c - 释放链表时堆栈溢出 : Segmentation fault after 100k nodes successfully freed

Question

我创建了一个链表，包含大约。 250k 节点使用递归函数在接收到节点时添加节点。我确实验证了此列表已成功链接。

当释放链表时，我使用了一个从根节点开始的递归函数，并沿着链表连续释放节点迭代移动游标。

大约。成功释放 100k 个节点我收到以下段错误:

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7a8f4d9 in new_do_write (to_do=39, 
    data=0x7ffff7ff5000 "cursor start  loop         : 0x19ffca0\n340\n", fp=0x7ffff7dd4400 <_IO_2_1_stdout_>)
    at fileops.c:538
538     fileops.c: No such file or directory.
(gdb) 

我多次成功的事实让我假设这不太可能是我代码的逻辑错误，而是必须与内存分配和释放有关，更多国际问题。

为了清楚起见，我打印了指针的分配等:

.....

cursor start  loop         : 0x19ffac0
currentNode start loop     : (nil)
currentNode (set to cursor): 0x19ffac0
cursor children[0] point to: 0x19ffbb0
Move cursor vorward, cursor: 0x19ffbb0
free old last (currentNode): 0x19ffac0
Iterate, pass cursor       : 0x19ffbb0
freecount: 87304
cursor start  loop         : 0x19ffbb0
currentNode start loop     : (nil)
currentNode (set to cursor): 0x19ffbb0
cursor children[0] point to: 0x19ffca0
Move cursor vorward, cursor: 0x19ffca0
free old last (currentNode): 0x19ffbb0
Iterate, pass cursor       : 0x19ffca0
freecount: 87305

Program received signal SIGSEGV, Segmentation fault.

Valgrind 显示堆栈溢出。我该如何解决这个问题？

==14352== Stack overflow in thread 1: can't grow stack to 0xffe801ff8
==14352== 
==14352== Process terminating with default action of signal 11 (SIGSEGV)
==14352==  Access not within mapped region at address 0xFFE801FF8
==14352==    at 0x4EAFFC5: _IO_file_write@@GLIBC_2.2.5 (fileops.c:1254)
==14352==  If you believe this happened as a result of a stack
==14352==  overflow in your program's main thread (unlikely but
==14352==  possible), you can try to increase the size of the
==14352==  main thread stack using the --main-stacksize= flag.
==14352==  The main thread stack size used in this run was 8388608.
==14352== Stack overflow in thread 1: can't grow stack to 0xffe801ff0
==14352== 
==14352== Process terminating with default action of signal 11 (SIGSEGV)
==14352==  Access not within mapped region at address 0xFFE801FF0
==14352==    at 0x4A256B0: _vgnU_freeres (in /usr/lib/valgrind/vgpreload_core-amd64-linux.so)
==14352==  If you believe this happened as a result of a stack
==14352==  overflow in your program's main thread (unlikely but
==14352==  possible), you can try to increase the size of the
==14352==  main thread stack using the --main-stacksize= flag.
==14352==  The main thread stack size used in this run was 8388608.
==14352== 
==14352== HEAP SUMMARY:
==14352==     in use at exit: 62,486,368 bytes in 278,957 blocks
==14352==   total heap usage: 366,221 allocs, 87,264 frees, 82,034,192 bytes allocated
==14352== 
==14352== LEAK SUMMARY:
==14352==    definitely lost: 0 bytes in 0 blocks
==14352==    indirectly lost: 0 bytes in 0 blocks
==14352==      possibly lost: 0 bytes in 0 blocks
==14352==    still reachable: 62,486,368 bytes in 278,957 blocks
==14352==         suppressed: 0 bytes in 0 blocks
==14352== Rerun with --leak-check=full to see details of leaked memory
==14352== 
==14352== For counts of detected and suppressed errors, rerun with: -v
==14352== Use --track-origins=yes to see where uninitialised values come from
==14352== ERROR SUMMARY: 4 errors from 2 contexts (suppressed: 0 from 0)
Segmentation fault

这是我的代码

头文件

// define global pointer variable root
extern struct node* rootNS;

源文件

struct node* rootNS;

// create root node in a function (not main)

    // at first function call send root to linked list that stores all created nodes
        if (x == 0)
        {   
            // allocate storage 
            rootNS = malloc(sizeof(struct node));
            rootNS->children[0] = NULL;
            x = 1;
            nodestore(rootNS);
        }



// function creating the linked list, nodes are past to the function

    bool nodestore(struct node* nodeAD)
    {
        // for debugging: Create nodecounter
        static int nodecounter = 0;
        nodecounter +=1;

        // create cursor at first function call
        static struct node* cursor;
        if (nodeAD == rootNS)
        {
            cursor = nodeAD;
            if (nodecounter == 1)
            {

            cursor->children[0] = NULL;
            }
        return true;
        }
    // append list
        // point last node (cursor) to new node
        cursor->children[0] = nodeAD;

        // set cursor to new node = last node
        cursor = nodeAD;

        return true;   
    }


// function freeing the linked list

    int unloader(struct node* cursor) 
    {
        // for debugging: Creat nodecounter
        static int nodecounter = -1;
        nodecounter +=1;

        // create helper pointer 
        struct node* currentNode = NULL;

        // check if end of linked list has been reached
        if(cursor->children[0] == NULL)
        {            
            free(cursor);
            free(root);
            return true;
        }
        else
        {
            // keep track of old last node before moving cursor
            currentNode = cursor;

            // move cursor forward
            cursor = cursor->children[0];

            // free old last node
            free(currentNode);

            // iterate passing new last node (cursor)
            return unloader(cursor);
        }

    }

Answer 1

您的 unloader 函数是递归的，因此每次调用 unloader 都会产生一个额外的堆栈帧...在 100k 次函数调用时，您会简单地溢出堆栈因为它长得太大了。我不知道你有什么编译器/系统，但是 ~100k 堆栈帧会为 2MB 堆栈提供~20 字节的帧大小(IIRC 是 Windows 上的默认值)，这听起来很适合你的代码。

解决此问题的唯一合理方法是将 unloader 更改为迭代函数(不再递归)。有多种方法可以增加默认堆栈大小，但具体方法取决于您的编译器/系统(通常不推荐在任何情况下使用)。