在C ++中覆蓋新的和刪除的通用內存分配崩潰

Question

我有以下代碼。 當我刪除分配的內存時，以下代碼崩潰：Rational :: deleteMemPool（）;

獲取輸出為

內存池值為00000000內存池值為003462E8內存池值為003462E8

//盡管我們有有效的指針，但此處用於刪除崩潰。

誰能幫我這是什么bug？

#include <string>
#include <iostream>


template < class T >
class MemoryPool {
public:
    MemoryPool (size_t size = EXPANSION_SIZE);
    ~MemoryPool ();
    inline void* alloc (size_t size); // Allocate a T element from the free list.
    inline void free (void *someElement); // Return a T element to the free list.
private:
    MemoryPool<T> *next; // next element on the free list.
    enum { EXPANSION_SIZE = 32}; // If the freeList is empty, expand it by this amount.
    void expandTheFreeList(int howMany = EXPANSION_SIZE); // Add free elements to the free list
};

template < class T > MemoryPool < T > :: MemoryPool (size_t size) {
    expandTheFreeList(size);
}

template < class T > MemoryPool < T > :: ~MemoryPool () {
    MemoryPool<T> *nextPtr = next;
    for (nextPtr = next; nextPtr != NULL; nextPtr = next) {
        next = next->next;
        delete [] nextPtr;
    }
}

template < class T > inline void* MemoryPool < T > :: alloc (size_t) {
    if (!next) {
        expandTheFreeList();
    }

    MemoryPool<T> *head = next;
    next = head->next;
    return head;
}

template < class T > inline void MemoryPool < T > :: free (void *doomed) {

    MemoryPool<T> *head = static_cast <MemoryPool<T> *> (doomed);
    head->next = next;
    next = head;
}

template < class T > void MemoryPool < T > :: expandTheFreeList(int howMany) {
    // We must allocate an object large enough to contain the next pointer.
    size_t size = (sizeof(T) > sizeof(MemoryPool<T> *)) ? sizeof(T) : sizeof(MemoryPool<T> *);
    void *pNewAlloc = new char[size];
    MemoryPool<T> *runner = static_cast <MemoryPool<T> *> (pNewAlloc);
    next = runner;
    for (int i = 0; i < howMany ; i++) {
        void *pNewAlloc = new char[size];
        runner->next = static_cast <MemoryPool<T> *> (pNewAlloc);
        runner = runner->next;
    }
    runner->next = 0;
}

class Rational {
public:
    Rational (int a = 0, int b = 1 ) : n(a), d(b) {}
    void *operator new(size_t size) { return memPool->alloc(size); }
    void operator delete(void *doomed,size_t size)  { memPool->free(doomed); }

    static void newMemPool() { 
        std::cout << "mempool value is " << Rational::memPool << std::endl;
        memPool = new MemoryPool <Rational>; 
        std::cout << "mempool value is " << Rational::memPool << std::endl;
    }
    static void deleteMemPool() { 
        std::cout << "mempool value is " << Rational::memPool << std::endl;
        delete memPool; 
    }

private:
    int n; // Numerator
    int d; // Denominator
    static MemoryPool <Rational> *memPool;
};

MemoryPool <Rational> *Rational::memPool = 0;
int main() {

    Rational *array[1000];

    Rational::newMemPool();


    // Start timing here
    for (int j = 0; j < 1; j++) {
        for (int i = 0; i < 10; i++) {
            array[i] = new Rational(i);
        }

        for (int i = 0; i < 10; i++) {
            delete array[i];
        }
    }

    // Stop timing here
    Rational::deleteMemPool();

}

堆棧跟蹤：

Stack trace:>
ReadParsing.exe!Rational::deleteMemPool() Line 75   C++
ReadParsing.exe!main() Line 107 C++
ReadParsing.exe!__tmainCRTStartup() Line 586 + 0x19 bytes   C
ReadParsing.exe!mainCRTStartup() Line 403   C
kernel32.dll!7c817077()

Answer 1

您如何刪除內存池中的塊有問題。 分配塊時，可以在expandTheFreeList(i)使用new char[size] 。

但是，當刪除這些塊時，可以使用delete [] nextPtr ：

template < class T > MemoryPool < T > :: ~MemoryPool () {
    MemoryPool<T> *nextPtr = next;
    for (nextPtr = next; nextPtr != NULL; nextPtr = next) {
        next = next->next;
        delete [] nextPtr;     //  <-- problem
    }
}

而且由於nextPtr是memoryPool<T>* ，所以您釋放了錯誤的內容（它最終遞歸到該析構函數中進行引導）。

將該問題行更改為：

delete [] reinterpret_cast<char*>(nextPtr);

似乎使事情不會崩潰。 當然，可能還有其他問題。