[Hacky prototype] Create a shared-memory high-performance reporting service.

services/blamer/public/cpp/blamer_interface.cc

+// Copyright 2017 The Chromium 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 "services/blamer/public/cpp/blamer_interface.h"
+
+#include <atomic>
+
+#include "services/blamer/public/interfaces/service_constants.mojom.h"
+#include "services/blamer/shared_memory_heap.h"
+
+namespace blamer {
+
+namespace {
+
+void OnConnectionError() {
+  // The service should outlast child processes.
+  NOTREACHED();
+}
+
+// Used to indicate that the right to create the singleton instance has been
+// acquired.
+BlamerInterface* kInstanceLockSentinel = reinterpret_cast<BlamerInterface*>(1);
+
+std::atomic<BlamerInterface*> g_instance(nullptr);
+
+}  // namespace
+
+BlamerInterface::~BlamerInterface() = default;
+
+BlamerInterface* BlamerInterface::CreateForProcess(
+    service_manager::Connector* connector) {
+  BlamerInterface* instance = g_instance.load();
+  if (instance != nullptr && instance != kInstanceLockSentinel)
+    return instance;
+
+  // Try to acquire the right to create the singleton.
+  if (instance == nullptr &&
+      g_instance.compare_exchange_strong(instance, kInstanceLockSentinel)) {
+    instance = new BlamerInterface(connector);
+    BlamerInterface* expected = kInstanceLockSentinel;
+    CHECK(g_instance.compare_exchange_strong(expected, instance));
+    return instance;
+  }
+
+  // Getting here means somebody else has the right to create the singleton.
+  // Wait until it's available.
+  while (true) {
+    instance = g_instance.load();
+    if (instance != nullptr && instance != kInstanceLockSentinel)
+      return instance;
+  }
+}
+
+BlamerInterface* BlamerInterface::GetForProcess() {
+  BlamerInterface* instance = g_instance.load();
+  if (instance == kInstanceLockSentinel)
+    return nullptr;
+  return instance;
+}
+
+BlamerInterface::BlamerInterface(service_manager::Connector* connector)
+    : shared_memory_heap_(nullptr) {
+  mojom::SharedMemoryHeapRegistryPtr heap_registry;
+  connector->BindInterface(mojom::kServiceName,
+                           mojo::MakeRequest(&heap_registry));
+  heap_registry.set_connection_error_handler(base::Bind(
+      &OnConnectionError));
+
+  // Create a shared memory heap for this process.
+  shared_memory_heap_.reset(new SharedMemoryHeap(std::move(heap_registry)));
+}
+
+}  // namespace blamer