // namespace
+
+
+MainThreadInterface::MainThreadInterface(Agent* agent, uv_loop_t* loop,
+                                         v8::Isolate* isolate,
+                                         v8::Platform* platform)
+                                         : agent_(agent), isolate_(isolate),
+                                           platform_(platform) {
+  main_thread_request_.reset(new AsyncAndInterface(uv_async_t(), this));
+  CHECK_EQ(0, uv_async_init(loop, &main_thread_request_->first,
+                            DispatchMessagesAsyncCallback));
+  // Inspector uv_async_t should not prevent main loop shutdown.
+  uv_unref(reinterpret_cast<uv_handle_t*>(&main_thread_request_->first));
+}
+
+MainThreadInterface::~MainThreadInterface() {
+  if (handle_)
+    handle_->Reset();
+}
+
+// static
+void MainThreadInterface::DispatchMessagesAsyncCallback(uv_async_t* async) {
+  AsyncAndInterface* asyncAndInterface =
+      node::ContainerOf(&AsyncAndInterface::first, async);
+  asyncAndInterface->second->DispatchMessages();
+}
+
+// static
+void MainThreadInterface::CloseAsync(AsyncAndInterface* pair) {
+  uv_close(reinterpret_cast<uv_handle_t*>(&pair->first), DisposePairCallback);
+}
+
+void MainThreadInterface::Post(std::unique_ptr<Request> request) {
+  Mutex::ScopedLock scoped_lock(requests_lock_);
+  bool needs_notify = requests_.empty();
+  requests_.push_back(std::move(request));
+  if (needs_notify) {
+    CHECK_EQ(0, uv_async_send(&main_thread_request_->first));
+    if (isolate_ != nullptr && platform_ != nullptr) {
+      platform_->CallOnForegroundThread(isolate_,
+                                        new DispatchMessagesTask(this));
+      isolate_->RequestInterrupt([](v8::Isolate* isolate, void* thread) {
+        static_cast<MainThreadInterface*>(thread)->DispatchMessages();
+      }, this);
+    }
+  }
+  incoming_message_cond_.Broadcast(scoped_lock);
+}
+
+bool MainThreadInterface::WaitForFrontendEvent() {
+  // We allow DispatchMessages reentry as we enter the pause. This is important
+  // to support debugging the code invoked by an inspector call, such
+  // as Runtime.evaluate
+  dispatching_messages_ = false;
+  if (dispatching_message_queue_.empty()) {
+    Mutex::ScopedLock scoped_lock(requests_lock_);
+    while (requests_.empty()) incoming_message_cond_.Wait(scoped_lock);
+  }
+  return true;
+}
+
+void MainThreadInterface::DispatchMessages() {
+  if (dispatching_messages_)
+    return;
+  dispatching_messages_ = true;
+  bool had_messages = false;
+  do {
+    if (dispatching_message_queue_.empty()) {
+      Mutex::ScopedLock scoped_lock(requests_lock_);
+      requests_.swap(dispatching_message_queue_);
+    }
+    had_messages = !dispatching_message_queue_.empty();
+    while (!dispatching_message_queue_.empty()) {
+      MessageQueue::value_type task;
+      std::swap(dispatching_message_queue_.front(), task);
+      dispatching_message_queue_.pop_front();
+      task->Call();
+    }
+  } while (had_messages);
+  dispatching_messages_ = false;
+}
+
+std::shared_ptr<MainThreadHandle> MainThreadInterface::GetHandle() {
+  if (handle_ == nullptr)
+    handle_ = std::make_shared<MainThreadHandle>(this);
+  return handle_;
+}
+
+std::unique_ptr<StringBuffer> Utf8ToStringView(const std::string& message) {
+  icu::UnicodeString utf16 = icu::UnicodeString::fromUTF8(
+      icu::StringPiece(message.data(), message.length()));
+  StringView view(reinterpret_cast<const uint16_t*>(utf16.getBuffer()),
+                  utf16.length());
+  return StringBuffer::create(view);
+}
+
+std::unique_ptr<InspectorSession> MainThreadHandle::Connect(
+    std::unique_ptr<InspectorSessionDelegate> delegate,
+    bool prevent_shutdown) {
+  return std::unique_ptr<InspectorSession>(
+      new CrossThreadInspectorSession(++next_session_id_,
+                                      shared_from_this(),
+                                      std::move(delegate),
+                                      prevent_shutdown));
+}
+
+bool MainThreadHandle::Post(std::unique_ptr<Request> request) {
+  Mutex::ScopedLock scoped_lock(block_lock_);
+  if (!main_thread_)
+    return false;
+  main_thread_->Post(std::move(request));
+  return true;
+}
+
+void MainThreadHandle::Reset() {
+  Mutex::ScopedLock scoped_lock(block_lock_);
+  main_thread_ = nullptr;
+}
+
+Agent* MainThreadHandle::GetInspectorAgent() {
+  Mutex::ScopedLock scoped_lock(block_lock_);
+  if (main_thread_ == nullptr)
+    return nullptr;
+  return main_thread_->inspector_agent();
+}
+
+std::unique_ptr<InspectorSessionDelegate>
+MainThreadHandle::MakeThreadSafeDelegate(
+    std::unique_ptr<InspectorSessionDelegate> delegate) {
+  return std::unique_ptr<InspectorSessionDelegate>(
+      new ThreadSafeDelegate(shared_from_this(), std::move(delegate)));
+}
+
+bool MainThreadHandle::Expired() {
+  Mutex::ScopedLock scoped_lock(block_lock_);
+  return main_thread_ == nullptr;
+}
+}  // namespace inspector
+}  // namespace node
diff --git a/src/inspector/main_thread_interface.h b/src/inspector/main_thread_interface.h
new file mode 100644
index 0000000000..75df5ffe80
--- /dev/null
+++ b/src/inspector/main_thread_interface.h
@@ -0,0 +1,99 @@
+#ifndef SRC_INSPECTOR_MAIN_THREAD_INTERFACE_H_
+#define SRC_INSPECTOR_MAIN_THREAD_INTERFACE_H_
+
+#if !HAVE_INSPECTOR
+#error("This header can only be used when inspector is enabled")
+#endif
+
+#include "env.h"
+#include "inspector_agent.h"
+#include "node_mutex.h"
+
+#include <deque>
+#include <memory>
+#include <unordered_map>
+#include <unordered_set>
+
+namespace v8_inspector {
+class StringBuffer;
+class StringView;
+}  // namespace v8_inspector
+
+namespace node {
+namespace inspector {
+class Request {
+ public:
+  virtual void Call() = 0;
+  virtual ~Request() {}
+};
+
+std::unique_ptr<v8_inspector::StringBuffer> Utf8ToStringView(
+    const std::string& message);
+
+using MessageQueue = std::deque<std::unique_ptr<Request>>;
+class MainThreadInterface;
+
+class MainThreadHandle : public std::enable_shared_from_this<MainThreadHandle> {
+ public:
+  explicit MainThreadHandle(MainThreadInterface* main_thread)
+                            : main_thread_(main_thread) {}
+  ~MainThreadHandle() {
+    CHECK_NULL(main_thread_);  // main_thread_ should have called Reset
+  }
+  std::unique_ptr<InspectorSession> Connect(
+      std::unique_ptr<InspectorSessionDelegate> delegate,
+      bool prevent_shutdown);
+  bool Post(std::unique_ptr<Request> request);
+  Agent* GetInspectorAgent();
+  std::unique_ptr<InspectorSessionDelegate> MakeThreadSafeDelegate(
+      std::unique_ptr<InspectorSessionDelegate> delegate);
+  bool Expired();
+
+ private:
+  void Reset();
+
+  MainThreadInterface* main_thread_;
+  Mutex block_lock_;
+  int next_session_id_ = 0;
+
+  friend class MainThreadInterface;
+};
+
+class MainThreadInterface {
+ public:
+  MainThreadInterface(Agent* agent, uv_loop_t*, v8::Isolate* isolate,
+                      v8::Platform* platform);
+  ~MainThreadInterface();
+
+  void DispatchMessages();
+  void Post(std::unique_ptr<Request> request);
+  bool WaitForFrontendEvent();
+  std::shared_ptr<MainThreadHandle> GetHandle();
+  Agent* inspector_agent() {
+    return agent_;
+  }
+
+ private:
+  using AsyncAndInterface = std::pair<uv_async_t, MainThreadInterface*>;
+
+  static void DispatchMessagesAsyncCallback(uv_async_t* async);
+  static void CloseAsync(AsyncAndInterface*);
+
+  MessageQueue requests_;
+  Mutex requests_lock_;   // requests_ live across threads
+  // This queue is to maintain the order of the messages for the cases
+  // when we reenter the DispatchMessages function.
+  MessageQueue dispatching_message_queue_;
+  bool dispatching_messages_ = false;
+  ConditionVariable incoming_message_cond_;
+  // Used from any thread
+  Agent* const agent_;
+  v8::Isolate* const isolate_;
+  v8::Platform* const platform_;
+  DeleteFnPtr<AsyncAndInterface, CloseAsync> main_thread_request_;
+  std::shared_ptr<MainThreadHandle> handle_;
+};
+
+}  // namespace inspector
+}  // namespace node
+#endif  // SRC_INSPECTOR_MAIN_THREAD_INTERFACE_H_
diff --git a/src/inspector_agent.cc b/src/inspector_agent.cc
index 2b03fd05b1..ebb8d8a161 100644
--- a/src/inspector_agent.cc
+++ b/src/inspector_agent.cc
@@ -1,6 +1,7 @@
 #include "inspector_agent.h"
 
