Use the Starboard message pump. (#4772)

The setup is similar to ATV/iOS where the existing platform main thread
is re-used and the UI message pump just attaches to it.

b/392620765
b/391414243

base/BUILD.gn

@@ -1006,6 +1006,12 @@ component("base") {
     ]
   }
 
+  if (is_starboard) {
+    sources += [
+      "message_loop/message_pump_ui_starboard.cc",
+      "message_loop/message_pump_ui_starboard.h",
+    ]
+  }
   if (is_linux || is_chromeos) {
     sources += [
       "debug/proc_maps_linux.cc",
@@ -1067,6 +1073,10 @@ component("base") {
     deps += [ "//base/time/buildflags:buildflags" ]
   }
 
+  if (is_starboard) {
+    deps += [ "//starboard($starboard_toolchain)" ]
+  }
+
   if (build_rust_json_reader) {
     deps += [ "//third_party/rust/serde_json_lenient/v0_1/wrapper" ]
   }

base/message_loop/message_pump_for_ui.h

@@ -14,6 +14,8 @@
 #include "base/message_loop/message_pump_win.h"
 #elif BUILDFLAG(IS_ANDROID)
 #include "base/message_loop/message_pump_android.h"
+#elif BUILDFLAG(IS_STARBOARD)
+#include "base/message_loop/message_pump_ui_starboard.h"
 #elif BUILDFLAG(IS_APPLE)
 #include "base/message_loop/message_pump.h"
 #elif BUILDFLAG(IS_NACL) || BUILDFLAG(IS_AIX)
@@ -34,6 +36,8 @@ using MessagePumpForUI = MessagePumpForUI;
 #elif BUILDFLAG(IS_ANDROID)
 // Android defines it as-is.
 using MessagePumpForUI = MessagePumpForUI;
+#elif BUILDFLAG(IS_STARBOARD)
+using MessagePumpForUI = MessagePumpUIStarboard;
 #elif BUILDFLAG(IS_APPLE)
 // MessagePumpForUI isn't bound to a specific impl on Mac. While each impl can
 // be represented by a plain MessagePump: MessagePumpMac::Create() must be used

base/message_loop/message_pump_ui_starboard.cc

@@ -15,6 +15,7 @@
 #include "base/message_loop/message_pump_ui_starboard.h"
 
 #include "base/logging.h"
+#include "base/notreached.h"
 #include "base/time/time.h"
 #include "starboard/event.h"
 #include "starboard/system.h"
@@ -107,11 +108,20 @@ void MessagePumpUIStarboard::Attach(Delegate* delegate) {
   // return control back to the Looper.
 
   SetDelegate(delegate);
+
+  run_loop_ = std::make_unique<RunLoop>();
+  // Since the RunLoop was just created above, BeforeRun should be guaranteed to
+  // return true (it only returns false if the RunLoop has been Quit already).
+  CHECK(run_loop_->BeforeRun());
 }
 
 void MessagePumpUIStarboard::Quit() {
   delegate_ = nullptr;
   CancelAll();
+  if (run_loop_) {
+    run_loop_->AfterRun();
+    run_loop_ = nullptr;
+  }
 }
 
 void MessagePumpUIStarboard::ScheduleWork() {

base/message_loop/message_pump_ui_starboard.h

@@ -19,6 +19,8 @@
 
 #include "base/base_export.h"
 #include "base/message_loop/message_pump.h"
+#include "base/message_loop/watchable_io_message_pump_posix.h"
+#include "base/run_loop.h"
 #include "base/synchronization/lock.h"
 #include "base/time/time.h"
 #include "starboard/event.h"
@@ -37,8 +39,28 @@ namespace base {
 // Starboard message pump as a MessageLoop. That would typically be for the
 // entire lifetime of the application, and in that case, the MessageLoop would
 // traditionally be deleted in the kSbEventStop handler.
-class BASE_EXPORT MessagePumpUIStarboard : public MessagePump {
+class BASE_EXPORT MessagePumpUIStarboard : public MessagePump, public WatchableIOMessagePumpPosix {
  public:
+
+  // TODO (cobalt b/393772370): Remove the stub FD support when x11/wayland are disabled.
+  class FdWatchController : public FdWatchControllerInterface {
+   public:
+    explicit FdWatchController(const Location& from_here): FdWatchControllerInterface(from_here) {}
+
+    FdWatchController(const FdWatchController&) = delete;
+    FdWatchController& operator=(const FdWatchController&) = delete;
+
+    ~FdWatchController() override {}
+
+    bool StopWatchingFileDescriptor() override {}
+  };
+
+  bool WatchFileDescriptor(int fd,
+                           bool persistent,
+                           int mode,
+                           FdWatchController* controller,
+                           FdWatcher* delegate) {}
+
   MessagePumpUIStarboard();
   virtual ~MessagePumpUIStarboard() { Quit(); }
 
