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

services/blamer/shared_memory_heap_registry.cc

Index: services/blamer/shared_memory_heap_registry.cc
diff --git a/services/blamer/shared_memory_heap_registry.cc b/services/blamer/shared_memory_heap_registry.cc
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+++ b/services/blamer/shared_memory_heap_registry.cc
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+// 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/shared_memory_heap_registry.h"
+
+#include <map>
+
+#include "base/process/process_handle.h"
+#include "base/lazy_instance.h"
+#include "base/metrics/persistent_memory_allocator.h"
+#include "services/blamer/public/interfaces/service_constants.mojom.h"
+#include "services/service_manager/public/cpp/connection.h"
+
+namespace blamer {
+
+namespace {
+
+// The identity of a heap slab, from the point of view of the blamer service.
+// This is the tuple of (process_id, slab_id).
+using HeapSlabId = std::pair<base::ProcessId, uint32_t>;
+
+// A heap slab. This holds the mojom shared memory handle, a mapping to the
+// underlying data, and a PersistentMemoryAllocator on top of that for safe
+// iteration of the underlying data.
+class HeapSlab {
+ public:
+  HeapSlab(mojom::SharedMemoryHeapSlabPtr slab)
+      : buffer_(std::move(slab->buffer)),
+        mapping_(buffer_->Map(slab->size)),
+        size_(slab->size),
+        allocator_(new base::PersistentMemoryAllocator(
+            mapping_.get(), size_, mojom::kPageSize, slab->id, nullptr, true)) {
+  }
+
+  ~HeapSlab() {}
+
+ private:
+  // A handle to the shared memory buffer. This is owned by the remote
+  // process.
+  mojo::ScopedSharedBufferHandle buffer_;
+
+  // A handle to the shared buffer mapping. This is permanently mapped.
+  // TODO(chrisha): Revisit this! They could be mapped in on demand!
+  mojo::ScopedSharedBufferMapping mapping_;
+
+  // The size of the slab.
+  uint32_t size_;
+
+  // A persistent memory allocator over this slab, allowing iteration and
+  // inspection.
+  std::unique_ptr<base::PersistentMemoryAllocator> allocator_;
+};
+
+// A map of heap slabs across all processes, indexed by their unique IDs.
+using HeapSlabMap = std::map<HeapSlabId, std::unique_ptr<HeapSlab>>;
+
+base::LazyInstance<HeapSlabMap>::Leaky g_heap_slab_map_ =
+  LAZY_INSTANCE_INITIALIZER;
+
+}  // namespace
+
+SharedMemoryHeapRegistry::SharedMemoryHeapRegistry(
+    service_manager::ServiceContextRefFactory* service_ref_factory)
+    : service_ref_factory_(service_ref_factory) {
+  service_ref_ = service_ref_factory_->CreateRef();
+}
+
+SharedMemoryHeapRegistry::~SharedMemoryHeapRegistry() = default;
+
+// static
+void SharedMemoryHeapRegistry::Create(
+      service_manager::ServiceContextRefFactory* service_ref_factory,
+      blamer::mojom::SharedMemoryHeapRegistryRequest request) {
+  mojo::MakeStrongBinding(
+      base::MakeUnique<SharedMemoryHeapRegistry>(service_ref_factory),
+      std::move(request));
+}
+
+void SharedMemoryHeapRegistry::RegisterSlab(
+    mojom::SharedMemoryHeapSlabPtr slab) {
+  // TODO(chrisha): Get the remote process ID from the channel?
+  base::ProcessId process_id = 0;
+
+  // Add the slab to the map.
+  // TODO(chrisha): A way to remove mappings for processes that die!
+  g_heap_slab_map_.Get().insert(std::make_pair(
+      HeapSlabId(process_id, slab->id),
+      base::MakeUnique<HeapSlab>(std::move(slab))));
+}
+
+}  // namespace blamer
+