如何在列表中间释放删除的节点，而没有阀门错误

Question

这是有助于演示和查看Valgrind Memcheck的OUPUT的一些测试。有人可以帮助我找出如何从列表中间删除和释放节点吗？如果我从"删除节点"部分中评论免费（cur）和免费（cur->锁），那么Memcheck告诉我我有记忆泄漏，但是如果我将它们保留在那里循环。有没有这个难题的方法？

TEST(UtilityGeneralUnittest, valgrindTests)
{
    //declare a node type
    typedef struct node{
        int size;
        int value;
        struct node *next;
        pthread_mutex_t *lock;
    }node_t;
    //make the head
    node_t *head;
    head = (node_t*)malloc(1 * sizeof(node_t));
    head->size = 0;
    head->next = NULL;
    head->lock = (pthread_mutex_t*)malloc(1 * sizeof(pthread_mutex_t));
    pthread_mutex_init(head->lock, NULL);
    //create array for storing values
    int array[10];

    //build a list with random numbers
    for (int i = 0; i < 10; i++)
    {
        node_t *newNode;
        newNode = (node_t*)malloc(1 * sizeof(node_t));
        newNode->value = rand() % 100 + 1;
        newNode->next = NULL;
        newNode->lock = (pthread_mutex_t*) malloc(1 * sizeof(pthread_mutex_t));
        pthread_mutex_init(newNode->lock, NULL);
        array[i] = newNode->value;
        if (head->next == NULL)
        {
            head->next = newNode;
            head->size++;
        }
        else
        {
            node_t *tmp = head->next;
            head->next = newNode;
            newNode->next = tmp;
            head->size++;
        }
    }
    // assert the list added nodes
    ASSERT_EQ(10, head->size);
    //sanity check; print the list
    node_t *printer = head;
    while(printer->next != NULL)
    {
        printer = printer->next;
        std::cout << "value: ";
        std::cout <<  printer->value << ", ";
    }
    std::cout << "n";
    // the meat and potatoes: deleting with locks.
    int removeMe = array[rand() % 10];
    bool verifyDel = true;
    int checkVal = removeMe;
    node_t *prev;
    node_t *cur;
    prev = head;
    pthread_mutex_lock(prev->lock);
    while((cur = prev->next) != NULL) //******** this is the problem
    {
        pthread_mutex_lock(cur->lock);
        if(cur->value == removeMe)
        {
            prev->next = cur->next;
            pthread_mutex_unlock(cur->lock);
            pthread_mutex_unlock(prev->lock);
            cur->next = NULL;
            head->size--;
            free(cur->lock); ///******** this is the problem
            free(cur); ///****** this is the problem
        }
        pthread_mutex_unlock(prev->lock);
        prev = cur;
    }
    //pthread_mutex_unlock(prev->lock);

    //verify node has been removed
    printer = head;
    while(printer->next != NULL)
    {
        printer = printer->next;
        if(printer->value == checkVal)
        {
            verifyDel = false;
        }
        std::cout << "value: ";
        std::cout <<  printer->value << ", ";
    }
    std::cout << "n";
    ASSERT_TRUE(verifyDel);
    //clean up: delete the list
    while((printer = head) != NULL)
    {
        head = head->next;
        free(printer->lock);
        free(printer);
        std::cout << "free!!!" << std::endl;
    }

}

Answer 1

查看您的循环（简化）：

while ((cur = prev->next) != NULL) //* problem
{
    if (cur->value == removeMe)
    {
        prev->next = cur->next;
        cur->next = NULL;
        free(cur);              //* problem
    }
    prev = cur;
}

问题在于分配prev = cur，但仅在评估if块时。这已经释放了cur，因此下次绕循环，cur=prev->next参考已删除存储。

您只有在未删除cur时才插入else分配prev来解决此问题：

while ((cur = prev->next)) {
    if (cur->value == removeMe) {
        prev->next = cur->next;
        cur->next = NULL;
        free(cur);
    } else {
        prev = cur;
    }
}