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base/debug/thread_heap_usage_tracker.h

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+// 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_THREAD_HEAP_USAGE_TRACKER_H_
+#define BASE_DEBUG_THREAD_HEAP_USAGE_TRACKER_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 {
+
+// Used to store the heap allocator usage in a scope.
+struct ThreadHeapUsage {
+  // 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 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;
+};
+
+// 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 not possible
+// to keep track of overhead, freed bytes and the allocation high water mark.
+class BASE_EXPORT ThreadHeapUsageTracker {
+ public:
+  ThreadHeapUsageTracker();
+  ~ThreadHeapUsageTracker();
+
+  // Start tracking heap usage on this thread.
+  // This may only be called on the thread where the instance is created.
+  // Note IsHeapTrackingEnabled() must be true.
+  void Start();
+
+  // Stop tracking heap usage on this thread and store the usage tallied.
+  // If |usage_is_exclusive| is true, the usage tallied won't be added to the
+  // outer scope's usage. If |usage_is_exclusive| is false, the usage tallied
+  // in this scope will also tally to any outer scope.
+  // This may only be called on the thread where the instance is created.
+  void Stop(bool usage_is_exclusive);
+
+  // After Stop() returns the usage tallied from Start() to Stop().
+  const ThreadHeapUsage& usage() const { return usage_; }
+
+  // Returns this thread's heap usage from the start of the innermost
+  // enclosing ThreadHeapUsageTracker instance, if any.
+  static ThreadHeapUsage GetUsageSnapshot();
+
+  // Enables the heap intercept. May only be called once, and only if the heap
+  // shim is available, e.g. if BUILDFLAG(USE_ALLOCATOR_SHIM) is
+  // true.
+  static void EnableHeapTracking();
+
+  // Returns true iff heap tracking is enabled.
+  static bool IsHeapTrackingEnabled();
+
+ protected:
+  // Exposed for testing only - note that it's safe to re-EnableHeapTracking()
+  // after calling this function in tests.
+  static void DisableHeapTrackingForTesting();
+
+  // Exposed for testing only.
+  static void EnsureTLSInitialized();
+
+  // Exposed to allow testing the shim without inserting it in the allocator
+  // shim chain.
+  static base::allocator::AllocatorDispatch* GetDispatchForTesting();
+
+ private:
+  ThreadChecker thread_checker_;
+
+  // The heap usage at Start(), or the difference from Start() to Stop().
+  ThreadHeapUsage usage_;
+
+  // This thread's heap usage, non-null from Start() to Stop().
+  ThreadHeapUsage* thread_usage_;
+};
+
+}  // namespace debug
+}  // namespace base
+
+#endif  // BASE_DEBUG_THREAD_HEAP_USAGE_TRACKER_H_