 #include "inspector_io.h"
+#include "inspector/main_thread_interface.h"
 #include "inspector/node_string.h"
 #include "inspector/tracing_agent.h"
 #include "node/inspector/protocol/Protocol.h"
@@ -49,7 +50,7 @@ class StartIoTask : public v8::Task {
   explicit StartIoTask(Agent* agent) : agent(agent) {}
 
   void Run() override {
-    agent->StartIoThread(false);
+    agent->StartIoThread();
   }
 
  private:
@@ -64,11 +65,11 @@ std::unique_ptr<StringBuffer> ToProtocolString(Isolate* isolate,
 
 // Called on the main thread.
 void StartIoThreadAsyncCallback(uv_async_t* handle) {
-  static_cast<Agent*>(handle->data)->StartIoThread(false);
+  static_cast<Agent*>(handle->data)->StartIoThread();
 }
 
 void StartIoInterrupt(Isolate* isolate, void* agent) {
-  static_cast<Agent*>(agent)->StartIoThread(false);
+  static_cast<Agent*>(agent)->StartIoThread();
 }
 
 
@@ -195,8 +196,10 @@ class ChannelImpl final : public v8_inspector::V8Inspector::Channel,
  public:
   explicit ChannelImpl(Environment* env,
                        const std::unique_ptr<V8Inspector>& inspector,
-                       std::unique_ptr<InspectorSessionDelegate> delegate)
-                       : delegate_(std::move(delegate)) {
+                       std::unique_ptr<InspectorSessionDelegate> delegate,
+                       bool prevent_shutdown)
+                       : delegate_(std::move(delegate)),
+                         prevent_shutdown_(prevent_shutdown) {
     session_ = inspector->connect(1, this, StringView());
     node_dispatcher_.reset(new protocol::UberDispatcher(this));
     tracing_agent_.reset(new protocol::TracingAgent(env));
@@ -208,7 +211,7 @@ class ChannelImpl final : public v8_inspector::V8Inspector::Channel,
     tracing_agent_.reset();  // Dispose before the dispatchers
   }
 
-  void dispatchProtocolMessage(const StringView& message) {
+  std::string dispatchProtocolMessage(const StringView& message) {
     std::unique_ptr<protocol::DictionaryValue> parsed;
     std::string method;
     node_dispatcher_->getCommandName(
@@ -219,6 +222,7 @@ class ChannelImpl final : public v8_inspector::V8Inspector::Channel,
     } else {
       node_dispatcher_->dispatch(std::move(parsed));
     }
+    return method;
   }
 
   void schedulePauseOnNextStatement(const std::string& reason) {
@@ -226,6 +230,10 @@ class ChannelImpl final : public v8_inspector::V8Inspector::Channel,
     session_->schedulePauseOnNextStatement(buffer->string(), buffer->string());
   }
 
+  bool preventShutdown() {
+    return prevent_shutdown_;
+  }
+
  private:
   void sendResponse(
       int callId,
@@ -263,6 +271,7 @@ class ChannelImpl final : public v8_inspector::V8Inspector::Channel,
   std::unique_ptr<InspectorSessionDelegate> delegate_;
   std::unique_ptr<v8_inspector::V8InspectorSession> session_;
   std::unique_ptr<protocol::UberDispatcher> node_dispatcher_;
+  bool prevent_shutdown_;
 };
 
 class InspectorTimer {
@@ -324,6 +333,44 @@ class InspectorTimerHandle {
  private:
   InspectorTimer* timer_;
 };
+
+class SameThreadInspectorSession : public InspectorSession {
+ public:
+  SameThreadInspectorSession(
+      int session_id, std::shared_ptr<NodeInspectorClient> client)
+      : session_id_(session_id), client_(client) {}
+  ~SameThreadInspectorSession() override;
+  void Dispatch(const v8_inspector::StringView& message) override;
+
+ private:
+  int session_id_;
+  std::weak_ptr<NodeInspectorClient> client_;
+};
+
+void NotifyClusterWorkersDebugEnabled(Environment* env) {
+  v8::Isolate* isolate = env->isolate();
+  HandleScope handle_scope(isolate);
+  auto context = env->context();
+
+  // Send message to enable debug in cluster workers
+  Local<Object> process_object = env->process_object();
+  Local<Value> emit_fn =
+      process_object->Get(context, FIXED_ONE_BYTE_STRING(isolate, "emit"))
+          .ToLocalChecked();
+  // In case the thread started early during the startup
+  if (!emit_fn->IsFunction())
+    return;
+
+  Local<Object> message = Object::New(isolate);
+  message->Set(context, FIXED_ONE_BYTE_STRING(isolate, "cmd"),
+               FIXED_ONE_BYTE_STRING(isolate, "NODE_DEBUG_ENABLED")).FromJust();
+  Local<Value> argv[] = {
+    FIXED_ONE_BYTE_STRING(isolate, "internalMessage"),
+    message
+  };
+  MakeCallback(env->isolate(), process_object, emit_fn.As<Function>(),
+               arraysize(argv), argv, {0, 0});
+}
 }  // namespace
 
 class NodeInspectorClient : public V8InspectorClient {
@@ -337,31 +384,18 @@ class NodeInspectorClient : public V8InspectorClient {
   }
 
   void runMessageLoopOnPause(int context_group_id) override {
-    runMessageLoop(false);
+    waiting_for_resume_ = true;
+    runMessageLoop();
   }
 
-  void runMessageLoop(bool ignore_terminated) {
-    if (running_nested_loop_)
-      return;
-    terminated_ = false;
-    running_nested_loop_ = true;
-    MultiIsolatePlatform* platform = env_->isolate_data()->platform();
-    while ((ignore_terminated || !terminated_) && waitForFrontendEvent()) {
-      while (platform->FlushForegroundTasks(env_->isolate())) {}
-    }
-    terminated_ = false;
-    running_nested_loop_ = false;
+  void waitForIoShutdown() {
+    waiting_for_io_shutdown_ = true;
+    runMessageLoop();
   }
 
-  bool waitForFrontendEvent() {
-    InspectorIo* io = env_->inspector_agent()->io();
-    if (io == nullptr)
-      return false;
-    return io->WaitForFrontendEvent();
-  }
-
-  double currentTimeMS() override {
-    return uv_hrtime() * 1.0 / NANOS_PER_MSEC;
+  void waitForFrontend() {
+    waiting_for_frontend_ = true;
+    runMessageLoop();
   }
 
   void maxAsyncCallStackDepthChanged(int depth) override {
@@ -398,16 +432,17 @@ class NodeInspectorClient : public V8InspectorClient {
   }
 
   void quitMessageLoopOnPause() override {
-    terminated_ = true;
+    waiting_for_resume_ = false;
   }
 
-  int connectFrontend(std::unique_ptr<InspectorSessionDelegate> delegate) {
+  int connectFrontend(std::unique_ptr<InspectorSessionDelegate> delegate,
+                      bool prevent_shutdown) {
     events_dispatched_ = true;
     int session_id = next_session_id_++;
     // TODO(addaleax): Revert back to using make_unique once we get issues
     // with CI resolved (i.e. revert the patch that added this comment).
     channels_[session_id].reset(
-        new ChannelImpl(env_, client_, std::move(delegate)));
+        new ChannelImpl(env_, client_, std::move(delegate), prevent_shutdown));
     return session_id;
   }
 
@@ -418,7 +453,10 @@ class NodeInspectorClient : public V8InspectorClient {
 
   void dispatchMessageFromFrontend(int session_id, const StringView& message) {
     events_dispatched_ = true;
-    channels_[session_id]->dispatchProtocolMessage(message);
+    std::string method =
+        channels_[session_id]->dispatchProtocolMessage(message);
+    if (waiting_for_frontend_)
+      waiting_for_frontend_ = method != "Runtime.runIfWaitingForDebugger";
   }
 
   Local<Context> ensureDefaultContextInGroup(int contextGroupId) override {
@@ -509,116 +547,150 @@ class NodeInspectorClient : public V8InspectorClient {
   }
 
   bool hasConnectedSessions() {
+    for (const auto& id_channel : channels_) {
+      // Other sessions are "invisible" more most purposes
+      if (id_channel.second->preventShutdown())
+        return true;
+    }
+    return false;
+  }
+
+  std::shared_ptr<MainThreadHandle> getThreadHandle() {
+    if (interface_ == nullptr) {
+      interface_.reset(new MainThreadInterface(
+          env_->inspector_agent(), env_->event_loop(), env_->isolate(),
+          env_->isolate_data()->platform()));
+    }
+    return interface_->GetHandle();
+  }
+
+  bool IsActive() {
     return !channels_.empty();
   }
 
  private:
+  bool shouldRunMessageLoop() {
+    if (waiting_for_frontend_)
+      return true;
+    if (waiting_for_io_shutdown_ || waiting_for_resume_)
+      return hasConnectedSessions();
+    return false;
+  }
+
+  void runMessageLoop() {
+    if (running_nested_loop_)
+      return;
+
+    running_nested_loop_ = true;
+
+    MultiIsolatePlatform* platform = env_->isolate_data()->platform();
+    while (shouldRunMessageLoop()) {
+      if (interface_ && hasConnectedSessions())
+        interface_->WaitForFrontendEvent();
+      while (platform->FlushForegroundTasks(env_->isolate())) {}
+    }
+    running_nested_loop_ = false;
+  }
+
+  double currentTimeMS() override {
+    return uv_hrtime() * 1.0 / NANOS_PER_MSEC;
+  }
+
   node::Environment* env_;
-  bool terminated_ = false;
   bool running_nested_loop_ = false;
   std::unique_ptr<V8Inspector> client_;
   std::unordered_map<int, std::unique_ptr<ChannelImpl>> channels_;
   std::unordered_map<void*, InspectorTimerHandle> timers_;
   int next_session_id_ = 1;
   bool events_dispatched_ = false;
+  bool waiting_for_resume_ = false;
+  bool waiting_for_frontend_ = false;
+  bool waiting_for_io_shutdown_ = false;
+  // Allows accessing Inspector from non-main threads
+  std::unique_ptr<MainThreadInterface> interface_;
 };
 
