libc/src/__support/time/linux/monotonicity.h

   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