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git-svn-id: https://leveldb.googlecode.com/svn/trunk@22 62dab493-f737-651d-591e-8d6aee1b9529

port/port_example.h

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-// 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();
-};
-
-// 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);
-};
-
-// ------------------ Checksumming -------------------
-
-// Store a 160-bit hash of "data[0..len-1]" in "hash_array[0]..hash_array[19]"
-extern void SHA1_Hash(const char* data, size_t len, char* hash_array);
-
-// ------------------ 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);
-
-// Attempt to snappy uncompress input[0,input_length-1] into *output.
-// Returns true if successful, false if the input is invalid lightweight
-// compressed data.
-extern bool Snappy_Uncompress(const char* input_data, size_t input_length,
-                              std::string* 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);
-
-}
-}
-
-#endif  // STORAGE_LEVELDB_PORT_PORT_EXAMPLE_H_