 Agent::Agent(Environment* env) : parent_env_(env) {}
 
-// Destructor needs to be defined here in implementation file as the header
-// does not have full definition of some classes.
-Agent::~Agent() {
-}
+Agent::~Agent() = default;
 
-bool Agent::Start(const char* path, const DebugOptions& options) {
-  path_ = path == nullptr ? "" : path;
+bool Agent::Start(const std::string& path, const DebugOptions& options) {
+  path_ = path;
   debug_options_ = options;
   client_ = std::make_shared<NodeInspectorClient>(parent_env_);
-  CHECK_EQ(0, uv_async_init(uv_default_loop(),
-                            &start_io_thread_async,
-                            StartIoThreadAsyncCallback));
-  start_io_thread_async.data = this;
-  uv_unref(reinterpret_cast<uv_handle_t*>(&start_io_thread_async));
+  if (parent_env_->is_main_thread()) {
+    CHECK_EQ(0, uv_async_init(parent_env_->event_loop(),
+                              &start_io_thread_async,
+                              StartIoThreadAsyncCallback));
+    uv_unref(reinterpret_cast<uv_handle_t*>(&start_io_thread_async));
+    start_io_thread_async.data = this;
+    // Ignore failure, SIGUSR1 won't work, but that should not block node start.
+    StartDebugSignalHandler();
+  }
 
-  // Ignore failure, SIGUSR1 won't work, but that should not block node start.
-  StartDebugSignalHandler();
-  if (options.inspector_enabled()) {
-    // This will return false if listen failed on the inspector port.
-    return StartIoThread(options.wait_for_connect());
+  bool wait_for_connect = options.wait_for_connect();
+  if (!options.inspector_enabled() || !StartIoThread()) {
+    return false;
+  }
+  if (wait_for_connect) {
+    HandleScope scope(parent_env_->isolate());
+    parent_env_->process_object()->DefineOwnProperty(
+        parent_env_->context(),
+        FIXED_ONE_BYTE_STRING(parent_env_->isolate(), "_breakFirstLine"),
+        True(parent_env_->isolate()),
+        static_cast<v8::PropertyAttribute>(v8::ReadOnly | v8::DontEnum))
+        .FromJust();
+    client_->waitForFrontend();
   }
   return true;
 }
 
-bool Agent::StartIoThread(bool wait_for_connect) {
+bool Agent::StartIoThread() {
   if (io_ != nullptr)
     return true;
 
   CHECK_NOT_NULL(client_);
 
-  io_ = std::unique_ptr<InspectorIo>(
-      new InspectorIo(parent_env_, path_, debug_options_, wait_for_connect));
-  if (!io_->Start()) {
-    client_.reset();
+  io_ = InspectorIo::Start(
+      client_->getThreadHandle(), path_, debug_options_);
+  if (io_ == nullptr) {
     return false;
   }
-
-  v8::Isolate* isolate = parent_env_->isolate();
-  HandleScope handle_scope(isolate);
-  auto context = parent_env_->context();
-
-  // Send message to enable debug in workers
-  Local<Object> process_object = parent_env_->process_object();
-  Local<Value> emit_fn =
-      process_object->Get(context, FIXED_ONE_BYTE_STRING(isolate, "emit"))
-          .ToLocalChecked();
-  // In case the thread started early during the startup
-  if (!emit_fn->IsFunction())
-    return true;
-
-  Local<Object> message = Object::New(isolate);
-  message->Set(context, FIXED_ONE_BYTE_STRING(isolate, "cmd"),
-               FIXED_ONE_BYTE_STRING(isolate, "NODE_DEBUG_ENABLED")).FromJust();
-  Local<Value> argv[] = {
-    FIXED_ONE_BYTE_STRING(isolate, "internalMessage"),
-    message
-  };
-  MakeCallback(parent_env_->isolate(), process_object, emit_fn.As<Function>(),
-               arraysize(argv), argv, {0, 0});
-
+  NotifyClusterWorkersDebugEnabled(parent_env_);
   return true;
 }
 
 void Agent::Stop() {
-  if (io_ != nullptr) {
-    io_->Stop();
-    io_.reset();
-  }
+  io_.reset();
 }
 
 std::unique_ptr<InspectorSession> Agent::Connect(
-    std::unique_ptr<InspectorSessionDelegate> delegate) {
-  int session_id = client_->connectFrontend(std::move(delegate));
+    std::unique_ptr<InspectorSessionDelegate> delegate,
+    bool prevent_shutdown) {
+  CHECK_NOT_NULL(client_);
+  int session_id = client_->connectFrontend(std::move(delegate),
+                                            prevent_shutdown);
   return std::unique_ptr<InspectorSession>(
-      new InspectorSession(session_id, client_));
+      new SameThreadInspectorSession(session_id, client_));
 }
 
 void Agent::WaitForDisconnect() {
   CHECK_NOT_NULL(client_);
+  if (client_->hasConnectedSessions()) {
+    fprintf(stderr, "Waiting for the debugger to disconnect...\n");
+    fflush(stderr);
+  }
   // TODO(addaleax): Maybe this should use an at-exit hook for the Environment
   // or something similar?
   client_->contextDestroyed(parent_env_->context());
   if (io_ != nullptr) {
-    io_->WaitForDisconnect();
-    // There is a bug in V8 Inspector (https://crbug.com/834056) that
-    // calls V8InspectorClient::quitMessageLoopOnPause when a session
-    // disconnects. We are using this flag to ignore those calls so the message
-    // loop is spinning as long as there's a reason to expect inspector messages
-    client_->runMessageLoop(true);
+    io_->StopAcceptingNewConnections();
+    client_->waitForIoShutdown();
   }
 }
 
 void Agent::FatalException(Local<Value> error, Local<v8::Message> message) {
-  if (!IsStarted())
+  if (!IsListening())
     return;
   client_->FatalException(error, message);
   WaitForDisconnect();
@@ -718,26 +790,35 @@ void Agent::ContextCreated(Local<Context> context, const ContextInfo& info) {
   client_->contextCreated(context, info);
 }
 
-bool Agent::IsWaitingForConnect() {
+bool Agent::WillWaitForConnect() {
   return debug_options_.wait_for_connect();
 }
 
-bool Agent::HasConnectedSessions() {
+bool Agent::IsActive() {
   if (client_ == nullptr)
     return false;
-  return client_->hasConnectedSessions();
+  return io_ != nullptr || client_->IsActive();
 }
 
-InspectorSession::InspectorSession(int session_id,
-                                   std::shared_ptr<NodeInspectorClient> client)
-                                   : session_id_(session_id), client_(client) {}
-
-InspectorSession::~InspectorSession() {
-  client_->disconnectFrontend(session_id_);
+void Agent::WaitForConnect() {
+  CHECK_NOT_NULL(client_);
+  client_->waitForFrontend();
 }
 
-void InspectorSession::Dispatch(const StringView& message) {
-  client_->dispatchMessageFromFrontend(session_id_, message);
+SameThreadInspectorSession::~SameThreadInspectorSession() {
+  auto client = client_.lock();
+  if (client)
+    client->disconnectFrontend(session_id_);
 }
+
+void SameThreadInspectorSession::Dispatch(
+    const v8_inspector::StringView& message) {
+  auto client = client_.lock();
+  if (client)
+    client->dispatchMessageFromFrontend(session_id_, message);
+}
+
+
+
 }  // namespace inspector
 }  // namespace node
diff --git a/src/inspector_agent.h b/src/inspector_agent.h
index 7295d048b6..dcd6e13aba 100644
--- a/src/inspector_agent.h
+++ b/src/inspector_agent.h
@@ -20,7 +20,6 @@ class StringView;
 namespace node {
 // Forward declaration to break recursive dependency chain with src/env.h.
 class Environment;
-class NodePlatform;
 struct ContextInfo;
 
 namespace inspector {
@@ -29,12 +28,8 @@ class NodeInspectorClient;
 
 class InspectorSession {
  public:
-  InspectorSession(int session_id, std::shared_ptr<NodeInspectorClient> client);
-  ~InspectorSession();
-  void Dispatch(const v8_inspector::StringView& message);
- private:
-  int session_id_;
-  std::shared_ptr<NodeInspectorClient> client_;
+  virtual ~InspectorSession() {}
+  virtual void Dispatch(const v8_inspector::StringView& message) = 0;
 };
 
 class InspectorSessionDelegate {
@@ -50,15 +45,21 @@ class Agent {
   ~Agent();
 
