2022-06-22_-_logate_v1.1.1_is_out

anonymous@undisclosed.example.com (Anonymous) — Wed, 22 Jun 2022 21:41:43 +0000

2022-06-22 - LogATE v1.1.1 is out

i'm pleased to announce that LogATE v1.1.1 is out! :) LogATE is a text-UI based tool, for analizing structured logs (in JSON format).

the key change, compared to last release is addition of JSON arrays support. while it sounds trivial, this was a big change, as it allowed for addition of wildcard statements, so that one search path may now interact with multiple elements in the array. this allows for robust filters, checking if given element exists in an array, what fields are there, etc…

enjoy using! :)

2022-06-22_-_tsan_bug

anonymous@undisclosed.example.com (Anonymous) — Wed, 22 Jun 2022 21:56:06 +0000

2022-06-22 - TSAN bug

while preparing release of latest LogATE version, i stumbled upon a bug in thread sanitizer. consider the following piece of code:

#include <thread>
#include <mutex>
#include <condition_variable>
 
int main()
{
  auto ready = false;
  std::mutex m;
  std::condition_variable cv;
 
  std::thread th{ [&]{
    // thread 1
    std::unique_lock<std::mutex> lock(m);
#if 0
    // OK!
    cv.wait( lock, [&]{ return ready; } );
#endif
#if 0
    // ERROR!
    cv.wait_until( lock, std::chrono::steady_clock::now() + std::chrono::minutes{1}, [&]{ return ready; } );
#endif
#if 1
    // ERROR!
    cv.wait_for( lock, std::chrono::minutes{1}, [&]{ return ready; } );
#endif
  } };
 
  {
    // thread 2
    std::this_thread::sleep_for( std::chrono::seconds{1} );  // we should be wait()ing here
    std::lock_guard<std::mutex> lock{m};
    ready = true;
    cv.notify_one();
  }
 
  th.join();
}

after compiling it with:

g++ -fsanitize=thread  -g3 -Wall -std=c++17 test.cpp -lpthread

we can see a very colorful output, indicating double-locking and race condition!

the same issue is reported with both gcc and clang. so the problem is in the code, right? well… no. the clue that the problem is elsewhere is when you change which version of wait() is selected: regular one works fine, while time-constrained versions (i.e. deadline and timeout) report issues as below. changing C++ library does not change the output, but changing a compiler version does help.

here are the bugs i found already reported for this:

gcc bug report¹⁾
clang bug report²⁾

i've spent quite a bit of time today, trying to narrow down the issue and making it small and reproducible issue. then it turned out it's a know problem. life… ;)

the problem has been observed on UTs. even though here it was false-positive, running automated tests with sanitizers is a really great thing to do. if you still do not do it – i strongly encourage you to start doing so! :)

¹⁾

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101978

²⁾

https://github.com/google/sanitizers/issues/1259

BaSzErr - blog:2022:06:22

2022-06-22_-_logate_v1.1.1_is_out

2022-06-22 - LogATE v1.1.1 is out

2022-06-22_-_tsan_bug

2022-06-22 - TSAN bug