c – 奇怪的shared_ptr行为
作者：互联网
我在c中发现了一个非常奇怪的std :: shared_ptr行为.
以下示例与标准指针完美配合.
但是,使用std :: shared_ptr会导致分段错误. (见下面的回溯)
我知道,从多个线程访问std :: shared_ptr是不安全的,因此我正在使用原子操作.即使是经典的锁也无法解决问题.
我使用gcc版本6.3.0 20170406(Ubuntu 6.3.0-12ubuntu2)与-Wall -O2 -g和-std = c 17
有人知道解决方案或代码崩溃的原因吗？
#include <iostream>
#include <thread>
#include <vector>
#include <mutex>
template <typename T>
class list {
private:
struct Node {
T value;
std::shared_ptr<Node> next;
Node() : next(nullptr) {}
};
std::shared_ptr<Node> head;
public:
// create dummy-nodes
explicit list() : head(std::make_shared<Node>()){
head->next = std::make_shared<Node>();
};
void push_front(T val) {
std::shared_ptr<Node> current;
std::shared_ptr<Node> next;
std::shared_ptr<Node> newNode = std::make_shared<Node>();
newNode->value = val;
do {
current = std::atomic_load<Node>(&head);
next = std::atomic_load<Node>(¤t->next);
newNode->next = next;
} while (!std::atomic_compare_exchange_weak<Node>(¤t->next, &next, newNode));
}
};
int main(int argc, char* argv[]) {
list<int> ll;
std::vector<std::thread> threads;
const int thread_count = 8;
const int local_count = 200000;
std::mutex m;
for (int i = 0; i < thread_count; i++) {
threads.push_back(std::thread([&ll, i, local_count, &m]() {
for (int j = local_count * i; j < local_count * (i + 1); j++) {
m.lock(); // optional for testing; doesnt solve the problem
ll.push_front(j);
m.unlock();
}
}));
}
for (auto& thrd : threads) {
thrd.join();
}
return 0;
}
GDB-回溯：
0x0000555555555d4e in std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>::_M_release (this=0x7fffd48eb0e0) at /usr/include/c++/6/bits/shared_ptr_base.h:150
150 _M_dispose();
(gdb) bt
#0 0x0000555555555d4e in std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>::_M_release (this=0x7fffd48eb0e0) at /usr/include/c++/6/bits/shared_ptr_base.h:150
#1 std::__shared_count<(__gnu_cxx::_Lock_policy)2>::~__shared_count (this=<optimized out>, __in_chrg=<optimized out>) at /usr/include/c++/6/bits/shared_ptr_base.h:662
#2 std::__shared_ptr<list<int>::Node, (__gnu_cxx::_Lock_policy)2>::~__shared_ptr (this=<optimized out>, __in_chrg=<optimized out>) at /usr/include/c++/6/bits/shared_ptr_base.h:928
#3 std::shared_ptr<list<int>::Node>::~shared_ptr (this=<optimized out>, __in_chrg=<optimized out>) at /usr/include/c++/6/bits/shared_ptr.h:93
#4 list<int>::Node::~Node (this=<optimized out>, __in_chrg=<optimized out>) at src/main.cpp:11
#5 __gnu_cxx::new_allocator<list<int>::Node>::destroy<list<int>::Node> (this=<optimized out>, __p=<optimized out>) at /usr/include/c++/6/ext/new_allocator.h:124
#6 std::allocator_traits<std::allocator<list<int>::Node> >::destroy<list<int>::Node> (__a=..., __p=<optimized out>) at /usr/include/c++/6/bits/alloc_traits.h:487
#7 std::_Sp_counted_ptr_inplace<list<int>::Node, std::allocator<list<int>::Node>, (__gnu_cxx::_Lock_policy)2>::_M_dispose (this=<optimized out>) at /usr/include/c++/6/bits/shared_ptr_base.h:529
#8 0x0000555555555d51 in std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>::_M_release (this=0x7fffd48eb110) at /usr/include/c++/6/bits/shared_ptr_base.h:150
#9 std::__shared_count<(__gnu_cxx::_Lock_policy)2>::~__shared_count (this=<optimized out>, __in_chrg=<optimized out>) at /usr/include/c++/6/bits/shared_ptr_base.h:662
#10 std::__shared_ptr<list<int>::Node, (__gnu_cxx::_Lock_policy)2>::~__shared_ptr (this=<optimized out>, __in_chrg=<optimized out>) at /usr/include/c++/6/bits/shared_ptr_base.h:928
#11 std::shared_ptr<list<int>::Node>::~shared_ptr (this=<optimized out>, __in_chrg=<optimized out>) at /usr/include/c++/6/bits/shared_ptr.h:93
