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

base/debug/scoped_thread_heap_usage.h

Index: base/debug/scoped_thread_heap_usage.h
diff --git a/base/debug/scoped_thread_heap_usage.h b/base/debug/scoped_thread_heap_usage.h
new file mode 100644
index 0000000000000000000000000000000000000000..011ba9e2588e635a27b1166f1072967a5c02d100
--- /dev/null
+++ b/base/debug/scoped_thread_heap_usage.h
@@ -0,0 +1,101 @@
+// 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.
+
+#ifndef BASE_DEBUG_SCOPED_THREAD_HEAP_USAGE_H_
+#define BASE_DEBUG_SCOPED_THREAD_HEAP_USAGE_H_
+
+#include <stdint.h>
+
+#include "base/allocator/features.h"
+#include "base/base_export.h"
+#include "base/threading/thread_checker.h"
+
+namespace base {
+namespace allocator {
+struct AllocatorDispatch;
+}  // namespace allocator
+
+namespace debug {
+
+// By keeping a tally on heap operations, it's possible to track:
+// - the number of alloc/free operations, where a realloc is zero or one
+//   of each, depending on the input parameters (see man realloc).
+// - the number of bytes allocated/freed.
+// - the number of estimated bytes of heap overhead used.
+// - the high-watermark amount of bytes allocated in the scope.
+// This in turn allows measuring the memory usage and memory usage churn over
+// a scope. Scopes must be cleanly nested, and each scope must be
+// destroyed on the thread where it's created.
+//
+// Note that this depends on the capabilities of the underlying heap shim. If
+// that shim can not yield a size estimate for an allocation, it's impossible to
+// keep track of overhead, freed bytes and the allocation high water mark.
+class BASE_EXPORT ScopedThreadHeapUsage {
+ public:
+  struct ThreadAllocatorUsage {
+    // The cumulative number of allocation operations.
+    uint64_t alloc_ops;
+
+    // The cumulative number of allocated bytes. Where available, this is
+    // inclusive heap padding and estimated or actual heap overhead.
+    uint64_t alloc_bytes;
+
+    // Where available, cumulative number of heap padding heap
+    // and overhead bytes.
+    uint64_t alloc_overhead_bytes;
+
+    // The cumulative number of free operations.
+    uint64_t free_ops;
+
+    // The cumulative number of bytes freed.
+    // Only recorded if the underlying heap shim can return the size of an
+    // allocation.
+    uint64_t free_bytes;
+
+    // The maximal value of alloc_bytes - free_bytes seen for this thread.
+    // Only recorded if the underlying heap shim supports returning the size of
+    // an allocation.
+    uint64_t max_allocated_bytes;
+  };
+
+  ScopedThreadHeapUsage();
+  ~ScopedThreadHeapUsage();
+
+  const ThreadAllocatorUsage& usage_at_creation() const {
+    return usage_at_creation_;
+  }
+
+  // Returns this thread's current allocator usage.
+  static ThreadAllocatorUsage Now();
+
+  // Initializes the TLS machinery this class uses. Must be called before
+  // creating instances of this class.
+  static void Initialize();
+
+  // Enables the heap intercept. May only be called once, and only if the heap
+  // shim is available, e.g. if BUILDFLAG(USE_EXPERIMENTAL_ALLOCATOR_SHIM) is
+  // true.
+  static void EnableHeapTracking();
+
+ protected:
+  // Exposed for testing only - note that it's safe to re-EnableHeapTracking()
+  // after calling this function in tests.
+  static void DisableHeapTrackingForTesting();
+
+  // Exposed to allow testing the shim without inserting it in the allocator
+  // shim chain.
+  static base::allocator::AllocatorDispatch* GetDispatchForTesting();
+
+ private:
+  static void EnsureTLSInitialized();
+
+  ThreadChecker thread_checker_;
+  // The allocator usage captured at creation of this instance.
+  ThreadAllocatorUsage usage_at_creation_;
+};
+
+}  // namespace debug
+}  // namespace base
+
+#endif  // BASE_DEBUG_SCOPED_THREAD_HEAP_USAGE_H_