[Linux] Move rendering to raster thread (#161879)

Fixes flutter/flutter#155045

*If you had to change anything in the [flutter/tests] repo, include a
link to the migration guide as per the [breaking change policy].*

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responsibilities.
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we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

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---------

Co-authored-by: Robert Ancell <robert.ancell@canonical.com>

Author: knopp

engine/src/flutter/shell/platform/linux/fl_engine.cc

@@ -356,7 +356,7 @@ static void fl_engine_post_task(FlutterTask task,
                                 void* user_data) {
   FlEngine* self = static_cast<FlEngine*>(user_data);
 
-  fl_task_runner_post_task(self->task_runner, task, target_time_nanos);
+  fl_task_runner_post_flutter_task(self->task_runner, task, target_time_nanos);
 }
 
 // Called when a platform message is received from the engine.
@@ -630,7 +630,6 @@ gboolean fl_engine_start(FlEngine* self, GError** error) {
   FlutterCustomTaskRunners custom_task_runners = {};
   custom_task_runners.struct_size = sizeof(FlutterCustomTaskRunners);
   custom_task_runners.platform_task_runner = &platform_task_runner;
-  custom_task_runners.render_task_runner = &platform_task_runner;
 
   g_autoptr(GPtrArray) command_line_args =
       g_ptr_array_new_with_free_func(g_free);

engine/src/flutter/shell/platform/linux/fl_renderer.cc

@@ -73,6 +73,14 @@ typedef struct {
 
   // Framebuffers to render keyed by view ID.
   GHashTable* framebuffers_by_view_id;
+
+  // Mutex used when blocking the raster thread until a task is completed on
+  // platform thread.
+  GMutex present_mutex;
+
+  // Condition to unblock the raster thread after task is completed on platform
+  // thread.
+  GCond present_condition;
 } FlRendererPrivate;
 
 G_DEFINE_TYPE_WITH_PRIVATE(FlRenderer, fl_renderer, G_TYPE_OBJECT)
@@ -301,6 +309,151 @@ static void render(FlRenderer* self,
   }
 }
 
