[英]Trying to learn boost::intrusive Q3 - When storing pointers in ICs, should I use smart_pointer?
我對侵入式容器的理解有了長足的進步。 我有一個運行“ while”的程序,然后在這樣的代碼行上運行:delete * it; (見下文):
....
// : public list_base_hook< void_pointer< ip::offset_ptr<void> > >
class OneDepthPrice : public list_base_hook<link_mode<auto_unlink>> // This is a derivation hook
{
public:
Provider provider;
Price price;
public:
list_member_hook<link_mode<auto_unlink>> member_hook_; // This is a member hook
OneDepthPrice(Provider prov, Price p) : provider(prov), price(p) {}
};
...
std::vector<OneDepthPrice *>& vecPrices
for (auto it = vecPrices.begin(); it != vecPrices.end(); ++it)
{
auto& e = *it;
#if DEBUG
std::cout << e->provider.name << "\n" << std::flush;
#endif
if(e->provider.name == newPrices.provider.name)
{
delete *it; //This is the offending line in the stack trace in the debugger.
it = vecPrices.erase(it);
}
}
該程序使用此堆棧跟蹤崩潰:
#0 0x407ddd boost::intrusive::list_node_traits<void*>::set_next(n=@0x7fffffffe2b8: 0x0,
next=@0x7fffffffe2b0: 0x706860) (/usr/local/include/boost/intrusive/detail/list_node.hpp:64)
#1 0x409189 boost::intrusive::circular_list_algorithms<boost::intrusive::list_node_traits<void*> >::unlink(this_node=@0x7fffffffe2e8: 0x706830) (/usr/local/include/boost/intrusive/circular_list_algorithms.hpp:140)
#2 0x407e2a boost::intrusive::generic_hook<boost::intrusive::get_list_node_algo<void*>, boost::intrusive::default_tag, (boost::intrusive::link_mode_type)2, (boost::intrusive::base_hook_type)1>::unlink(this=0x706830) (/usr/local/include/boost/intrusive/detail/generic_hook.hpp:180)
#3 0x406b5c boost::intrusive::detail::destructor_impl<boost::intrusive::generic_hook<boost::intrusive::get_list_node_algo<void*>, boost::intrusive::default_tag, (boost::intrusive::link_mode_type)2, (boost::intrusive::base_hook_type)1> >(hook=...) (/usr/local/include/boost/intrusive/detail/utilities.hpp:371)
#4 0x405b13 boost::intrusive::generic_hook<boost::intrusive::get_list_node_algo<void*>, boost::intrusive::default_tag, (boost::intrusive::link_mode_type)2, (boost::intrusive::base_hook_type)1>::~generic_hook(this=0x706830, __in_chrg=<optimized out>) (/usr/local/include/boost/intrusive/detail/generic_hook.hpp:160)
#5 0x40534a boost::intrusive::list_base_hook<boost::intrusive::link_mode<(boost::intrusive::link_mode_type)2>, void, void>::~list_base_hook(this=0x706830, __in_chrg=<optimized out>) (/usr/local/include/boost/intrusive/list_hook.hpp:86)
#6 0x405546 OneDepthPrice::~OneDepthPrice(this=0x706830, __in_chrg=<optimized out>) (/home/idf/Documents/TestCPPArrays/TestCPPArrays.cpp:86)
#7 0x403728 UpdateBunchTogether(vectogether=..., vecPrices=..., newPrices=...) (/home/idf/Documents/TestCPPArrays/TestCPPArrays.cpp:291)
#8 0x404765 main() (/home/idf/Documents/TestCPPArrays/TestCPPArrays.cpp:558)
這是一個奇怪的錯誤,因為該程序不是多線程的,但運行了一段時間卻沒有任何障礙。 我不確定發生了什么,但是也許我需要使用smart_pointers?
將我的評論移至答案。 當您這樣做時:
for (auto it = vecPrices.begin(); it != vecPrices.end(); ++it)
{
auto& e = *it;
if(e->provider.name == newPrices.provider.name)
{
delete *it; //This is the offending line in the stack trace in the debugger.
it = vecPrices.erase(it);
}
}
擦除時可以正確更新迭代器,但是可以無條件地增加它。 這很不好,原因有兩個:可能無法刪除下一個對象,並且如果erase()
返回end()
那么您就越過了向量的末尾。
為了安全擦除,您需要執行以下操作:
for (auto it = vecPrices.begin(); it != vecPrices.end(); /* nothing */)
{
auto& e = *it;
if(e->provider.name == newPrices.provider.name)
{
delete *it; //This is the offending line in the stack trace in the debugger.
it = vecPrices.erase(it);
}
else
{
++it; // this is where we increment
}
}
實際上加速侵入你擔心在那里的對象將參考所有的時間 (因為引用是所有的地方)。
也許您只想要weak_ptr。 似乎您正在嘗試實現垃圾回收。 這是一個使用weak_ptr稍作修改的想法:
#include <vector>
#include <map>
#include <boost/weak_ptr.hpp>
#include <boost/make_shared.hpp>
#include <iostream>
using std::string;
using boost::shared_ptr;
using boost::weak_ptr;
using boost::make_shared;
struct Person {
string name_;
Person(string name) : name_(move(name)) {}
using tag = weak_ptr<void>;
tag track() const { return tracking_tag; }
private:
shared_ptr<void> tracking_tag = make_shared<char>('x');
};
template <typename T>
inline bool IsDeleted(weak_ptr<T> const& v) {
return !v.lock();
}
enum favcolor { red, blue, pink, magenta, beige } favorite_color;
template <typename Map> size_t garbage_collect(Map& map)
{
size_t collected = 0;
for (auto it = map.begin(); it!=map.end();)
{
if (IsDeleted(it->first))
++collected, it = map.erase(it);
else
++it;
}
return collected;
}
int main()
{
std::vector<Person> people;
for (auto&& name : { "John", "Mike", "Garbarek", "Milou", "Confucius", "Kiplat" })
people.emplace_back(name);
struct Properties {
favcolor favorite_color;
struct Car { string brand; int year; } vehicle;
};
std::map<Person::tag, Properties> associated {
{ people[0].track(), Properties { magenta, { "Chevy", 1986 } } },
{ people[2].track(), Properties { pink, { "Kia", 2011 } } },
};
for (auto& p : people) std::cout << p.name_ << " "; std::cout << "\n";
std::cout << "Defined properties: " << associated.size() << "\n";
people.erase(std::remove_if(people.begin(), people.end(), [](Person const& p) { return p.name_[1] == 'o'; }), people.end());
for (auto& p : people) std::cout << p.name_ << " "; std::cout << "\n";
std::cout << "Defined properties before garbage collect: " << associated.size() << "\n";
auto count = garbage_collect(associated);
std::cout << "Defined properties after garbage collect: " << associated.size() << " (" << count << " collected)\n";
}
輸出:
John Mike Garbarek Milou Confucius Kiplat
Defined properties: 2
Mike Garbarek Milou Kiplat
Defined properties before garbage collect: 2
Defined properties after garbage collect: 1 (1 collected)
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