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C++ unordered_map find（）或insert（）上的SIGSEGV

分类: 技术问答 • 2022-08-27 11:34:47
问题描述：

目前我正在尝试为我们需要为大学构建的数据库系统实现某种基本的文件访问层。要做到这一点，我被要求在内存中缓存页面。要快速确定哪些页面已加载，我将它们全部存储在unordered_map中。C++ unordered_map find（）或insert（）上的SIGSEGV

现在的问题是，在对这个函数进行一些调用后，SIGSEGV出现在unordered_map的_M_find_before_node中。我尝试使用gdb调试它，但我不知道到哪里寻找它，因为在调用unordered_map中出现错误：

#0 0x0000000000402ab0 in std::_Hashtable<unsigned long, std::pair<unsigned long const, BufferFrame>, std::allocator<std::pair<unsigned long const, BufferFrame> >, std::__detail::_Select1st, std::equal_to<unsigned long>, std::hash<unsigned long>, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<false, false, true> >::_M_find_before_node (this=0x608038, __n=2, [email protected]: 2, __code=2) at /usr/include/c++/4.9/bits/hashtable.h:1442 
#1 0x0000000000402286 in std::_Hashtable<unsigned long, std::pair<unsigned long const, BufferFrame>, std::allocator<std::pair<unsigned long const, BufferFrame> >, std::__detail::_Select1st, std::equal_to<unsigned long>, std::hash<unsigned long>, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<false, false, true> >::_M_find_node (this=0x608038, __bkt=2, [email protected]: 2, __c=2) at /usr/include/c++/4.9/bits/hashtable.h:625 
#2 0x0000000000401cd6 in std::_Hashtable<unsigned long, std::pair<unsigned long const, BufferFrame>, std::allocator<std::pair<unsigned long const, BufferFrame> >, std::__detail::_Select1st, std::equal_to<unsigned long>, std::hash<unsigned long>, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<false, false, true> >::find (this=0x608038, [email protected]: 2) at /usr/include/c++/4.9/bits/hashtable.h:1304 
#3 0x000000000040198f in std::unordered_map<unsigned long, BufferFrame, std::hash<unsigned long>, std::equal_to<unsigned long>, std::allocator<std::pair<unsigned long const, BufferFrame> > >::find (
this=0x608038, [email protected]: 2) at /usr/include/c++/4.9/bits/unordered_map.h:574 
#4 0x00000000004013dd in BufferManager::fixPage (this=0x608030, pageId=2, exclusive=true) at BufferManager.cpp:36 
#5 0x0000000000404268 in main (argc=4, argv=0x7fffffffe2c8) at buffertest.cpp:87