+static gboolean present_layers(FlRenderer* self,
+                               FlutterViewId view_id,
+                               const FlutterLayer** layers,
+                               size_t layers_count) {
+  FlRendererPrivate* priv = reinterpret_cast<FlRendererPrivate*>(
+      fl_renderer_get_instance_private(self));
+
+  g_return_val_if_fail(FL_IS_RENDERER(self), FALSE);
+
+  // ignore incoming frame with wrong dimensions in trivial case with just one
+  // layer
+  if (priv->blocking_main_thread && layers_count == 1 &&
+      layers[0]->offset.x == 0 && layers[0]->offset.y == 0 &&
+      (layers[0]->size.width != priv->target_width ||
+       layers[0]->size.height != priv->target_height)) {
+    return TRUE;
+  }
+
+  priv->had_first_frame = true;
+
+  fl_renderer_unblock_main_thread(self);
+
+  g_autoptr(GPtrArray) framebuffers =
+      g_ptr_array_new_with_free_func(g_object_unref);
+  for (size_t i = 0; i < layers_count; ++i) {
+    const FlutterLayer* layer = layers[i];
+    switch (layer->type) {
+      case kFlutterLayerContentTypeBackingStore: {
+        const FlutterBackingStore* backing_store = layer->backing_store;
+        FlFramebuffer* framebuffer =
+            FL_FRAMEBUFFER(backing_store->open_gl.framebuffer.user_data);
+        g_ptr_array_add(framebuffers, g_object_ref(framebuffer));
+      } break;
+      case kFlutterLayerContentTypePlatformView: {
+        // TODO(robert-ancell) Not implemented -
+        // https://github.com/flutter/flutter/issues/41724
+      } break;
+    }
+  }
+
+  GWeakRef* ref = static_cast<GWeakRef*>(
+      g_hash_table_lookup(priv->views, GINT_TO_POINTER(view_id)));
+  g_autoptr(FlRenderable) renderable =
+      ref != nullptr ? FL_RENDERABLE(g_weak_ref_get(ref)) : nullptr;
+  if (renderable == nullptr) {
+    return TRUE;
+  }
+
+  if (view_id == flutter::kFlutterImplicitViewId) {
+    // Store for rendering later
+    g_hash_table_insert(priv->framebuffers_by_view_id, GINT_TO_POINTER(view_id),
+                        g_ptr_array_ref(framebuffers));
+  } else {
+    // Composite into a single framebuffer.
+    if (framebuffers->len > 1) {
+      size_t width = 0, height = 0;
+
+      for (guint i = 0; i < framebuffers->len; i++) {
+        FlFramebuffer* framebuffer =
+            FL_FRAMEBUFFER(g_ptr_array_index(framebuffers, i));
+
+        size_t w = fl_framebuffer_get_width(framebuffer);
+        size_t h = fl_framebuffer_get_height(framebuffer);
+        if (w > width) {
+          width = w;
+        }
+        if (h > height) {
+          height = h;
+        }
+      }
+
+      FlFramebuffer* view_framebuffer =
+          fl_framebuffer_new(priv->general_format, width, height);
+      glBindFramebuffer(GL_DRAW_FRAMEBUFFER,
+                        fl_framebuffer_get_id(view_framebuffer));
+      render(self, framebuffers, width, height);
+      g_ptr_array_set_size(framebuffers, 0);
+      g_ptr_array_add(framebuffers, view_framebuffer);
+    }
+
+    // Read back pixel values.
+    FlFramebuffer* framebuffer =
+        FL_FRAMEBUFFER(g_ptr_array_index(framebuffers, 0));
+    size_t width = fl_framebuffer_get_width(framebuffer);
+    size_t height = fl_framebuffer_get_height(framebuffer);
+    size_t data_length = width * height * 4;
+    g_autofree uint8_t* data = static_cast<uint8_t*>(malloc(data_length));
+    glBindFramebuffer(GL_READ_FRAMEBUFFER, fl_framebuffer_get_id(framebuffer));
+    glReadPixels(0, 0, width, height, priv->general_format, GL_UNSIGNED_BYTE,
+                 data);
+
+    // Write into a texture in the views context.
+    fl_renderable_make_current(renderable);
+    FlFramebuffer* view_framebuffer =
+        fl_framebuffer_new(priv->general_format, width, height);
+    glBindFramebuffer(GL_DRAW_FRAMEBUFFER,
+                      fl_framebuffer_get_id(view_framebuffer));
+    glBindTexture(GL_TEXTURE_2D,
+                  fl_framebuffer_get_texture_id(view_framebuffer));
+    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA,
+                 GL_UNSIGNED_BYTE, data);
+
+    g_autoptr(GPtrArray) secondary_framebuffers =
+        g_ptr_array_new_with_free_func(g_object_unref);
+    g_ptr_array_add(secondary_framebuffers, g_object_ref(view_framebuffer));
+    g_hash_table_insert(priv->framebuffers_by_view_id, GINT_TO_POINTER(view_id),
+                        g_ptr_array_ref(secondary_framebuffers));
+  }
+
+  fl_renderable_redraw(renderable);
+
+  return TRUE;
+}
+
+typedef struct {
+  FlRenderer* self;
+
+  FlutterViewId view_id;
+
+  const FlutterLayer** layers;
+  size_t layers_count;
+
+  gboolean result;
+
+  gboolean finished;
+} PresentLayersData;
+
+// Perform the present on the main thread.
+static void present_layers_task_cb(gpointer user_data) {
+  PresentLayersData* data = static_cast<PresentLayersData*>(user_data);
+  FlRendererPrivate* priv = reinterpret_cast<FlRendererPrivate*>(
+      fl_renderer_get_instance_private(data->self));
+
+  // Perform the present.
+  fl_renderer_make_current(data->self);
+  data->result = present_layers(data->self, data->view_id, data->layers,
+                                data->layers_count);
+  fl_renderer_clear_current(data->self);
+
+  // Complete fl_renderer_present_layers().
+  g_autoptr(GMutexLocker) locker = g_mutex_locker_new(&priv->present_mutex);
+  data->finished = TRUE;
+  g_cond_signal(&priv->present_condition);
+}
+
 static void fl_renderer_dispose(GObject* object) {
   FlRenderer* self = FL_RENDERER(object);
   FlRendererPrivate* priv = reinterpret_cast<FlRendererPrivate*>(
@@ -311,6 +464,8 @@ static void fl_renderer_dispose(GObject* object) {
   g_weak_ref_clear(&priv->engine);
   g_clear_pointer(&priv->views, g_hash_table_unref);
   g_clear_pointer(&priv->framebuffers_by_view_id, g_hash_table_unref);
+  g_mutex_clear(&priv->present_mutex);
+  g_cond_clear(&priv->present_condition);
 
