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ldionne - Group Reviewers
Restricted Project - Commits
- rG695138ca8405: [libc++] implement std::`jthread`
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Event Timeline
libcxx/include/__thread/formatter.h | ||
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1 ↗ | (On Diff #526039) | Would it be possible to granularize these headers in a separate patch? That should be a quick NFC to review. |
libcxx/include/__thread/jthread.h | ||
11–12 | ||
42–43 | Note to self: this is tested. | |
49 | Let's make sure we have a test for this note:
(near https://eel.is/c++draft/thread.jthread.class#thread.jthread.cons-5) Edit: We do already have a test! | |
72 | Do you have a test for self-assignment? Edit: Of course, you do. | |
133 | ||
libcxx/include/__thread/this_thread.h | ||
10 ↗ | (On Diff #526039) | Same here and elsewhere when you do it in another patch. |
libcxx/test/std/thread/thread.jthread/assign.move.pass.cpp | ||
38 | I think we don't have a test for the case where the source thread isn't joinable. | |
libcxx/test/std/thread/thread.jthread/cons.func.token.pass.cpp | ||
112 | TEST_HAS_NO_EXCEPTIONS | |
148 | Per your suggestion, we might be able to test https://eel.is/c++draft/thread.jthread.class#thread.jthread.cons-8 by setting multiple threads' affinity to the same core. It might not be possible to test this in a robust way, and I think it would be reasonable not to. |
libcxx/include/__stop_token/stop_state.h | ||
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19–21 | #include <__thread/thread.h>? I think this might require exporting * or std.__threading_support.__thread_id from the modulemap. | |
libcxx/test/std/thread/thread.jthread/dtor.pass.cpp | ||
25 | ||
31 | assert(jt.joinable()); // test the test Those are just suggestions, I'm actually not sure how much I like this. |
libcxx/test/std/thread/thread.jthread/dtor.pass.cpp | ||
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40–46 | To increase the confidence in this test, we could instead spawn more threads and do the same check. That should get the probability that join() isn't called but the test still passes down. Also, I'd leave a short comment behind explaining this particularity of the test (i.e. it's not going to catch issues 100%). | |
libcxx/test/std/thread/thread.jthread/join.pass.cpp | ||
29 | Same comment here about non-determinism. |
I didn't do an in depth review, I mainly looked at the code out of curiosity.
libcxx/include/__thread/jthread.h | ||
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67 |
libcxx/test/std/thread/thread.jthread/join.pass.cpp | ||
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85 | 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. |
libcxx/test/std/thread/thread.jthread/join.pass.cpp | ||
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85 | had a looked at TSAN's code TSAN_INTERCEPTOR(int, pthread_join, void *th, void **ret) { SCOPED_INTERCEPTOR_RAW(pthread_join, th, ret); Tid tid = ThreadConsumeTid(thr, pc, (uptr)th); ThreadIgnoreBegin(thr, pc); int res = BLOCK_REAL(pthread_join)(th, ret); ThreadIgnoreEnd(thr); if (res == 0) { ThreadJoin(thr, pc, tid); } return res; } ThreadConsumeTid calls ConsumeThreadUserId, which
From what I can see, the first time join is called, the user id is removed. then join throws. so I guess this is a TSAN problem? |
I'll pick up that patch as well per discussion with Hui.
libcxx/include/__thread/jthread.h | ||
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2 | Let's mark this as experimental. | |
libcxx/test/std/thread/thread.jthread/join.pass.cpp | ||
85 | This seems like we should file a bug report against ASAN for this one. | |
103 | Let's move this to a different test like join.deadlock.pass.cpp and mark it as UNSUPPORTED on Windows with a comment. We can also mark it as UNSUPPORTED on ASAN with a link to the bug report. |
I don't think any of my comments really require me to take another look. This is really good, thank you!
