CentralCache.cpp

//
// Created by ASUS on 2026/3/23.
//
#include "PageCache.h"
#include "CentralCache.h"
CentralCache CentralCache::_sInt;//CentralCache的饿汉对象
size_t CentralCache::FetchRangeObj(void*& start,void*& end,size_t size,size_t batchNum) {
    size_t index=SizeClass::index(size);
    _spanLists[index]._mtx.lock();
    Span* span=GetOneSpan(_spanLists[index],size);
    assert(span);
    assert(span->_freelist);
    start=end=span->_freelist;
    size_t actualNum=1;
    size_t i=0;
    while (i<batchNum-1&&*reinterpret_cast<void**>(end)!=nullptr) {
        end=*reinterpret_cast<void**>(end);
        actualNum++;
        i++;
    }
    span->_freelist=*reinterpret_cast<void**>(end);
    span->_usecount+=actualNum;//给tc分了多少就给useCount加多少
    *reinterpret_cast<void**>(end)=nullptr;
    _spanLists[index]._mtx.unlock();
    return actualNum;
}
Span* CentralCache::GetOneSpan(SpanList& list,size_t size) {
    Span* it=list.Begin();
    while (it!=list.End()) {
        if (it->_freelist!=nullptr) {
            return it;
        }
        else {
            it=it->_next;
        }
    }
    //解掉桶锁，让其他向该cc桶进行操作的线程能拿到锁
    list._mtx.unlock();
    size_t k=PageCache::NumMovePage(size);
    PageCache::GetInstance()->_pageMtx.lock();
    Span* span=PageCache::GetInstance()->newSpan(k);
    span->_isUse=true;
    PageCache::GetInstance()->_pageMtx.unlock();
    /*
     *_pageID是pageID类型（size_t或者unsigned long long）的，不能直接赋值给指针
     */
    char *start=(char*)(span->_pageId<<PAGE_SHIFT);
    char *end=(char*)(start+(span->_n<<PAGE_SHIFT));
    //开始切分span管理空间
    span->_freelist=start;
    void* tail=start;
    start+=size;
    int i=0;
    while (start<end) {
        ++i;
        *reinterpret_cast<void**>(tail)=start;
        start+=size;
        tail=*reinterpret_cast<void**>(tail);
    }
    *reinterpret_cast<void**>(tail)=nullptr;
    //切好span以后
    list._mtx.lock();
    list.PushFront(span);
    return span;
}
void CentralCache::ReleaseListToSpans(void*start,size_t size) {
    size_t index=SizeClass::index(size);
    _spanLists[index]._mtx.lock();
    while (start) {
        void* next=*reinterpret_cast<void**>(start);
        Span* span=PageCache::GetInstance()->MapObjectToSpan(start);
        *reinterpret_cast<void**>(start)=span->_freelist;
        span->_freelist=start;
        span->_usecount--;
        if (span->_usecount==0) {
            _spanLists[index].Erase(span);
            span->_freelist=nullptr;
            span->_next=nullptr;
            span->_prev=nullptr;
            //归还span,解掉当前桶锁
            _spanLists[index]._mtx.unlock();
            //将这个span交给pc管理
            PageCache::GetInstance()->_pageMtx.lock();
            PageCache::GetInstance()->ReleaseSpanToPageCache(span);
            PageCache::GetInstance()->_pageMtx.unlock();
            //归还完毕,再加上当前桶的桶锁
            _spanLists[index]._mtx.lock();
        }
        start=next;
    }
    _spanLists[index]._mtx.unlock();
}