   G_OBJECT_CLASS(fl_renderer_parent_class)->dispose(object);
 }
@@ -327,6 +482,8 @@ static void fl_renderer_init(FlRenderer* self) {
   priv->framebuffers_by_view_id = g_hash_table_new_full(
       g_direct_hash, g_direct_equal, nullptr,
       reinterpret_cast<GDestroyNotify>(g_ptr_array_unref));
+  g_mutex_init(&priv->present_mutex);
+  g_cond_init(&priv->present_condition);
 }
 
 void fl_renderer_set_engine(FlRenderer* self, FlEngine* engine) {
@@ -454,114 +611,37 @@ gboolean fl_renderer_present_layers(FlRenderer* self,
                                     FlutterViewId view_id,
                                     const FlutterLayer** layers,
                                     size_t layers_count) {
+  // Detach the context from raster thread. Needed because blitting
+  // will be done on the main thread, which will make the context current.
+  fl_renderer_clear_current(self);
+
   FlRendererPrivate* priv = reinterpret_cast<FlRendererPrivate*>(
       fl_renderer_get_instance_private(self));
+  g_autoptr(FlEngine) engine = FL_ENGINE(g_weak_ref_get(&priv->engine));
+
+  // Schedule the present to run on the main thread.
+  FlTaskRunner* task_runner = fl_engine_get_task_runner(engine);
+  PresentLayersData data = {
+      .self = self,
+      .view_id = view_id,
+      .layers = layers,
+      .layers_count = layers_count,
+      .result = FALSE,
+      .finished = FALSE,
+  };
+  fl_task_runner_post_callback(task_runner, present_layers_task_cb, &data);
 