libcxx/include/CMakeLists.txt | ||
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672 | Not attached: let's mention this in UsingLibcxx.rst where we have a list of experimental features. | |
libcxx/include/__stop_token/stop_state.h | ||
18 | I think you can simply replace this by __thread/id.h now that it has been split out of __thread/thread.h. This might reduce dependencies a bit. | |
libcxx/include/__thread/jthread.h | ||
32–34 | I would remove this since there's already one in <thread>. We want to revisit how we're handling missing capabilities like this (in some cases we just omit the contents of headers, in other cases like _LIBCPP_HAS_NO_THREADS we have a hard error). Removing this doesn't change anything but it avoids giving the impression that this is the definite way we want to handle those. | |
52 | I might suggest making __init_thread a static member function and passing __stop_source_ to it explicitly. Otherwise we're calling a member function at a point where the object isn't fully initialized yet, which seems questionable. I don't think there's any real issue here, it's more a matter of style / clarity. | |
libcxx/test/std/thread/thread.jthread/cons.func.token.pass.cpp | ||
151 | Let's add a link to https://eel.is/c++draft/thread.jthread.class#thread.jthread.cons-8 in this comment. Also, if you don't have a concrete idea of how this might be done (portably etc..), let's not make this a TODO. If we don't realistically plan on fixing it, it shouldn't be a TODO. We can say instead: // Per https://eel.is/c++draft/thread.jthread.class#thread.jthread.cons-8: // // Throws: system_error if unable to start the new thread. // Error conditions: // resource_unavailable_try_again - the system lacked the necessary resources to create another thread, // or the system-imposed limit on the number of threads in a process would be exceeded. // // Unfortunately, this is extremely hard to test portably so we don't have a test for this error condition right now. | |
libcxx/test/std/thread/thread.jthread/cons.move.pass.cpp | ||
35 | https://eel.is/c++draft/thread.jthread.class#thread.jthread.cons-10 says that j1.get_id() should be id(), so we might as well assert that. | |
libcxx/test/std/thread/thread.jthread/detach.pass.cpp | ||
37 | To troubleshoot whether the CI issue is that this curly brace is taking forever to complete and then the main thread finishes before the detached thread is done, you could insert a sleep at the end of the test. If that is indeed the issue, I can't think of another way to solve this problem since you don't have any handle to the thread once you've detached it. It's kind of lame but it might be acceptable to insert a short sleep with a comment at the end if it reliably solves this issue. | |
70–72 | ||
libcxx/test/std/thread/thread.jthread/dtor.pass.cpp | ||
63–64 | ||
libcxx/test/std/thread/thread.jthread/get_id.pass.cpp | ||
24–29 | Suggestion: static_assert(noexcept(std::declval<std::jthread>().get_id())); This seems a bit simpler. This applies in a few other tests as well. | |
libcxx/test/std/thread/thread.jthread/get_stop_token.pass.cpp | ||
38 | That way if we returned a reference, the test would fail. You probably want to do this in the other tests too. | |
libcxx/test/std/thread/thread.jthread/join.deadlock.pass.cpp | ||
13 ↗ | (On Diff #556829) | This should be a link to the github issue! |
36 ↗ | (On Diff #556829) | We could do UNSUPPORTED: no-exceptions instead. |
libcxx/test/std/thread/thread.jthread/joinable.pass.cpp | ||
40–45 | I think we should check two cases here:
You can use an atomic variable to signal that. | |
libcxx/test/std/thread/thread.jthread/typedef.compile.pass.cpp | ||
2 | I would suggest renaming this to types.compile.pass.cpp, I think it is a bit more consistent with the rest of the test suite. |
libcxx/test/std/thread/thread.jthread/join.pass.cpp | ||
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85 |
TSAN Asan for similar case make sure result is success INTERCEPTOR(int, pthread_join, void *thread, void **retval) { int result; asanThreadArgRetval().Join((uptr)thread, [&]() { result = REAL(pthread_join)(thread, retval); return !result; }); return result; } |
Not attached: let's mention this in UsingLibcxx.rst where we have a list of experimental features.