10215300402
/
LevelDB-course-Lab
rozštěpen z 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.

								//

								// An Env is an interface used by the leveldb implementation to access

								// operating system functionality like the filesystem etc.  Callers

								// may wish to provide a custom Env object when opening a database to

								// get fine gain control; e.g., to rate limit file system operations.


								#ifndef STORAGE_LEVELDB_INCLUDE_ENV_H_

								#define STORAGE_LEVELDB_INCLUDE_ENV_H_


								#include <cstdarg>

								#include <string>

								#include <vector>

								#include <stdint.h>

								#include "leveldb/status.h"


								namespace leveldb {


								class FileLock;

								class RandomAccessFile;

								class SequentialFile;

								class Slice;

								class WritableFile;


								class Env {

								 public:

								  Env() { }

								  virtual ~Env();


								  // Return a default environment suitable for the current operating

								  // system.  Sophisticated users may wish to provide their own Env

								  // implementation instead of relying on this default environment.

								  //

								  // The result of Default() belongs to leveldb and must never be deleted.

								  static Env* Default();


								  // Create a brand new sequentially-readable file with the specified name.

								  // On success, stores a pointer to the new file in *result and returns OK.

								  // On failure stores NULL in *result and returns non-OK.  If the file does

								  // not exist, returns a non-OK status.

								  //

								  // The returned file will only be accessed by one thread at a time.

								  virtual Status NewSequentialFile(const std::string& fname,

								                                   SequentialFile** result) = 0;


								  // Create a brand new random access read-only file with the

								  // specified name.  On success, stores a pointer to the new file in

								  // *result and returns OK.  On failure stores NULL in *result and

								  // returns non-OK.  If the file does not exist, returns a non-OK

								  // status.

								  //

								  // The returned file may be concurrently accessed by multiple threads.

								  virtual Status NewRandomAccessFile(const std::string& fname,

								                                     RandomAccessFile** result) = 0;


								  // Create an object that writes to a new file with the specified

								  // name.  Deletes any existing file with the same name and creates a

								  // new file.  On success, stores a pointer to the new file in

								  // *result and returns OK.  On failure stores NULL in *result and

								  // returns non-OK.

								  //

								  // The returned file will only be accessed by one thread at a time.

								  virtual Status NewWritableFile(const std::string& fname,

								                                 WritableFile** result) = 0;


								  // Returns true iff the named file exists.

								  virtual bool FileExists(const std::string& fname) = 0;


								  // Store in *result the names of the children of the specified directory.

								  // The names are relative to "dir".

								  // Original contents of *results are dropped.

								  virtual Status GetChildren(const std::string& dir,

								                             std::vector<std::string>* result) = 0;


								  // Delete the named file.

								  virtual Status DeleteFile(const std::string& fname) = 0;


								  // Create the specified directory.

								  virtual Status CreateDir(const std::string& dirname) = 0;


								  // Delete the specified directory.

								  virtual Status DeleteDir(const std::string& dirname) = 0;


								  // Store the size of fname in *file_size.

								  virtual Status GetFileSize(const std::string& fname, uint64_t* file_size) = 0;


								  // Rename file src to target.

								  virtual Status RenameFile(const std::string& src,

								                            const std::string& target) = 0;


								  // Lock the specified file.  Used to prevent concurrent access to

								  // the same db by multiple processes.  On failure, stores NULL in

								  // *lock and returns non-OK.

								  //

								  // On success, stores a pointer to the object that represents the

								  // acquired lock in *lock and returns OK.  The caller should call

								  // UnlockFile(*lock) to release the lock.  If the process exits,

								  // the lock will be automatically released.

								  //

								  // If somebody else already holds the lock, finishes immediately

								  // with a failure.  I.e., this call does not wait for existing locks

								  // to go away.

								  //

								  // May create the named file if it does not already exist.

								  virtual Status LockFile(const std::string& fname, FileLock** lock) = 0;


								  // Release the lock acquired by a previous successful call to LockFile.

								  // REQUIRES: lock was returned by a successful LockFile() call

								  // REQUIRES: lock has not already been unlocked.

								  virtual Status UnlockFile(FileLock* lock) = 0;


								  // Arrange to run "(*function)(arg)" once in a background thread.

								  //

								  // "function" may run in an unspecified thread.  Multiple functions

								  // added to the same Env may run concurrently in different threads.

								  // I.e., the caller may not assume that background work items are

								  // serialized.

								  virtual void Schedule(

								      void (*function)(void* arg),

								      void* arg) = 0;


								  // Start a new thread, invoking "function(arg)" within the new thread.

								  // When "function(arg)" returns, the thread will be destroyed.

								  virtual void StartThread(void (*function)(void* arg), void* arg) = 0;


								  // *path is set to a temporary directory that can be used for testing. It may

								  // or many not have just been created. The directory may or may not differ

								  // between runs of the same process, but subsequent calls will return the

								  // same directory.

								  virtual Status GetTestDirectory(std::string* path) = 0;


								  // Write an entry to the log file with the specified format.

								  virtual void Logv(WritableFile* log, const char* format, va_list ap) = 0;


								  // Returns the number of micro-seconds since some fixed point in time. Only

								  // useful for computing deltas of time.

								  virtual uint64_t NowMicros() = 0;


								  // Sleep/delay the thread for the perscribed number of micro-seconds.

								  virtual void SleepForMicroseconds(int micros) = 0;


								 private:

								  // No copying allowed

								  Env(const Env&);

								  void operator=(const Env&);

								};


								// A file abstraction for reading sequentially through a file

								class SequentialFile {

								 public:

								  SequentialFile() { }

								  virtual ~SequentialFile();


								  // Read up to "n" bytes from the file.  "scratch[0..n-1]" may be

								  // written by this routine.  Sets "*result" to the data that was

								  // read (including if fewer than "n" bytes were successfully read).

