Reland of: components/metrics: Add runtime memory leak detector

components/metrics/leak_detector/call_stack_manager.cc

+// Copyright 2015 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 "components/metrics/leak_detector/call_stack_manager.h"
+
+#include <algorithm>  // For std::copy.
+#include <new>
+#include <vector>
+
+#include "base/hash.h"
+#include "components/metrics/leak_detector/custom_allocator.h"
+
+namespace metrics {
+namespace leak_detector {
+
+CallStackManager::CallStackManager() {}
+
+CallStackManager::~CallStackManager() {
+  // Free all call stack objects and clear |call_stacks_|. Unfortunately,
+  // freeing an element of |call_stacks_| while iterating over it may result in
+  // undefined behavior since |call_stacks_| needs to access the memory pointed
+  // to by its members.
+
+  // Instead, copy all call stack objects' pointers into a local vector and
+  // clear |call_stacks_|. Then free the objects using the pointers stored in
+  // the local vector.
+  std::vector<CallStack*, CallStackPointerAllocator> temp_call_stacks;
+  temp_call_stacks.reserve(call_stacks_.size());
+  temp_call_stacks.assign(call_stacks_.begin(), call_stacks_.end());
+  call_stacks_.clear();
+
+  for (CallStack* call_stack : temp_call_stacks) {
+    CustomAllocator::Free(call_stack->stack,
+                          call_stack->depth * sizeof(*call_stack->stack));
+    call_stack->stack = nullptr;
+    call_stack->depth = 0;
+
+    CustomAllocator::Free(call_stack, sizeof(CallStack));
+  }
+}
+
+const CallStack* CallStackManager::GetCallStack(size_t depth,
+                                                const void* const stack[]) {
+  // Temporarily create a call stack object for lookup in |call_stacks_|.
+  CallStack temp;
+  temp.depth = depth;
+  temp.stack = const_cast<const void**>(stack);
+  // This is the only place where the call stack's hash is computed. This value
+  // can be reused in the created object to avoid further hash computation.
+  temp.hash =
+      base::Hash(reinterpret_cast<const char*>(stack), sizeof(*stack) * depth);
+
+  auto iter = call_stacks_.find(&temp);
+  if (iter != call_stacks_.end())
+    return *iter;
+
+  // Since |call_stacks_| stores CallStack pointers rather than actual objects,
+  // create new call objects manually here.
+  CallStack* call_stack =
+      new (CustomAllocator::Allocate(sizeof(CallStack))) CallStack;
+  call_stack->depth = depth;
+  call_stack->hash = temp.hash;  // Don't run the hash function again.
+  call_stack->stack = reinterpret_cast<const void**>(
+      CustomAllocator::Allocate(sizeof(*stack) * depth));
+  std::copy(stack, stack + depth, call_stack->stack);
+
+  call_stacks_.insert(call_stack);
+  return call_stack;
+}
+
+bool CallStackManager::CallStackPointerEqual::operator()(
+    const CallStack* c1,
+    const CallStack* c2) const {
+  return c1->depth == c2->depth && c1->hash == c2->hash &&
+         std::equal(c1->stack, c1->stack + c1->depth, c2->stack);
+}
+
+}  // namespace leak_detector
+}  // namespace metrics