mapped_file.h

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//
// Copyright RIME Developers
// Distributed under the BSD License
//
// 2011-06-27 GONG Chen <chen.sst@gmail.com>
//
#ifndef RIME_MAPPED_FILE_H_
#define RIME_MAPPED_FILE_H_
 
#include <stdint.h>
#include <algorithm>
#include <cstring>
#include <rime_api.h>
#include <rime/common.h>
 
namespace rime {
 
// basic data structure
 
// Limitation: cannot point to itself (zero is used to represent NULL pointer)
template <class T = char, class Offset = int32_t>
class OffsetPtr {
 public:
  OffsetPtr() = default;
  OffsetPtr(Offset offset) : offset_(offset) {}
  OffsetPtr(const T* ptr) : OffsetPtr(to_offset(ptr)) {}
  OffsetPtr(const OffsetPtr<T>& ptr) : OffsetPtr(ptr.get()) {}
  OffsetPtr<T>& operator=(const OffsetPtr<T>& ptr) {
    offset_ = to_offset(ptr.get());
    return *this;
  }
  OffsetPtr<T>& operator=(const T* ptr) {
    offset_ = to_offset(ptr);
    return *this;
  }
  operator bool() const { return !!offset_; }
  T* operator->() const { return get(); }
  T& operator*() const { return *get(); }
  T& operator[](size_t index) const { return *(get() + index); }
  T* get() const {
    if (!offset_)
      return NULL;
    return reinterpret_cast<T*>((char*)&offset_ + offset_);
  }
 
 private:
  Offset to_offset(const T* ptr) const {
    return ptr ? (char*)ptr - (char*)(&offset_) : 0;
  }
  Offset offset_ = 0;
};
 
struct String {
  OffsetPtr<char> data;
  const char* c_str() const { return data.get(); }
  size_t length() const { return c_str() ? strlen(c_str()) : 0; }
  bool empty() const { return !data || !data[0]; }
};
 
template <class T, class Size = uint32_t>
struct Array {
  Size size;
  T at[1];
  T* begin() { return &at[0]; }
  T* end() { return &at[0] + size; }
  const T* begin() const { return &at[0]; }
  const T* end() const { return &at[0] + size; }
};
 
template <class T, class Size = uint32_t>
struct List {
  Size size;
  OffsetPtr<T> at;
  T* begin() { return &at[0]; }
  T* end() { return &at[0] + size; }
  const T* begin() const { return &at[0]; }
  const T* end() const { return &at[0] + size; }
};
 
// MappedFile class definition
 
class MappedFileImpl;
 
class RIME_DLL MappedFile {
 protected:
  explicit MappedFile(const path& file_path);
  virtual ~MappedFile();
 
  bool Create(size_t capacity);
  bool OpenReadOnly();
  bool OpenReadWrite();
  bool Flush();
  bool Resize(size_t capacity);
  bool ShrinkToFit();
 
  template <class T>
  T* Allocate(size_t count = 1);
 
  template <class T>
  Array<T>* CreateArray(size_t array_size);
 
  String* CreateString(const string& str);
  bool CopyString(const string& src, String* dest);
 
  size_t capacity() const;
  char* address() const;
 
 public:
  // noncpyable
  MappedFile(const MappedFile&) = delete;
  MappedFile& operator=(const MappedFile&) = delete;
 
  bool Exists() const;
  bool IsOpen() const;
  void Close();
  bool Remove();
 
  template <class T>
  T* Find(size_t offset);
 
  const path& file_path() const { return file_path_; }
  size_t file_size() const { return size_; }
 
 private:
  path file_path_;
  size_t size_ = 0;
  the<MappedFileImpl> file_;
};
 
// member function definitions
 
#define RIME_ALIGNED(size, T) ((size + alignof(T) - 1) & ~(alignof(T) - 1))
 
template <class T>
T* MappedFile::Allocate(size_t count) {
  if (!IsOpen())
    return NULL;
 
  size_t used_space = RIME_ALIGNED(size_, T);
  size_t required_space = sizeof(T) * count;
  size_t file_size = capacity();
  if (used_space + required_space > file_size) {
    // not enough space; grow the file
    size_t new_size = (std::max)(used_space + required_space, file_size * 2);
    if (!Resize(new_size) || !OpenReadWrite())
      return NULL;
  }
  T* ptr = reinterpret_cast<T*>(address() + used_space);
  std::memset((void*)ptr, 0, required_space);
  size_ = used_space + required_space;
  return ptr;
}
 
template <class T>
T* MappedFile::Find(size_t offset) {
  if (!IsOpen() || offset > size_)
    return NULL;
  return reinterpret_cast<T*>(address() + offset);
}
 
template <class T>
Array<T>* MappedFile::CreateArray(size_t array_size) {
  size_t num_bytes = sizeof(Array<T>) + sizeof(T) * (array_size - 1);
  Array<T>* ret = reinterpret_cast<Array<T>*>(Allocate<char>(num_bytes));
  if (!ret)
    return NULL;
  ret->size = array_size;
  return ret;
}
 
}  // namespace rime
 
#endif  // RIME_MAPPED_FILE_H_