   // Create client_, may create io_ if option enabled
-  bool Start(const char* path, const DebugOptions& options);
+  bool Start(const std::string& path, const DebugOptions& options);
   // Stop and destroy io_
   void Stop();
 
-  bool IsStarted() { return !!client_; }
-
-  // IO thread started, and client connected
-  bool IsWaitingForConnect();
+  bool IsListening() { return io_ != nullptr; }
+  // Returns true if the Node inspector is actually in use. It will be true
+  // if either the user explicitely opted into inspector (e.g. with the
+  // --inspect command line flag) or if inspector JS API had been used.
+  bool IsActive();
 
+  // Option is set to wait for session connection
+  bool WillWaitForConnect();
+  // Blocks till frontend connects and sends "runIfWaitingForDebugger"
+  void WaitForConnect();
+  // Blocks till all the sessions with "WaitForDisconnectOnShutdown" disconnect
   void WaitForDisconnect();
   void FatalException(v8::Local<v8::Value> error,
                       v8::Local<v8::Message> message);
@@ -77,22 +78,20 @@ class Agent {
   void EnableAsyncHook();
   void DisableAsyncHook();
 
-  // Called by the WS protocol and JS binding to create inspector sessions.
+  // Called to create inspector sessions that can be used from the main thread.
   // The inspector responds by using the delegate to send messages back.
   std::unique_ptr<InspectorSession> Connect(
-      std::unique_ptr<InspectorSessionDelegate> delegate);
+      std::unique_ptr<InspectorSessionDelegate> delegate,
+      bool prevent_shutdown);
 
   void PauseOnNextJavascriptStatement(const std::string& reason);
 
-  // Returns true as long as there is at least one connected session.
-  bool HasConnectedSessions();
-
   InspectorIo* io() {
     return io_.get();
   }
 
   // Can only be called from the main thread.
-  bool StartIoThread(bool wait_for_connect);
+  bool StartIoThread();
 
   // Calls StartIoThread() from off the main thread.
   void RequestIoThreadStart();
@@ -105,7 +104,9 @@ class Agent {
                        const node::Persistent<v8::Function>& fn);
 
   node::Environment* parent_env_;
+  // Encapsulates majority of the Inspector functionality
   std::shared_ptr<NodeInspectorClient> client_;
+  // Interface for transports, e.g. WebSocket server
   std::unique_ptr<InspectorIo> io_;
   std::string path_;
   DebugOptions debug_options_;
diff --git a/src/inspector_io.cc b/src/inspector_io.cc
index 78ecce7398..41fea546a8 100644
--- a/src/inspector_io.cc
+++ b/src/inspector_io.cc
@@ -1,6 +1,7 @@
 #include "inspector_io.h"
 
 #include "inspector_socket_server.h"
+#include "inspector/main_thread_interface.h"
 #include "inspector/node_string.h"
 #include "env-inl.h"
 #include "debug_utils.h"
@@ -11,23 +12,16 @@
 #include "util.h"
 #include "zlib.h"
 
-#include <sstream>
-#include <unicode/unistr.h>
-
+#include <deque>
 #include <string.h>
 #include <vector>
 
-
 namespace node {
 namespace inspector {
 namespace {
-using AsyncAndAgent = std::pair<uv_async_t, Agent*>;
 using v8_inspector::StringBuffer;
 using v8_inspector::StringView;
 
-template <typename Transport>
-using TransportAndIo = std::pair<Transport*, InspectorIo*>;
-
 std::string ScriptPath(uv_loop_t* loop, const std::string& script_name) {
   std::string script_path;
 
@@ -64,45 +58,151 @@ std::string GenerateID() {
   return uuid;
 }
 
-void HandleSyncCloseCb(uv_handle_t* handle) {
-  *static_cast<bool*>(handle->data) = true;
-}
+class RequestToServer {
+ public:
+  RequestToServer(TransportAction action,
+                  int session_id,
+                  std::unique_ptr<v8_inspector::StringBuffer> message)
+                  : action_(action),
+                    session_id_(session_id),
+                    message_(std::move(message)) {}
 
-void CloseAsyncAndLoop(uv_async_t* async) {
-  bool is_closed = false;
-  async->data = &is_closed;
-  uv_close(reinterpret_cast<uv_handle_t*>(async), HandleSyncCloseCb);
-  while (!is_closed)
-    uv_run(async->loop, UV_RUN_ONCE);
-  async->data = nullptr;
-  CheckedUvLoopClose(async->loop);
-}
+  void Dispatch(InspectorSocketServer* server) const {
+    switch (action_) {
+      case TransportAction::kKill:
+        server->TerminateConnections();
+        // Fallthrough
+      case TransportAction::kStop:
+        server->Stop();
+        break;
+      case TransportAction::kSendMessage:
+        server->Send(
+            session_id_,
+            protocol::StringUtil::StringViewToUtf8(message_->string()));
+        break;
+    }
+  }
 
-// Delete main_thread_req_ on async handle close
-void ReleasePairOnAsyncClose(uv_handle_t* async) {
-  std::unique_ptr<AsyncAndAgent> pair(node::ContainerOf(&AsyncAndAgent::first,
-      reinterpret_cast<uv_async_t*>(async)));
-  // Unique_ptr goes out of scope here and pointer is deleted.
-}
+ private:
+  TransportAction action_;
+  int session_id_;
+  std::unique_ptr<v8_inspector::StringBuffer> message_;
+};
 
+class RequestQueueData {
+ public:
+  using MessageQueue = std::deque<RequestToServer>;
+
+  explicit RequestQueueData(uv_loop_t* loop)
+                            : handle_(std::make_shared<RequestQueue>(this)) {
+    int err = uv_async_init(loop, &async_, [](uv_async_t* async) {
+      RequestQueueData* wrapper =
+          node::ContainerOf(&RequestQueueData::async_, async);
+      wrapper->DoDispatch();
+    });
+    CHECK_EQ(0, err);
+  }
+
+  static void CloseAndFree(RequestQueueData* queue);
+
+  void Post(int session_id,
+            TransportAction action,
+            std::unique_ptr<StringBuffer> message) {
+    Mutex::ScopedLock scoped_lock(state_lock_);
+    bool notify = messages_.empty();
+    messages_.emplace_back(action, session_id, std::move(message));
+    if (notify) {
+      CHECK_EQ(0, uv_async_send(&async_));
+      incoming_message_cond_.Broadcast(scoped_lock);
+    }
+  }
+
+  void Wait() {
+    Mutex::ScopedLock scoped_lock(state_lock_);
+    if (messages_.empty()) {
+      incoming_message_cond_.Wait(scoped_lock);
+    }
+  }
+
+  void SetServer(InspectorSocketServer* server) {
+    server_ = server;
+  }
+
+  std::shared_ptr<RequestQueue> handle() {
+    return handle_;
+  }
+
+ private:
+  ~RequestQueueData() = default;
+
+  MessageQueue GetMessages() {
+    Mutex::ScopedLock scoped_lock(state_lock_);
+    MessageQueue messages;
+    messages_.swap(messages);
+    return messages;
+  }
+
+  void DoDispatch() {
+    if (server_ == nullptr)
+      return;
+    for (const auto& request : GetMessages()) {
+      request.Dispatch(server_);
+    }
+  }
+
+  std::shared_ptr<RequestQueue> handle_;
+  uv_async_t async_;
+  InspectorSocketServer* server_ = nullptr;
+  MessageQueue messages_;
+  Mutex state_lock_;  // Locked before mutating the queue.
+  ConditionVariable incoming_message_cond_;
+};
 }  // namespace
 
-std::unique_ptr<StringBuffer> Utf8ToStringView(const std::string& message) {
-  icu::UnicodeString utf16 =
-    icu::UnicodeString::fromUTF8(icu::StringPiece(message.data(),
-      message.length()));
-  StringView view(reinterpret_cast<const uint16_t*>(utf16.getBuffer()),
-                  utf16.length());
-  return StringBuffer::create(view);
-}
+class RequestQueue {
+ public:
+  explicit RequestQueue(RequestQueueData* data) : data_(data) {}
 
+  void Reset() {
+    Mutex::ScopedLock scoped_lock(lock_);
+    data_ = nullptr;
+  }
+
+  void Post(int session_id,
+            TransportAction action,
+            std::unique_ptr<StringBuffer> message) {
+    Mutex::ScopedLock scoped_lock(lock_);
+    if (data_ != nullptr)
+      data_->Post(session_id, action, std::move(message));
+  }
+
+  void SetServer(InspectorSocketServer* server) {
+    Mutex::ScopedLock scoped_lock(lock_);
+    if (data_ != nullptr)
+      data_->SetServer(server);
+  }
+
+  bool Expired() {
+    Mutex::ScopedLock scoped_lock(lock_);
+    return data_ == nullptr;
+  }
+
+ private:
+  RequestQueueData* data_;
+  Mutex lock_;
+};
 
 class IoSessionDelegate : public InspectorSessionDelegate {
  public:
-  explicit IoSessionDelegate(InspectorIo* io, int id) : io_(io), id_(id) { }
-  void SendMessageToFrontend(const v8_inspector::StringView& message) override;
+  explicit IoSessionDelegate(std::shared_ptr<RequestQueue> queue, int id)
+                             : request_queue_(queue), id_(id) { }
+  void SendMessageToFrontend(const v8_inspector::StringView& message) override {
+    request_queue_->Post(id_, TransportAction::kSendMessage,
+                         StringBuffer::create(message));
+  }
+
  private:
-  InspectorIo* io_;
+  std::shared_ptr<RequestQueue> request_queue_;
   int id_;
 };
 
