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359 行
13 KiB
359 行
13 KiB
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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//
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// An Env is an interface used by the leveldb implementation to access
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// operating system functionality like the filesystem etc. Callers
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// may wish to provide a custom Env object when opening a database to
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// get fine gain control; e.g., to rate limit file system operations.
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//
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// All Env implementations are safe for concurrent access from
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// multiple threads without any external synchronization.
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#ifndef STORAGE_LEVELDB_INCLUDE_ENV_H_
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#define STORAGE_LEVELDB_INCLUDE_ENV_H_
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#include <stdarg.h>
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#include <stdint.h>
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#include <string>
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#include <vector>
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#include "leveldb/export.h"
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#include "leveldb/status.h"
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namespace leveldb {
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class FileLock;
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class Logger;
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class RandomAccessFile;
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class SequentialFile;
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class Slice;
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class WritableFile;
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class LEVELDB_EXPORT Env {
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public:
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Env() = default;
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Env(const Env&) = delete;
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Env& operator=(const Env&) = delete;
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virtual ~Env();
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// Return a default environment suitable for the current operating
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// system. Sophisticated users may wish to provide their own Env
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// implementation instead of relying on this default environment.
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//
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// The result of Default() belongs to leveldb and must never be deleted.
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static Env* Default();
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// Create an object that sequentially reads the file with the specified name.
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// On success, stores a pointer to the new file in *result and returns OK.
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// On failure stores nullptr in *result and returns non-OK. If the file does
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// not exist, returns a non-OK status. Implementations should return a
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// NotFound status when the file does not exist.
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//
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// The returned file will only be accessed by one thread at a time.
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virtual Status NewSequentialFile(const std::string& fname,
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SequentialFile** result) = 0;
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// Create an object supporting random-access reads from the file with the
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// specified name. On success, stores a pointer to the new file in
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// *result and returns OK. On failure stores nullptr in *result and
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// returns non-OK. If the file does not exist, returns a non-OK
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// status. Implementations should return a NotFound status when the file does
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// not exist.
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//
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// The returned file may be concurrently accessed by multiple threads.
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virtual Status NewRandomAccessFile(const std::string& fname,
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RandomAccessFile** result) = 0;
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// Create an object that writes to a new file with the specified
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// name. Deletes any existing file with the same name and creates a
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// new file. On success, stores a pointer to the new file in
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// *result and returns OK. On failure stores nullptr in *result and
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// returns non-OK.
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//
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// The returned file will only be accessed by one thread at a time.
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virtual Status NewWritableFile(const std::string& fname,
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WritableFile** result) = 0;
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// Create an object that either appends to an existing file, or
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// writes to a new file (if the file does not exist to begin with).
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// On success, stores a pointer to the new file in *result and
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// returns OK. On failure stores nullptr in *result and returns
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// non-OK.
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//
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// The returned file will only be accessed by one thread at a time.
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//
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// May return an IsNotSupportedError error if this Env does
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// not allow appending to an existing file. Users of Env (including
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// the leveldb implementation) must be prepared to deal with
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// an Env that does not support appending.
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virtual Status NewAppendableFile(const std::string& fname,
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WritableFile** result);
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// Returns true iff the named file exists.
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virtual bool FileExists(const std::string& fname) = 0;
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// Store in *result the names of the children of the specified directory.
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// The names are relative to "dir".
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// Original contents of *results are dropped.
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virtual Status GetChildren(const std::string& dir,
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std::vector<std::string>* result) = 0;
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// Delete the named file.
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virtual Status DeleteFile(const std::string& fname) = 0;
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// Create the specified directory.
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virtual Status CreateDir(const std::string& dirname) = 0;
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// Delete the specified directory.
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virtual Status DeleteDir(const std::string& dirname) = 0;
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// Store the size of fname in *file_size.
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virtual Status GetFileSize(const std::string& fname, uint64_t* file_size) = 0;
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// Rename file src to target.
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virtual Status RenameFile(const std::string& src,
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const std::string& target) = 0;
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// Lock the specified file. Used to prevent concurrent access to
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// the same db by multiple processes. On failure, stores nullptr in
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// *lock and returns non-OK.
