Enable sharding of AllocationRegister on desktop.

base/trace_event/sharded_allocation_register.h

+// 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.
+
+#ifndef BASE_TRACE_EVENT_SHARDED_ALLOCATION_REGISTER_H_
+#define BASE_TRACE_EVENT_SHARDED_ALLOCATION_REGISTER_H_
+
+#include <memory>
+#include <unordered_map>
+#include <vector>
+
+#include "base/atomicops.h"
+#include "base/base_export.h"
+#include "base/macros.h"
+#include "base/synchronization/lock.h"
+#include "base/trace_event/heap_profiler_allocation_register.h"
+
+namespace base {
+namespace trace_event {
+
+class TraceEventMemoryOverhead;
+
+// This container holds allocations, and context for each allocation [in the
+// form of a back trace].
+// This container is thread-safe.
+class BASE_EXPORT ShardedAllocationRegister {
+ public:
+  ShardedAllocationRegister();
+
+  // Must be initialized before the container can be used.
+  void Initialize();
+  bool IsInitialized() const;
+
+  void SetEnabled(bool enabled);
+  bool IsEnabled() const;

[Primiano Tucci (use gerrit), 2017/05/22 16:37:51]

this could be an in-line is_enabled()  const { return base::subtle..... } so it
gets inlined in the caller.
(but fine even without if you have any reason against)

[erikchen, 2017/05/22 17:10:43]

Done.

+
+  ~ShardedAllocationRegister();
+
+  // Inserts allocation details into the container. If the address was present
+  // already, its details are updated. |address| must not be null.
+  //
+  // Returns true if an insert occurred. Inserts may fail because the table
+  // is full.
+  bool Insert(const void* address,
+              size_t size,
+              const AllocationContext& context);
+
+  // Removes the address from the container if it is present. It is ok to call
+  // this with a null pointer.
+  void Remove(const void* address);
+
+  // Estimates memory overhead including |sizeof(AllocationRegister)|.
+  void EstimateTraceMemoryOverhead(TraceEventMemoryOverhead* overhead) const;
+
+  using MetricsMap = std::unordered_map<AllocationContext, AllocationMetrics>;

[Primiano Tucci (use gerrit), 2017/05/22 16:37:51]

nit: structs and type declarations should go on the top of the section, move to
line 28.
practically this confused me a bunch of times because line 55 above has
AllocationMetrics, but that is declared in another file. this OutputMetrics is
declared in an adjacent line but is used only in line 65. Hence moving them up
solves the confusion by not having it  adjacent to something that seems similar.

[erikchen, 2017/05/22 17:10:43]

Done.

+  struct OutputMetrics {
+    // Total size of allocated objects.
+    size_t size;
+    // Total count of allocated objects.
+    size_t count;
+  };
+
+  // Updates |map| with all allocated objects and their statistics.
+  // Returns aggregate statistics.
+  OutputMetrics UpdateAndReturnsMetrics(MetricsMap& map) const;
+
+ private:
+  struct RegisterAndLock {
+    RegisterAndLock();
+    ~RegisterAndLock();
+    AllocationRegister allocation_register;
+    Lock lock;
+  };
+  std::vector<std::unique_ptr<RegisterAndLock>> allocation_registers_;
+
+  // This member needs to be checked on every allocation and deallocation [fast
+  // path] when heap profiling is enabled. Using a lock here causes significant
+  // contention.
+  base::subtle::Atomic32 enabled_;
+
+  DISALLOW_COPY_AND_ASSIGN(ShardedAllocationRegister);
+};
+
+}  // namespace trace_event
+}  // namespace base
+
+#endif  // BASE_TRACE_EVENT_SHARDED_ALLOCATION_REGISTER_H_