@@ -110,361 +210,133 @@ class IoSessionDelegate : public InspectorSessionDelegate {
 // mostly session start, message received, and session end.
 class InspectorIoDelegate: public node::inspector::SocketServerDelegate {
  public:
-  InspectorIoDelegate(InspectorIo* io, const std::string& target_id,
+  InspectorIoDelegate(std::shared_ptr<RequestQueueData> queue,
+                      std::shared_ptr<MainThreadHandle> main_threade,
+                      const std::string& target_id,
                       const std::string& script_path,
-                      const std::string& script_name, bool wait);
+                      const std::string& script_name);
   ~InspectorIoDelegate() {
-    io_->ServerDone();
   }
-  // Calls PostIncomingMessage() with appropriate InspectorAction:
-  //   kStartSession
+
   void StartSession(int session_id, const std::string& target_id) override;
-  //   kSendMessage
   void MessageReceived(int session_id, const std::string& message) override;
-  //   kEndSession
   void EndSession(int session_id) override;
 
   std::vector<std::string> GetTargetIds() override;
   std::string GetTargetTitle(const std::string& id) override;
   std::string GetTargetUrl(const std::string& id) override;
-
   void AssignServer(InspectorSocketServer* server) override {
-    server_ = server;
+    request_queue_->SetServer(server);
   }
 
  private:
-  InspectorIo* io_;
-  int session_id_;
+  std::shared_ptr<RequestQueueData> request_queue_;
+  std::shared_ptr<MainThreadHandle> main_thread_;
+  std::unordered_map<int, std::unique_ptr<InspectorSession>> sessions_;
   const std::string script_name_;
   const std::string script_path_;
   const std::string target_id_;
-  bool waiting_;
-  InspectorSocketServer* server_;
 };
 
-void InterruptCallback(v8::Isolate*, void* agent) {
-  InspectorIo* io = static_cast<Agent*>(agent)->io();
-  if (io != nullptr)
-    io->DispatchMessages();
+// static
+std::unique_ptr<InspectorIo> InspectorIo::Start(
+    std::shared_ptr<MainThreadHandle> main_thread,
+    const std::string& path,
+    const DebugOptions& options) {
+  auto io = std::unique_ptr<InspectorIo>(
+      new InspectorIo(main_thread, path, options));
+  if (io->request_queue_->Expired()) {  // Thread is not running
+    return nullptr;
+  }
+  return io;
 }
 
-class DispatchMessagesTask : public v8::Task {
- public:
-  explicit DispatchMessagesTask(Agent* agent) : agent_(agent) {}
-
-  void Run() override {
-    InspectorIo* io = agent_->io();
-    if (io != nullptr)
-      io->DispatchMessages();
-  }
-
- private:
-  Agent* agent_;
-};
-
-InspectorIo::InspectorIo(Environment* env, const std::string& path,
-                         const DebugOptions& options, bool wait_for_connect)
-                         : options_(options), thread_(), state_(State::kNew),
-                           parent_env_(env), thread_req_(),
-                           platform_(parent_env_->isolate_data()->platform()),
-                           dispatching_messages_(false), script_name_(path),
-                           wait_for_connect_(wait_for_connect), port_(-1),
-                           id_(GenerateID()) {
-  main_thread_req_ = new AsyncAndAgent({uv_async_t(), env->inspector_agent()});
-  CHECK_EQ(0, uv_async_init(env->event_loop(), &main_thread_req_->first,
-                            InspectorIo::MainThreadReqAsyncCb));
-  uv_unref(reinterpret_cast<uv_handle_t*>(&main_thread_req_->first));
-  CHECK_EQ(0, uv_sem_init(&thread_start_sem_, 0));
+InspectorIo::InspectorIo(std::shared_ptr<MainThreadHandle> main_thread,
+                         const std::string& path,
+                         const DebugOptions& options)
+                         : main_thread_(main_thread), options_(options),
+                           thread_(), script_name_(path), id_(GenerateID()) {
+  Mutex::ScopedLock scoped_lock(thread_start_lock_);
+  CHECK_EQ(uv_thread_create(&thread_, InspectorIo::ThreadMain, this), 0);
+  thread_start_condition_.Wait(scoped_lock);
 }
 
 InspectorIo::~InspectorIo() {
-  uv_sem_destroy(&thread_start_sem_);
-  uv_close(reinterpret_cast<uv_handle_t*>(&main_thread_req_->first),
-           ReleasePairOnAsyncClose);
-}
-
-bool InspectorIo::Start() {
-  CHECK_EQ(state_, State::kNew);
-  CHECK_EQ(uv_thread_create(&thread_, InspectorIo::ThreadMain, this), 0);
-  uv_sem_wait(&thread_start_sem_);
-
-  if (state_ == State::kError) {
-    return false;
-  }
-  state_ = State::kAccepting;
-  if (wait_for_connect_) {
-    DispatchMessages();
-  }
-  return true;
-}
-
-void InspectorIo::Stop() {
-  CHECK_IMPLIES(sessions_.empty(), state_ == State::kAccepting);
-  Write(TransportAction::kKill, 0, StringView());
+  request_queue_->Post(0, TransportAction::kKill, nullptr);
   int err = uv_thread_join(&thread_);
   CHECK_EQ(err, 0);
-  state_ = State::kShutDown;
-  DispatchMessages();
 }
 
-bool InspectorIo::IsStarted() {
-  return platform_ != nullptr;
-}
-
-void InspectorIo::WaitForDisconnect() {
-  if (state_ == State::kAccepting)
-    state_ = State::kDone;
-  if (!sessions_.empty()) {
-    state_ = State::kShutDown;
-    Write(TransportAction::kStop, 0, StringView());
-    fprintf(stderr, "Waiting for the debugger to disconnect...\n");
-    fflush(stderr);
-  }
+void InspectorIo::StopAcceptingNewConnections() {
+  request_queue_->Post(0, TransportAction::kStop, nullptr);
 }
 
 // static
 void InspectorIo::ThreadMain(void* io) {
-  static_cast<InspectorIo*>(io)->ThreadMain<InspectorSocketServer>();
+  static_cast<InspectorIo*>(io)->ThreadMain();
 }
 
-// static
-template <typename Transport>
-void InspectorIo::IoThreadAsyncCb(uv_async_t* async) {
-  TransportAndIo<Transport>* transport_and_io =
-      static_cast<TransportAndIo<Transport>*>(async->data);
-  if (transport_and_io == nullptr) {
-    return;
-  }
-  Transport* transport = transport_and_io->first;
-  InspectorIo* io = transport_and_io->second;
-  MessageQueue<TransportAction> outgoing_message_queue;
-  io->SwapBehindLock(&io->outgoing_message_queue_, &outgoing_message_queue);
-  for (const auto& outgoing : outgoing_message_queue) {
-    int session_id = std::get<1>(outgoing);
-    switch (std::get<0>(outgoing)) {
-    case TransportAction::kKill:
-      transport->TerminateConnections();
-      // Fallthrough
-    case TransportAction::kStop:
-      transport->Stop();
-      break;
-    case TransportAction::kSendMessage:
-      transport->Send(session_id,
-                      protocol::StringUtil::StringViewToUtf8(
-                          std::get<2>(outgoing)->string()));
-      break;
-    case TransportAction::kAcceptSession:
-      transport->AcceptSession(session_id);
-      break;
-    case TransportAction::kDeclineSession:
-      transport->DeclineSession(session_id);
-      break;
-    }
-  }
-}
-
-template <typename Transport>
 void InspectorIo::ThreadMain() {
   uv_loop_t loop;
   loop.data = nullptr;
   int err = uv_loop_init(&loop);
   CHECK_EQ(err, 0);
-  thread_req_.data = nullptr;
-  err = uv_async_init(&loop, &thread_req_, IoThreadAsyncCb<Transport>);
-  CHECK_EQ(err, 0);
+  std::shared_ptr<RequestQueueData> queue(new RequestQueueData(&loop),
+                                          RequestQueueData::CloseAndFree);
   std::string script_path = ScriptPath(&loop, script_name_);
-  auto delegate = std::unique_ptr<InspectorIoDelegate>(
-      new InspectorIoDelegate(this, id_, script_path, script_name_,
-                              wait_for_connect_));
-  Transport server(std::move(delegate), &loop, options_.host_name(),
-                   options_.port());
-  TransportAndIo<Transport> queue_transport(&server, this);
-  thread_req_.data = &queue_transport;
-  if (!server.Start()) {
-    state_ = State::kError;  // Safe, main thread is waiting on semaphore
-    CloseAsyncAndLoop(&thread_req_);
-    uv_sem_post(&thread_start_sem_);
-    return;
-  }
-  port_ = server.Port();  // Safe, main thread is waiting on semaphore.
-  if (!wait_for_connect_) {
-    uv_sem_post(&thread_start_sem_);
+  std::unique_ptr<InspectorIoDelegate> delegate(
+      new InspectorIoDelegate(queue, main_thread_, id_,
+                              script_path, script_name_));
+  InspectorSocketServer server(std::move(delegate), &loop,
+                               options_.host_name(), options_.port());
+  request_queue_ = queue->handle();
+  // Its lifetime is now that of the server delegate
+  queue.reset();
+  {
+    Mutex::ScopedLock scoped_lock(thread_start_lock_);
+    if (server.Start()) {
+      port_ = server.Port();
+    }
+    thread_start_condition_.Broadcast(scoped_lock);
   }
   uv_run(&loop, UV_RUN_DEFAULT);
-  thread_req_.data = nullptr;
   CheckedUvLoopClose(&loop);
 }
 