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//
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// On success, stores a pointer to the object that represents the
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// acquired lock in *lock and returns OK. The caller should call
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// UnlockFile(*lock) to release the lock. If the process exits,
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// the lock will be automatically released.
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//
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// If somebody else already holds the lock, finishes immediately
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// with a failure. I.e., this call does not wait for existing locks
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// to go away.
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//
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// May create the named file if it does not already exist.
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virtual Status LockFile(const std::string& fname, FileLock** lock) = 0;
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// Release the lock acquired by a previous successful call to LockFile.
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// REQUIRES: lock was returned by a successful LockFile() call
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// REQUIRES: lock has not already been unlocked.
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virtual Status UnlockFile(FileLock* lock) = 0;
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// Arrange to run "(*function)(arg)" once in a background thread.
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//
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// "function" may run in an unspecified thread. Multiple functions
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// added to the same Env may run concurrently in different threads.
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// I.e., the caller may not assume that background work items are
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// serialized.
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virtual void Schedule(
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void (*function)(void* arg),
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void* arg) = 0;
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// Start a new thread, invoking "function(arg)" within the new thread.
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// When "function(arg)" returns, the thread will be destroyed.
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virtual void StartThread(void (*function)(void* arg), void* arg) = 0;
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// *path is set to a temporary directory that can be used for testing. It may
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// or many not have just been created. The directory may or may not differ
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// between runs of the same process, but subsequent calls will return the
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// same directory.
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virtual Status GetTestDirectory(std::string* path) = 0;
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// Create and return a log file for storing informational messages.
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virtual Status NewLogger(const std::string& fname, Logger** result) = 0;
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// Returns the number of micro-seconds since some fixed point in time. Only
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// useful for computing deltas of time.
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virtual uint64_t NowMicros() = 0;
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// Sleep/delay the thread for the prescribed number of micro-seconds.
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virtual void SleepForMicroseconds(int micros) = 0;
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};
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// A file abstraction for reading sequentially through a file
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class LEVELDB_EXPORT SequentialFile {
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public:
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SequentialFile() = default;
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SequentialFile(const SequentialFile&) = delete;
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SequentialFile& operator=(const SequentialFile&) = delete;
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virtual ~SequentialFile();
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// Read up to "n" bytes from the file. "scratch[0..n-1]" may be
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// written by this routine. Sets "*result" to the data that was
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// read (including if fewer than "n" bytes were successfully read).
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// May set "*result" to point at data in "scratch[0..n-1]", so
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// "scratch[0..n-1]" must be live when "*result" is used.
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// If an error was encountered, returns a non-OK status.
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//
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// REQUIRES: External synchronization
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virtual Status Read(size_t n, Slice* result, char* scratch) = 0;
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// Skip "n" bytes from the file. This is guaranteed to be no
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// slower that reading the same data, but may be faster.
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//
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// If end of file is reached, skipping will stop at the end of the
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// file, and Skip will return OK.
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//
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// REQUIRES: External synchronization
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virtual Status Skip(uint64_t n) = 0;
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};
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// A file abstraction for randomly reading the contents of a file.
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class LEVELDB_EXPORT RandomAccessFile {
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public:
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RandomAccessFile() = default;
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RandomAccessFile(const RandomAccessFile&) = delete;
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RandomAccessFile& operator=(const RandomAccessFile&) = delete;
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virtual ~RandomAccessFile();
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// Read up to "n" bytes from the file starting at "offset".
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// "scratch[0..n-1]" may be written by this routine. Sets "*result"
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// to the data that was read (including if fewer than "n" bytes were
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// successfully read). May set "*result" to point at data in
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// "scratch[0..n-1]", so "scratch[0..n-1]" must be live when
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// "*result" is used. If an error was encountered, returns a non-OK
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// status.
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//
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// Safe for concurrent use by multiple threads.
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virtual Status Read(uint64_t offset, size_t n, Slice* result,
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char* scratch) const = 0;
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};
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// A file abstraction for sequential writing. The implementation
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// must provide buffering since callers may append small fragments
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// at a time to the file.
