Author: Arthur O'Dwyer Date: 2021-11-05T15:59:12-04:00 New Revision: 216200aff2681407b5e799738b09a047771d86ec
URL: https://github.com/llvm/llvm-project/commit/216200aff2681407b5e799738b09a047771d86ec DIFF: https://github.com/llvm/llvm-project/commit/216200aff2681407b5e799738b09a047771d86ec.diff LOG: [libc++] Fix hang in counting_semaphore::try_acquire Before this patch, `try_acquire` blocks instead of returning false. This is because `__libcpp_thread_poll_with_backoff` interprets zero as meaning infinite, causing `try_acquire` to wait indefinitely. Thanks to Pablo Busse (pabusse) for the patch! Differential Revision: https://reviews.llvm.org/D98334 (cherry picked from commit c92a253cf0ddcf905707b4e9265b42570ce409d9) Added: Modified: libcxx/include/semaphore libcxx/test/std/thread/thread.semaphore/try_acquire.pass.cpp Removed: ################################################################################ diff --git a/libcxx/include/semaphore b/libcxx/include/semaphore index 1128b36d9527..db03fb967ed1 100644 --- a/libcxx/include/semaphore +++ b/libcxx/include/semaphore @@ -105,17 +105,22 @@ public: _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY bool try_acquire_for(chrono::duration<Rep, Period> const& __rel_time) { - auto const __test_fn = [this]() -> bool { - auto __old = __a.load(memory_order_acquire); - while(1) { - if (__old == 0) - return false; - if(__a.compare_exchange_strong(__old, __old - 1, memory_order_acquire, memory_order_relaxed)) - return true; - } - }; + if (__rel_time == chrono::duration<Rep, Period>::zero()) + return try_acquire(); + auto const __test_fn = [this]() { return try_acquire(); }; return __libcpp_thread_poll_with_backoff(__test_fn, __libcpp_timed_backoff_policy(), __rel_time); } + _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY + bool try_acquire() + { + auto __old = __a.load(memory_order_acquire); + while (true) { + if (__old == 0) + return false; + if (__a.compare_exchange_strong(__old, __old - 1, memory_order_acquire, memory_order_relaxed)) + return true; + } + } }; #define _LIBCPP_SEMAPHORE_MAX (numeric_limits<ptr diff _t>::max()) @@ -156,14 +161,14 @@ public: _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY bool try_acquire() { - return try_acquire_for(chrono::nanoseconds::zero()); + return __semaphore.try_acquire(); } template <class Clock, class Duration> _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY bool try_acquire_until(chrono::time_point<Clock, Duration> const& __abs_time) { auto const current = Clock::now(); - if(current >= __abs_time) + if (current >= __abs_time) return try_acquire(); else return try_acquire_for(__abs_time - current); diff --git a/libcxx/test/std/thread/thread.semaphore/try_acquire.pass.cpp b/libcxx/test/std/thread/thread.semaphore/try_acquire.pass.cpp index 35cb6ce7dc82..5a5ab72d05df 100644 --- a/libcxx/test/std/thread/thread.semaphore/try_acquire.pass.cpp +++ b/libcxx/test/std/thread/thread.semaphore/try_acquire.pass.cpp @@ -27,14 +27,17 @@ int main(int, char**) std::counting_semaphore<> s(1); assert(s.try_acquire()); + assert(!s.try_acquire()); s.release(); assert(s.try_acquire()); + assert(!s.try_acquire()); s.release(2); std::thread t = support::make_test_thread([&](){ assert(s.try_acquire()); }); t.join(); assert(s.try_acquire()); + assert(!s.try_acquire()); return 0; } _______________________________________________ llvm-branch-commits mailing list llvm-branch-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-branch-commits