-template <typename ActionType>
-bool InspectorIo::AppendMessage(MessageQueue<ActionType>* queue,
-                                ActionType action, int session_id,
-                                std::unique_ptr<StringBuffer> buffer) {
-  Mutex::ScopedLock scoped_lock(state_lock_);
-  bool trigger_pumping = queue->empty();
-  queue->push_back(std::make_tuple(action, session_id, std::move(buffer)));
-  return trigger_pumping;
-}
-
-template <typename ActionType>
-void InspectorIo::SwapBehindLock(MessageQueue<ActionType>* vector1,
-                                 MessageQueue<ActionType>* vector2) {
-  Mutex::ScopedLock scoped_lock(state_lock_);
-  vector1->swap(*vector2);
-}
-
-void InspectorIo::PostIncomingMessage(InspectorAction action, int session_id,
-                                      const std::string& message) {
-  Debug(parent_env_, DebugCategory::INSPECTOR_SERVER,
-        ">>> %s\n", message.c_str());
-  if (AppendMessage(&incoming_message_queue_, action, session_id,
-                    Utf8ToStringView(message))) {
-    Agent* agent = main_thread_req_->second;
-    v8::Isolate* isolate = parent_env_->isolate();
-    platform_->CallOnForegroundThread(isolate,
-                                      new DispatchMessagesTask(agent));
-    isolate->RequestInterrupt(InterruptCallback, agent);
-    CHECK_EQ(0, uv_async_send(&main_thread_req_->first));
-  }
-  Mutex::ScopedLock scoped_lock(state_lock_);
-  incoming_message_cond_.Broadcast(scoped_lock);
-}
-
 std::vector<std::string> InspectorIo::GetTargetIds() const {
   return { id_ };
 }
 
-TransportAction InspectorIo::Attach(int session_id) {
-  Agent* agent = parent_env_->inspector_agent();
-  fprintf(stderr, "Debugger attached.\n");
-  sessions_[session_id] = agent->Connect(std::unique_ptr<IoSessionDelegate>(
-      new IoSessionDelegate(this, session_id)));
-  return TransportAction::kAcceptSession;
-}
-
-void InspectorIo::DispatchMessages() {
-  if (dispatching_messages_)
-    return;
-  dispatching_messages_ = true;
-  bool had_messages = false;
-  do {
-    if (dispatching_message_queue_.empty())
-      SwapBehindLock(&incoming_message_queue_, &dispatching_message_queue_);
-    had_messages = !dispatching_message_queue_.empty();
-    while (!dispatching_message_queue_.empty()) {
-      MessageQueue<InspectorAction>::value_type task;
-      std::swap(dispatching_message_queue_.front(), task);
-      dispatching_message_queue_.pop_front();
-      int id = std::get<1>(task);
-      StringView message = std::get<2>(task)->string();
-      switch (std::get<0>(task)) {
-      case InspectorAction::kStartSession:
-        Write(Attach(id), id, StringView());
-        break;
-      case InspectorAction::kStartSessionUnconditionally:
-        Attach(id);
-        break;
-      case InspectorAction::kEndSession:
-        sessions_.erase(id);
-        if (!sessions_.empty())
-          continue;
-        if (state_ == State::kShutDown) {
-          state_ = State::kDone;
-        } else {
-          state_ = State::kAccepting;
-        }
-        break;
-      case InspectorAction::kSendMessage:
-        auto session = sessions_.find(id);
-        if (session != sessions_.end() && session->second) {
-          session->second->Dispatch(message);
-        }
-        break;
-      }
-    }
-  } while (had_messages);
-  dispatching_messages_ = false;
-}
-
-// static
-void InspectorIo::MainThreadReqAsyncCb(uv_async_t* req) {
-  AsyncAndAgent* pair = node::ContainerOf(&AsyncAndAgent::first, req);
-  // Note that this may be called after io was closed or even after a new
-  // one was created and ran.
-  InspectorIo* io = pair->second->io();
-  if (io != nullptr)
-    io->DispatchMessages();
-}
-
-void InspectorIo::Write(TransportAction action, int session_id,
-                        const StringView& inspector_message) {
-  std::string message_str =
-      protocol::StringUtil::StringViewToUtf8(inspector_message);
-  Debug(parent_env_, DebugCategory::INSPECTOR_SERVER,
-        "<<< %s\n", message_str.c_str());
-  AppendMessage(&outgoing_message_queue_, action, session_id,
-                StringBuffer::create(inspector_message));
-  int err = uv_async_send(&thread_req_);
-  CHECK_EQ(0, err);
-}
-
-bool InspectorIo::WaitForFrontendEvent() {
-  // We allow DispatchMessages reentry as we enter the pause. This is important
-  // to support debugging the code invoked by an inspector call, such
-  // as Runtime.evaluate
-  dispatching_messages_ = false;
-  Mutex::ScopedLock scoped_lock(state_lock_);
-  if (sessions_.empty())
-    return false;
-  if (dispatching_message_queue_.empty() && incoming_message_queue_.empty()) {
-    incoming_message_cond_.Wait(scoped_lock);
-  }
-  return true;
-}
-
-InspectorIoDelegate::InspectorIoDelegate(InspectorIo* io,
-                                         const std::string& target_id,
-                                         const std::string& script_path,
-                                         const std::string& script_name,
-                                         bool wait)
-                                         : io_(io),
-                                           session_id_(0),
-                                           script_name_(script_name),
-                                           script_path_(script_path),
-                                           target_id_(target_id),
-                                           waiting_(wait),
-                                           server_(nullptr) { }
-
+InspectorIoDelegate::InspectorIoDelegate(
+    std::shared_ptr<RequestQueueData> queue,
+    std::shared_ptr<MainThreadHandle> main_thread,
+    const std::string& target_id,
+    const std::string& script_path,
+    const std::string& script_name)
+    : request_queue_(queue), main_thread_(main_thread),
+      script_name_(script_name), script_path_(script_path),
+      target_id_(target_id) {}
 
 void InspectorIoDelegate::StartSession(int session_id,
                                        const std::string& target_id) {
-  session_id_ = session_id;
-  InspectorAction action = InspectorAction::kStartSession;
-  if (waiting_) {
-    action = InspectorAction::kStartSessionUnconditionally;
-    server_->AcceptSession(session_id);
+  auto session = main_thread_->Connect(
+      std::unique_ptr<InspectorSessionDelegate>(
+          new IoSessionDelegate(request_queue_->handle(), session_id)), true);
+  if (session) {
+    sessions_[session_id] = std::move(session);
+    fprintf(stderr, "Debugger attached.\n");
   }
-  io_->PostIncomingMessage(action, session_id, "");
 }
 
 void InspectorIoDelegate::MessageReceived(int session_id,
                                           const std::string& message) {
-  // TODO(pfeldman): Instead of blocking execution while debugger
-  // engages, node should wait for the run callback from the remote client
-  // and initiate its startup. This is a change to node.cc that should be
-  // upstreamed separately.
-  if (waiting_) {
-    if (message.find("\"Runtime.runIfWaitingForDebugger\"") !=
-        std::string::npos) {
-      waiting_ = false;
-      io_->ResumeStartup();
-    }
-  }
-  io_->PostIncomingMessage(InspectorAction::kSendMessage, session_id,
-                           message);
+  auto session = sessions_.find(session_id);
+  if (session != sessions_.end())
+    session->second->Dispatch(Utf8ToStringView(message)->string());
 }
 
 void InspectorIoDelegate::EndSession(int session_id) {
-  io_->PostIncomingMessage(InspectorAction::kEndSession, session_id, "");
+  sessions_.erase(session_id);
 }
 
 std::vector<std::string> InspectorIoDelegate::GetTargetIds() {
@@ -479,10 +351,17 @@ std::string InspectorIoDelegate::GetTargetUrl(const std::string& id) {
   return "file://" + script_path_;
 }
 
-void IoSessionDelegate::SendMessageToFrontend(
-    const v8_inspector::StringView& message) {
-  io_->Write(TransportAction::kSendMessage, id_, message);
+// static
+void RequestQueueData::CloseAndFree(RequestQueueData* queue) {
+  queue->handle_->Reset();
+  queue->handle_.reset();
+  uv_close(reinterpret_cast<uv_handle_t*>(&queue->async_),
+           [](uv_handle_t* handle) {
+    uv_async_t* async = reinterpret_cast<uv_async_t*>(handle);
+    RequestQueueData* wrapper =
+        node::ContainerOf(&RequestQueueData::async_, async);
+    delete wrapper;
+  });
 }
-
 }  // namespace inspector
 }  // namespace node
diff --git a/src/inspector_io.h b/src/inspector_io.h
index c897a44a52..7c43d212f0 100644
--- a/src/inspector_io.h
+++ b/src/inspector_io.h
@@ -6,8 +6,6 @@
 #include "node_mutex.h"
 #include "uv.h"
 
-#include <deque>
-#include <unordered_map>
 #include <memory>
 #include <stddef.h>
 
