Repo created

TMessagesProj/jni/voip/webrtc/base/android/reached_addresses_bitset.h

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+// Copyright 2019 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_ANDROID_REACHED_ADDRESSES_BITSET_H_
+#define BASE_ANDROID_REACHED_ADDRESSES_BITSET_H_
+
+#include <atomic>
+#include <vector>
+
+#include "base/base_export.h"
+
+namespace base {
+
+template <typename T>
+class NoDestructor;
+
+namespace android {
+
+// ReachedAddressesBitset is a set that stores addresses for the
+// ReachedCodeProfiler in compact form. Its main features are lock-free
+// thread-safety and fast adding of elements.
+//
+// The addresses are kept with |kBytesGranularity| to save the storage space.
+//
+// Once insterted, elements cannot be erased from the set.
+//
+// All methods can be called from any thread.
+class BASE_EXPORT ReachedAddressesBitset {
+ public:
+  // Returns an instance of ReachedAddressesBitset having enough storage space
+  // to keep all addresses from the .text section.
+  // Returns nullptr if SUPPORTS_CODE_ORDERING isn't defined.
+  // This instance is stored in the .bss section of the binary, meaning that it
+  // doesn't incur the binary size overhead and it doesn't increase the resident
+  // memory footprint when not used.
+  static ReachedAddressesBitset* GetTextBitset();
+
+  // Inserts |address| into the bitset iff |address| lies in the range between
+  // |start_address_| and |end_address_|.
+  void RecordAddress(uintptr_t address);
+
+  // Returns a list of recorded addresses in the form of offsets from
+  // |start_address_|.
+  std::vector<uint32_t> GetReachedOffsets() const;
+
+ private:
+  friend class ReachedAddressesBitsetTest;
+  friend class NoDestructor<ReachedAddressesBitset>;
+
+  // Represents the number of bytes that are mapped into the same bit in the
+  // bitset.
+  static constexpr size_t kBytesGranularity = 4;
+
+  // Constructs a ReachedAddressesBitset on top of an external storage of
+  // |storage_size| pointed by |storage_ptr|. This external storage must outlive
+  // the constructed bitset instance. The size of storage must be large enough
+  // to fit all addresses in the range between |start_address| and
+  // |end_address|.
+  ReachedAddressesBitset(uintptr_t start_address,
+                         uintptr_t end_address,
+                         std::atomic<uint32_t>* storage_ptr,
+                         size_t storage_size);
+
+  size_t NumberOfReachableElements() const;
+
+  uintptr_t start_address_;
+  uintptr_t end_address_;
+  std::atomic<uint32_t>* reached_;
+};
+
+}  // namespace android
+}  // namespace base
+
+#endif  // BASE_ANDROID_REACHED_ADDRESSES_BITSET_H_