@@ -83,6 +105,9 @@ class BASE_EXPORT MessagePumpUIStarboard : public MessagePump {
   // If the delegate has been removed, Quit() has been called.
   bool should_quit() const { return delegate_ == nullptr; }
 
+  // Maintain a RunLoop attached to the starboard thread.
+  std::unique_ptr<RunLoop> run_loop_;
+
   // The MessagePump::Delegate configured in Start().
   Delegate* delegate_;
 

base/run_loop.h

@@ -286,6 +286,12 @@ class BASE_EXPORT RunLoop {
   friend class MessagePumpUIApplication;
 #endif
 
+#if BUILDFLAG(IS_STARBOARD)
+  // Starboard doesn't support the blocking RunLoop::Run, so it calls
+  // BeforeRun and AfterRun directly.
+  friend class MessagePumpUIStarboard;
+#endif  // BUILDFLAG(IS_STARBOARD)
+
   // Support for //base/test/scoped_run_loop_timeout.h.
   friend class test::ScopedRunLoopTimeout;
   friend class test::ScopedDisableRunLoopTimeout;

base/task/current_thread.cc

@@ -149,7 +149,7 @@ MessagePumpForUI* CurrentUIThread::GetMessagePumpForUI() const {
   return static_cast<MessagePumpForUI*>(current_->GetMessagePump());
 }
 
-#if BUILDFLAG(IS_OZONE) && !BUILDFLAG(IS_FUCHSIA) && !BUILDFLAG(IS_WIN)
+#if BUILDFLAG(IS_OZONE) && !BUILDFLAG(IS_FUCHSIA) && !BUILDFLAG(IS_WIN) && !BUILDFLAG(IS_STARBOARD)
 bool CurrentUIThread::WatchFileDescriptor(
     int fd,
     bool persistent,

base/task/current_thread.h

@@ -213,7 +213,16 @@ class BASE_EXPORT CurrentUIThread : public CurrentThread {
 
   CurrentUIThread* operator->() { return this; }
 
-#if BUILDFLAG(IS_OZONE) && !BUILDFLAG(IS_FUCHSIA) && !BUILDFLAG(IS_WIN)
+// TODO (cobalt b/393772370): Remove when x11/wayland are disabled.
+#if BUILDFLAG(IS_STARBOARD)
+  bool WatchFileDescriptor(int fd,
+                           bool persistent,
+                           MessagePumpForUI::Mode mode,
+                           MessagePumpForUI::FdWatchController* controller,
+                           MessagePumpForUI::FdWatcher* delegate) { return false; }
+#endif
+
+#if BUILDFLAG(IS_OZONE) && !BUILDFLAG(IS_FUCHSIA) && !BUILDFLAG(IS_WIN) && !BUILDFLAG(IS_STARBOARD)
   static_assert(
       std::is_base_of<WatchableIOMessagePumpPosix, MessagePumpForUI>::value,
       "CurrentThreadForUI::WatchFileDescriptor is supported only"

base/task/sequence_manager/sequence_manager_impl.cc

@@ -337,6 +337,14 @@ void SequenceManagerImpl::BindToMessagePump(std::unique_ptr<MessagePump> pump) {
     controller_->AttachToMessagePump();
   }
 #endif
+
+  // On Starboard attach to the Starboard loop.
+#if BUILDFLAG(IS_STARBOARD)
+  if (settings_.message_loop_type == MessagePumpType::UI) {
+    controller_->AttachToMessagePump();
+  }
+#endif  // BUILDFLAG(IS_STARBOARD)
+
 }
 
 void SequenceManagerImpl::BindToCurrentThread() {

base/task/sequence_manager/thread_controller.h

@@ -132,7 +132,7 @@ class BASE_EXPORT ThreadController {
   // Returns true if the current run loop should quit when idle.
   virtual bool ShouldQuitRunLoopWhenIdle() = 0;
 
-#if BUILDFLAG(IS_IOS) || BUILDFLAG(IS_ANDROID)
+#if BUILDFLAG(IS_IOS) || BUILDFLAG(IS_ANDROID) || BUILDFLAG(IS_STARBOARD)
   // On iOS, the main message loop cannot be Run().  Instead call
   // AttachToMessagePump(), which connects this ThreadController to the
   // UI thread's CFRunLoop and allows PostTask() to work.

