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Diffstat (limited to 'src/rocksdb/third-party/folly/folly/detail/Futex.cpp')
-rw-r--r-- | src/rocksdb/third-party/folly/folly/detail/Futex.cpp | 263 |
1 files changed, 263 insertions, 0 deletions
diff --git a/src/rocksdb/third-party/folly/folly/detail/Futex.cpp b/src/rocksdb/third-party/folly/folly/detail/Futex.cpp new file mode 100644 index 000000000..62d6ea2b2 --- /dev/null +++ b/src/rocksdb/third-party/folly/folly/detail/Futex.cpp @@ -0,0 +1,263 @@ +// Copyright (c) 2011-present, Facebook, Inc. All rights reserved. +// This source code is licensed under both the GPLv2 (found in the +// COPYING file in the root directory) and Apache 2.0 License +// (found in the LICENSE.Apache file in the root directory). + +#include <folly/detail/Futex.h> +#include <folly/portability/SysSyscall.h> +#include <stdint.h> +#include <string.h> +#include <array> +#include <cerrno> + +#include <folly/synchronization/ParkingLot.h> + +#ifdef __linux__ +#include <linux/futex.h> +#endif + +#ifndef _WIN32 +#include <unistd.h> +#endif + +using namespace std::chrono; + +namespace folly { +namespace detail { + +namespace { + +//////////////////////////////////////////////////// +// native implementation using the futex() syscall + +#ifdef __linux__ + +/// Certain toolchains (like Android's) don't include the full futex API in +/// their headers even though they support it. Make sure we have our constants +/// even if the headers don't have them. +#ifndef FUTEX_WAIT_BITSET +#define FUTEX_WAIT_BITSET 9 +#endif +#ifndef FUTEX_WAKE_BITSET +#define FUTEX_WAKE_BITSET 10 +#endif +#ifndef FUTEX_PRIVATE_FLAG +#define FUTEX_PRIVATE_FLAG 128 +#endif +#ifndef FUTEX_CLOCK_REALTIME +#define FUTEX_CLOCK_REALTIME 256 +#endif + +int nativeFutexWake(const void* addr, int count, uint32_t wakeMask) { + long rv = syscall( + __NR_futex, + addr, /* addr1 */ + FUTEX_WAKE_BITSET | FUTEX_PRIVATE_FLAG, /* op */ + count, /* val */ + nullptr, /* timeout */ + nullptr, /* addr2 */ + wakeMask); /* val3 */ + + /* NOTE: we ignore errors on wake for the case of a futex + guarding its own destruction, similar to this + glibc bug with sem_post/sem_wait: + https://sourceware.org/bugzilla/show_bug.cgi?id=12674 */ + if (rv < 0) { + return 0; + } + return static_cast<int>(rv); +} + +template <class Clock> +struct timespec timeSpecFromTimePoint(time_point<Clock> absTime) { + auto epoch = absTime.time_since_epoch(); + if (epoch.count() < 0) { + // kernel timespec_valid requires non-negative seconds and nanos in [0,1G) + epoch = Clock::duration::zero(); + } + + // timespec-safe seconds and nanoseconds; + // chrono::{nano,}seconds are `long long int` + // whereas timespec uses smaller types + using time_t_seconds = duration<std::time_t, seconds::period>; + using long_nanos = duration<long int, nanoseconds::period>; + + auto secs = duration_cast<time_t_seconds>(epoch); + auto nanos = duration_cast<long_nanos>(epoch - secs); + struct timespec result = {secs.count(), nanos.count()}; + return result; +} + +FutexResult nativeFutexWaitImpl( + const void* addr, + uint32_t expected, + system_clock::time_point const* absSystemTime, + steady_clock::time_point const* absSteadyTime, + uint32_t waitMask) { + assert(absSystemTime == nullptr || absSteadyTime == nullptr); + + int op = FUTEX_WAIT_BITSET | FUTEX_PRIVATE_FLAG; + struct timespec ts; + struct timespec* timeout = nullptr; + + if (absSystemTime != nullptr) { + op |= FUTEX_CLOCK_REALTIME; + ts = timeSpecFromTimePoint(*absSystemTime); + timeout = &ts; + } else if (absSteadyTime != nullptr) { + ts = timeSpecFromTimePoint(*absSteadyTime); + timeout = &ts; + } + + // Unlike FUTEX_WAIT, FUTEX_WAIT_BITSET requires an absolute timeout + // value - http://locklessinc.com/articles/futex_cheat_sheet/ + long rv = syscall( + __NR_futex, + addr, /* addr1 */ + op, /* op */ + expected, /* val */ + timeout, /* timeout */ + nullptr, /* addr2 */ + waitMask); /* val3 */ + + if (rv == 0) { + return FutexResult::AWOKEN; + } else { + switch (errno) { + case ETIMEDOUT: + assert(timeout != nullptr); + return FutexResult::TIMEDOUT; + case EINTR: + return FutexResult::INTERRUPTED; + case EWOULDBLOCK: + return FutexResult::VALUE_CHANGED; + default: + assert(false); + // EINVAL, EACCESS, or EFAULT. EINVAL means there was an invalid + // op (should be impossible) or an invalid timeout (should have + // been sanitized by timeSpecFromTimePoint). EACCESS or EFAULT + // means *addr points to invalid memory, which is unlikely because + // the caller should have segfaulted already. We can either + // crash, or return a value that lets the process continue for + // a bit. We choose the latter. VALUE_CHANGED probably turns the + // caller into a spin lock. + return FutexResult::VALUE_CHANGED; + } + } +} + +#endif // __linux__ + +/////////////////////////////////////////////////////// +// compatibility implementation using standard C++ API + +using Lot = ParkingLot<uint32_t>; +Lot parkingLot; + +int emulatedFutexWake(const void* addr, int count, uint32_t waitMask) { + int woken = 0; + parkingLot.unpark(addr, [&](const uint32_t& mask) { + if ((mask & waitMask) == 0) { + return UnparkControl::RetainContinue; + } + assert(count > 0); + count--; + woken++; + return count > 0 ? UnparkControl::RemoveContinue + : UnparkControl::RemoveBreak; + }); + return woken; +} + +template <typename F> +FutexResult emulatedFutexWaitImpl( + F* futex, + uint32_t expected, + system_clock::time_point const* absSystemTime, + steady_clock::time_point const* absSteadyTime, + uint32_t waitMask) { + static_assert( + std::is_same<F, const Futex<std::atomic>>::value || + std::is_same<F, const Futex<EmulatedFutexAtomic>>::value, + "Type F must be either Futex<std::atomic> or Futex<EmulatedFutexAtomic>"); + ParkResult res; + if (absSystemTime) { + res = parkingLot.park_until( + futex, + waitMask, + [&] { return *futex == expected; }, + [] {}, + *absSystemTime); + } else if (absSteadyTime) { + res = parkingLot.park_until( + futex, + waitMask, + [&] { return *futex == expected; }, + [] {}, + *absSteadyTime); + } else { + res = parkingLot.park( + futex, waitMask, [&] { return *futex == expected; }, [] {}); + } + switch (res) { + case ParkResult::Skip: + return FutexResult::VALUE_CHANGED; + case ParkResult::Unpark: + return FutexResult::AWOKEN; + case ParkResult::Timeout: + return FutexResult::TIMEDOUT; + } + + return FutexResult::INTERRUPTED; +} + +} // namespace + +///////////////////////////////// +// Futex<> overloads + +int futexWakeImpl( + const Futex<std::atomic>* futex, + int count, + uint32_t wakeMask) { +#ifdef __linux__ + return nativeFutexWake(futex, count, wakeMask); +#else + return emulatedFutexWake(futex, count, wakeMask); +#endif +} + +int futexWakeImpl( + const Futex<EmulatedFutexAtomic>* futex, + int count, + uint32_t wakeMask) { + return emulatedFutexWake(futex, count, wakeMask); +} + +FutexResult futexWaitImpl( + const Futex<std::atomic>* futex, + uint32_t expected, + system_clock::time_point const* absSystemTime, + steady_clock::time_point const* absSteadyTime, + uint32_t waitMask) { +#ifdef __linux__ + return nativeFutexWaitImpl( + futex, expected, absSystemTime, absSteadyTime, waitMask); +#else + return emulatedFutexWaitImpl( + futex, expected, absSystemTime, absSteadyTime, waitMask); +#endif +} + +FutexResult futexWaitImpl( + const Futex<EmulatedFutexAtomic>* futex, + uint32_t expected, + system_clock::time_point const* absSystemTime, + steady_clock::time_point const* absSteadyTime, + uint32_t waitMask) { + return emulatedFutexWaitImpl( + futex, expected, absSystemTime, absSteadyTime, waitMask); +} + +} // namespace detail +} // namespace folly |