@@ -16,17 +14,14 @@
 #endif
 
 
-// Forward declaration to break recursive dependency chain with src/env.h.
-namespace node {
-class Environment;
-}  // namespace node
-
 namespace v8_inspector {
 class StringBuffer;
 class StringView;
 }  // namespace v8_inspector
 
 namespace node {
+// Forward declaration to break recursive dependency chain with src/env.h.
+class Environment;
 namespace inspector {
 
 std::string FormatWsAddress(const std::string& host, int port,
@@ -34,143 +29,64 @@ std::string FormatWsAddress(const std::string& host, int port,
                             bool include_protocol);
 
 class InspectorIoDelegate;
-
-enum class InspectorAction {
-  kStartSession,
-  kStartSessionUnconditionally,  // First attach with --inspect-brk
-  kEndSession,
-  kSendMessage
-};
+class MainThreadHandle;
+class RequestQueue;
 
 // kKill closes connections and stops the server, kStop only stops the server
 enum class TransportAction {
   kKill,
   kSendMessage,
-  kStop,
-  kAcceptSession,
-  kDeclineSession
+  kStop
 };
 
 class InspectorIo {
  public:
-  InspectorIo(node::Environment* env, const std::string& path,
-              const DebugOptions& options, bool wait_for_connect);
+  // Start the inspector agent thread, waiting for it to initialize
+  // bool Start();
+  // Returns empty pointer if thread was not started
+  static std::unique_ptr<InspectorIo> Start(
+      std::shared_ptr<MainThreadHandle> main_thread, const std::string& path,
+      const DebugOptions& options);
 
+  // Will block till the transport thread shuts down
   ~InspectorIo();
-  // Start the inspector agent thread, waiting for it to initialize,
-  // and waiting as well for a connection if wait_for_connect.
-  bool Start();
-  // Stop the inspector agent thread.
-  void Stop();
 
-  bool IsStarted();
-
-  void WaitForDisconnect();
-  // Called from thread to queue an incoming message and trigger
-  // DispatchMessages() on the main thread.
-  void PostIncomingMessage(InspectorAction action, int session_id,
-                           const std::string& message);
-  void ResumeStartup() {
-    uv_sem_post(&thread_start_sem_);
-  }
-  void ServerDone() {
-    uv_close(reinterpret_cast<uv_handle_t*>(&thread_req_), nullptr);
-  }
-  bool WaitForFrontendEvent();
-
-  int port() const { return port_; }
+  void StopAcceptingNewConnections();
   std::string host() const { return options_.host_name(); }
+  int port() const { return port_; }
   std::vector<std::string> GetTargetIds() const;
 
  private:
-  template <typename Action>
-  using MessageQueue =
-      std::deque<std::tuple<Action, int,
-                  std::unique_ptr<v8_inspector::StringBuffer>>>;
-  enum class State {
-    kNew,
-    kAccepting,
-    kDone,
-    kError,
-    kShutDown
-  };
-
-  // Callback for main_thread_req_'s uv_async_t
-  static void MainThreadReqAsyncCb(uv_async_t* req);
+  InspectorIo(std::shared_ptr<MainThreadHandle> handle,
+              const std::string& path, const DebugOptions& options);
 
   // Wrapper for agent->ThreadMain()
   static void ThreadMain(void* agent);
 
   // Runs a uv_loop_t
-  template <typename Transport> void ThreadMain();
-  // Called by ThreadMain's loop when triggered by thread_req_, writes
-  // messages from outgoing_message_queue to the InspectorSockerServer
-  template <typename Transport> static void IoThreadAsyncCb(uv_async_t* async);
-
-  void DispatchMessages();
-  // Write action to outgoing_message_queue, and wake the thread
-  void Write(TransportAction action, int session_id,
-             const v8_inspector::StringView& message);
-  // Thread-safe append of message to a queue. Return true if the queue
-  // used to be empty.
-  template <typename ActionType>
-  bool AppendMessage(MessageQueue<ActionType>* vector, ActionType action,
-                     int session_id,
-                     std::unique_ptr<v8_inspector::StringBuffer> buffer);
-  // Used as equivalent of a thread-safe "pop" of an entire queue's content.
-  template <typename ActionType>
-  void SwapBehindLock(MessageQueue<ActionType>* vector1,
-                      MessageQueue<ActionType>* vector2);
-  // Attach session to an inspector. Either kAcceptSession or kDeclineSession
-  TransportAction Attach(int session_id);
+  void ThreadMain();
 
+  // This is a thread-safe object that will post async tasks. It lives as long
+  // as an Inspector object lives (almost as long as an Isolate).
+  std::shared_ptr<MainThreadHandle> main_thread_;
+  // Used to post on a frontend interface thread, lives while the server is
+  // running
+  std::shared_ptr<RequestQueue> request_queue_;
   const DebugOptions options_;
 
   // The IO thread runs its own uv_loop to implement the TCP server off
   // the main thread.
   uv_thread_t thread_;
-  // Used by Start() to wait for thread to initialize, or for it to initialize
-  // and receive a connection if wait_for_connect was requested.
-  uv_sem_t thread_start_sem_;
-
-  State state_;
-  node::Environment* parent_env_;
-
-  // Attached to the uv_loop in ThreadMain()
-  uv_async_t thread_req_;
-  // Note that this will live while the async is being closed - likely, past
-  // the parent object lifespan
-  std::pair<uv_async_t, Agent*>* main_thread_req_;
-  // Will be used to post tasks from another thread
-  v8::Platform* const platform_;
-
-  // Message queues
-  ConditionVariable incoming_message_cond_;
-  Mutex state_lock_;  // Locked before mutating either queue.
-  MessageQueue<InspectorAction> incoming_message_queue_;
-  MessageQueue<TransportAction> outgoing_message_queue_;
-  // This queue is to maintain the order of the messages for the cases
-  // when we reenter the DispatchMessages function.
-  MessageQueue<InspectorAction> dispatching_message_queue_;
-
-  bool dispatching_messages_;
 
+  // For setting up interthread communications
+  Mutex thread_start_lock_;
+  ConditionVariable thread_start_condition_;
   std::string script_name_;
-  std::string script_path_;
-  const bool wait_for_connect_;
-  int port_;
-  std::unordered_map<int, std::unique_ptr<InspectorSession>> sessions_;
+  int port_ = -1;
   // May be accessed from any thread
   const std::string id_;
-
-  friend class DispatchMessagesTask;
-  friend class IoSessionDelegate;
-  friend void InterruptCallback(v8::Isolate*, void* agent);
 };
 
-std::unique_ptr<v8_inspector::StringBuffer> Utf8ToStringView(
-    const std::string& message);
-
 }  // namespace inspector
 }  // namespace node
 
diff --git a/src/inspector_js_api.cc b/src/inspector_js_api.cc
index 13e91f283c..268c25aeb4 100644
--- a/src/inspector_js_api.cc
+++ b/src/inspector_js_api.cc
@@ -66,7 +66,7 @@ class JSBindingsConnection : public AsyncWrap {
                          callback_(env->isolate(), callback) {
     Agent* inspector = env->inspector_agent();
     session_ = inspector->Connect(std::unique_ptr<JSBindingsSessionDelegate>(
-        new JSBindingsSessionDelegate(env, this)));
+        new JSBindingsSessionDelegate(env, this)), false);
   }
 
   void OnMessage(Local<Value> value) {
@@ -116,7 +116,7 @@ class JSBindingsConnection : public AsyncWrap {
 
 static bool InspectorEnabled(Environment* env) {
   Agent* agent = env->inspector_agent();
-  return agent->io() != nullptr || agent->HasConnectedSessions();
+  return agent->IsActive();
 }
 
 void AddCommandLineAPI(const FunctionCallbackInfo<Value>& info) {
@@ -251,8 +251,9 @@ void Open(const FunctionCallbackInfo<Value>& args) {
   if (args.Length() > 2 && args[2]->IsBoolean()) {
     wait_for_connect = args[2]->BooleanValue(env->context()).FromJust();
   }
-
-  agent->StartIoThread(wait_for_connect);
+  agent->StartIoThread();
+  if (wait_for_connect)
+    agent->WaitForConnect();
 }
 
 void Url(const FunctionCallbackInfo<Value>& args) {
@@ -283,7 +284,7 @@ void Initialize(Local<Object> target, Local<Value> unused,
   Agent* agent = env->inspector_agent();
   env->SetMethod(target, "consoleCall", InspectorConsoleCall);
   env->SetMethod(target, "addCommandLineAPI", AddCommandLineAPI);
-  if (agent->IsWaitingForConnect())
+  if (agent->WillWaitForConnect())
     env->SetMethod(target, "callAndPauseOnStart", CallAndPauseOnStart);
   env->SetMethod(target, "open", Open);
   env->SetMethod(target, "url", Url);
diff --git a/src/inspector_socket_server.cc b/src/inspector_socket_server.cc
index 174dc7c726..1621b408b4 100644
--- a/src/inspector_socket_server.cc
+++ b/src/inspector_socket_server.cc
@@ -173,11 +173,8 @@ class SocketSession {
   InspectorSocket* ws_socket() {
     return ws_socket_.get();
   }
-  void set_ws_key(const std::string& ws_key) {
-    ws_key_ = ws_key;
-  }
-  void Accept() {
-    ws_socket_->AcceptUpgrade(ws_key_);
+  void Accept(const std::string& ws_key) {
+    ws_socket_->AcceptUpgrade(ws_key);
   }
   void Decline() {
     ws_socket_->CancelHandshake();
@@ -208,7 +205,6 @@ class SocketSession {
   const int id_;
   InspectorSocket::Pointer ws_socket_;
   const int server_port_;
-  std::string ws_key_;
 };
 
 class ServerSocket {
@@ -260,11 +256,11 @@ void InspectorSocketServer::SessionStarted(int session_id,
                                            const std::string& ws_key) {
   SocketSession* session = Session(session_id);
   if (!TargetExists(id)) {
-    Session(session_id)->Decline();
+    session->Decline();
     return;
   }
   connected_sessions_[session_id].first = id;
-  session->set_ws_key(ws_key);
+  session->Accept(ws_key);
   delegate_->StartSession(session_id, id);
 }
 