base/task/sequence_manager/thread_controller_impl.cc

@@ -363,11 +363,11 @@ MessagePump* ThreadControllerImpl::GetBoundMessagePump() const {
   return nullptr;
 }
 
-#if BUILDFLAG(IS_IOS) || BUILDFLAG(IS_ANDROID)
+#if BUILDFLAG(IS_IOS) || BUILDFLAG(IS_ANDROID) || BUILDFLAG(IS_STARBOARD)
 void ThreadControllerImpl::AttachToMessagePump() {
   NOTREACHED();
 }
-#endif  // BUILDFLAG(IS_IOS) || BUILDFLAG(IS_ANDROID)
+#endif  // BUILDFLAG(IS_IOS) || BUILDFLAG(IS_ANDROID) || BUILDFLAG(IS_STARBOARD)
 
 #if BUILDFLAG(IS_IOS)
 void ThreadControllerImpl::DetachFromMessagePump() {

base/task/sequence_manager/thread_controller_impl.h

@@ -61,7 +61,7 @@ class BASE_EXPORT ThreadControllerImpl : public ThreadController,
   void SetTaskExecutionAllowed(bool allowed) override;
   bool IsTaskExecutionAllowed() const override;
   MessagePump* GetBoundMessagePump() const override;
-#if BUILDFLAG(IS_IOS) || BUILDFLAG(IS_ANDROID)
+#if BUILDFLAG(IS_IOS) || BUILDFLAG(IS_ANDROID) || BUILDFLAG(IS_STARBOARD)
   void AttachToMessagePump() override;
 #endif
 #if BUILDFLAG(IS_IOS)

base/task/sequence_manager/thread_controller_with_message_pump_impl.cc

@@ -738,6 +738,10 @@ void ThreadControllerWithMessagePumpImpl::AttachToMessagePump() {
   main_thread_only().can_change_batch_size = false;
   static_cast<MessagePumpForUI*>(pump_.get())->Attach(this);
 }
+#elif BUILDFLAG(IS_STARBOARD)
+void ThreadControllerWithMessagePumpImpl::AttachToMessagePump() {
+  static_cast<MessagePumpForUI*>(pump_.get())->Attach(this);
+}
 #endif
 
 bool ThreadControllerWithMessagePumpImpl::ShouldQuitRunLoopWhenIdle() {

base/task/sequence_manager/thread_controller_with_message_pump_impl.h

@@ -74,7 +74,7 @@ class BASE_EXPORT ThreadControllerWithMessagePumpImpl
   bool IsTaskExecutionAllowed() const override;
   MessagePump* GetBoundMessagePump() const override;
   void PrioritizeYieldingToNative(base::TimeTicks prioritize_until) override;
-#if BUILDFLAG(IS_IOS) || BUILDFLAG(IS_ANDROID)
+#if BUILDFLAG(IS_IOS) || BUILDFLAG(IS_ANDROID) || BUILDFLAG(IS_STARBOARD)
   void AttachToMessagePump() override;
 #endif
 #if BUILDFLAG(IS_IOS)

base/test/BUILD.gn

@@ -222,6 +222,12 @@ static_library("test_support") {
     ]
   }
 
+  if (is_starboard) {
+    sources += [
+      "test_support_starboard.cc",
+      "test_support_starboard.h",
+    ]
+  }
   if (is_android) {
     sources += [
       "android/java_handler_thread_helpers.cc",

base/test/test_suite.cc

@@ -90,6 +90,9 @@
 #include "base/allocator/partition_alloc_support.h"
 #endif  // BUILDFLAG(USE_PARTITION_ALLOC)
 
+#if BUILDFLAG(IS_STARBOARD)
+#include "base/test/test_support_starboard.h"
+#endif
 namespace base {
 
 namespace {
@@ -624,6 +627,10 @@ void TestSuite::Initialize() {
   InitAndroidTestMessageLoop();
 #endif  // else BUILDFLAG(IS_ANDROID)
 