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class LEVELDB_EXPORT WritableFile {
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public:
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WritableFile() = default;
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WritableFile(const WritableFile&) = delete;
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WritableFile& operator=(const WritableFile&) = delete;
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virtual ~WritableFile();
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virtual Status Append(const Slice& data) = 0;
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virtual Status Close() = 0;
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virtual Status Flush() = 0;
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virtual Status Sync() = 0;
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};
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// An interface for writing log messages.
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class LEVELDB_EXPORT Logger {
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public:
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Logger() = default;
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Logger(const Logger&) = delete;
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Logger& operator=(const Logger&) = delete;
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virtual ~Logger();
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// Write an entry to the log file with the specified format.
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virtual void Logv(const char* format, va_list ap) = 0;
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};
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// Identifies a locked file.
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class LEVELDB_EXPORT FileLock {
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public:
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FileLock() = default;
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FileLock(const FileLock&) = delete;
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FileLock& operator=(const FileLock&) = delete;
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virtual ~FileLock();
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};
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// Log the specified data to *info_log if info_log is non-null.
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void Log(Logger* info_log, const char* format, ...)
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# if defined(__GNUC__) || defined(__clang__)
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__attribute__((__format__ (__printf__, 2, 3)))
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# endif
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;
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// A utility routine: write "data" to the named file.
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LEVELDB_EXPORT Status WriteStringToFile(Env* env, const Slice& data,
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const std::string& fname);
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// A utility routine: read contents of named file into *data
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LEVELDB_EXPORT Status ReadFileToString(Env* env, const std::string& fname,
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std::string* data);
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// An implementation of Env that forwards all calls to another Env.
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// May be useful to clients who wish to override just part of the
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// functionality of another Env.
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class LEVELDB_EXPORT EnvWrapper : public Env {
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public:
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// Initialize an EnvWrapper that delegates all calls to *t.
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explicit EnvWrapper(Env* t) : target_(t) { }
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virtual ~EnvWrapper();
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// Return the target to which this Env forwards all calls.
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Env* target() const { return target_; }
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// The following text is boilerplate that forwards all methods to target().
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Status NewSequentialFile(const std::string& f, SequentialFile** r) override {
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return target_->NewSequentialFile(f, r);
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}
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Status NewRandomAccessFile(const std::string& f,
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RandomAccessFile** r) override {
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return target_->NewRandomAccessFile(f, r);
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}
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Status NewWritableFile(const std::string& f, WritableFile** r) override {
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return target_->NewWritableFile(f, r);
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}
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Status NewAppendableFile(const std::string& f, WritableFile** r) override {
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return target_->NewAppendableFile(f, r);
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}
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bool FileExists(const std::string& f) override {
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return target_->FileExists(f);
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}
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Status GetChildren(const std::string& dir,
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std::vector<std::string>* r) override {
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return target_->GetChildren(dir, r);
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}
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Status DeleteFile(const std::string& f) override {
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return target_->DeleteFile(f);
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}
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Status CreateDir(const std::string& d) override {
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return target_->CreateDir(d);
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}
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Status DeleteDir(const std::string& d) override {
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return target_->DeleteDir(d);
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}
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Status GetFileSize(const std::string& f, uint64_t* s) override {
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return target_->GetFileSize(f, s);
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}
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Status RenameFile(const std::string& s, const std::string& t) override {
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return target_->RenameFile(s, t);
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}
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Status LockFile(const std::string& f, FileLock** l) override {
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return target_->LockFile(f, l);
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}
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Status UnlockFile(FileLock* l) override { return target_->UnlockFile(l); }
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void Schedule(void (*f)(void*), void* a) override {
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return target_->Schedule(f, a);
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}
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void StartThread(void (*f)(void*), void* a) override {
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return target_->StartThread(f, a);
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}
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Status GetTestDirectory(std::string* path) override {
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return target_->GetTestDirectory(path);
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}
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Status NewLogger(const std::string& fname, Logger** result) override {
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return target_->NewLogger(fname, result);
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}
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uint64_t NowMicros() override {
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return target_->NowMicros();
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}
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void SleepForMicroseconds(int micros) override {
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target_->SleepForMicroseconds(micros);
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}
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private:
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Env* target_;
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};
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} // namespace leveldb
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#endif // STORAGE_LEVELDB_INCLUDE_ENV_H_
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