pstack显示问号

Question

在linux上运行pstack {pid}时，有时会显示?？为了一些记录。这是什么原因呢？如果只是优化，我怎么知道真正的相关代码呢？

#0  0x00000037d620b3dc in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
#1  0x00000000008c83db in boost::condition_variable::wait(boost::unique_lock<boost::mutex>&) ()
#2  0x0000000000d95f7b in mongo::SimpleRWLock::lock_shared() ()
#3  0x00000000008bce47 in mongo::Lock::DBRead::lockOther(mongo::StringData const&) ()
#4  0x00000000008bfc86 in mongo::Lock::DBRead::lockDB(std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) ()
#5  0x00000000008c1eb0 in mongo::Lock::DBRead::DBRead(mongo::StringData const&) ()
#6  0x000000000081fa35 in mongo::Client::ReadContext::ReadContext(std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) ()
**#7  0x0000000000b852bb in ?? ()**
#8  0x00000000008ab646 in mongo::CmdServerStatus::run(std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, mongo::BSONObj&, int, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&, mongo::BSONObjBuilder&, bool) ()

Answer 1

连我都不知道为什么只有一张唱片显示"??"，但我已经找到了解决办法，知道什么是"??“在这种情况下表示。

我在生产中得到了以前的堆栈。我在DEV env中运行流量(在DEV中，我使用-ggdb选项编译并使用--nostrip安装)，我得到了以下堆栈：

Thread 2 (Thread 0x7fb112c27700 (LWP 29881)):
#0  0x0000003af460b43c in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
#1  0x00000000008661cb in boost::condition_variable::wait(boost::unique_lock<boost::mutex>&) ()
#2  0x0000000000d093e3 in mongo::SimpleRWLock::lock_shared() ()
#3  0x00000000008e0cfb in mongo::Lock::DBRead::lockOther(mongo::StringData const&) ()
#4  0x00000000008e2701 in mongo::Lock::DBRead::lockDB(std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) ()
#5  0x00000000008e3557 in mongo::Lock::DBRead::DBRead(mongo::StringData const&) ()
#6  0x0000000000859d00 in mongo::Client::ReadContext::ReadContext(std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, std::basic_string<char, std::char_traits<char>
, std::allocator<char> > const&) ()
#7  0x0000000000b5a6c0 in mongo::(anonymous namespace)::RecordStats::generateSection(mongo::BSONElement const&) const ()
#8  0x00000000008c4934 in mongo::CmdServerStatus::run(std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, mongo::BSONObj&, int, std::basic_string<char, std::char_tr
aits<char>, std::allocator<char> >&, mongo::BSONObjBuilder&, bool) ()
#9  0x00000000008ef0d4 in mongo::_execCommand(mongo::Command*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, mongo::BSONObj&, int, std::basic_string<char, std
::char_traits<char>, std::allocator<char> >&, mongo::BSONObjBuilder&, bool) ()