#include"PageCache.h"
//类内声明，类外初始化
PageCache PageCache::_sInst;
// 向系统申请k页内存
void* PageCache::SystemAllocPage(size_t k)
{
return ::SystemAlloc(k);
}
//申请num页的内存
Span* PageCache::NewSpan(size_t num)
{
std::lock_guard lock(_mtx);
//针对直接申请大于128页的内存，直接向系统要
if (num >= 128)
{
//在系统申请
void* ptr = SystemAllocPage(num);
Span* span = new Span;
span->_pageId = (ADDRES_INT)ptr >> PAGE_SHIFT;
span->_n = num;
{
//std::lock_guard lock(_map_mtx);
_idSpanMap[span->_pageId] = span;
}
return span;
}
else
{
if (!_spanList[num - 1].isEmpty())
_spanList[num - 1].isEmpty();
//走到这里说明没有内存，需要向后判断是否有num页的内存
//向后找
for (int i = num; i < 128; i++)
{
if (!_spanList[i].isEmpty())
{
//切num页给_spanList[num - 1]
Span* span = _spanList[i].PopFront();
//切出来的内存---采用尾切
Span* split = new Span;
split->_n = num;
split->_next = nullptr;
//span中有多页，它存储的页号是第一页的页号，因此这里的页号应该是切出来的页数+初始页号
split->_pageId = span->_pageId+span->_n-num;
// 改变切出来span的页号和span的映射关系
{
//std::lock_guard lock(_map_mtx);
for (PageID i = 0; i < num; ++i)
{
_idSpanMap[split->_pageId + i] = split;
}
}
//将Span剩余的页挂在对应的位置
span->_n -= num;
_spanList[span->_n - 1].PushFront(span);
return split;
}
}
//走到这里说明page cache中没有内存,向系统申请
Span* bigSpan = new Span;
void* memory = SystemAllocPage(MAX_PAGE);
//计算出页号
bigSpan->_pageId = (size_t)memory >> 12;
bigSpan->_n = MAX_PAGE;
// 按页号和span映射关系建立，也就是这么多个页都映射在这个span中
{
//std::lock_guard lock(_map_mtx);
for (PageID i = 0; i < bigSpan->_n; ++i)
{
PageID id = bigSpan->_pageId + i;
_idSpanMap[id] = bigSpan;
}
}
//将内存链接到spanlist中
_spanList[MAX_PAGE - 1].Insert(_spanList[MAX_PAGE - 1].Begin(), bigSpan);
//重新切割
return NewSpan(num);
}
}
//通过内存地址在map中查找对应的span
Span* PageCache::GetSpanToMap(void* mem)
{
//根据内存计算页号
PageID id = (ADDRES_INT)mem >> PAGE_SHIFT;
//在map中查找
auto ret = _idSpanMap.get(id);
if (ret != nullptr)
{
return ret;
}
else
{
assert(false);
return nullptr;
}
}
// 释放空闲span回到Pagecache，并合并相邻的span
void PageCache::ReleaseSpanToPageCache(Span* span)
{
if (span->_n >= MAX_PAGE)
{
//大于128页的内存直接还给系统内存
_idSpanMap.erase(span->_pageId);
//根据页号计算地址
void* ptr = (void*)(span->_pageId << PAGE_SHIFT);
SystemFree(ptr);
delete span;
return;
}
std::lock_guard lock(_mtx);
// 检查前后空闲span页，进行合并,解决内存碎片问题
// 向前合并
while (1)
{
PageID preId = span->_pageId - 1;
Span* preSpan = _idSpanMap.get(preId);
if (preSpan == nullptr)
{
break;
}
// 如果前一个页的span还在使用中，结束向前合并
if (preSpan->_usecount != 0)
{
break;
}
// 开始合并...
// 超过128页，不需要合并了
if (preSpan->_n + span->_n >= MAX_PAGE)
{
break;
}
// 从对应的span链表中解下来，再合并
_spanList[preSpan->_n].Erase(preSpan);
span->_pageId = preSpan->_pageId;
span->_n += preSpan->_n;
// 更新页之间映射关系
{
//std::lock_guard lock(_map_mtx);
for (PageID i = 0; i < preSpan->_n; ++i)
{
_idSpanMap[preSpan->_pageId + i] = span;
}
}
delete preSpan;
}
// 向后合并
while (1)
{
PageID nextId = span->_pageId + span->_n;
Span* nextSpan = _idSpanMap.get(nextId);
if (nextSpan == nullptr)
{
break;
}
//Span* nextSpan = ret->second;
if (nextSpan->_usecount != 0)
{
break;
}
// 超过128页，不需要合并了
if (nextSpan->_n + span->_n >= MAX_PAGE)
{
break;
}
_spanList[nextSpan->_n].Erase(nextSpan);
span->_n += nextSpan->_n;
{
//std::lock_guard lock(_map_mtx);
for (PageID i = 0; i < nextSpan->_n; ++i)
{
_idSpanMap[nextSpan->_pageId + i] = span;
}
}
delete nextSpan;
}
// 合并出的大span，插入到对应的链表中
_spanList[span->_n].PushFront(span);
}