c++ - 在 C++ 中使用 new 和 delete 在可变大小内存分配器中崩溃

Question

我正在编写一个可变大小的内存池工具，如下所示。

我没有这方面的堆栈跟踪。通过逐步我发现它在 Rational::deleteMemPool() 中崩溃；

我不确定为什么会这样？欢迎任何意见。

谢谢!

//MemoryChunk 用于将不同大小的内存块串成一系列 block 。

class MemoryChunk {
public:
    MemoryChunk (MemoryChunk *nextChunk, size_t chunkSize);
    ~MemoryChunk() {delete mem; }

    inline void *alloc (size_t size);
    inline void free (void* someElement);

    // Pointer to next memory chunk on the list.
    MemoryChunk *nextMemChunk() {return next;}
    // How much space do we have left on this memory chunk?
    size_t spaceAvailable() { return chunkSize - bytesAlreadyAllocated; }

    // this is the default size of a single memory chunk.
    enum { DEFAULT_CHUNK_SIZE = 4096 };
private:

    // The MemoryChunk class is a cleaner version of NextOnFreeList. It separates the next pointer from
    // the actual memory used for the allocated object. It uses explicit next and mem pointers, with no 
    // need for casting.

    MemoryChunk *next;
    void *mem;

    // The size of a single memory chunk.
    size_t chunkSize;
    // This many bytes already allocated on the current memory chunk.
    size_t bytesAlreadyAllocated;
};

MemoryChunk::MemoryChunk(MemoryChunk *nextChunk, size_t reqSize) {
    chunkSize = (reqSize > DEFAULT_CHUNK_SIZE) ? reqSize : DEFAULT_CHUNK_SIZE;
    next = nextChunk;
    bytesAlreadyAllocated = 0;
    mem = new char [chunkSize];
}

void* MemoryChunk :: alloc (size_t requestSize) {
    void *addr = static_cast <void*> (static_cast <char*> (mem) + bytesAlreadyAllocated);
    bytesAlreadyAllocated += requestSize;
    return addr;
}

inline void MemoryChunk :: free (void *doomed) {}

class ByteMemoryPool {
public:
    ByteMemoryPool (size_t initSize = MemoryChunk::DEFAULT_CHUNK_SIZE);
    ~ByteMemoryPool ();

    // Allocate memory from private pool.
    inline void *alloc (size_t size);
    // Free memory previously allocated from the pool
    inline void free (void* someElement);
private:

    // A list of memory chunks. This is our private storage.
    MemoryChunk *listOfMemoryChunks;
    // Add one memory chunk to our private storage
    void expandStorage(size_t reqSize);
};

// Construct the ByteMemoryPool object. Build the private storage.
ByteMemoryPool :: ByteMemoryPool (size_t initSize) {
    expandStorage(initSize);
}

ByteMemoryPool :: ~ByteMemoryPool () {

    MemoryChunk *memChunk = listOfMemoryChunks;
    while (memChunk) {
        listOfMemoryChunks = memChunk->nextMemChunk();
        delete memChunk;
        memChunk = listOfMemoryChunks;
    }
}

void* ByteMemoryPool :: alloc (size_t requestSize) {
    size_t space = listOfMemoryChunks->spaceAvailable();
    if ( space < requestSize ) {
        expandStorage(requestSize);
    }   
    return listOfMemoryChunks->alloc(requestSize);
}

inline void ByteMemoryPool :: free (void *doomed) {
    listOfMemoryChunks->free(doomed);
}

void ByteMemoryPool :: expandStorage(size_t reqSize) {
    listOfMemoryChunks = new MemoryChunk(listOfMemoryChunks, reqSize);
}

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() { memPool = new ByteMemoryPool;}
    static void deleteMemPool() { delete memPool; }
private:
    int n; // Numerator
    int d; // Denominator
    static ByteMemoryPool *memPool;
};

ByteMemoryPool* 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 < 5; i++) {
            array[i] = new Rational(i);
        }

        for (int i = 0; i < 5; i++) {
            delete array[i];
        }
    }

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

Answer 1

next 和 nextChunk 似乎没有指向任何地方。同样在 MemoryChunk 的析构函数中，您需要删除数组。这是 10 的入门级，除非我没看错代码。