DoubleBuffer.h 2.1 KB

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  1. /*
  2. * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
  3. *
  4. * SPDX-License-Identifier: BSD-2-Clause
  5. */
  6. #pragma once
  7. #include <AK/Types.h>
  8. #include <Kernel/KBuffer.h>
  9. #include <Kernel/Locking/Mutex.h>
  10. #include <Kernel/Thread.h>
  11. #include <Kernel/UserOrKernelBuffer.h>
  12. namespace Kernel {
  13. class DoubleBuffer {
  14. public:
  15. [[nodiscard]] static OwnPtr<DoubleBuffer> try_create(size_t capacity = 65536);
  16. [[nodiscard]] KResultOr<size_t> write(const UserOrKernelBuffer&, size_t);
  17. [[nodiscard]] KResultOr<size_t> write(const u8* data, size_t size)
  18. {
  19. return write(UserOrKernelBuffer::for_kernel_buffer(const_cast<u8*>(data)), size);
  20. }
  21. [[nodiscard]] KResultOr<size_t> read(UserOrKernelBuffer&, size_t);
  22. [[nodiscard]] KResultOr<size_t> read(u8* data, size_t size)
  23. {
  24. auto buffer = UserOrKernelBuffer::for_kernel_buffer(data);
  25. return read(buffer, size);
  26. }
  27. [[nodiscard]] KResultOr<size_t> peek(UserOrKernelBuffer&, size_t);
  28. [[nodiscard]] KResultOr<size_t> peek(u8* data, size_t size)
  29. {
  30. auto buffer = UserOrKernelBuffer::for_kernel_buffer(data);
  31. return peek(buffer, size);
  32. }
  33. bool is_empty() const { return m_empty; }
  34. size_t space_for_writing() const { return m_space_for_writing; }
  35. size_t immediately_readable() const
  36. {
  37. return (m_read_buffer->size - m_read_buffer_index) + m_write_buffer->size;
  38. }
  39. void set_unblock_callback(Function<void()> callback)
  40. {
  41. VERIFY(!m_unblock_callback);
  42. m_unblock_callback = move(callback);
  43. }
  44. private:
  45. explicit DoubleBuffer(size_t capacity, NonnullOwnPtr<KBuffer> storage);
  46. void flip();
  47. void compute_lockfree_metadata();
  48. struct InnerBuffer {
  49. u8* data { nullptr };
  50. size_t size;
  51. };
  52. InnerBuffer* m_write_buffer { nullptr };
  53. InnerBuffer* m_read_buffer { nullptr };
  54. InnerBuffer m_buffer1;
  55. InnerBuffer m_buffer2;
  56. NonnullOwnPtr<KBuffer> m_storage;
  57. Function<void()> m_unblock_callback;
  58. size_t m_capacity { 0 };
  59. size_t m_read_buffer_index { 0 };
  60. size_t m_space_for_writing { 0 };
  61. bool m_empty { true };
  62. mutable Mutex m_lock { "DoubleBuffer" };
  63. };
  64. }