[Impeller] Fix a race that can abort the process if the Vulkan context is destroyed while pipeline creation tasks are pending

impeller/base/base_unittests.cc

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 #include "flutter/testing/testing.h"
+#include "impeller/base/promise.h"
 #include "impeller/base/strings.h"
 #include "impeller/base/thread.h"
 
@@ -233,5 +234,21 @@ TEST(ConditionVariableTest, TestsCriticalSectionAfterWait) {
   ASSERT_EQ(sum, kThreadCount);
 }
 
+TEST(BaseTest, NoExceptionPromiseValue) {
+  NoExceptionPromise<int> wrapper;
+  std::future future = wrapper.get_future();
+  wrapper.set_value(123);
+  ASSERT_EQ(future.get(), 123);
+}
+
+TEST(BaseTest, NoExceptionPromiseEmpty) {
+  auto wrapper = std::make_shared<NoExceptionPromise<int>>();
+  std::future future = wrapper->get_future();
+
+  // Destroy the empty promise with the future still pending. Verify that the
+  // process does not abort while destructing the promise.
+  wrapper.reset();
+}
+
 }  // namespace testing
 }  // namespace impeller

impeller/base/promise.h

@@ -17,6 +17,34 @@ std::future<T> RealizedFuture(T t) {
   return future;
 }
 
+// Wraps a std::promise and completes the promise with a value during
+// destruction if the promise does not already have a value.
+//
+// By default the std::promise destructor will complete an empty promise with an
+// exception. This will fail because Flutter is built without exception support.
+template <typename T>
+class NoExceptionPromise {
+ public:
+  NoExceptionPromise() = default;
+
+  ~NoExceptionPromise() {
+    if (!value_set_) {
+      promise_.set_value({});
+    }
+  }
+
+  std::future<T> get_future() { return promise_.get_future(); }
+
+  void set_value(const T& value) {
+    promise_.set_value(value);
+    value_set_ = true;
+  }
+
+ private:
+  std::promise<T> promise_;
+  bool value_set_ = false;
+};
+
 }  // namespace impeller
 
 #endif  // FLUTTER_IMPELLER_BASE_PROMISE_H_

impeller/renderer/backend/vulkan/pipeline_library_vk.cc

@@ -170,7 +170,7 @@ PipelineFuture<PipelineDescriptor> PipelineLibraryVK::GetPipeline(
   }
 
   auto promise = std::make_shared<
-      std::promise<std::shared_ptr<Pipeline<PipelineDescriptor>>>>();
+      NoExceptionPromise<std::shared_ptr<Pipeline<PipelineDescriptor>>>>();
   auto pipeline_future =
       PipelineFuture<PipelineDescriptor>{descriptor, promise->get_future()};
   pipelines_[descriptor] = pipeline_future;