InvoDB/invodb/file/page_manager.cpp

//
// Created by YuhangQ on 2021/9/24.
//

#include "page_manager.h"
#include "btree/list.h"



int PageManager::loadDatabase(const char *filename) {
    Instance().stream.open(filename);
    Instance().stream.seekp(0, std::ios::end);
    int index = Instance().stream.tellp() / 1024;
    if(index == 0) {
        StoragePage(0).save();
        StoragePage(1).save();
        StoragePage(2).save();
    }
    return 0;
}

std::shared_ptr<StoragePage> PageManager::getPage(const int &index) {

    if(cache.exist(index)) {
        return cache.get(index);
    }

    auto page = std::make_shared<StoragePage>(index);
    // 调整指针位置
    stream.clear();
    stream.seekg((long long)index * 1024);
    stream.read(*page, 1024);
    return page;
}

void PageManager::setPage(const int &index, const StoragePage &page) {
    cache.put(index, std::make_shared<StoragePage>(page));

    stream.clear();
    stream.seekg((long long)index * 1024);
    stream.write(page, 1024);
}

int PageManager::allocate() {

//     try to allocate from free block list
    auto page = getPage(0);
    int index =  page->getIntStartFrom(0);
    if(index != 0) {
        auto allocatePage = getPage(index);

        page->setIntStartFrom(0, allocatePage->next());
        // reset
        allocatePage->clear();
        allocatePage->save();
        page->save();
        //printf("allocate: %d\n", index);
        return index;
    }


    // allocate block at the end
    stream.seekp(0, std::ios::end);
    index = stream.tellp() / 1024;
    setPage(index, StoragePage(index));
    return index;
}

void PageManager::release(const int &index, const bool &next) {
    auto page = getPage(0);
    int head = page->getIntStartFrom(0);
    auto releasePage = getPage(index);
    releasePage->setNext(head);
    page->setIntStartFrom(0, releasePage->getAddress());
    page->save();
    releasePage->save();
    //printf("release: %d\n", index);

}

nlohmann::json PageManager::readJSONFromFile(const int &index) {
    std::string content;

    auto page = getPage(index);
    while(true) {
        for(int i=0; i<1016; i++) {
            if((*page)[i] == '\0') break;
            content.push_back((*page)[i]);
        }
        if(page->next() == 0) break;
        page = getPage(page->next());
    }

    return nlohmann::json::parse(content);
}

int PageManager::saveJSONToFile(const nlohmann::json& json) {
    std::string content = json.dump();
    int size = content.size();

    auto page = getPage(allocate());
    int res = page->getAddress();
    int p = 0;
    while(p < size) {
        int len = std::min(size - p, 1016);
        page->setStartFrom(0, &content.c_str()[p], len);
        page->save();
        p += len;
        if(p < size) {
            int newPage = allocate();
            int lastPage = page->getAddress();
            page->setNext(newPage);
            page->save();
            page = getPage(newPage);
            page->setLast(lastPage);
            page->save();
        }
    }
    return res;
}