Revert "Reduce app startup latency by initializing the engine on a separate thread (flutter#166918)" (flutter#167427)

This reverts commit c53fdbd.

See flutter#167418

Author: jason-simmons

engine/src/flutter/common/settings.h

@@ -16,7 +16,6 @@
 #include "flutter/fml/build_config.h"
 #include "flutter/fml/closure.h"
 #include "flutter/fml/mapping.h"
-#include "flutter/fml/task_queue_id.h"
 #include "flutter/fml/time/time_point.h"
 #include "flutter/fml/unique_fd.h"
 
@@ -71,10 +70,8 @@ class FrameTiming {
 };
 
 using TaskObserverAdd =
-    std::function<fml::TaskQueueId(intptr_t /* key */,
-                                   fml::closure /* callback */)>;
-using TaskObserverRemove =
-    std::function<void(fml::TaskQueueId /* queue */, intptr_t /* key */)>;
+    std::function<void(intptr_t /* key */, fml::closure /* callback */)>;
+using TaskObserverRemove = std::function<void(intptr_t /* key */)>;
 using UnhandledExceptionCallback =
     std::function<bool(const std::string& /* error */,
                        const std::string& /* stack trace */)>;
@@ -362,20 +359,9 @@ struct Settings {
   /// This is used by the runOnPlatformThread API.
   bool enable_platform_isolates = false;
 
-  enum class MergedPlatformUIThread {
-    // Use separate threads for the UI and platform task runners.
-    kDisabled,
-    // Use the platform thread for both the UI and platform task runners.
-    kEnabled,
-    // Start the engine on a separate UI thread and then move the UI task
-    // runner to the platform thread after the engine is initialized.
-    // This can improve app launch latency by allowing other work to run on
-    // the platform thread during engine startup.
-    kMergeAfterLaunch
-  };
-
-  MergedPlatformUIThread merged_platform_ui_thread =
-      MergedPlatformUIThread::kEnabled;
+  // If true, the UI thread is the platform thread on supported
+  // platforms.
+  bool merged_platform_ui_thread = true;
 };
 
 }  // namespace flutter

engine/src/flutter/fml/platform/fuchsia/task_observers.cc

@@ -16,16 +16,14 @@ void ExecuteAfterTaskObservers() {
   }
 }
 
-fml::TaskQueueId CurrentMessageLoopAddAfterTaskObserver(intptr_t key,
-                                                        fit::closure observer) {
+void CurrentMessageLoopAddAfterTaskObserver(intptr_t key,
+                                            fit::closure observer) {
   if (observer) {
     tTaskObservers[key] = std::move(observer);
   }
-  return fml::TaskQueueId::Invalid();
 }
 
-void CurrentMessageLoopRemoveAfterTaskObserver(fml::TaskQueueId queue_id,
-                                               intptr_t key) {
+void CurrentMessageLoopRemoveAfterTaskObserver(intptr_t key) {
   tTaskObservers.erase(key);
 }
 

engine/src/flutter/fml/platform/fuchsia/task_observers.h

@@ -7,8 +7,6 @@
 
 #include <lib/fit/function.h>
 
-#include "flutter/fml/task_queue_id.h"
-
 namespace fml {
 
 // Executes all closures that were registered via
@@ -32,11 +30,10 @@ namespace fml {
 // somehow.
 void ExecuteAfterTaskObservers();
 
-fml::TaskQueueId CurrentMessageLoopAddAfterTaskObserver(intptr_t key,
-                                                        fit::closure observer);
+void CurrentMessageLoopAddAfterTaskObserver(intptr_t key,
+                                            fit::closure observer);
 
-void CurrentMessageLoopRemoveAfterTaskObserver(fml::TaskQueueId queue_id,
-                                               intptr_t key);
+void CurrentMessageLoopRemoveAfterTaskObserver(intptr_t key);
 
 }  // namespace fml
 

engine/src/flutter/fml/task_queue_id.h

@@ -25,8 +25,6 @@ class TaskQueueId {
   /// Intializes a task queue with the given value as it's ID.
   explicit TaskQueueId(size_t value) : value_(value) {}
 