@@ -404,6 +400,8 @@ bool InspectorSocketServer::Start() {
 }
 
 void InspectorSocketServer::Stop() {
+  if (state_ == ServerState::kStopped)
+    return;
   CHECK_EQ(state_, ServerState::kRunning);
   state_ = ServerState::kStopped;
   server_sockets_.clear();
@@ -446,23 +444,6 @@ void InspectorSocketServer::Accept(int server_port,
   }
 }
 
-void InspectorSocketServer::AcceptSession(int session_id) {
-  SocketSession* session = Session(session_id);
-  if (session == nullptr) {
-    delegate_->EndSession(session_id);
-  } else {
-    session->Accept();
-  }
-}
-
-void InspectorSocketServer::DeclineSession(int session_id) {
-  auto it = connected_sessions_.find(session_id);
-  if (it != connected_sessions_.end()) {
-    it->second.first.clear();
-    it->second.second->Decline();
-  }
-}
-
 void InspectorSocketServer::Send(int session_id, const std::string& message) {
   SocketSession* session = Session(session_id);
   if (session != nullptr) {
diff --git a/src/inspector_socket_server.h b/src/inspector_socket_server.h
index bbc2195095..271be6ec55 100644
--- a/src/inspector_socket_server.h
+++ b/src/inspector_socket_server.h
@@ -54,10 +54,6 @@ class InspectorSocketServer {
   void Send(int session_id, const std::string& message);
   //   kKill
   void TerminateConnections();
-  //   kAcceptSession
-  void AcceptSession(int session_id);
-  //   kDeclineSession
-  void DeclineSession(int session_id);
   int Port() const;
 
   // Session connection lifecycle
diff --git a/src/node.cc b/src/node.cc
index bbf76853ed..a9318cb82b 100644
--- a/src/node.cc
+++ b/src/node.cc
@@ -323,11 +323,12 @@ static struct {
     // Inspector agent can't fail to start, but if it was configured to listen
     // right away on the websocket port and fails to bind/etc, this will return
     // false.
-    return env->inspector_agent()->Start(script_path, options);
+    return env->inspector_agent()->Start(
+        script_path == nullptr ? "" : script_path, options);
   }
 
   bool InspectorStarted(Environment* env) {
-    return env->inspector_agent()->IsStarted();
+    return env->inspector_agent()->IsListening();
   }
 #endif  // HAVE_INSPECTOR
 
@@ -1510,7 +1511,7 @@ void InitGroups(const FunctionCallbackInfo<Value>& args) {
 
 static void WaitForInspectorDisconnect(Environment* env) {
 #if HAVE_INSPECTOR
-  if (env->inspector_agent()->HasConnectedSessions()) {
+  if (env->inspector_agent()->IsActive()) {
     // Restore signal dispositions, the app is done and is no longer
     // capable of handling signals.
 #if defined(__POSIX__) && !defined(NODE_SHARED_MODE)
@@ -3517,7 +3518,7 @@ static void ParseArgs(int* argc,
 static void StartInspector(Environment* env, const char* path,
                            DebugOptions debug_options) {
 #if HAVE_INSPECTOR
-  CHECK(!env->inspector_agent()->IsStarted());
+  CHECK(!env->inspector_agent()->IsListening());
   v8_platform.StartInspector(env, path, debug_options);
 #endif  // HAVE_INSPECTOR
 }
@@ -3660,7 +3661,7 @@ static void DebugProcess(const FunctionCallbackInfo<Value>& args) {
 static void DebugEnd(const FunctionCallbackInfo<Value>& args) {
 #if HAVE_INSPECTOR
   Environment* env = Environment::GetCurrent(args);
-  if (env->inspector_agent()->IsStarted()) {
+  if (env->inspector_agent()->IsListening()) {
     env->inspector_agent()->Stop();
   }
 #endif
diff --git a/src/signal_wrap.cc b/src/signal_wrap.cc
index 346f442f61..f44b232a1a 100644
--- a/src/signal_wrap.cc
+++ b/src/signal_wrap.cc
@@ -92,7 +92,7 @@ class SignalWrap : public HandleWrap {
 #if defined(__POSIX__) && HAVE_INSPECTOR
     if (signum == SIGPROF) {
       Environment* env = Environment::GetCurrent(args);
-      if (env->inspector_agent()->IsStarted()) {
+      if (env->inspector_agent()->IsListening()) {
         ProcessEmitWarning(env,
                            "process.on(SIGPROF) is reserved while debugging");
         return;
diff --git a/test/cctest/test_inspector_socket_server.cc b/test/cctest/test_inspector_socket_server.cc
index 60b7eefc5e..349356ef56 100644
--- a/test/cctest/test_inspector_socket_server.cc
+++ b/test/cctest/test_inspector_socket_server.cc
@@ -14,7 +14,6 @@ static const char CLIENT_CLOSE_FRAME[] = "\x88\x80\x2D\x0E\x1E\xFA";
 static const char SERVER_CLOSE_FRAME[] = "\x88\x00";
 
 static const char MAIN_TARGET_ID[] = "main-target";
-static const char UNCONNECTABLE_TARGET_ID[] = "unconnectable-target";
 
 static const char WS_HANDSHAKE_RESPONSE[] =
     "HTTP/1.1 101 Switching Protocols\r\n"
@@ -258,10 +257,6 @@ class ServerHolder {
     return server_->done();
   }
 
-  void Connected() {
-    connected++;
-  }
-
   void Disconnected() {
     disconnected++;
   }
@@ -270,9 +265,10 @@ class ServerHolder {
     delegate_done = true;
   }
 
-  void PrepareSession(int id) {
+  void Connected(int id) {
     buffer_.clear();
     session_id_ = id;
+    connected++;
   }
 
   void Received(const std::string& message) {
@@ -319,15 +315,9 @@ class TestSocketServerDelegate : public SocketServerDelegate {
 
   void StartSession(int session_id, const std::string& target_id) override {
     session_id_ = session_id;
-    harness_->PrepareSession(session_id_);
     CHECK_NE(targets_.end(),
              std::find(targets_.begin(), targets_.end(), target_id));
-    if (target_id == UNCONNECTABLE_TARGET_ID) {
-      server_->DeclineSession(session_id);
-      return;
-    }
-    harness_->Connected();
-    server_->AcceptSession(session_id);
+    harness_->Connected(session_id_);
   }
 
   void MessageReceived(int session_id, const std::string& message) override {
@@ -363,7 +353,7 @@ ServerHolder::ServerHolder(bool has_targets, uv_loop_t* loop,
                            const std::string host, int port, FILE* out) {
   std::vector<std::string> targets;
   if (has_targets)
-    targets = { MAIN_TARGET_ID, UNCONNECTABLE_TARGET_ID };
+    targets = { MAIN_TARGET_ID };
   std::unique_ptr<TestSocketServerDelegate> delegate(
       new TestSocketServerDelegate(this, targets));
   server_.reset(
@@ -414,15 +404,6 @@ TEST_F(InspectorSocketServerTest, InspectorSessions) {
 
   well_behaved_socket.Close();
 
-  // Declined connection
-  SocketWrapper declined_target_socket(&loop);
-  declined_target_socket.Connect(HOST, server.port());
-  declined_target_socket.Write(WsHandshakeRequest(UNCONNECTABLE_TARGET_ID));
-  declined_target_socket.Expect("HTTP/1.0 400 Bad Request");
-  declined_target_socket.ExpectEOF();
-  EXPECT_EQ(1, server.connected);
-  EXPECT_EQ(1, server.disconnected);
-
   // Bogus target - start session callback should not even be invoked
   SocketWrapper bogus_target_socket(&loop);
   bogus_target_socket.Connect(HOST, server.port());
@@ -491,7 +472,7 @@ TEST_F(InspectorSocketServerTest, ServerWithoutTargets) {
   // Declined connection
   SocketWrapper socket(&loop);
   socket.Connect(HOST, server.port());
-  socket.Write(WsHandshakeRequest(UNCONNECTABLE_TARGET_ID));
+  socket.Write(WsHandshakeRequest("any target id"));
   socket.Expect("HTTP/1.0 400 Bad Request");
   socket.ExpectEOF();
   server->Stop();
diff --git a/test/parallel/test-warn-sigprof.js b/test/parallel/test-warn-sigprof.js
index 71ac25443b..e5335215d7 100644
--- a/test/parallel/test-warn-sigprof.js
+++ b/test/parallel/test-warn-sigprof.js
@@ -1,3 +1,4 @@
+// Flags: --inspect=0
 'use strict';
 const common = require('../common');