为了试验线程清理器,我创建了一个小型 C++ 程序,该程序有意包含数据竞争。确实,tsan 确实检测到了错误,太棒了!但是我对生成的消息感到困惑......
- 它报告了一个写-写数据竞争,我本来预计会出现一个读写竞争。我希望
find()
不要写在我的容器中。如果我进一步进行小的代码调整以尝试获取 的const
版本set::find()
,似乎仍然存在相同的写入竞争。 - 它显示了 4 字节原子写入和同一地址的 8 字节写入之间的写入冲突。容器类中的同一个字段被两种不同的访问类型访问,这似乎很奇怪。
是否可以选择使用find()
不写入 STL 容器的 const?
这是经过测试的 C++ 程序:
/*****************************************************************************
* Small example with an inter-thread data race that is not obvious.
* the error is a consequence of the non-threadsafeness of the STL containers.
* Threading is created through portable C++11 constructs.
* Tsan does detect the data race(?).
*
* Compile with one of:
* g++-4.8 -std=c++11 -g -Wall -o race-stl11b race-stl11b.cc -pthread
* g++-4.8 -std=c++11 -g -Wall -fsanitize=thread -fPIE -o race-stl11b-tsan race-stl11b.cc -ltsan -pie -pthread
******************************************************************************/
#include <iostream>
#include <thread>
#include <set>
int main()
{
// create an empty bucket
std::set<int> bucket;
// Use a background task to insert value '5' in the bucket
std::thread t([&](){ bucket.insert(5); });
// Check if value '3' is in the bucket (not expected :-)
bool contains3 = bucket.find(3) != bucket.cend();
std::cout << "Foreground find done: " << contains3 << std::endl;
// Wait for the background thread to finish
t.join();
// verify that value '5' did arrive in the bucket
bool contains5 = bucket.find(5) != bucket.cend();
std::cout << "Background insert: " << contains5 << std::endl;
return 0;
}
这是 tsan 输出的(部分):
WARNING: ThreadSanitizer: data race (pid=21774)
Write of size 8 at 0x7d080000bfc8 by thread T1:
#0 <null> <null>:0 (libtsan.so.0+0x00000001e2c0)
#1 deallocate /usr/include/c++/4.8/ext/new_allocator.h:110 (exe+0x000000002a79)
#2 deallocate /usr/include/c++/4.8/bits/alloc_traits.h:377 (exe+0x000000002962)
#3 _M_destroy /usr/include/c++/4.8/bits/shared_ptr_base.h:417 (exe+0x00000000306b)
#4 <null> <null>:0 (libstdc++.so.6+0x0000000b5f8a)
Previous atomic write of size 4 at 0x7d080000bfc8 by main thread:
#0 <null> <null>:0 (libtsan.so.0+0x00000000da45)
#1 __exchange_and_add /usr/include/c++/4.8/ext/atomicity.h:49 (exe+0x000000001c9f)
#2 __exchange_and_add_dispatch /usr/include/c++/4.8/ext/atomicity.h:82 (exe+0x000000001d56)
#3 std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>::_M_release() /usr/include/c++/4.8/bits/shared_ptr_base.h:141 (exe+0x00000000390d)
#4 std::__shared_count<(__gnu_cxx::_Lock_policy)2>::~__shared_count() /usr/include/c++/4.8/bits/shared_ptr_base.h:553 (exe+0x00000000363c)
#5 std::__shared_ptr<std::thread::_Impl_base, (__gnu_cxx::_Lock_policy)2>::~__shared_ptr() /usr/include/c++/4.8/bits/shared_ptr_base.h:810
(exe+0x00000000351b)
#6 std::shared_ptr<std::thread::_Impl_base>::~shared_ptr() /usr/include/c++/4.8/bits/shared_ptr.h:93 (exe+0x000000003547)
#7 thread<main()::__lambda0> /usr/include/c++/4.8/thread:135 (exe+0x0000000020c3)
#8 main /home/......./race-stl11b.cc:22 (exe+0x000000001e38)
感谢您的任何反馈,乔斯