refactored

storage/include/storage/disk_manager.h

@@ -0,0 +1,45 @@
+#ifndef DISK_MANAGER_H
+#define DISK_MANAGER_H
+#include <cstdio>
+#include <string>
+#include "storage/config.h"
+class DiskManager {
+  /**
+   * The Data Structure on Disk:
+   * [Internal Page] [Page 1] [Page 2] .....
+   * In Internal Page, the first meta_data_size bytes are used to store
+   * metadata(first_empty_page_id, current_total_page_count, current_none_empty_page_count), the rest are allocated to
+   * raw_data_memory.
+   * When a page is Deallocated, the first sizeof(page_id_t) bytes are used to store the next empty page
+   * id, then update first_empty_page_id, just like a list. To avoid unnecessary cache, use C style file operation
+   * instead of fstream. Note that the page_id is the offset of the page in the file, as the first page is internal,
+   * thus page_id is 1-based. In the list of empty pages, if the there is no next empty page, the value is 0(the same
+   * for first_empty_page_id).
+   */
+ public:
+  explicit DiskManager(const std::string &file_path_, bool renew = false);
+  ~DiskManager();
+  char *RawDataMemory();
+  size_t RawDatMemorySize();
+  void FullyFlush();
+  void Close();
+  void ReadPage(page_id_t page_id, char *page_data_ptr);
+  void WritePage(page_id_t page_id, const char *page_data_ptr);  // in fact, the page_id is the offest
+  bool CurrentFileIsNew();
+  page_id_t AllocNewEmptyPageId();
+  void DeallocatePage(page_id_t page_id);
+  size_t CurrentTotalPageCount();
+  size_t CurrentNoneEmptyPageCount();
+
+ private:
+  std::string file_path;
+  page_id_t first_empty_page_id;
+  size_t current_total_page_count;
+  size_t current_none_empty_page_count;
+  static const size_t meta_data_size = sizeof(page_id_t) + sizeof(size_t) + sizeof(size_t);
+  char *raw_data_memory;
+  FILE *fp;
+  bool is_new;
+  char *page_buf;
+};
+#endif