/*
- * 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.
*/
#include <folly/detail/Futex.h>
+#include <boost/intrusive/list.hpp>
+#include <folly/Indestructible.h>
+#include <folly/ScopeGuard.h>
+#include <folly/hash/Hash.h>
+#include <folly/portability/SysSyscall.h>
#include <stdint.h>
#include <string.h>
+#include <array>
+#include <cerrno>
#include <condition_variable>
#include <mutex>
-#include <boost/intrusive/list.hpp>
-#include <folly/Hash.h>
-#include <folly/ScopeGuard.h>
#ifdef __linux__
-# include <errno.h>
-# include <linux/futex.h>
-# include <sys/syscall.h>
+#include <linux/futex.h>
#endif
using namespace std::chrono;
-namespace folly { namespace detail {
+namespace folly {
+namespace detail {
namespace {
#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(void* addr, int count, uint32_t wakeMask) {
- int rv = syscall(SYS_futex,
+ int rv = syscall(__NR_futex,
addr, /* addr1 */
FUTEX_WAKE_BITSET | FUTEX_PRIVATE_FLAG, /* op */
count, /* val */
nullptr, /* addr2 */
wakeMask); /* val3 */
- assert(rv >= 0);
-
+ /* 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 rv;
}
struct timespec
timeSpecFromTimePoint(time_point<Clock> absTime)
{
- auto duration = absTime.time_since_epoch();
- if (duration.count() < 0) {
+ auto epoch = absTime.time_since_epoch();
+ if (epoch.count() < 0) {
// kernel timespec_valid requires non-negative seconds and nanos in [0,1G)
- duration = Clock::duration::zero();
+ epoch = Clock::duration::zero();
}
- auto secs = duration_cast<seconds>(duration);
- auto nanos = duration_cast<nanoseconds>(duration - secs);
+
+ // 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;
}
// Unlike FUTEX_WAIT, FUTEX_WAIT_BITSET requires an absolute timeout
// value - http://locklessinc.com/articles/futex_cheat_sheet/
- int rv = syscall(SYS_futex,
+ int rv = syscall(__NR_futex,
addr, /* addr1 */
op, /* op */
expected, /* val */
std::mutex mutex_;
boost::intrusive::list<EmulatedFutexWaitNode> waiters_;
- static const size_t kNumBuckets = 4096;
- static EmulatedFutexBucket* gBuckets;
- static std::once_flag gBucketInit;
+ static constexpr size_t const kNumBuckets = kIsMobile ? 256 : 4096;
static EmulatedFutexBucket& bucketFor(void* addr) {
- std::call_once(gBucketInit, [](){
- gBuckets = new EmulatedFutexBucket[kNumBuckets];
- });
- uint64_t mixedBits = folly::hash::twang_mix64(
- reinterpret_cast<uintptr_t>(addr));
- return gBuckets[mixedBits % kNumBuckets];
+ // Statically allocating this lets us use this in allocation-sensitive
+ // contexts. This relies on the assumption that std::mutex won't dynamically
+ // allocate memory, which we assume to be the case on Linux and iOS.
+ static Indestructible<std::array<EmulatedFutexBucket, kNumBuckets>>
+ gBuckets;
+ uint64_t mixedBits =
+ folly::hash::twang_mix64(reinterpret_cast<uintptr_t>(addr));
+ return (*gBuckets)[mixedBits % kNumBuckets];
}
};
-EmulatedFutexBucket* EmulatedFutexBucket::gBuckets;
-std::once_flag EmulatedFutexBucket::gBucketInit;
-
int emulatedFutexWake(void* addr, int count, uint32_t waitMask) {
auto& bucket = EmulatedFutexBucket::bucketFor(addr);
std::unique_lock<std::mutex> bucketLock(bucket.mutex_);
return numAwoken;
}
+template <typename F>
FutexResult emulatedFutexWaitImpl(
- void* addr,
- uint32_t expected,
- time_point<system_clock>* absSystemTime,
- time_point<steady_clock>* absSteadyTime,
- uint32_t waitMask) {
+ F* futex,
+ uint32_t expected,
+ time_point<system_clock>* absSystemTime,
+ time_point<steady_clock>* absSteadyTime,
+ uint32_t waitMask) {
+ static_assert(
+ std::is_same<F, Futex<std::atomic>>::value ||
+ std::is_same<F, Futex<EmulatedFutexAtomic>>::value,
+ "Type F must be either Futex<std::atomic> or Futex<EmulatedFutexAtomic>");
+ void* addr = static_cast<void*>(futex);
auto& bucket = EmulatedFutexBucket::bucketFor(addr);
EmulatedFutexWaitNode node(addr, waitMask);
{
std::unique_lock<std::mutex> bucketLock(bucket.mutex_);
- uint32_t actual;
- memcpy(&actual, addr, sizeof(uint32_t));
- if (actual != expected) {
+ if (futex->load(std::memory_order_relaxed) != expected) {
return FutexResult::VALUE_CHANGED;
}
return FutexResult::AWOKEN;
}
-} // anon namespace
-
+} // namespace
/////////////////////////////////
// Futex<> specializations
this, expected, absSystemTime, absSteadyTime, waitMask);
}
-}} // namespace folly::detail
+} // namespace detail
+} // namespace folly
projects / folly.git / blobdiff