Implement a ScopedThreadHeapUsage class to allow profiling per-thread heap usage.

base/debug/scoped_heap_usage.cc

+// Copyright 2016 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 "base/debug/scoped_heap_usage.h"
+
+#include "base/allocator/features.h"
+#include "build/build_config.h"
+
+#if defined(OS_MACOSX) || defined(OS_IOS)
+#include <malloc/malloc.h>
+#else
+#include <malloc.h>
+#endif
+#include <stdint.h>
+
+#include "base/allocator/allocator_shim.h"
+#include "base/threading/thread_local_storage.h"
+
+namespace base {
+namespace debug {
+
+#if BUILDFLAG(USE_EXPERIMENTAL_ALLOCATOR_SHIM)

[Primiano Tucci (use gerrit), 2016/08/24 14:11:46]

I think you can just restrict this #if to the Initialize and Teardown method and
CHECK(false) in the #else case.

[Sigurður Ásgeirsson, 2016/09/01 15:18:18]

Done.

+namespace {
+
+using base::allocator::AllocatorDispatch;
+
+ThreadLocalStorage::StaticSlot g_thread_allocator_usage = TLS_INITIALIZER;
+
+ScopedHeapUsage::AllocatorUsage* const kInitializingSentinel =
+    reinterpret_cast<ScopedHeapUsage::AllocatorUsage*>(-1);
+
+// Forward declared as it needs to delegate memory allocation to the next
+// lower shim.
+ScopedHeapUsage::AllocatorUsage* GetOrCreateThreadUsage();
+
+size_t GetAllocSizeEstimate(const AllocatorDispatch* next, void* ptr) {

[Primiano Tucci (use gerrit), 2016/08/24 15:28:47]

So at this point, if we shim GetAllocSize, there should be a global entry point
declared/defined in allocator_shim.h/cc, e.g.

BASE_EXPORT size_t GetAllocSizeEstimate(void* ptr) next to UncheckedAlloc, and
that should be implemented like:

 {
  const allocator::AllocatorDispatch* const chain_head = GetChainHead();
  return chain_head->get_alloc_size_function(chain_head, ptr);
}

[Sigurður Ásgeirsson, 2016/09/01 15:18:18]

I can add this if you like, but I don't agree with your reasoning in the point
below.

+  if (ptr == nullptr || !next->get_size_estimate_function)
+    return 0U;
+
+  return next->get_size_estimate_function(next, ptr);
+}
+
+void RecordAlloc(const AllocatorDispatch* next, void* ptr, size_t size) {
+  ScopedHeapUsage::AllocatorUsage* usage = GetOrCreateThreadUsage();
+  if (usage == nullptr)
+    return;
+
+  usage->alloc_ops++;
+  size_t estimate = GetAllocSizeEstimate(next, ptr);

[Primiano Tucci (use gerrit), 2016/08/24 14:11:46]

yeah here I'd just call GetAllocSizeEstimate(ptr), declared in
allocator_extensions (or whatever, as long as it's just a global function). No
need to use the shim chain.

[Sigurður Ásgeirsson, 2016/09/01 15:18:18]

As-is, I can test the functionality of this shim in isolation against a mocked
"next" dispatch implementation. If this starts calling on global functions that
refer to the shim chain head, then that's no longer possible.

+  if (estimate) {
+    usage->alloc_bytes += estimate;
+    usage->alloc_overhead_bytes += size - estimate;
+  } else {
+    usage->alloc_bytes += size;
+  }
+
+  uint64_t allocated_bytes = usage->alloc_bytes - usage->free_bytes;
+  if (allocated_bytes > usage->max_allocated_bytes)
+    usage->max_allocated_bytes = allocated_bytes;
+}
+
+void RecordFree(const AllocatorDispatch* next, void* ptr) {
+  ScopedHeapUsage::AllocatorUsage* usage = GetOrCreateThreadUsage();
+  if (usage == nullptr)
+    return;
+
+  size_t estimate = GetAllocSizeEstimate(next, ptr);
+  usage->free_ops++;
+  usage->free_bytes += estimate;
+}
+
+void* AllocFn(const AllocatorDispatch* self, size_t size) {
+  void* ret = self->next->alloc_function(self, size);
+  if (ret != nullptr)
+    RecordAlloc(self->next, ret, size);
+
+  return ret;
+}
+
+void* AllocZeroInitializedFn(const AllocatorDispatch* self,
+                             size_t n,
+                             size_t size) {
+  void* ret = self->next->alloc_zero_initialized_function(self, n, size);
+  if (ret != nullptr)
+    RecordAlloc(self->next, ret, size);
+
+  return ret;
+}
+
+void* AllocAlignedFn(const AllocatorDispatch* self,
+                     size_t alignment,
+                     size_t size) {
+  void* ret = self->next->alloc_aligned_function(self, alignment, size);
+  if (ret != nullptr)
+    RecordAlloc(self->next, ret, size);
+
+  return ret;
+}
+
+void* ReallocFn(const AllocatorDispatch* self, void* address, size_t size) {
+  if (address != nullptr)
+    RecordFree(self->next, address);
+
+  void* ret = self->next->realloc_function(self, address, size);
+  if (ret != nullptr)

[Primiano Tucci (use gerrit), 2016/08/24 14:11:46]

I'd probably be a bit more conservative here and do
if (ret != nullptr && size != 0)

The reason being: the manpage for relloc seems to suggest that
realloc(non_zero_address, 0 /*size*/) (which is essentially a free) can return
non-null.
Quoting from return value: "If size was equal to 0, either NULL or a pointer
suitable to be passed to free() is returned"

[Sigurður Ásgeirsson, 2016/09/01 15:18:18]

Done.

