compiler-rt/lib/scudo/standalone/condition_variable.h

   1 //===-- condition_variable.h ------------------------------------*- 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 SCUDO_CONDITION_VARIABLE_H_
  10 #define SCUDO_CONDITION_VARIABLE_H_
  11
  12 #include "condition_variable_base.h"
  13
  14 #include "common.h"
  15 #include "platform.h"
  16
  17 #include "condition_variable_linux.h"
  18
  19 namespace scudo {
  20
  21 // A default implementation of default condition variable. It doesn't do a real
  22 // `wait`, instead it spins a short amount of time only.
  23 class ConditionVariableDummy
  24     : public ConditionVariableBase<ConditionVariableDummy> {
  25 public:
  26   void notifyAllImpl(UNUSED HybridMutex &M) REQUIRES(M) {}
  27
  28   void waitImpl(UNUSED HybridMutex &M) REQUIRES(M) {
  29     M.unlock();
  30
  31     constexpr u32 SpinTimes = 64;
  32     volatile u32 V = 0;
  33     for (u32 I = 0; I < SpinTimes; ++I) {
  34       u32 Tmp = V + 1;
  35       V = Tmp;
  36     }
  37
  38     M.lock();
  39   }
  40 };
  41
  42 template <typename Config, typename = const bool>
  43 struct ConditionVariableState {
  44   static constexpr bool enabled() { return false; }
  45   // This is only used for compilation purpose so that we won't end up having
  46   // many conditional compilations. If you want to use `ConditionVariableDummy`,
  47   // define `ConditionVariableT` in your allocator configuration. See
  48   // allocator_config.h for more details.
  49   using ConditionVariableT = ConditionVariableDummy;
  50 };
  51
  52 template <typename Config>
  53 struct ConditionVariableState<Config, decltype(Config::UseConditionVariable)> {
  54   static constexpr bool enabled() { return true; }
  55   using ConditionVariableT = typename Config::ConditionVariableT;
  56 };
  57
  58 } // namespace scudo
  59
  60 #endif // SCUDO_CONDITION_VARIABLE_H_