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  1. // Copyright (c) 2011 The LevelDB Authors. All rights reserved.
  2. // Use of this source code is governed by a BSD-style license that can be
  3. // found in the LICENSE file. See the AUTHORS file for names of contributors.
  4. //
  5. // This file contains the specification, but not the implementations,
  6. // of the types/operations/etc. that should be defined by a platform
  7. // specific port_<platform>.h file. Use this file as a reference for
  8. // how to port this package to a new platform.
  9. #ifndef STORAGE_LEVELDB_PORT_PORT_EXAMPLE_H_
  10. #define STORAGE_LEVELDB_PORT_PORT_EXAMPLE_H_
  11. namespace leveldb {
  12. namespace port {
  13. // TODO(jorlow): Many of these belong more in the environment class rather than
  14. // here. We should try moving them and see if it affects perf.
  15. // The following boolean constant must be true on a little-endian machine
  16. // and false otherwise.
  17. static const bool kLittleEndian = true /* or some other expression */;
  18. // ------------------ Threading -------------------
  19. // A Mutex represents an exclusive lock.
  20. class Mutex {
  21. public:
  22. Mutex();
  23. ~Mutex();
  24. // Lock the mutex. Waits until other lockers have exited.
  25. // Will deadlock if the mutex is already locked by this thread.
  26. void Lock();
  27. // Unlock the mutex.
  28. // REQUIRES: This mutex was locked by this thread.
  29. void Unlock();
  30. // Optionally crash if this thread does not hold this mutex.
  31. // The implementation must be fast, especially if NDEBUG is
  32. // defined. The implementation is allowed to skip all checks.
  33. void AssertHeld();
  34. };
  35. class CondVar {
  36. public:
  37. explicit CondVar(Mutex* mu);
  38. ~CondVar();
  39. // Atomically release *mu and block on this condition variable until
  40. // either a call to SignalAll(), or a call to Signal() that picks
  41. // this thread to wakeup.
  42. // REQUIRES: this thread holds *mu
  43. void Wait();
  44. // If there are some threads waiting, wake up at least one of them.
  45. void Signal();
  46. // Wake up all waiting threads.
  47. void SignallAll();
  48. };
  49. // Thread-safe initialization.
  50. // Used as follows:
  51. // static port::OnceType init_control = LEVELDB_ONCE_INIT;
  52. // static void Initializer() { ... do something ...; }
  53. // ...
  54. // port::InitOnce(&init_control, &Initializer);
  55. typedef intptr_t OnceType;
  56. #define LEVELDB_ONCE_INIT 0
  57. extern void InitOnce(port::OnceType*, void (*initializer)());
  58. // A type that holds a pointer that can be read or written atomically
  59. // (i.e., without word-tearing.)
  60. class AtomicPointer {
  61. private:
  62. intptr_t rep_;
  63. public:
  64. // Initialize to arbitrary value
  65. AtomicPointer();
  66. // Initialize to hold v
  67. explicit AtomicPointer(void* v) : rep_(v) { }
  68. // Read and return the stored pointer with the guarantee that no
  69. // later memory access (read or write) by this thread can be
  70. // reordered ahead of this read.
  71. void* Acquire_Load() const;
  72. // Set v as the stored pointer with the guarantee that no earlier
  73. // memory access (read or write) by this thread can be reordered
  74. // after this store.
  75. void Release_Store(void* v);
  76. // Read the stored pointer with no ordering guarantees.
  77. void* NoBarrier_Load() const;
  78. // Set va as the stored pointer with no ordering guarantees.
  79. void NoBarrier_Store(void* v);
  80. };
  81. // ------------------ Compression -------------------
  82. // Store the snappy compression of "input[0,input_length-1]" in *output.
  83. // Returns false if snappy is not supported by this port.
  84. extern bool Snappy_Compress(const char* input, size_t input_length,
  85. std::string* output);
  86. // If input[0,input_length-1] looks like a valid snappy compressed
  87. // buffer, store the size of the uncompressed data in *result and
  88. // return true. Else return false.
  89. extern bool Snappy_GetUncompressedLength(const char* input, size_t length,
  90. size_t* result);
  91. // Attempt to snappy uncompress input[0,input_length-1] into *output.
  92. // Returns true if successful, false if the input is invalid lightweight
  93. // compressed data.
  94. //
  95. // REQUIRES: at least the first "n" bytes of output[] must be writable
  96. // where "n" is the result of a successful call to
  97. // Snappy_GetUncompressedLength.
  98. extern bool Snappy_Uncompress(const char* input_data, size_t input_length,
  99. char* output);
  100. // ------------------ Miscellaneous -------------------
  101. // If heap profiling is not supported, returns false.
  102. // Else repeatedly calls (*func)(arg, data, n) and then returns true.
  103. // The concatenation of all "data[0,n-1]" fragments is the heap profile.
  104. extern bool GetHeapProfile(void (*func)(void*, const char*, int), void* arg);
  105. } // namespace port
  106. } // namespace leveldb
  107. #endif // STORAGE_LEVELDB_PORT_PORT_EXAMPLE_H_