1 //===--- timeout linux implementation ---------------------------*- C++ -*-===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 9 #ifndef LLVM_LIBC_SRC___SUPPORT_TIME_LINUX_MONOTONICITY_H 10 #define LLVM_LIBC_SRC___SUPPORT_TIME_LINUX_MONOTONICITY_H 11 12 #include "hdr/time_macros.h" 13 #include "src/__support/libc_assert.h" 14 #include "src/__support/macros/config.h" 15 #include "src/__support/time/linux/abs_timeout.h" 16 #include "src/__support/time/linux/clock_conversion.h" 17 namespace LIBC_NAMESPACE_DECL { 18 namespace internal { 19 // This function is separated from abs_timeout. 20 // This function pulls in the dependency to clock_conversion.h, 21 // which may transitively depend on vDSO hence futex. However, this structure 22 // would be passed to futex, so we need to avoid cyclic dependencies. 23 // This function is going to be used in timed locks. Pthread generally uses 24 // realtime clocks for timeouts. However, due to non-monotoncity, realtime 25 // clocks reportedly lead to undesired behaviors. Therefore, we also provide a 26 // method to convert the timespec to a monotonic clock relative to the time of 27 // function call. 28 LIBC_INLINE void ensure_monotonicity(AbsTimeout &timeout) { 29 if (timeout.is_realtime()) { 30 auto res = AbsTimeout::from_timespec( 31 convert_clock(timeout.get_timespec(), CLOCK_REALTIME, CLOCK_MONOTONIC), 32 false); 33 34 LIBC_ASSERT(res.has_value()); 35 if (!res.has_value()) 36 __builtin_unreachable(); 37 38 timeout = *res; 39 } 40 } 41 } // namespace internal 42 } // namespace LIBC_NAMESPACE_DECL 43 44 #endif // LLVM_LIBC_SRC___SUPPORT_TIME_LINUX_MONOTONICITY_H 45