24 实战页式内存管理 上

参考

https://blog.51cto.com/13475106/category6.html及狄泰软件相关课程

 

课程设计目标(Qt下实现)
1.用代码描述：页表，页框表，任务结构
2.用代码实现：页请求，页置换
3.模拟任务的页面访问过程(访问虚拟内存)
4.模拟操作系统中的任务调度(扩展)

 

 

 

 

 

 

 

实现的流程图如下所示

代码实现

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#include <QtCore/QCoreApplication> #include <QList> #include <iostream> #include <ctime>   using namespace std;   #define PAGE_NUM  (0xFF + 1) #define FRAME_NUM (0x04) #define FP_NONE   (-1)   struct FrameItem {     int pid;    // the task which use the frame     int pnum;   // the page which the frame hold       FrameItem()     {         pid = FP_NONE;         pnum = FP_NONE;     } };   class PageTable {     int m_pt[PAGE_NUM]; public:     PageTable()     {         for(int i=0; i<PAGE_NUM; i++)         {             m_pt[i] = FP_NONE;         }     }       int& operator[] (int i)     {         if( (0 <= i) && (i < length()) )         {             return m_pt[i];         }         else         {             QCoreApplication::exit(-1);         }     }       int length()     {         return PAGE_NUM;     } };   class PCB {     int m_pid;               // task id     PageTable m_pageTable;   // page table for the task     int* m_pageSerial;       // simulate the page serial access     int m_pageSerialCount;   // page access count     int m_next;              // the next page index to access public:     PCB(int pid)     {         m_pid = pid;         m_pageSerialCount = qrand() % 5 + 5;         m_pageSerial = new int[m_pageSerialCount];           for(int i=0; i<m_pageSerialCount; i++)         {             m_pageSerial[i] = qrand() % 8;         }           m_next = 0;     }       int getPID()     {         return m_pid;     }       PageTable& getPageTable()     {         return m_pageTable;     }       int getNextPage()     {         int ret = m_next++;           if( ret < m_pageSerialCount )         {             ret = m_pageSerial[ret];         }         else         {             ret = FP_NONE;         }           return ret;     }       bool running()     {         return (m_next < m_pageSerialCount);     }       void printPageSerial()     {         QString s = "";           for(int i=0; i<m_pageSerialCount; i++)         {             s += QString::number(m_pageSerial[i]) + " ";         }           cout << ("Task" + QString::number(m_pid) + " : " + s).toStdString() << endl;     }       ~PCB()     {         delete[] m_pageSerial;     } };   FrameItem FrameTable[FRAME_NUM]; QList<PCB*> TaskTable;   int GetFrameItem(); void AccessPage(PCB& pcb); int RequestPage(int pid, int page); int SwapPage(); void PrintLog(QString log); void PrintPageMap(int pid, int page, int frame); void PrintFatalError(QString s, int pid, int page);   int GetFrameItem() {     int ret = FP_NONE;       for(int i=0; i<FRAME_NUM; i++)     {         if( FrameTable[i].pid == FP_NONE )         {             ret = i;             break;         }     }       return ret; }   void AccessPage(PCB& pcb) {     int pid = pcb.getPID();     PageTable& pageTable = pcb.getPageTable();     int page = pcb.getNextPage();       if( page != FP_NONE )     {         PrintLog("Access Task" + QString::number(pid) + " for Page" + QString::number(page));           if( pageTable[page] != FP_NONE )         {             PrintLog("Find target page in page table.");             PrintPageMap(pid, page, pageTable[page]);         }         else         {             PrintLog("Target page is NOT found, need to request page ...");               pageTable[page] = RequestPage(pid, page);               if( pageTable[page] != FP_NONE )             {                 PrintPageMap(pid, page, pageTable[page]);             }             else             {                 PrintFatalError("Can NOT request page from disk...", pid, page);             }         }     }     else     {         PrintLog("Task" + QString::number(pid) + " is finished!");     } }   int RequestPage(int pid, int page) {     int frame = GetFrameItem();       if( frame != FP_NONE )     {         PrintLog("Get a frame to hold page content: Frame" + QString::number(frame));     }     else     {         PrintLog("No free frame to allocate, need to swap page out.");           frame = SwapPage();           if( frame != FP_NONE )         {             PrintLog("Succeed to swap lazy page out.");         }         else         {             PrintFatalError("Failed to swap page out.", pid, FP_NONE);         }     }       PrintLog("Load content from disk to Frame" + QString::number(frame));       FrameTable[frame].pid = pid;     FrameTable[frame].pnum = page;       return frame; }   int Random() {     // just random select     int obj = qrand() % FRAME_NUM;       PrintLog("Random select a frame to swap page content out: Frame" + QString::number(obj));     PrintLog("Write the selected page content back to disk.");       FrameTable[obj].pid = FP_NONE;     FrameTable[obj].pnum = FP_NONE;       for(int i=0, f=0; (i<TaskTable.count()) && !f; i++)     {         PageTable& pt = TaskTable[i]->getPageTable();           for(int j=0; j<pt.length(); j++)         {             if( pt[j] == obj )             {                 pt[j] = FP_NONE;                 f = 1;                 break;             }         }     }       return obj; }   int SwapPage() {     return Random(); }   void PrintLog(QString log) {     cout << log.toStdString() << endl; }   void PrintPageMap(int pid, int page, int frame) {     QString s = "Task" + QString::number(pid) + " : ";       s += "Page" + QString::number(page) + " ==> Frame" + QString::number(frame);       cout << s.toStdString() << endl; }   void PrintFatalError(QString s, int pid, int page) {     s += " Task" + QString::number(pid) + ": Page" + QString::number(page);       cout << s.toStdString() << endl;       QCoreApplication::exit(-2); }   int main(int argc, char *argv[]) {     QCoreApplication a(argc, argv);     int index = 0;       qsrand(time(NULL));       TaskTable.append(new PCB(1));     TaskTable.append(new PCB(2));       PrintLog("Task Page Serial:");       for(int i=0; i<TaskTable.count(); i++)     {         TaskTable[i]->printPageSerial();     }       PrintLog("==== Running ====");       while( true )     {         if( TaskTable[index]->running() )         {             AccessPage(*TaskTable[index]);         }           index = (index + 1) % TaskTable.count();           cin.get();     }           return a.exec(); }