目标：我想尽快修改内部信息，并从多个线程同步访问这些信息。
我简化了代码，但这是我试图实现的。
我有2个共享指针。
其中一个叫做 m_mutable_data 而另一个叫 m_const_data.
m_mutable_data 是以字符串保护的方式更新的。m_const_data 每隔60s更新一次m_mutable_data的内容，也是以strand guarded的方式。
这是唯一的地方 m_const_data 用新数据重置共享指针。m_const_data 被许多线程同步读取，每秒1000次以上。
编码
class black_list_container : public std::enable_shared_from_this<black_list_container>
{
struct meta_data
{
bool blacked;
}
struct black_list_data
{
std::unordered_map<uint32_t,meta_data> data;
}
public:
#pragma optimize( "", off )
bool is_blacked(uint32_t id)
{
// This call is called from many different threads (1000+ calls per second)
// should be synchronous and as fast as possible
auto c = m_const_data;
return c->data[id].blacked;
}
#pragma optimize( "", on )
#pragma optimize( "", off )
void update_const_data()
{
// Called internaly by timer every 60s to update m_const_data with contents of m_mutable_data
// Guarded with strand
m_strand->post([self{shared_from_this()}]{
auto snapshot = new black_list_data();
snapshot->data = m_mutable_data->data;
m_const_data.reset(snapshot);
});
}
#pragma optimize( "", on )
private:
void internal_modification_mutable_data()
{
// Called internaly by different metrics
// Guarded with strand
m_strand->post([self{shared_from_this()}]{
// .... do some modification on internal m_mutable_data
});
}
boost::asio::io_context::strand m_strand;
std::shared_ptr<black_list_data> m_mutable_data;
std::shared_ptr<black_list_data> m_const_data;
};
很少，这段代码在方法'is_blacked'中的第1行崩溃。
auto c = m_const_data;
这个是回溯
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
Core was generated by `./STRATUM-01'.
Program terminated with signal 6, Aborted.
#0 0x00007fe09aaf1387 in raise () from /lib64/libc.so.6
Missing separate debuginfos, use: debuginfo-install glibc-2.17-307.el7.1.x86_64 libgcc-4.8.5-39.el7.x86_64 libstdc++-4.8.5-39.el7.x86_64
(gdb) bt
#0 0x00007fe09aaf1387 in raise () from /lib64/libc.so.6
#1 0x00007fe09aaf2a78 in abort () from /lib64/libc.so.6
#2 0x00007fe09ab33ed7 in __libc_message () from /lib64/libc.so.6
#3 0x00007fe09ab3c299 in _int_free () from /lib64/libc.so.6
#4 0x00000000005fae36 in std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>::_M_release (this=0x7fe0440aeaa0) at /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/shared_ptr_base.h:154
#5 0x00000000006b9205 in ~__shared_count (this=<synthetic pointer>, __in_chrg=<optimized out>) at /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/shared_ptr_base.h:684
#6 ~__shared_ptr (this=<synthetic pointer>, __in_chrg=<optimized out>) at /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/shared_ptr_base.h:1123
#7 ~shared_ptr (this=<synthetic pointer>, __in_chrg=<optimized out>) at /opt/rh/devtoolset-7/root/usr/include/c++/7/bits/shared_ptr.h:93
#8 black_list_container_impl::is_blacked (this=0x7fe08c287e50, id=23654) at /var/lib/jenkins/workspace/validator/src/black_list_container.cpp:69
我不太清楚为什么在第7帧中调用销毁shared_ptr的功能
很明显，我没有达到我的目标，所以请指导我进入模式，真正实现我的目标，以线安全的方式。
我知道我可以使用
std::atomic<std::shared_ptr<black_list_data>> m_const_data;
但这是否会影响从多个不同线程读取信息的性能？
我想我在这篇文章中找到了问题的答案。原子智能指针.
所以，我必须修改以下代码 update_const_data() 到
auto snapshot = std::make_shared<black_list_data>();
snapshot->data = m_mutable_data->data;
std::atomic_store(&m_const_data, snapshot);
和代码 is_blacked() 到
auto c = std::atomic_load(&m_const_data);