-  static TaskQueueId Invalid() { return TaskQueueId(kInvalid); }
-
   operator size_t() const {  // NOLINT(google-explicit-constructor)
     return value_;
   }

engine/src/flutter/lib/ui/painting/image_decoder.cc

@@ -55,7 +55,7 @@ ImageDecoder::ImageDecoder(
 
 ImageDecoder::~ImageDecoder() = default;
 
-fml::TaskRunnerAffineWeakPtr<ImageDecoder> ImageDecoder::GetWeakPtr() const {
+fml::WeakPtr<ImageDecoder> ImageDecoder::GetWeakPtr() const {
   return weak_factory_.GetWeakPtr();
 }
 

engine/src/flutter/lib/ui/painting/image_decoder.h

@@ -44,7 +44,7 @@ class ImageDecoder {
                       uint32_t target_height,
                       const ImageResult& result) = 0;
 
-  fml::TaskRunnerAffineWeakPtr<ImageDecoder> GetWeakPtr() const;
+  fml::WeakPtr<ImageDecoder> GetWeakPtr() const;
 
  protected:
   TaskRunners runners_;
@@ -57,7 +57,7 @@ class ImageDecoder {
       fml::WeakPtr<IOManager> io_manager);
 
  private:
-  fml::TaskRunnerAffineWeakPtrFactory<ImageDecoder> weak_factory_;
+  fml::WeakPtrFactory<ImageDecoder> weak_factory_;
 
   FML_DISALLOW_COPY_AND_ASSIGN(ImageDecoder);
 };

engine/src/flutter/lib/ui/painting/image_generator_registry.cc

@@ -79,8 +79,8 @@ ImageGeneratorRegistry::CreateCompatibleGenerator(const sk_sp<SkData>& buffer) {
   return nullptr;
 }
 
-fml::TaskRunnerAffineWeakPtr<ImageGeneratorRegistry>
-ImageGeneratorRegistry::GetWeakPtr() const {
+fml::WeakPtr<ImageGeneratorRegistry> ImageGeneratorRegistry::GetWeakPtr()
+    const {
   return weak_factory_.GetWeakPtr();
 }
 

engine/src/flutter/lib/ui/painting/image_generator_registry.h

@@ -58,7 +58,7 @@ class ImageGeneratorRegistry {
   std::shared_ptr<ImageGenerator> CreateCompatibleGenerator(
       const sk_sp<SkData>& buffer);
 
-  fml::TaskRunnerAffineWeakPtr<ImageGeneratorRegistry> GetWeakPtr() const;
+  fml::WeakPtr<ImageGeneratorRegistry> GetWeakPtr() const;
 
  private:
   struct PrioritizedFactory {
@@ -85,7 +85,7 @@ class ImageGeneratorRegistry {
   using FactorySet = std::set<PrioritizedFactory, Compare>;
   FactorySet image_generator_factories_;
   size_t nonce_;
-  fml::TaskRunnerAffineWeakPtrFactory<ImageGeneratorRegistry> weak_factory_;
+  fml::WeakPtrFactory<ImageGeneratorRegistry> weak_factory_;
 };
 
 }  // namespace flutter

engine/src/flutter/lib/ui/ui_dart_state.cc

@@ -24,9 +24,8 @@ UIDartState::Context::Context(
     fml::TaskRunnerAffineWeakPtr<SnapshotDelegate> snapshot_delegate,
     fml::WeakPtr<IOManager> io_manager,
     fml::RefPtr<SkiaUnrefQueue> unref_queue,
-    fml::TaskRunnerAffineWeakPtr<ImageDecoder> image_decoder,
-    fml::TaskRunnerAffineWeakPtr<ImageGeneratorRegistry>
-        image_generator_registry,
+    fml::WeakPtr<ImageDecoder> image_decoder,
+    fml::WeakPtr<ImageGeneratorRegistry> image_generator_registry,
     std::string advisory_script_uri,
     std::string advisory_script_entrypoint,
     bool deterministic_rendering_enabled,
@@ -59,7 +58,6 @@ UIDartState::UIDartState(
     const UIDartState::Context& context)
     : add_callback_(std::move(add_callback)),
       remove_callback_(std::move(remove_callback)),
-      callback_queue_id_(fml::TaskQueueId::kInvalid),
       logger_prefix_(std::move(logger_prefix)),
       is_root_isolate_(is_root_isolate),
       unhandled_exception_callback_(std::move(unhandled_exception_callback)),
@@ -180,12 +178,10 @@ void UIDartState::AddOrRemoveTaskObserver(bool add) {
   }
   FML_DCHECK(add_callback_ && remove_callback_);
   if (add) {
-    callback_queue_id_ =
-        add_callback_(reinterpret_cast<intptr_t>(this),
-                      [this]() { this->FlushMicrotasksNow(); });
+    add_callback_(reinterpret_cast<intptr_t>(this),
+                  [this]() { this->FlushMicrotasksNow(); });
   } else {
-    remove_callback_(callback_queue_id_, reinterpret_cast<intptr_t>(this));
-    callback_queue_id_ = fml::TaskQueueId::Invalid();
+    remove_callback_(reinterpret_cast<intptr_t>(this));
   }
 }
 