我也尝试过使用的valgrind调试它，因为我想到了我在错误出现之前的某个时间点可能会被忽视。这给了我以下输出：

==27031== Memcheck, a memory error detector 
==27031== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al. 
==27031== Using Valgrind-3.10.0 and LibVEX; rerun with -h for copyright info 
==27031== Command: ./buffer-test 11 3 1 
==27031== 
==27031== Invalid write of size 8 
==27031== at 0x401642: std::__detail::_Hash_node_base::_Hash_node_base() (hashtable_policy.h:234) 
==27031== by 0x4020A0: std::_Hashtable<std::string, std::pair<std::string const, int>, std::allocator<std::pair<std::string const, int> >, std::__detail::_Select1st, std::equal_to<std::string>, std::hash<std::string>, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<true, false, true> >::_Hashtable(unsigned long, std::hash<std::string> const&, std::__detail::_Mod_range_hashing const&, std::__detail::_Default_ranged_hash const&, std::equal_to<std::string> const&, std::__detail::_Select1st const&, std::allocator<std::pair<std::string const, int> > const&) (hashtable.h:799) 
==27031== by 0x401BB5: std::_Hashtable<std::string, std::pair<std::string const, int>, std::allocator<std::pair<std::string const, int> >, std::__detail::_Select1st, std::equal_to<std::string>, std::hash<std::string>, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<true, false, true> >::_Hashtable(unsigned long, std::hash<std::string> const&, std::equal_to<std::string> const&, std::allocator<std::pair<std::string const, int> > const&) (hashtable.h:420) 
==27031== by 0x4018DC: std::unordered_map<std::string, int, std::hash<std::string>, std::equal_to<std::string>, std::allocator<std::pair<std::string const, int> > >::unordered_map(unsigned long, std::hash<std::string> const&, std::equal_to<std::string> const&, std::allocator<std::pair<std::string const, int> > const&) (unordered_map.h:143) 
==27031== by 0x401257: BufferManager::BufferManager(unsigned int) (BufferManager.cpp:21) 
==27031== by 0x4041B6: main (buffertest.cpp:79) 
==27031== Address 0x5c1d0e0 is 16 bytes after a block of size 64 alloc'd 
==27031== at 0x4C29180: operator new(unsigned long) (vg_replace_malloc.c:324) 
==27031== by 0x4041A3: main (buffertest.cpp:79) 
==27031== 
==27031== Invalid write of size 8 
==27031== at 0x4020A5: std::_Hashtable<std::string, std::pair<std::string const, int>, std::allocator<std::pair<std::string const, int> >, std::__detail::_Select1st, std::equal_to<std::string>, std::hash<std::string>, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<true, false, true> >::_Hashtable(unsigned long, std::hash<std::string> const&, std::__detail::_Mod_range_hashing const&, std::__detail::_Default_ranged_hash const&, std::equal_to<std::string> const&, std::__detail::_Select1st const&, std::allocator<std::pair<std::string const, int> > const&) (hashtable.h:799) 
==27031== by 0x401BB5: std::_Hashtable<std::string, std::pair<std::string const, int>, std::allocator<std::pair<std::string const, int> >, std::__detail::_Select1st, std::equal_to<std::string>, std::hash<std::string>, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<true, false, true> >::_Hashtable(unsigned long, std::hash<std::string> const&, std::equal_to<std::string> const&, std::allocator<std::pair<std::string const, int> > const&) (hashtable.h:420) 
==27031== by 0x4018DC: std::unordered_map<std::string, int, std::hash<std::string>, std::equal_to<std::string>, std::allocator<std::pair<std::string const, int> > >::unordered_map(unsigned long, std::hash<std::string> const&, std::equal_to<std::string> const&, std::allocator<std::pair<std::string const, int> > const&) (unordered_map.h:143) 
==27031== by 0x401257: BufferManager::BufferManager(unsigned int) (BufferManager.cpp:21) 
==27031== by 0x4041B6: main (buffertest.cpp:79) 
==27031== Address 0x5c1d0e8 is 24 bytes after a block of size 64 in arena "client" 
==27031== 

valgrind: m_mallocfree.c:304 (get_bszB_as_is): Assertion 'bszB_lo == bszB_hi' failed. 
valgrind: Heap block lo/hi size mismatch: lo = 128, hi = 0. 
This is probably caused by your program erroneously writing past the 
end of a heap block and corrupting heap metadata. If you fix any 
invalid writes reported by Memcheck, this assertion failure will 
probably go away. Please try that before reporting this as a bug. 


