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форк від building_data_management_systems.Xuanzhou.2024Fall.DaSE/leveldb_base


								// Copyright (c) 2011 The LevelDB Authors. All rights reserved.

								// Use of this source code is governed by a BSD-style license that can be

								// found in the LICENSE file. See the AUTHORS file for names of contributors.

								//

								// This file contains the specification, but not the implementations,

								// of the types/operations/etc. that should be defined by a platform

								// specific port_<platform>.h file.  Use this file as a reference for

								// how to port this package to a new platform.


								#ifndef STORAGE_LEVELDB_PORT_PORT_EXAMPLE_H_

								#define STORAGE_LEVELDB_PORT_PORT_EXAMPLE_H_


								namespace leveldb {

								namespace port {


								// TODO(jorlow): Many of these belong more in the environment class rather than

								//               here. We should try moving them and see if it affects perf.


								// The following boolean constant must be true on a little-endian machine

								// and false otherwise.

								static const bool kLittleEndian = true /* or some other expression */;


								// ------------------ Threading -------------------


								// A Mutex represents an exclusive lock.

								class Mutex {

								 public:

								  Mutex();

								  ~Mutex();


								  // Lock the mutex.  Waits until other lockers have exited.

								  // Will deadlock if the mutex is already locked by this thread.

								  void Lock();


								  // Unlock the mutex.

								  // REQUIRES: This mutex was locked by this thread.

								  void Unlock();


								  // Optionally crash if this thread does not hold this mutex.

								  // The implementation must be fast, especially if NDEBUG is

								  // defined.  The implementation is allowed to skip all checks.

								  void AssertHeld();

								};


								class CondVar {

								 public:

								  explicit CondVar(Mutex* mu);

								  ~CondVar();


								  // Atomically release *mu and block on this condition variable until

								  // either a call to SignalAll(), or a call to Signal() that picks

								  // this thread to wakeup.

								  // REQUIRES: this thread holds *mu

								  void Wait();


								  // If there are some threads waiting, wake up at least one of them.

								  void Signal();


								  // Wake up all waiting threads.

								  void SignallAll();

								};


								// Thread-safe initialization.

								// Used as follows:

								//      static port::OnceType init_control = LEVELDB_ONCE_INIT;

								//      static void Initializer() { ... do something ...; }

								//      ...

								//      port::InitOnce(&init_control, &Initializer);

								typedef intptr_t OnceType;

								#define LEVELDB_ONCE_INIT 0

								extern void InitOnce(port::OnceType*, void (*initializer)());


								// A type that holds a pointer that can be read or written atomically

								// (i.e., without word-tearing.)

								class AtomicPointer {

								 private:

								  intptr_t rep_;

								 public:

								  // Initialize to arbitrary value

								  AtomicPointer();


								  // Initialize to hold v

								  explicit AtomicPointer(void* v) : rep_(v) { }


								  // Read and return the stored pointer with the guarantee that no

								  // later memory access (read or write) by this thread can be

								  // reordered ahead of this read.

								  void* Acquire_Load() const;


								  // Set v as the stored pointer with the guarantee that no earlier

								  // memory access (read or write) by this thread can be reordered

								  // after this store.

								  void Release_Store(void* v);


								  // Read the stored pointer with no ordering guarantees.

								  void* NoBarrier_Load() const;


								  // Set va as the stored pointer with no ordering guarantees.

								  void NoBarrier_Store(void* v);

								};


								// ------------------ Compression -------------------


								// Store the snappy compression of "input[0,input_length-1]" in *output.

								// Returns false if snappy is not supported by this port.

								extern bool Snappy_Compress(const char* input, size_t input_length,

								                            std::string* output);


								// If input[0,input_length-1] looks like a valid snappy compressed

								// buffer, store the size of the uncompressed data in *result and

								// return true.  Else return false.

								extern bool Snappy_GetUncompressedLength(const char* input, size_t length,

								                                         size_t* result);


								// Attempt to snappy uncompress input[0,input_length-1] into *output.

								// Returns true if successful, false if the input is invalid lightweight

								// compressed data.

								//

								// REQUIRES: at least the first "n" bytes of output[] must be writable

								// where "n" is the result of a successful call to

								// Snappy_GetUncompressedLength.

								extern bool Snappy_Uncompress(const char* input_data, size_t input_length,

								                              char* output);


								// ------------------ Miscellaneous -------------------


								// If heap profiling is not supported, returns false.

								// Else repeatedly calls (*func)(arg, data, n) and then returns true.

								// The concatenation of all "data[0,n-1]" fragments is the heap profile.

								extern bool GetHeapProfile(void (*func)(void*, const char*, int), void* arg);


								}  // namespace port

								}  // namespace leveldb


								#endif  // STORAGE_LEVELDB_PORT_PORT_EXAMPLE_H_