@@ -194,13 +190,12 @@ UIDartState::GetSnapshotDelegate() const {
   return context_.snapshot_delegate;
 }
 
-fml::TaskRunnerAffineWeakPtr<ImageDecoder> UIDartState::GetImageDecoder()
-    const {
+fml::WeakPtr<ImageDecoder> UIDartState::GetImageDecoder() const {
   return context_.image_decoder;
 }
 
-fml::TaskRunnerAffineWeakPtr<ImageGeneratorRegistry>
-UIDartState::GetImageGeneratorRegistry() const {
+fml::WeakPtr<ImageGeneratorRegistry> UIDartState::GetImageGeneratorRegistry()
+    const {
   return context_.image_generator_registry;
 }
 

engine/src/flutter/lib/ui/ui_dart_state.h

@@ -48,9 +48,8 @@ class UIDartState : public tonic::DartState {
             fml::TaskRunnerAffineWeakPtr<SnapshotDelegate> snapshot_delegate,
             fml::WeakPtr<IOManager> io_manager,
             fml::RefPtr<SkiaUnrefQueue> unref_queue,
-            fml::TaskRunnerAffineWeakPtr<ImageDecoder> image_decoder,
-            fml::TaskRunnerAffineWeakPtr<ImageGeneratorRegistry>
-                image_generator_registry,
+            fml::WeakPtr<ImageDecoder> image_decoder,
+            fml::WeakPtr<ImageGeneratorRegistry> image_generator_registry,
             std::string advisory_script_uri,
             std::string advisory_script_entrypoint,
             bool deterministic_rendering_enabled,
@@ -77,13 +76,12 @@ class UIDartState : public tonic::DartState {
     fml::RefPtr<SkiaUnrefQueue> unref_queue;
 
     /// The image decoder.
-    fml::TaskRunnerAffineWeakPtr<ImageDecoder> image_decoder;
+    fml::WeakPtr<ImageDecoder> image_decoder;
 
     /// Cascading registry of image generator builders. Given compressed image
     /// bytes as input, this is used to find and create image generators, which
     /// can then be used for image decoding.
-    fml::TaskRunnerAffineWeakPtr<ImageGeneratorRegistry>
-        image_generator_registry;
+    fml::WeakPtr<ImageGeneratorRegistry> image_generator_registry;
 
     /// The advisory script URI (only used for debugging). This does not affect
     /// the code being run in the isolate in any way.
@@ -146,10 +144,9 @@ class UIDartState : public tonic::DartState {
 
   fml::TaskRunnerAffineWeakPtr<SnapshotDelegate> GetSnapshotDelegate() const;
 
-  fml::TaskRunnerAffineWeakPtr<ImageDecoder> GetImageDecoder() const;
+  fml::WeakPtr<ImageDecoder> GetImageDecoder() const;
 
-  fml::TaskRunnerAffineWeakPtr<ImageGeneratorRegistry>
-  GetImageGeneratorRegistry() const;
+  fml::WeakPtr<ImageGeneratorRegistry> GetImageGeneratorRegistry() const;
 
   std::shared_ptr<IsolateNameServer> GetIsolateNameServer() const;
 
@@ -208,7 +205,6 @@ class UIDartState : public tonic::DartState {
 
   const TaskObserverAdd add_callback_;
   const TaskObserverRemove remove_callback_;
-  fml::TaskQueueId callback_queue_id_;
   const std::string logger_prefix_;
   Dart_Port main_port_ = ILLEGAL_PORT;
   const bool is_root_isolate_;