+#if BUILDFLAG(IS_STARBOARD)
+  InitStarboardTestMessageLoop();
+#endif
+
   CHECK(debug::EnableInProcessStackDumping());
 #if BUILDFLAG(IS_WIN)
   RouteStdioToConsole(true);

base/test/test_support_starboard.cc

@@ -0,0 +1,64 @@
+// Copyright 2025 The Chromium Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/logging.h"
+#include "base/memory/raw_ptr.h"
+#include "base/memory/singleton.h"
+#include "base/message_loop/message_pump.h"
+#include "base/message_loop/message_pump_default.h"
+#include "base/message_loop/message_pump_for_ui.h"
+#include "base/synchronization/waitable_event.h"
+
+namespace {
+
+class MessagePumpForUIStub : public base::MessagePumpUIStarboard {
+ public:
+
+  MessagePumpForUIStub() : base::MessagePumpForUI(), default_pump_ (new base::MessagePumpDefault) { }
+  ~MessagePumpForUIStub() override {}
+
+  // Similar to Android, in Starboad tests there isn't a native thread, 
+  // as such RunLoop::Run() should be  used to run the loop instead of attaching
+  // and delegating to the native  loop. 
+  // As such, this override ignores the Attach() request.
+  void Attach(base::MessagePump::Delegate* delegate) override {}
+
+  // --- Delegate to the MessagePumpDefault Implementation ---
+
+  virtual void Run(Delegate* delegate) override {
+   default_pump_->Run(delegate); 
+  }
+
+  virtual void Quit() override {
+   default_pump_->Quit(); 
+  }
+
+  virtual void ScheduleWork() override {
+   default_pump_->ScheduleWork(); 
+  }
+
+  virtual void ScheduleDelayedWork(
+      const Delegate::NextWorkInfo& next_work_info) override {
+   default_pump_->ScheduleDelayedWork(next_work_info); 
+  }
+
+ private:
+  std::unique_ptr<base::MessagePumpDefault> default_pump_;
+};
+
+std::unique_ptr<base::MessagePump> CreateMessagePumpForUIStub() {
+  return std::unique_ptr<base::MessagePump>(new MessagePumpForUIStub());
+}
+
+}  // namespace
+
+namespace base {
+
+
+void InitStarboardTestMessageLoop() {
+  if (!MessagePump::IsMessagePumpForUIFactoryOveridden())
+    MessagePump::OverrideMessagePumpForUIFactory(&CreateMessagePumpForUIStub);
+}
+
+}  // namespace base

base/test/test_support_starboard.h

@@ -0,0 +1,15 @@
+// Copyright 2025 The Chromium Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_TEST_TEST_SUPPORT_STARBOARD_H_
+#define BASE_TEST_TEST_SUPPORT_STARBOARD_H_
+
+namespace base {
+
+// Init the message loop for tests on Starboard.
+void InitStarboardTestMessageLoop();
+
+}  // namespace base
+
+#endif  // BASE_TEST_TEST_SUPPORT_STARBOARD_H_

base/threading/thread_restrictions.h

@@ -216,9 +216,9 @@ class BrowserGpuChannelHostFactory;
 class BrowserMainLoop;
 class BrowserProcessIOThread;
 class BrowserTestBase;
-#if BUILDFLAG(IS_IOS)
+#if BUILDFLAG(IS_IOS) || BUILDFLAG(IS_STARBOARD)
 class ContentMainRunnerImpl;
-#endif  // BUILDFLAG(IS_IOS)
+#endif  // BUILDFLAG(IS_IOS) || BUILDFLAG(IS_STARBOARD)
 class DesktopCaptureDevice;
 class DWriteFontCollectionProxy;
 class DWriteFontProxyImpl;
@@ -1006,9 +1006,9 @@ class BASE_EXPORT PermanentThreadAllowance {
   friend class base::TestCustomDisallow;
   friend class content::BrowserMainLoop;
   friend class content::BrowserTestBase;
-#if BUILDFLAG(IS_IOS)
+#if BUILDFLAG(IS_IOS) || BUILDFLAG(IS_STARBOARD)
   friend class content::ContentMainRunnerImpl;
-#endif  // BUILDFLAG(IS_IOS)
+#endif  // BUILDFLAG(IS_IOS) || BUILDFLAG(IS_STARBOARD)
   friend class web::WebMainLoop;
 
   static void AllowBlocking() EMPTY_BODY_IF_DCHECK_IS_OFF;

build/config/ozone.gni

@@ -89,7 +89,9 @@ declare_args() {
       ozone_platform_wayland = true
     } else if (is_linux) {
       ozone_platform = "x11"
-      ozone_platform_wayland = true
+      if (!is_starboard) {
+        ozone_platform_wayland = true
+      }
       ozone_platform_x11 = true
     } else if (is_fuchsia) {
       ozone_platform = "flatland"