All creation of pipeline variants from a pipeline.

impeller/base/BUILD.gn

@@ -10,6 +10,8 @@ impeller_component("base") {
     "allocation.h",
     "base.h",
     "config.h",
+    "promise.cc",
+    "promise.h",
     "strings.cc",
     "strings.h",
     "validation.cc",

impeller/base/base.h

@@ -4,5 +4,6 @@
 
 #pragma once
 
+#include "impeller/base/promise.h"
 #include "impeller/base/strings.h"
 #include "impeller/base/validation.h"

impeller/base/promise.cc

@@ -0,0 +1,11 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "impeller/base/promise.h"
+
+namespace impeller {
+
+//
+
+}  // namespace impeller

impeller/base/promise.h

@@ -0,0 +1,19 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#pragma once
+
+#include <future>
+
+namespace impeller {
+
+template <class T>
+std::future<T> RealizedFuture(T t) {
+  std::promise<T> promise;
+  auto future = promise.get_future();
+  promise.set_value(std::move(t));
+  return future;
+}
+
+}  // namespace impeller

impeller/renderer/backend/metal/pipeline_library_mtl.mm

@@ -81,24 +81,33 @@
   // created till the first instance of the creation invokes its completion
   // callback.
 
-  auto thiz = shared_from_this();
+  auto weak_this = weak_from_this();
 
   auto completion_handler =
       ^(id<MTLRenderPipelineState> _Nullable render_pipeline_state,
         NSError* _Nullable error) {
         if (error != nil) {
-          FML_LOG(ERROR) << "Could not create render pipeline: "
+          VALIDATION_LOG << "Could not create render pipeline: "
                          << error.localizedDescription.UTF8String;
           promise->set_value(nullptr);
-        } else {
-          auto new_pipeline = std::shared_ptr<PipelineMTL>(new PipelineMTL(
-              descriptor,                                        //
-              render_pipeline_state,                             //
-              CreateDepthStencilDescriptor(descriptor, device_)  //
-              ));
-          promise->set_value(new_pipeline);
-          this->SavePipeline(descriptor, new_pipeline);
+          return;
         }
+
+        auto strong_this = weak_this.lock();
+        if (!strong_this) {
+          VALIDATION_LOG << "Library was collected before a pending pipeline "
+                            "creation could finish.";
+          promise->set_value(nullptr);
+          return;
+        }
+        auto new_pipeline = std::shared_ptr<PipelineMTL>(new PipelineMTL(
+            weak_this,
+            descriptor,                                        //
+            render_pipeline_state,                             //
+            CreateDepthStencilDescriptor(descriptor, device_)  //
+            ));
+        promise->set_value(new_pipeline);
+        this->SavePipeline(descriptor, new_pipeline);
       };
   [device_ newRenderPipelineStateWithDescriptor:GetMTLRenderPipelineDescriptor(
                                                     descriptor)

impeller/renderer/backend/metal/pipeline_mtl.h

@@ -30,7 +30,8 @@ class PipelineMTL final : public Pipeline,
   id<MTLDepthStencilState> depth_stencil_state_;
   bool is_valid_ = false;
 
-  PipelineMTL(PipelineDescriptor desc,
+  PipelineMTL(std::weak_ptr<PipelineLibrary> library,
+              PipelineDescriptor desc,
               id<MTLRenderPipelineState> state,
               id<MTLDepthStencilState> depth_stencil_state);
 

impeller/renderer/backend/metal/pipeline_mtl.mm

@@ -6,10 +6,11 @@
 
 namespace impeller {
 
-PipelineMTL::PipelineMTL(PipelineDescriptor desc,
+PipelineMTL::PipelineMTL(std::weak_ptr<PipelineLibrary> library,
+                         PipelineDescriptor desc,
                          id<MTLRenderPipelineState> state,
                          id<MTLDepthStencilState> depth_stencil_state)
-    : Pipeline(std::move(desc)),
+    : Pipeline(std::move(library), std::move(desc)),
       pipeline_state_(state),
       depth_stencil_state_(depth_stencil_state) {
   if (!pipeline_state_) {

impeller/renderer/pipeline.cc

@@ -4,22 +4,22 @@
 
 #include "impeller/renderer/pipeline.h"
 
+#include "impeller/base/base.h"
 #include "impeller/renderer/context.h"
 #include "impeller/renderer/pipeline_library.h"
 
 namespace impeller {
 
-Pipeline::Pipeline(PipelineDescriptor desc) : desc_(std::move(desc)) {}
+Pipeline::Pipeline(std::weak_ptr<PipelineLibrary> library,
+                   PipelineDescriptor desc)
+    : library_(std::move(library)), desc_(std::move(desc)) {}
 
 Pipeline::~Pipeline() = default;
 
 PipelineFuture CreatePipelineFuture(const Context& context,
                                     std::optional<PipelineDescriptor> desc) {
   if (!context.IsValid()) {
-    std::promise<std::shared_ptr<Pipeline>> promise;
-    auto future = promise.get_future();
-    promise.set_value(nullptr);
-    return future;
+    return RealizedFuture<std::shared_ptr<Pipeline>>(nullptr);
   }
 
   return context.GetPipelineLibrary()->GetRenderPipeline(std::move(desc));
@@ -29,4 +29,24 @@ const PipelineDescriptor& Pipeline::GetDescriptor() const {
   return desc_;
 }
 
+PipelineFuture Pipeline::CreateVariant(
+    std::function<void(PipelineDescriptor& desc)> descriptor_callback) const {
+  if (!descriptor_callback) {
+    return RealizedFuture<std::shared_ptr<Pipeline>>(nullptr);
+  }
+
+  auto copied_desc = desc_;
+
+  descriptor_callback(copied_desc);
+
+  auto library = library_.lock();
+  if (!library) {
+    VALIDATION_LOG << "The library from which this pipeline was created was "
+                      "already collected.";
+    return RealizedFuture<std::shared_ptr<Pipeline>>(nullptr);
+  }
+
+  return library->GetRenderPipeline(std::move(copied_desc));
+}
+
 }  // namespace impeller

impeller/renderer/pipeline.h

@@ -44,10 +44,14 @@ class Pipeline {
 
   const PipelineDescriptor& GetDescriptor() const;
 
+  PipelineFuture CreateVariant(
+      std::function<void(PipelineDescriptor& desc)> descriptor_callback) const;
+
  protected:
-  Pipeline(PipelineDescriptor desc);
+  Pipeline(std::weak_ptr<PipelineLibrary> library, PipelineDescriptor desc);
 
  private:
+  const std::weak_ptr<PipelineLibrary> library_;
   const PipelineDescriptor desc_;
 
   FML_DISALLOW_COPY_AND_ASSIGN(Pipeline);