-tcmalloc-/PageCache.cpp at main · bugkeep/-tcmalloc- · GitHub

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//
// Created by ASUS on 2026/3/23.
//

#include "PageCache.h"
PageCache PageCache::_sInst;//单例对象
Span *PageCache::newSpan(size_t k) {
    assert(k>0&&k<PAGE_NUM);
    //k桶中有span
    if (!_spanLists[k].Empty()) {
        Span* span=_spanLists[k].PopFront();
        for (PageID i=0;i<span->_n;i++) {
            _idSpanMap[span->_pageId+i]=span;
        }
        return span;
    }
    //k号桶没有span
    for (int i=k+1;i<PAGE_NUM;i++) {
        if (!_spanLists[i].Empty()) {
            Span* nspan=_spanLists[i].PopFront();
            Span* kspan=new Span();
            //分一个k页
            kspan->_pageId=nspan->_pageId;
            kspan->_n=k;
            //分一个n-k页
            nspan->_pageId+=k;
            nspan->_n-=k;
            _spanLists[nspan->_n].PushFront(nspan);
            //再把n-k页的span边缘映射一下，方便后续合并
            _idSpanMap[nspan->_pageId]=nspan;
            _idSpanMap[nspan->_pageId+nspan->_n-1]=nspan;
            for (PageID i=0;i<kspan->_n;i++) {
                _idSpanMap[kspan->_pageId+i]=kspan;
            }

            return kspan;
        }
    }
    //k号桶和后面的桶都没有span
    void* ptr=SystemAlloc(PAGE_NUM-1);
    Span* bigSpan=new Span;
    bigSpan->_pageId=((PageID)ptr)>>PAGE_SHIFT;
    bigSpan->_n=PAGE_NUM-1;
    //将这个span放到对应哈希桶中
    _spanLists[PAGE_NUM-1].PushFront(bigSpan);
    //递归调用走一二的逻辑
    return newSpan(k);
}
Span* PageCache::MapObjectToSpan(void* obj) {
    PageID id=(((PageID)obj)>>PAGE_SHIFT);
    auto ret=_idSpanMap.find(id);
    if (ret!=_idSpanMap.end()) {
        return ret->second;
    }
    else {
        assert(false);
        return nullptr;
    }
}
void PageCache::ReleaseSpanToPageCache(Span* span) {
    while (1) {
        PageID leftID=span->_pageId-1;
        auto ret=_idSpanMap.find(leftID);
        if (ret==_idSpanMap.end()) {
            break;
        }
        Span* leftSpan=ret->second;
        if (leftSpan->_isUse==true) {
            break;
        }
        if (leftSpan->_n + span->_n > PAGE_NUM - 1) {
            break;
        }
        // 1. 先把左侧旧span的边界映射删掉
        _idSpanMap.erase(leftSpan->_pageId);
        _idSpanMap.erase(leftSpan->_pageId + leftSpan->_n - 1);

        // 2. 从桶中摘掉
        _spanLists[leftSpan->_n].Erase(leftSpan);

        // 3. 合并到当前span
        span->_pageId = leftSpan->_pageId;
        span->_n += leftSpan->_n;

        // 4. 删除旧span对象
        delete leftSpan;
    }
    while (1) {
        PageID rightID=span->_pageId+span->_n;
        auto it=_idSpanMap.find(rightID);
        if (it==_idSpanMap.end()) {
            break;
        }
        Span* rightSpan=it->second;
        if (rightSpan->_isUse==true) {
            break;
        }
        if (span->_n+rightSpan->_n>PAGE_NUM-1) {
            break;
        }
        // 1. 先把右侧旧span的边界映射删掉
        _idSpanMap.erase(rightSpan->_pageId);
        _idSpanMap.erase(rightSpan->_pageId + rightSpan->_n - 1);

        // 2. 从桶中摘掉
        _spanLists[rightSpan->_n].Erase(rightSpan);

        // 3. 合并
        span->_n += rightSpan->_n;

        // 4. 删除旧span
        delete rightSpan;
    }
    _spanLists[span->_n].PushFront(span);
    span->_isUse=false;
    //映射当前span的边缘页，后续还可以对这个span进行合并
    _idSpanMap[span->_pageId]=span;
    _idSpanMap[span->_pageId+span->_n-1]=span;
}