Futex（快速用户空间互斥量）是一个32位的无符号整型原子变量，它允许对该值执行futex()系统调用。它以模板化的方式设计，使其能够与确定性调度测试（DeterministicSchedule）正确交互。
h源码：
enum class FutexResult {VALUE_CHANGED, /* futex value didn't match expected */AWOKEN, /* wakeup by matching futex wake, or spurious wakeup */INTERRUPTED, /* wakeup by interrupting signal */TIMEDOUT, /* wakeup by expiring deadline */
};/*** Futex is an atomic 32 bit unsigned integer that provides access to the* futex() syscall on that value. It is templated in such a way that it* can interact properly with DeterministicSchedule testing.** If you don't know how to use futex(), you probably shouldn't be using* this class. Even if you do know how, you should have a good reason* (and benchmarks to back you up).*/
template <template <typename> class Atom = std::atomic>
struct Futex : Atom<uint32_t> {Futex() : Atom<uint32_t>() {}explicit constexpr Futex(uint32_t init) : Atom<uint32_t>(init) {}/** Puts the thread to sleep if this->load() == expected. Returns true when* it is returning because it has consumed a wake() event, false for any* other return (signal, this->load() != expected, or spurious wakeup). */FutexResult futexWait(uint32_t expected, uint32_t waitMask = -1) {auto rv = futexWaitImpl(expected, nullptr, nullptr, waitMask);assert(rv != FutexResult::TIMEDOUT);return rv;}/** Similar to futexWait but also accepts a deadline until when the wait call* may block.** Optimal clock types: std::chrono::system_clock, std::chrono::steady_clock.* NOTE: On some systems steady_clock is just an alias for system_clock,* and is not actually steady.** For any other clock type, now() will be invoked twice. */template <class Clock, class Duration = typename Clock::duration>FutexResult futexWaitUntil(uint32_t expected,std::chrono::time_point<Clock, Duration> const& deadline,uint32_t waitMask = -1) {using Target = typename std::conditional<Clock::is_steady,std::chrono::steady_clock,std::chrono::system_clock>::type;auto const converted = time_point_conv<Target>(deadline);return converted == Target::time_point::max()? futexWaitImpl(expected, nullptr, nullptr, waitMask): futexWaitImpl(expected, converted, waitMask);}/** Wakens up to count waiters where (waitMask & wakeMask) !=* 0, returning the number of awoken threads, or -1 if an error* occurred. Note that when constructing a concurrency primitive* that can guard its own destruction, it is likely that you will* want to ignore EINVAL here (as well as making sure that you* never touch the object after performing the memory store that* is the linearization point for unlock or control handoff).* See https://sourceware.org/bugzilla/show_bug.cgi?id=13690 */int futexWake(int count = std::numeric_limits<int>::max(),uint32_t wakeMask = -1);private:/** Optimal when TargetClock is the same type as Clock.** Otherwise, both Clock::now() and TargetClock::now() must be invoked. */template <typename TargetClock, typename Clock, typename Duration>static typename TargetClock::time_point time_point_conv(std::chrono::time_point<Clock, Duration> const& time) {using std::chrono::duration_cast;using TimePoint = std::chrono::time_point<Clock, Duration>;using TargetDuration = typename TargetClock::duration;using TargetTimePoint = typename TargetClock::time_point;if (time == TimePoin