host stacktrace: 
==27031== at 0x380A48EF: show_sched_status_wrk (m_libcassert.c:319) 
==27031== by 0x380A49E4: report_and_quit (m_libcassert.c:390) 
==27031== by 0x380A4B66: vgPlain_assert_fail (m_libcassert.c:455) 
==27031== by 0x380B170D: get_bszB_as_is (m_mallocfree.c:302) 
==27031== by 0x380B170D: get_bszB (m_mallocfree.c:312) 
==27031== by 0x380B170D: get_pszB (m_mallocfree.c:386) 
==27031== by 0x380B170D: vgPlain_describe_arena_addr (m_mallocfree.c:1532) 
==27031== by 0x3809DC93: vgPlain_describe_addr (m_addrinfo.c:188) 
==27031== by 0x3809C73B: vgMemCheck_update_Error_extra (mc_errors.c:1133) 
==27031== by 0x380A05BA: vgPlain_maybe_record_error (m_errormgr.c:818) 
==27031== by 0x3809BCB2: vgMemCheck_record_address_error (mc_errors.c:753) 
==27031== by 0x803EDF459: ??? 
==27031== by 0x802D95EEF: ??? 
==27031== by 0x3807295F: vgMemCheck_malloc (mc_malloc_wrappers.c:388) 
==27031== by 0x4020A0: std::_Hashtable<std::string, std::pair<std::string const, int>, std::allocator<std::pair<std::string const, int> >, std::__detail::_Select1st, std::equal_to<std::string>, std::hash<std::string>, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<true, false, true> >::_Hashtable(unsigned long, std::hash<std::string> const&, std::__detail::_Mod_range_hashing const&, std::__detail::_Default_ranged_hash const&, std::equal_to<std::string> const&, std::__detail::_Select1st const&, std::allocator<std::pair<std::string const, int> > const&) (hashtable.h:799) 

sched status: 
    running_tid=1 

Thread 1: status = VgTs_Runnable 
==27031== at 0x401682: std::__detail::_Prime_rehash_policy::_Prime_rehash_policy(float) (hashtable_policy.h:464) 
==27031== by 0x4020C4: std::_Hashtable<std::string, std::pair<std::string const, int>, std::allocator<std::pair<std::string const, int> >, std::__detail::_Select1st, std::equal_to<std::string>, std::hash<std::string>, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<true, false, true> >::_Hashtable(unsigned long, std::hash<std::string> const&, std::__detail::_Mod_range_hashing const&, std::__detail::_Default_ranged_hash const&, std::equal_to<std::string> const&, std::__detail::_Select1st const&, std::allocator<std::pair<std::string const, int> > const&) (hashtable.h:799) 
==27031== by 0x401BB5: std::_Hashtable<std::string, std::pair<std::string const, int>, std::allocator<std::pair<std::string const, int> >, std::__detail::_Select1st, std::equal_to<std::string>, std::hash<std::string>, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<true, false, true> >::_Hashtable(unsigned long, std::hash<std::string> const&, std::equal_to<std::string> const&, std::allocator<std::pair<std::string const, int> > const&) (hashtable.h:420) 
==27031== by 0x4018DC: std::unordered_map<std::string, int, std::hash<std::string>, std::equal_to<std::string>, std::allocator<std::pair<std::string const, int> > >::unordered_map(unsigned long, std::hash<std::string> const&, std::equal_to<std::string> const&, std::allocator<std::pair<std::string const, int> > const&) (unordered_map.h:143) 
==27031== by 0x401257: BufferManager::BufferManager(unsigned int) (BufferManager.cpp:21) 
==27031== by 0x4041B6: main (buffertest.cpp:79) 


Note: see also the FAQ in the source distribution. 
It contains workarounds to several common problems. 
In particular, if Valgrind aborted or crashed after 
identifying problems in your program, there's a good chance 
that fixing those problems will prevent Valgrind aborting or 
crashing, especially if it happened in m_mallocfree.c. 

If that doesn't help, please report this bug to: www.valgrind.org 

In the bug report, send all the above text, the valgrind 
version, and what OS and version you are using. Thanks.

