--- /dev/null
+// 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 <vector>
+#include <stdint.h>
+#include "leveldb/status.h"
+
+namespace leveldb {
+
+class FileLock;
+class Logger;
+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;
+
+ // Create and return a log file for storing informational messages.
+ virtual Status NewLogger(const std::string& fname, 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;
+
+ 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;
+
+ private:
+ // No copying allowed
+ SequentialFile(const SequentialFile&);
+ void operator=(const SequentialFile&);
+};
+
+// 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;
+
+ private:
+ // No copying allowed
+ RandomAccessFile(const RandomAccessFile&);
+ void operator=(const RandomAccessFile&);
+};
+
+// 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&);
+};
+
+// An interface for writing log messages.
+class Logger {
+ public:
+ Logger() { }
+ virtual ~Logger();
+
+ // Write an entry to the log file with the specified format.
+ virtual void Logv(const char* format, va_list ap) = 0;
+
+ 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-NULL.
+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, 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 Status NewLogger(const std::string& fname, Logger** result) {
+ return target_->NewLogger(fname, result);
+ }
+ uint64_t NowMicros() {
+ return target_->NowMicros();
+ }
+ void SleepForMicroseconds(int micros) {
+ target_->SleepForMicroseconds(micros);
+ }
+ private:
+ Env* target_;
+};
+
+} // namespace leveldb
+
+#endif // STORAGE_LEVELDB_INCLUDE_ENV_H_
git://git.novaco.in / novacoin.git / blobdiff