#12 list<int>::Node::~Node (this=<optimized out>, __in_chrg=<optimized out>) at src/main.cpp:11
#13 __gnu_cxx::new_allocator<list<int>::Node>::destroy<list<int>::Node> (this=<optimized out>, __p=<optimized out>) at /usr/include/c++/6/ext/new_allocator.h:124
#14 std::allocator_traits<std::allocator<list<int>::Node> >::destroy<list<int>::Node> (__a=..., __p=<optimized out>) at /usr/include/c++/6/bits/alloc_traits.h:487
#15 std::_Sp_counted_ptr_inplace<list<int>::Node, std::allocator<list<int>::Node>, (__gnu_cxx::_Lock_policy)2>::_M_dispose (this=<optimized out>) at /usr/include/c++/6/bits/shared_ptr_base.h:529
#16 0x0000555555555d51 in std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>::_M_release (this=0x7fffd48eb140) at /usr/include/c++/6/bits/shared_ptr_base.h:150
#17 std::__shared_count<(__gnu_cxx::_Lock_policy)2>::~__shared_count (this=<optimized out>, __in_chrg=<optimized out>) at /usr/include/c++/6/bits/shared_ptr_base.h:662
#18 std::__shared_ptr<list<int>::Node, (__gnu_cxx::_Lock_policy)2>::~__shared_ptr (this=<optimized out>, __in_chrg=<optimized out>) at /usr/include/c++/6/bits/shared_ptr_base.h:928
#19 std::shared_ptr<list<int>::Node>::~shared_ptr (this=<optimized out>, __in_chrg=<optimized out>) at /usr/include/c++/6/bits/shared_ptr.h:93
#20 list<int>::Node::~Node (this=<optimized out>, __in_chrg=<optimized out>) at src/main.cpp:11
#21 __gnu_cxx::new_allocator<list<int>::Node>::destroy<list<int>::Node> (this=<optimized out>, __p=<optimized out>) at /usr/include/c++/6/ext/new_allocator.h:124
#22 std::allocator_traits<std::allocator<list<int>::Node> >::destroy<list<int>::Node> (__a=..., __p=<optimized out>) at /usr/include/c++/6/bits/alloc_traits.h:487
#23 std::_Sp_counted_ptr_inplace<list<int>::Node, std::allocator<list<int>::Node>, (__gnu_cxx::_Lock_policy)2>::_M_dispose (this=<optimized out>) at /usr/include/c++/6/bits/shared_ptr_base.h:529
#24 0x0000555555555d51 in std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>::_M_release (this=0x7fffd48eb170) at /usr/include/c++/6/bits/shared_ptr_base.h:150
#25 std::__shared_count<(__gnu_cxx::_Lock_policy)2>::~__shared_count (this=<optimized out>, __in_chrg=<optimized out>) at /usr/include/c++/6/bits/shared_ptr_base.h:662
#26 std::__shared_ptr<list<int>::Node, (__gnu_cxx::_Lock_policy)2>::~__shared_ptr (this=<optimized out>, __in_chrg=<optimized out>) at /usr/include/c++/6/bits/shared_ptr_base.h:928
#27 std::shared_ptr<list<int>::Node>::~shared_ptr (this=<optimized out>, __in_chrg=<optimized out>) at /usr/include/c++/6/bits/shared_ptr.h:93
#28 list<int>::Node::~Node (this=<optimized out>, __in_chrg=<optimized out>) at src/main.cpp:11
#29 __gnu_cxx::new_allocator<list<int>::Node>::destroy<list<int>::Node> (this=<optimized out>, __p=<optimized out>) at /usr/include/c++/6/ext/new_allocator.h:124
#30 std::allocator_traits<std::allocator<list<int>::Node> >::destroy<list<int>::Node> (__a=..., __p=<optimized out>) at /usr/include/c++/6/bits/alloc_traits.h:487
#31 std::_Sp_counted_ptr_inplace<list<int>::Node, std::allocator<list<int>::Node>, (__gnu_cxx::_Lock_policy)2>::_M_dispose (this=<optimized out>) at /usr/include/c++/6/bits/shared_ptr_base.h:529
#32 0x0000555555555d51 in std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>::_M_release (this=0x7fffd48eb1a0) at /usr/include/c++/6/bits/shared_ptr_base.h:150
#33 std::__shared_count<(__gnu_cxx::_Lock_policy)2>::~__shared_count (this=<optimized out>, __in_chrg=<optimized out>) at /usr/include/c++/6/bits/shared_ptr_base.h:662
#34 std::__shared_ptr<list<int>::Node, (__gnu_cxx::_Lock_policy)2>::~__shared_ptr (this=<optimized out>, __in_chrg=<optimized out>) at /usr/include/c++/6/bits/shared_ptr_base.h:928