								  // If an error was encountered, returns a non-OK status.

								  //

								  // REQUIRES: External synchronization

								  virtual Status Read(size_t n, Slice* result, char* scratch) = 0;

								};


								// A file abstraction for randomly reading the contents of a file.

								class RandomAccessFile {

								 public:

								  RandomAccessFile() { }

								  virtual ~RandomAccessFile();


								  // Read up to "n" bytes from the file starting at "offset".

								  // "scratch[0..n-1]" may be written by this routine.  Sets "*result"

								  // to the data that was read (including if fewer than "n" bytes were

								  // successfully read).  If an error was encountered, returns a

								  // non-OK status.

								  //

								  // Safe for concurrent use by multiple threads.

								  virtual Status Read(uint64_t offset, size_t n, Slice* result,

								                      char* scratch) const = 0;

								};


								// A file abstraction for sequential writing.  The implementation

								// must provide buffering since callers may append small fragments

								// at a time to the file.

								class WritableFile {

								 public:

								  WritableFile() { }

								  virtual ~WritableFile();


								  virtual Status Append(const Slice& data) = 0;

								  virtual Status Close() = 0;

								  virtual Status Flush() = 0;

								  virtual Status Sync() = 0;


								 private:

								  // No copying allowed

								  WritableFile(const WritableFile&);

								  void operator=(const WritableFile&);

								};


								// Identifies a locked file.

								class FileLock {

								 public:

								  FileLock() { }

								  virtual ~FileLock();

								 private:

								  // No copying allowed

								  FileLock(const FileLock&);

								  void operator=(const FileLock&);

								};


								// Log the specified data to *info_log if info_log is non-NULL.

								extern void Log(Env* env, WritableFile* info_log, const char* format, ...)

								#   if defined(__GNUC__) || defined(__clang__)

								    __attribute__((__format__ (__printf__, 3, 4)))

								#   endif

								    ;


								// A utility routine: write "data" to the named file.

								extern Status WriteStringToFile(Env* env, const Slice& data,

								                                const std::string& fname);


								// A utility routine: read contents of named file into *data

								extern Status ReadFileToString(Env* env, const std::string& fname,

								                               std::string* data);


								// An implementation of Env that forwards all calls to another Env.

								// May be useful to clients who wish to override just part of the

								// functionality of another Env.

								class EnvWrapper : public Env {

								 public:

								  // Initialize an EnvWrapper that delegates all calls to *target

								  explicit EnvWrapper(Env* target) : target_(target) { }

								  virtual ~EnvWrapper();


								  // Return the target to which this Env forwards all calls

								  Env* target() const { return target_; }


								  // The following text is boilerplate that forwards all methods to target()

								  Status NewSequentialFile(const std::string& f, SequentialFile** r) {

								    return target_->NewSequentialFile(f, r);

								  }

								  Status NewRandomAccessFile(const std::string& f, RandomAccessFile** r) {

								    return target_->NewRandomAccessFile(f, r);

								  }

								  Status NewWritableFile(const std::string& f, WritableFile** r) {

								    return target_->NewWritableFile(f, r);

								  }

								  bool FileExists(const std::string& f) { return target_->FileExists(f); }

								  Status GetChildren(const std::string& dir, std::vector<std::string>* r) {

								    return target_->GetChildren(dir, r);

								  }

								  Status DeleteFile(const std::string& f) { return target_->DeleteFile(f); }

								  Status CreateDir(const std::string& d) { return target_->CreateDir(d); }

								  Status DeleteDir(const std::string& d) { return target_->DeleteDir(d); }

								  Status GetFileSize(const std::string& f, uint64_t* s) {

								    return target_->GetFileSize(f, s);

								  }

								  Status RenameFile(const std::string& s, const std::string& t) {

								    return target_->RenameFile(s, t);

								  }

								  Status LockFile(const std::string& f, FileLock** l) {

								    return target_->LockFile(f, l);

								  }

								  Status UnlockFile(FileLock* l) { return target_->UnlockFile(l); }

								  void Schedule(void (*f)(void*), void* a) {

								    return target_->Schedule(f, a);

								  }

								  void StartThread(void (*f)(void*), void* a) {

								    return target_->StartThread(f, a);

								  }

								  virtual Status GetTestDirectory(std::string* path) {

								    return target_->GetTestDirectory(path);

								  }

								  virtual void Logv(WritableFile* log, const char* format, va_list ap) {

								    return target_->Logv(log, format, ap);

								  }

								  uint64_t NowMicros() {

								    return target_->NowMicros();

								  }

								  void SleepForMicroseconds(int micros) {

								    target_->SleepForMicroseconds(micros);

								  }

								 private:

								  Env* target_;

								};


								}


								#endif  // STORAGE_LEVELDB_INCLUDE_ENV_H_