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rocksdb/include/leveldb/env.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.
//
// 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.
//
// All Env implementations are safe for concurrent access from
// multiple threads without any external synchronization.
#ifndef STORAGE_LEVELDB_INCLUDE_ENV_H_
#define STORAGE_LEVELDB_INCLUDE_ENV_H_
#include <cstdarg>
#include <string>
#include <memory>
#include <vector>
#include <stdint.h>
#include "leveldb/status.h"
namespace leveldb {
class FileLock;
class Logger;
class RandomAccessFile;
class SequentialFile;
class Slice;
class WritableFile;
using std::unique_ptr;
using std::shared_ptr;
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 nullptr 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,
unique_ptr<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 nullptr 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,
unique_ptr<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 nullptr 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,
unique_ptr<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. Returns error if directory exists.
virtual Status CreateDir(const std::string& dirname) = 0;
// Creates directory if missing. Return Ok if it exists, or successful in
// Creating.
virtual Status CreateDirIfMissing(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;
// Store the last modification time of fname in *file_mtime.
virtual Status GetFileModificationTime(const std::string& fname,
uint64_t* file_mtime) = 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 nullptr 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;
// Create and return a log file for storing informational messages.
virtual Status NewLogger(const std::string& fname,
shared_ptr<Logger>* result) = 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;
// Get the current host name.
virtual Status GetHostName(char* name, uint64_t len) = 0;
// Get the number of seconds since the Epoch, 1970-01-01 00:00:00 (UTC).
virtual Status GetCurrentTime(int64_t* unix_time) = 0;
// Get full directory name for this db.
virtual Status GetAbsolutePath(const std::string& db_path,
std::string* output_path) = 0;
// The number of background worker threads for this environment.
// default: 1
virtual void SetBackgroundThreads(int number) = 0;
// Converts seconds-since-Jan-01-1970 to a printable string
virtual std::string TimeToString(uint64_t time) = 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).
// May set "*result" to point at data in "scratch[0..n-1]", so
// "scratch[0..n-1]" must be live when "*result" is used.
// If an error was encountered, returns a non-OK status.
//
// REQUIRES: External synchronization
virtual Status Read(size_t n, Slice* result, char* scratch) = 0;
// Skip "n" bytes from the file. This is guaranteed to be no
// slower that reading the same data, but may be faster.
//
// If end of file is reached, skipping will stop at the end of the
// file, and Skip will return OK.
//
// REQUIRES: External synchronization
virtual Status Skip(uint64_t n) = 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). May set "*result" to point at data in
// "scratch[0..n-1]", so "scratch[0..n-1]" must be live when
// "*result" is used. 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;
// Tries to get an unique ID for this file that will be the same each time
// the file is opened (and will stay the same while the file is open).
// Furthermore, it tries to make this ID at most "max_size" bytes. If such an
// ID can be created this function returns the length of the ID and places it
// in "id"; otherwise, this function returns 0, in which case "id" may more
// may not have been modified.
//
// This function guarantees, for IDs from a given environment, two unique ids
// cannot be made equal to eachother by adding arbitrary bytes to one of
// them. That is, no unique ID is the prefix of another.
//
// This function guarantees that the returned ID will not be interpretable as
// a single varint.
//
// Note: these IDs are only valid for the duration of the process.
virtual size_t GetUniqueId(char* id, size_t max_size) const {
return 0; // Default implementation to prevent issues with backwards
// compatibility.
};
};
// 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() : last_preallocated_block_(0), preallocation_block_size_ (0) {
}
virtual ~WritableFile();
virtual Status Append(const Slice& data) = 0;
virtual Status Close() = 0;
virtual Status Flush() = 0;
virtual Status Sync() = 0; // sync data
/*
* Sync data and/or metadata as well.
* By default, sync only metadata.
* Override this method for environments where we need to sync
* metadata as well.
*/
virtual Status Fsync() {
return Sync();
}
/*
* Get the size of valid data in the file.
*/
virtual uint64_t GetFileSize() {
return 0;
}
/*
* Get and set the default pre-allocation block size for writes to
* this file. If non-zero, then Allocate will be used to extend the
* underlying storage of a file (generally via fallocate) if the Env
* instance supports it.