-  g_return_val_if_fail(FL_IS_RENDERER(self), FALSE);
-
-  // ignore incoming frame with wrong dimensions in trivial case with just one
-  // layer
-  if (priv->blocking_main_thread && layers_count == 1 &&
-      layers[0]->offset.x == 0 && layers[0]->offset.y == 0 &&
-      (layers[0]->size.width != priv->target_width ||
-       layers[0]->size.height != priv->target_height)) {
-    return TRUE;
-  }
-
-  priv->had_first_frame = true;
-
-  fl_renderer_unblock_main_thread(self);
-
-  g_autoptr(GPtrArray) framebuffers =
-      g_ptr_array_new_with_free_func(g_object_unref);
-  for (size_t i = 0; i < layers_count; ++i) {
-    const FlutterLayer* layer = layers[i];
-    switch (layer->type) {
-      case kFlutterLayerContentTypeBackingStore: {
-        const FlutterBackingStore* backing_store = layer->backing_store;
-        FlFramebuffer* framebuffer =
-            FL_FRAMEBUFFER(backing_store->open_gl.framebuffer.user_data);
-        g_ptr_array_add(framebuffers, g_object_ref(framebuffer));
-      } break;
-      case kFlutterLayerContentTypePlatformView: {
-        // TODO(robert-ancell) Not implemented -
-        // https://github.com/flutter/flutter/issues/41724
-      } break;
-    }
-  }
-
-  GWeakRef* ref = static_cast<GWeakRef*>(
-      g_hash_table_lookup(priv->views, GINT_TO_POINTER(view_id)));
-  g_autoptr(FlRenderable) renderable =
-      ref != nullptr ? FL_RENDERABLE(g_weak_ref_get(ref)) : nullptr;
-  if (renderable == nullptr) {
-    return TRUE;
-  }
-
-  if (view_id == flutter::kFlutterImplicitViewId) {
-    // Store for rendering later
-    g_hash_table_insert(priv->framebuffers_by_view_id, GINT_TO_POINTER(view_id),
-                        g_ptr_array_ref(framebuffers));
-  } else {
-    // Composite into a single framebuffer.
-    if (framebuffers->len > 1) {
-      size_t width = 0, height = 0;
-
-      for (guint i = 0; i < framebuffers->len; i++) {
-        FlFramebuffer* framebuffer =
-            FL_FRAMEBUFFER(g_ptr_array_index(framebuffers, i));
-
-        size_t w = fl_framebuffer_get_width(framebuffer);
-        size_t h = fl_framebuffer_get_height(framebuffer);
-        if (w > width) {
-          width = w;
-        }
-        if (h > height) {
-          height = h;
-        }
-      }
-
-      FlFramebuffer* view_framebuffer =
-          fl_framebuffer_new(priv->general_format, width, height);
-      glBindFramebuffer(GL_DRAW_FRAMEBUFFER,
-                        fl_framebuffer_get_id(view_framebuffer));
-      render(self, framebuffers, width, height);
-      g_ptr_array_set_size(framebuffers, 0);
-      g_ptr_array_add(framebuffers, view_framebuffer);
-    }
-
-    // Read back pixel values.
-    FlFramebuffer* framebuffer =
-        FL_FRAMEBUFFER(g_ptr_array_index(framebuffers, 0));
-    size_t width = fl_framebuffer_get_width(framebuffer);
-    size_t height = fl_framebuffer_get_height(framebuffer);
-    size_t data_length = width * height * 4;
-    g_autofree uint8_t* data = static_cast<uint8_t*>(malloc(data_length));
-    glBindFramebuffer(GL_READ_FRAMEBUFFER, fl_framebuffer_get_id(framebuffer));
-    glReadPixels(0, 0, width, height, priv->general_format, GL_UNSIGNED_BYTE,
-                 data);
-
-    // Write into a texture in the views context.
-    fl_renderable_make_current(renderable);
-    FlFramebuffer* view_framebuffer =
-        fl_framebuffer_new(priv->general_format, width, height);
-    glBindFramebuffer(GL_DRAW_FRAMEBUFFER,
-                      fl_framebuffer_get_id(view_framebuffer));
-    glBindTexture(GL_TEXTURE_2D,
-                  fl_framebuffer_get_texture_id(view_framebuffer));
-    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA,
-                 GL_UNSIGNED_BYTE, data);
-
-    g_autoptr(GPtrArray) secondary_framebuffers =
-        g_ptr_array_new_with_free_func(g_object_unref);
-    g_ptr_array_add(secondary_framebuffers, g_object_ref(view_framebuffer));
-    g_hash_table_insert(priv->framebuffers_by_view_id, GINT_TO_POINTER(view_id),
-                        g_ptr_array_ref(secondary_framebuffers));
+  // Block until present completes.
+  g_autoptr(GMutexLocker) locker = g_mutex_locker_new(&priv->present_mutex);
+  while (!data.finished) {
+    g_cond_wait(&priv->present_condition, &priv->present_mutex);
   }
 
-  fl_renderable_redraw(renderable);
+  // Restore the context to the raster thread in case the engine needs it
+  // to do some cleanup.
+  fl_renderer_make_current(self);
 
-  return TRUE;
+  return data.result;
 }
 
 void fl_renderer_setup(FlRenderer* self) {