C ++ unordered_map SIGSEGV在find（）或insert（）上

Question

目前，我正在嘗試為我們需要為大學構建的數據庫系統實現某種基本的文件訪問層。 為此，我被要求在內存中緩存頁面。 為了快速確定尚未加載哪些頁面，我將所有頁面存儲在unordered_map中。

現在的問題是，在對該函數進行一些調用之后，SIGSEGV出現在unordered_map的_M_find_before_node內。 我嘗試使用gdb調試它，但是我不知道在哪里尋找它，因為在調用unordered_map時發生錯誤：

#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, __k=@0x7fffffffe050: 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, __key=@0x7fffffffe050: 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, __k=@0x7fffffffe050: 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, __x=@0x7fffffffe050: 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

我還嘗試使用valgrind對其進行調試，因為我想到在出現錯誤之前的某個時間點我可能會注意到一個未注意到的內存損壞。 這給了我以下輸出：

==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，我無法弄清楚這些錯誤想告訴我什么。 它們發生的代碼甚至沒有使用此unordered_map做任何事情，它只是構造函數。

我將不勝感激任何幫助或想法如何解決此問題。 以下是我的代碼的來源（相關行）。 如果您需要更多信息或希望我進行任何測試，我們很樂意將其提供給您。

BufferManager.hpp（已更新）

#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（部件）（已更新）：

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

到目前為止，我所嘗試的是用BufferFrame *代替unordered_map中的BufferFrame，該FrameFrame並沒有改變任何東西。 即使將其替換為int似乎也沒有任何效果。

編輯：更新了BufferManager.hpp和BufferManager.cpp以使用unordered_map。

EDIT2：首先： 謝謝大家，我試圖幫助我

我發現了問題：這是Makefile中的錯誤，導致我的.o文件之一無法重新生成。 這導致使用不同版本的BufferFrame.hpp的不同文件。 顯然，這必定會導致bizzarre內存錯誤（就像我得到的一樣）。

Answer 1

似乎代碼正在返回對局部變量的引用。

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

您可能需要將設計更改為

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

甚至

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

我還建議將BufferFrame創建為帶有構造函數和析構函數的正確C ++類，以便它管理自己的內存。

Answer 2

請仔細查看以下兩個方面：

• 在哪里將“ pageSize”設置為什么值？ 我什么也看不到。
• 您是否真的需要在分配“框架”的同時混合“ new”和malloc？
• 您沒有顯示使用后如何清理BufferFrame對象。
• 如果您要執行new + free或malloc + delete，則會遇到麻煩。

我會按照Arun的建議為BufferFrame使用ctor和dtor。