*/
void SetPreallocationBlockSize(size_t size) {
preallocation_block_size_ = size;
}
virtual void GetPreallocationStatus(size_t* block_size,
size_t* last_allocated_block) {
*last_allocated_block = last_preallocated_block_;
*block_size = preallocation_block_size_;
}
protected:
// PrepareWrite performs any necessary preparation for a write
// before the write actually occurs. This allows for pre-allocation
// of space on devices where it can result in less file
// fragmentation and/or less waste from over-zealous filesystem
// pre-allocation.
void PrepareWrite(size_t offset, size_t len) {
if (preallocation_block_size_ == 0) {
return;
}
// If this write would cross one or more preallocation blocks,
// determine what the last preallocation block necesessary to
// cover this write would be and Allocate to that point.
const auto block_size = preallocation_block_size_;
size_t new_last_preallocated_block =
(offset + len + block_size - 1) / block_size;
if (new_last_preallocated_block > last_preallocated_block_) {
size_t num_spanned_blocks =
new_last_preallocated_block - last_preallocated_block_;
Allocate(block_size * last_preallocated_block_,
block_size * num_spanned_blocks);
last_preallocated_block_ = new_last_preallocated_block;
}
}
/*
* Pre-allocate space for a file.
*/
virtual Status Allocate(off_t offset, off_t len) {
return Status::OK();
}
private:
size_t last_preallocated_block_;
size_t preallocation_block_size_;
// No copying allowed
WritableFile(const WritableFile&);
void operator=(const WritableFile&);
};
// An interface for writing log messages.
class Logger {
public:
enum { DO_NOT_SUPPORT_GET_LOG_FILE_SIZE = -1 };
Logger() { }
virtual ~Logger();
// Write an entry to the log file with the specified format.
virtual void Logv(const char* format, va_list ap) = 0;
virtual size_t GetLogFileSize() const {
return DO_NOT_SUPPORT_GET_LOG_FILE_SIZE;
}
private:
// No copying allowed
Logger(const Logger&);
void operator=(const Logger&);
};
// 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-nullptr.
extern void Log(const shared_ptr<Logger>& info_log, const char* format, ...)
# if defined(__GNUC__) || defined(__clang__)
__attribute__((__format__ (__printf__, 2, 3)))
# endif
;
extern void Log(Logger* info_log, const char* format, ...)
# if defined(__GNUC__) || defined(__clang__)
__attribute__((__format__ (__printf__, 2, 3)))
# 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 *t
explicit EnvWrapper(Env* t) : target_(t) { }
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,
unique_ptr<SequentialFile>* r) {
return target_->NewSequentialFile(f, r);
}
Status NewRandomAccessFile(const std::string& f,
unique_ptr<RandomAccessFile>* r) {
return target_->NewRandomAccessFile(f, r);
}
Status NewWritableFile(const std::string& f, unique_ptr<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 CreateDirIfMissing(const std::string& d) {
return target_->CreateDirIfMissing(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 GetFileModificationTime(const std::string& fname,
uint64_t* file_mtime) {
return target_->GetFileModificationTime(fname, file_mtime);
}
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 Status NewLogger(const std::string& fname,
shared_ptr<Logger>* result) {
return target_->NewLogger(fname, result);
}
uint64_t NowMicros() {
return target_->NowMicros();
}
void SleepForMicroseconds(int micros) {
target_->SleepForMicroseconds(micros);
}
Status GetHostName(char* name, uint64_t len) {
return target_->GetHostName(name, len);
}
Status GetCurrentTime(int64_t* unix_time) {
return target_->GetCurrentTime(unix_time);
}
Status GetAbsolutePath(const std::string& db_path,
std::string* output_path) {
return target_->GetAbsolutePath(db_path, output_path);
}
void SetBackgroundThreads(int num) {
return target_->SetBackgroundThreads(num);
}
std::string TimeToString(uint64_t time) {
return target_->TimeToString(time);
}
private:
Env* target_;
};
} // namespace leveldb
#endif // STORAGE_LEVELDB_INCLUDE_ENV_H_