+    RecordAlloc(self->next, ret, size);
+
+  return ret;
+}
+
+void FreeFn(const AllocatorDispatch* self, void* address) {
+  if (address)

[Primiano Tucci (use gerrit), 2016/08/24 14:11:46]

small nit:y ou seem to mix if (address) with if (address != nullptr).
I think both are fine, as long as long as you are consistent :)

[Sigurður Ásgeirsson, 2016/09/01 15:18:18]

Done.

+    RecordFree(self->next, address);
+  self->next->free_function(self, address);
+}
+
+// The dispatch for the heap interept used.

[Primiano Tucci (use gerrit), 2016/08/24 14:11:46]

typo: s/interept/intercept/

[Sigurður Ásgeirsson, 2016/09/01 15:18:18]

Done.

+AllocatorDispatch allocator_dispatch = {
+    &AllocFn, &AllocZeroInitializedFn, &AllocAlignedFn, &ReallocFn, &FreeFn,
+    nullptr};
+
+ScopedHeapUsage::AllocatorUsage* GetOrCreateThreadUsage() {
+  ScopedHeapUsage::AllocatorUsage* allocator_usage =
+      static_cast<ScopedHeapUsage::AllocatorUsage*>(
+          g_thread_allocator_usage.Get());
+  if (allocator_usage == kInitializingSentinel)
+    return nullptr;  // Re-entrancy case.
+
+  if (!allocator_usage) {
+    g_thread_allocator_usage.Set(kInitializingSentinel);
+
+    const AllocatorDispatch* next = allocator_dispatch.next;

[Primiano Tucci (use gerrit), 2016/08/24 14:11:46]

given the fact that you have a sentinel I think you can safely just do:

allocator_usage = new AllocatorUsage
g_thread_....set .

Even if you re-enter in the current hook you should be forwarded by the AllocFn.

[Sigurður Ásgeirsson, 2016/09/01 15:18:18]

Done.

+    allocator_usage = reinterpret_cast<ScopedHeapUsage::AllocatorUsage*>(
+        next->alloc_zero_initialized_function(next, 1,
+                                              sizeof(*allocator_usage)));
+    g_thread_allocator_usage.Set(allocator_usage);
+  }
+
+  return allocator_usage;
+}
+
+void FreeAllocatorUsage(void* allocator_usage) {
+  const AllocatorDispatch* next = allocator_dispatch.next;
+  next->free_function(next, allocator_usage);
+}
+
+}  // namespace
+
+ScopedHeapUsage::ScopedHeapUsage() : thread_usage_(GetOrCreateThreadUsage()) {

[Primiano Tucci (use gerrit), 2016/08/24 14:11:46]

given that you initialize the other fields in the ctor body I'd probably just
move this there for consistency?

[Sigurður Ásgeirsson, 2016/09/01 15:18:18]

Done.

+  usage_at_creation_ = *thread_usage_;
+  // Reset the max allocation tally for this scope.
+  thread_usage_->max_allocated_bytes = 0U;
+}
+
+ScopedHeapUsage::~ScopedHeapUsage() {
+  if (usage_at_creation_.max_allocated_bytes >
+      thread_usage_->max_allocated_bytes) {

[Primiano Tucci (use gerrit), 2016/08/24 14:11:46]

out of curiosity are you caching thread_usage_ here?
In other words, I wonder whether this would be more readable if you don't have
the thread_usage_ field and here you just do:

usage = GetOrCreateThreadUsage();
if (at_creation.max > usage.max) usage.max = at_creation.max; 

[Sigurður Ásgeirsson, 2016/09/01 15:18:18]

Done. This does require two TLS lookups per instance, which should be no biggie.

+    // Restore the outer scope's max allocation tally, as it's larger than
+    // our scope's max.
+    thread_usage_->max_allocated_bytes = usage_at_creation_.max_allocated_bytes;
+  }
+}
+
+ScopedHeapUsage::AllocatorUsage ScopedHeapUsage::Now() {
+  AllocatorUsage* usage = GetOrCreateThreadUsage();
+  return *usage;
+}
+
+void ScopedHeapUsage::Initialize() {
+  if (!g_thread_allocator_usage.initialized())
+    g_thread_allocator_usage.Initialize(FreeAllocatorUsage);
+
+  InsertAllocatorDispatch(&allocator_dispatch);
+}
+
+void ScopedHeapUsage::TearDownForTesting() {
+  RemoveAllocatorDispatchForTesting(&allocator_dispatch);
+}
+#endif  // BUILDFLAG(USE_EXPERIMENTAL_ALLOCATOR_SHIM)
+
+}  // namespace debug
+}  // namespace base