可悲的是我无法弄清楚这些错误想告诉我什么。它们发生的代码甚至没有对这个unordered_map做任何事情，它只是构造函数。

我将不胜感激任何帮助或想法如何解决这个问题。 以下是我的代码（相关行）的来源。如果您需要更多信息或希望我进行任何测试，我会很乐意将其提供给您。

BufferManager.hpp（更新）

#ifndef BUFFER_MANAGER_HPP 
#include "BufferFrame.hpp" 
#include <stdint.h> 
#include <unordered_map> 

class BufferManager { 

public: 
    BufferManager(const unsigned int pageCount); 
    BufferFrame& fixPage(const uint64_t pageId, const bool exclusive); 
    void unfixPage(BufferFrame& frame, const bool isDirty); 
    ~BufferManager(); 

private: 
    uint64_t pageCount; 
    std::unordered_map<uint64_t, BufferFrame *> pages; 
    std::unordered_map<std::string, int> files; 
}; 


#define BUFFER_MANAGER_HPP 
#endif

BufferManager.cpp（部分）（更新）：

BufferManager::BufferManager(const unsigned int pageCount) { 
    this->pageCount = pageCount; 
    std::cout << "BufferFrame constructor" << std::endl; 
} 

BufferFrame& BufferManager::fixPage(const uint64_t pageId, const bool exclusive) { 
    std::cout << "fixPage called with pageId: " << pageId << " requesting exclusive: " << exclusive<< std::endl; 

    std::cout << "Pages.size(): " << pages.size() << std::endl; 

    //Test if we got the frame in the buffer 
    BufferFrame * frame; 
    std::unordered_map<uint64_t, BufferFrame *>::const_iterator got = pages.find(pageId); 
    if (got == pages.end()) { 
     frame = new BufferFrame(); 
     frame->data = malloc(pageSize); 
     frame->pageId = pageId; 
     frame->isDirty = false; 

     std::pair<uint64_t, BufferFrame *> element(pageId, frame); 
     pages.insert(element); 
     std::cout << "fixPage of page: " << pageId << " (empty page used. Load not implemented!)" << std::endl; 
    } 
    else { 
     frame = got->second; 
     std::cout << "fixPage of page: " << pageId << " (Page loaded from map)" << std::endl; 
    } 
    return *frame; 
}

BufferFrame.hpp：

#ifndef BUFFER_FRAME_HPP 
#include <stdint.h> 

class BufferFrame { 
    friend class BufferManager; 

public: 

    void* getData(); 

private: 

    void * data; 
    uint64_t pageId; 
    bool isDirty; 
}; 



#define BUFFER_FRAME_HPP 
#endif

我试过到目前为止正在用一个BufferFrame *替换unordered_map内的BufferFrame，它并没有改变任何东西。即使用int替换它也没有任何效果。

编辑：更新BufferManager.hpp和BufferManager.cpp使用unordered_map。

EDIT2：首先：感谢所有，那些试图帮我

我发现这个问题：这是在Makefile引起我的.o文件一个不被错误再生。这导致使用不同版本的BufferFrame.hpp的不同文件。这显然必须导致bizzarre记忆错误（就像我得到的那些）。

答

看来代码正在返回对局部变量的引用。

BufferFrame& BufferManager::fixPage(
    .... 
    BufferFrame frame; 
    .... 
    return frame;

您可能需要您的设计更改为

std::unordered_map<uint64_t, BufferFrame *> pages;

甚至

std::unordered_map<uint64_t, std::shared_ptr<BufferFrame> > pages;

我还建议创建BufferFrame作为一个适当的C++类构造函数和析构函数，使它管理自己的记忆。

+0

这实际上是我的第一个想法，如何做到这一点。我只是删除了指针，因为在调试的时候我用完了想法。反正你是对的，它不能那样工作。但改回它并没有改变错误。稍后我会将BufferFrame更改为适当的C++类，但这不应该成为问题。无论如何，如果它改变了任何事情，我会通知你。 – Sebastian

答

请看仔细这两方面：

  • 在哪里“的pageSize”设置到什么值？我看不到任何东西。
  • 你真的需要混合'new'和malloc，同时分配'frame'。
  • 您没有显示如何在使用后清理BufferFrame对象。
  • 如果你正在做新的+免费或malloc +删除，你有麻烦。

我愿意与Arun建议的BufferFrame的ctor和dtor一起使用。

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