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目前我正在嘗試爲我們需要爲大學構建的數據庫系統實現某種基本的文件訪問層。要做到這一點，我被要求在內存中緩存頁面。要快速確定哪些頁面已加載，我將它們全部存儲在unordered_map中。C++ unordered_map find（）或insert（）上的SIGSEGV
現在的問題是，在對這個函數進行一些調用後，SIGSEGV出現在unordered_map的_M_find_before_node中。我嘗試使用gdb調試它，但我不知道到哪裏尋找它，因爲在調用unordered_map中出現錯誤：
#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, [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
我也嘗試過使用的valgrind調試它，因爲我想到了我在錯誤出現之前的某個時間點可能會被忽視。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麼。它們發生的代碼甚至沒有對這個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這個問題。 以下是我的代碼（相關行）的來源。如果您需要更多信息或希望我進行任何測試，我會很樂意將其提供給您。
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
我試過到目前爲止正在用一個BufferFrame *替換unordered_map內的BufferFrame，它並沒有改變任何東西。即使用int替換它也沒有任何效果。
編輯：更新BufferManager.hpp和BufferManager.cpp使用unordered_map。
EDIT2：首先：感謝所有，那些試圖幫我
我發現這個問題：這是在Makefile引起我的.o文件一個不被錯誤再生。這導致使用不同版本的BufferFrame.hpp的不同文件。這顯然必須導致bizzarre記憶錯誤（就像我得到的那些）。
這實際上是我的第一個想法，如何做到這一點。我只是刪除了指針，因爲在調試的時候我用完了想法。反正你是對的，它不能那樣工作。但改回它並沒有改變錯誤。稍後我會將BufferFrame更改爲適當的C++類，但這不應該成爲問題。無論如何，如果它改變了任何事情，我會通知你。 – Sebastian