/*
- * Copyright 2014 Facebook, Inc.
+ * Copyright 2017 Facebook, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
#pragma once
#include <atomic>
+#include <cassert>
#include <chrono>
#include <limits>
-#include <assert.h>
-#include <unistd.h>
+
#include <boost/noncopyable.hpp>
+#include <folly/portability/Unistd.h>
+
namespace folly { namespace detail {
enum class FutexResult {
template <template <typename> class Atom = std::atomic>
struct Futex : Atom<uint32_t>, boost::noncopyable {
- explicit Futex(uint32_t init = 0) : Atom<uint32_t>(init) {}
+ explicit constexpr Futex(uint32_t init = 0) : 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
"futexWaitUntil only knows std::chrono::{system_clock,steady_clock}");
assert((std::is_same<Clock, system_clock>::value) || Clock::is_steady);
- auto duration = absTime.time_since_epoch();
+ // We launder the clock type via a std::chrono::duration so that we
+ // can compile both the true and false branch. Tricky case is when
+ // steady_clock has a higher precision than system_clock (Xcode 6,
+ // for example), for which time_point<system_clock> construction
+ // refuses to do an implicit duration conversion. (duration is
+ // happy to implicitly convert its denominator causing overflow, but
+ // refuses conversion that might cause truncation.) We use explicit
+ // duration_cast to work around this. Truncation does not actually
+ // occur (unless Duration != Clock::duration) because the missing
+ // implicit conversion is in the untaken branch.
+ Duration absTimeDuration = absTime.time_since_epoch();
if (std::is_same<Clock, system_clock>::value) {
- time_point<system_clock> absSystemTime(duration);
+ time_point<system_clock> absSystemTime(
+ duration_cast<system_clock::duration>(absTimeDuration));
return futexWaitImpl(expected, &absSystemTime, nullptr, waitMask);
} else {
- time_point<steady_clock> absSteadyTime(duration);
+ time_point<steady_clock> absSteadyTime(
+ duration_cast<steady_clock::duration>(absTimeDuration));
return futexWaitImpl(expected, nullptr, &absSteadyTime, waitMask);
}
}
- /** Wakens up to count waiters where (waitMask & wakeMask) != 0,
- * returning the number of awoken threads. */
+ /** 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);
EmulatedFutexAtomic() noexcept = default;
constexpr /* implicit */ EmulatedFutexAtomic(T init) noexcept
: std::atomic<T>(init) {}
- EmulatedFutexAtomic(const EmulatedFutexAtomic& rhs) = delete;
+ // It doesn't copy or move
+ EmulatedFutexAtomic(EmulatedFutexAtomic&& rhs) = delete;
};
/* Available specializations, with definitions elsewhere */
-template<>
+template <>
int Futex<std::atomic>::futexWake(int count, uint32_t wakeMask);
-template<>
+template <>
FutexResult Futex<std::atomic>::futexWaitImpl(
uint32_t expected,
std::chrono::time_point<std::chrono::system_clock>* absSystemTime,
std::chrono::time_point<std::chrono::steady_clock>* absSteadyTime,
uint32_t waitMask);
-template<>
+template <>
int Futex<EmulatedFutexAtomic>::futexWake(int count, uint32_t wakeMask);
-template<>
+template <>
FutexResult Futex<EmulatedFutexAtomic>::futexWaitImpl(
uint32_t expected,
std::chrono::time_point<std::chrono::system_clock>* absSystemTime,