fully passed entire test

test/MemoryRiver.hpp

@@ -16,16 +16,27 @@ using std::string;
 template <class T, int info_len = 2>
 class MemoryRiver {
  private:
-  union Page {
+  struct ElementPair {
     T data;
+    size_t nxt_blank;
+  };
+  const static size_t max_element_in_page = (4096 - sizeof(size_t)) / sizeof(ElementPair);
+  struct DataType {
+    size_t elements_count;
+    ElementPair elements[max_element_in_page];
+  };
+  union Page {
+    DataType dat;
     char filler[4096];
   };
+  // data_id = frame_id * max_element_in_page + element_id
   std::string file_name;
   DiskManager *disk_manager;
   BufferPoolManager *bpm;
+  size_t first_blank_element_pair_id;
   char *raw_mem;
   static_assert(info_len * sizeof(int) <= 4000, "info_len should be less than 4000");
-  static_assert(sizeof(T) <= 4096, "T should be less than 4096");
+  static_assert(sizeof(T) <= 4088, "T should be less than 4088");
 
  public:
   MemoryRiver() : disk_manager(nullptr), bpm(nullptr), file_name("") {}
@@ -34,8 +45,10 @@ class MemoryRiver {
     disk_manager = new DiskManager(file_name);
     bpm = new BufferPoolManager(100, 5, disk_manager);
     raw_mem = bpm->RawDataMemory();
+    memcpy(&first_blank_element_pair_id, raw_mem, sizeof(size_t));
   }
   void CloseFile() {
+    memcpy(raw_mem, &first_blank_element_pair_id, sizeof(size_t));
     bpm->FlushAllPages();
     file_name = "";
     delete bpm;
@@ -49,7 +62,7 @@ class MemoryRiver {
 
   void initialise(string FN = "") {
     if (file_name != "") {
-      std::string name_bak=file_name;
+      std::string name_bak = file_name;
       CloseFile();
       file_name = name_bak;
     }
@@ -59,40 +72,74 @@ class MemoryRiver {
     bpm = new BufferPoolManager(100, 5, disk_manager);
     raw_mem = bpm->RawDataMemory();
     memset(raw_mem, 0, bpm->RawDatMemorySize());
+    first_blank_element_pair_id = 0;
   }
 
   void get_info(int &tmp, int n) {
     if (n > info_len) return;
-    n--;
+    n += 2;
     memcpy(&tmp, raw_mem + n * sizeof(int), sizeof(int));
   }
 
   void write_info(int tmp, int n) {
     if (n > info_len) return;
-    n--;
+    n += 2;
     memcpy(raw_mem + n * sizeof(int), &tmp, sizeof(int));
   }
 
   int write(T &t) {
-    frame_id_t frame_id;
-    BasicPageGuard guard = bpm->NewPageGuarded(&frame_id);
-    guard.AsMut<Page>()->data = t;
-    return frame_id;
+    size_t element_id = first_blank_element_pair_id;
+    size_t res_id = 0;
+    if (element_id != 0) {
+      res_id = element_id;
+      frame_id_t frame_id = element_id / max_element_in_page;
+      element_id %= max_element_in_page;
+      WritePageGuard guard = bpm->FetchPageWrite(frame_id);
+      first_blank_element_pair_id = guard.AsMut<Page>()->dat.elements[element_id].nxt_blank;
+      guard.AsMut<Page>()->dat.elements[element_id].data = t;
+      guard.AsMut<Page>()->dat.elements_count++;
+    } else {
+      frame_id_t frame_id;
+      BasicPageGuard guard = bpm->NewPageGuarded(&frame_id);
+      guard.AsMut<Page>()->dat.elements[0].data = t;
+      element_id = frame_id * max_element_in_page;
+      res_id = element_id;
+      if (max_element_in_page > 1) first_blank_element_pair_id = element_id + 1;
+      for (size_t i = 1; i < max_element_in_page - 1; i++) {
+        guard.AsMut<Page>()->dat.elements[i].nxt_blank = element_id + i + 1;
+      }
+      guard.AsMut<Page>()->dat.elements[max_element_in_page - 1].nxt_blank = 0;
+      guard.AsMut<Page>()->dat.elements_count = 1;
+    }
+    return res_id;
   }
 
   void update(T &t, const int index) {
-    WritePageGuard guard = bpm->FetchPageWrite(index);
-    guard.AsMut<Page>()->data = t;
+    size_t frame_id = index / max_element_in_page;
+    WritePageGuard guard = bpm->FetchPageWrite(frame_id);
+    guard.AsMut<Page>()->dat.elements[index % max_element_in_page].data = t;
   }
 
   //读出位置索引index对应的T对象的值并赋值给t，保证调用的index都是由write函数产生
   void read(T &t, const int index) {
-    ReadPageGuard guard = bpm->FetchPageRead(index);
-    t = guard.As<Page>()->data;
+    size_t frame_id = index / max_element_in_page;
+    ReadPageGuard guard = bpm->FetchPageRead(frame_id);
+    t = guard.As<Page>()->dat.elements[index % max_element_in_page].data;
   }
 
   //删除位置索引index对应的对象(不涉及空间回收时，可忽略此函数)，保证调用的index都是由write函数产生
-  void Delete(int index) { bpm->DeletePage(index); }
+  void Delete(int index) {
+    size_t frame_id = index / max_element_in_page;
+    WritePageGuard guard = bpm->FetchPageWrite(frame_id);
+    size_t element_id = index % max_element_in_page;
+    guard.AsMut<Page>()->dat.elements[element_id].nxt_blank = first_blank_element_pair_id;
+    first_blank_element_pair_id = index;
+    guard.AsMut<Page>()->dat.elements_count--;
+    if (guard.AsMut<Page>()->dat.elements_count == 0) {
+      guard.Drop();
+      bpm->DeletePage(frame_id);
+    }
+  }
 };
 
 #endif  // BPT_MEMORYRIVER_HPP