[libcxx-commits] [PATCH] D151559: [libc++] implement std::`jthread`

[Louis Dionne via Phabricator via libcxx-commits]

ldionne added a subscriber: vitalybuka.
ldionne added inline comments.


================
Comment at: libcxx/test/std/thread/thread.jthread/join.pass.cpp:84
+
+  // resource_deadlock_would_occur - if deadlock is detected or get_id() == this_thread::get_id().
+  {
----------------
This test is failing with:

```
ThreadSanitizer: CHECK failed: sanitizer_thread_registry.cpp:348 "((t)) != (0)" (0x0, 0x0) (tid=3411214)
    #0 __tsan::CheckUnwind() <null> (t.tmp.exe+0xcbd1b) (BuildId: d7fd9285e8961410872ba6334aecc0115d0ff192)
    #1 __sanitizer::CheckFailed(char const*, int, char const*, unsigned long long, unsigned long long) <null> (t.tmp.exe+0x45042) (BuildId: d7fd9285e8961410872ba6334aecc0115d0ff192)
    #2 __sanitizer::ThreadRegistry::ConsumeThreadUserId(unsigned long) <null> (t.tmp.exe+0x43e94) (BuildId: d7fd9285e8961410872ba6334aecc0115d0ff192)
    #3 pthread_join <null> (t.tmp.exe+0x604bb) (BuildId: d7fd9285e8961410872ba6334aecc0115d0ff192)
    #4 std::__1::__libcpp_thread_join[abi:v170000](unsigned long*) /home/libcxx-builder/.buildkite-agent/builds/google-libcxx-builder-69f521df8409-1/llvm-project/libcxx-ci/build/generic-tsan/include/c++/v1/__threading_support:398:10 (libc++.so.1+0x73358) (BuildId: 71b8f06279b5e8117756a82c1e642e312c2a0e30)
    #5 std::__1::thread::join() /home/libcxx-builder/.buildkite-agent/builds/google-libcxx-builder-69f521df8409-1/llvm-project/libcxx-ci/libcxx/src/thread.cpp:51:14 (libc++.so.1+0x73358)
    #6 std::__1::jthread::join[abi:v170000]() /home/libcxx-builder/.buildkite-agent/builds/google-libcxx-builder-69f521df8409-1/llvm-project/libcxx-ci/build/generic-tsan/include/c++/v1/__thread/jthread.h:91:49 (t.tmp.exe+0xed5f9) (BuildId: d7fd9285e8961410872ba6334aecc0115d0ff192)
    #7 std::__1::jthread::~jthread[abi:v170000]() /home/libcxx-builder/.buildkite-agent/builds/google-libcxx-builder-69f521df8409-1/llvm-project/libcxx-ci/build/generic-tsan/include/c++/v1/__thread/jthread.h:60:7 (t.tmp.exe+0xed708) (BuildId: d7fd9285e8961410872ba6334aecc0115d0ff192)
    #8 main /home/libcxx-builder/.buildkite-agent/builds/google-libcxx-builder-69f521df8409-1/llvm-project/libcxx-ci/libcxx/test/std/thread/thread.jthread/join.pass.cpp:108:3 (t.tmp.exe+0xe836d) (BuildId: d7fd9285e8961410872ba6334aecc0115d0ff192)
    #9 __libc_start_call_main csu/../sysdeps/nptl/libc_start_call_main.h:58:16 (libc.so.6+0x29d8f) (BuildId: 69389d485a9793dbe873f0ea2c93e02efaa9aa3d)
    #10 __libc_start_main csu/../csu/libc-start.c:392:3 (libc.so.6+0x29e3f) (BuildId: 69389d485a9793dbe873f0ea2c93e02efaa9aa3d)
    #11 _start <null> (t.tmp.exe+0x30484) (BuildId: d7fd9285e8961410872ba6334aecc0115d0ff192)
```

What might be happening is that TSAN instruments `pthread_join` and it thinks that the thread has already been joined when you call it the second time in the destructor. But in reality, the thread wasn't joined the first time around because of the system error. You might be able to figure out what's going on by looking at how these functions are interposed, I think it's in compiler-rt. @vitalybuka Might be able to provide more information as well.

If that's the case, then the issue would be that TSAN's internal state is inconsistent with reality and the fix would be in TSAN. I'm not sure, I'm just guessing.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D151559/new/

https://reviews.llvm.org/D151559