#35 std::shared_ptr<list<int>::Node>::~shared_ptr (this=<optimized out>, __in_chrg=<optimized out>) at /usr/include/c++/6/bits/shared_ptr.h:93
#36 list<int>::Node::~Node (this=<optimized out>, __in_chrg=<optimized out>) at src/main.cpp:11
#37 __gnu_cxx::new_allocator<list<int>::Node>::destroy<list<int>::Node> (this=<optimized out>, __p=<optimized out>) at /usr/include/c++/6/ext/new_allocator.h:124
#38 std::allocator_traits<std::allocator<list<int>::Node> >::destroy<list<int>::Node> (__a=..., __p=<optimized out>) at /usr/include/c++/6/bits/alloc_traits.h:487
#39 std::_Sp_counted_ptr_inplace<list<int>::Node, std::allocator<list<int>::Node>, (__gnu_cxx::_Lock_policy)2>::_M_dispose (this=<optimized out>) at /usr/include/c++/6/bits/shared_ptr_base.h:529
#40 0x0000555555555d51 in std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>::_M_release (this=0x7fffd48eb1d0) at /usr/include/c++/6/bits/shared_ptr_base.h:150
#41 std::__shared_count<(__gnu_cxx::_Lock_policy)2>::~__shared_count (this=<optimized out>, __in_chrg=<optimized out>) at /usr/include/c++/6/bits/shared_ptr_base.h:662
#42 std::__shared_ptr<list<int>::Node, (__gnu_cxx::_Lock_policy)2>::~__shared_ptr (this=<optimized out>, __in_chrg=<optimized out>) at /usr/include/c++/6/bits/shared_ptr_base.h:928
#43 std::shared_ptr<list<int>::Node>::~shared_ptr (this=<optimized out>, __in_chrg=<optimized out>) at /usr/include/c++/6/bits/shared_ptr.h:93
#44 list<int>::Node::~Node (this=<optimized out>, __in_chrg=<optimized out>) at src/main.cpp:11
#45 __gnu_cxx::new_allocator<list<int>::Node>::destroy<list<int>::Node> (this=<optimized out>, __p=<optimized out>) at /usr/include/c++/6/ext/new_allocator.h:124
#46 std::allocator_traits<std::allocator<list<int>::Node> >::destroy<list<int>::Node> (__a=..., __p=<optimized out>) at /usr/include/c++/6/bits/alloc_traits.h:487
#47 std::_Sp_counted_ptr_inplace<list<int>::Node, std::allocator<list<int>::Node>, (__gnu_cxx::_Lock_policy)2>::_M_dispose (this=<optimized out>) at /usr/include/c++/6/bits/shared_ptr_base.h:529
#48 0x0000555555555d51 in std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>::_M_release (this=0x7fffd48eb200) at /usr/include/c++/6/bits/shared_ptr_base.h:150
#49 std::__shared_count<(__gnu_cxx::_Lock_policy)2>::~__shared_count (this=<optimized out>, __in_chrg=<optimized out>) at /usr/include/c++/6/bits/shared_ptr_base.h:662
#50 std::__shared_ptr<list<int>::Node, (__gnu_cxx::_Lock_policy)2>::~__shared_ptr (this=<optimized out>, __in_chrg=<optimized out>) at /usr/include/c++/6/bits/shared_ptr_base.h:928
#51 std::shared_ptr<list<int>::Node>::~shared_ptr (this=<optimized out>, __in_chrg=<optimized out>) at /usr/include/c++/6/bits/shared_ptr.h:93
#52 list<int>::Node::~Node (this=<optimized out>, __in_chrg=<optimized out>) at src/main.cpp:11
#53 __gnu_cxx::new_allocator<list<int>::Node>::destroy<list<int>::Node> (this=<optimized out>, __p=<optimized out>) at /usr/include/c++/6/ext/new_allocator.h:124
#54 std::allocator_traits<std::allocator<list<int>::Node> >::destroy<list<int>::Node> (__a=..., __p=<optimized out>) at /usr/include/c++/6/bits/alloc_traits.h:487
#55 std::_Sp_counted_ptr_inplace<list<int>::Node, std::allocator<list<int>::Node>, (__gnu_cxx::_Lock_policy)2>::_M_dispose (this=<optimized out>) at /usr/include/c++/6/bits/shared_ptr_base.h:529
解决方法:
这是智能指针和列表节点的经典问题：节点的析构函数是递归的,最终会耗尽堆栈.这就是堆栈跟踪显示的内容：堆栈溢出.
在CppCon 2016: Herb Sutter “Leak-Freedom in C++… By Default.”他们正好讨论这个问题.
标签：lock-free,c,c11,shared-ptr,atomic 来源： https://codeday.me/bug/20190724/1523022.html